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i  P34  .T442  A  text-book  of  human 


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A   TEXT-BOOK   OF 
HUMAN   PHYSIOLOGY 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/textbookofhumanpOOtige 


A  TEXT-BOOK    OF 

HUMAN  PHYSIOLOGl 


r 


BY 


DR.   ROBERT   TIGERSTEDT 

PROFESSOR   OF    PHYSIOLOGY    IN   THE   UNIVERSITY   OF   HELSINGFORS, 
FINLAND 


TRANSLATED  FROM  THE  THIRD  GERMAN   EDITION 
AND   EDITED   BY 

JOHN   R.   MURLIN,   A.M.,  Ph.D. 

ASSISTANT   PROFESSOR   OF    PHYSIOLOGY    IN   THE   UNIVERSITY^    AND 
BELLEVUE   HOSPITAL    MEDICAL   COLLEGE,    NEW    YORK   CITY 


WITH  AN  INTRODUCTION  TO  THE  ENGLISH   EDITION 

BY 

Professor  GRAHAM  LUSK,  Ph.D.,  f.r.s.  (Edinb.) 


NEW     YORK     AND     LONDON 

D .     A  P  P  L  E  T  O  N     AND     CO  M  P  A  N  Y 

1906 


Copyright,  litOCi,  iiy 
D.   ArPLKTON    AND   COMPANY 


PRINTED  AT  THE  APPLETON  PRESS 
NEW  YORK,  U.  S.  A. 


PREFACE   TO   THE   FIRST   EDITION 


,  To  set' fixed  limits  to  the  subject  matter  of  phvsiolog}'  is  a  very  difficult 
task,  because,  properly  conceived,  large  portions  of  the  entire  group  of  medical 
and  biological  sciences  belong  to  its  province.  A  text-book  designed  primarily 
for  medical  students  can,  however,  regard  the  field  as  somewhat  more  re- 
stricted; for  the  prospective  physician  has  abundant  opportunity  to  amplify 
his  knowledge  of  the  bodily  functions  from  his  other  studies.  Hence  in  this 
book  I  have  followed  the  usual  custom  and  have  brought  together  only  so 
much  of  our  information  respecting  the  human  body  as  can  be  described 
as  pertaining  to  its  normal  functions.  The  discoveries  made  in  the  realms 
of  practical  medicine,  of  experimental  patholog}'  and  of  pharmacology,  which 
in  many  respects  are  so  full  of  significance  for  the  processes  of  the  body,  are, 
therefore,  for  the  most  part  passed  by.  In  like  manner  the  facts  of  compara- 
tive physiology  have  been  alluded  to  only  in  exceptional  cases,  since  an  ex- 
haustive discussion  of  them  would  have  increased  the  size  of  the  book  to  a 
not  inconsiderable  extent. 

For  the  same  reason  I  have  been  unable  to  find  a  place  for  the  short 
histological  discussion  customary  in  text-books.  I  do  not  regard  this  as  an 
error,  for  a  necessarily  brief  and  superficial  resume  of  the  most  important 
histological  facts  could  be  of  no  great  service,  since  the  student  needs  a  more 
extensive  knowledge  of  the  finer  structure  of  the  body  and  must  in  any  case 
obtain  this  from  the  text-books  devoted  especially  to  that  subject.  I  do  not 
therefore  at  all  mistake  the  great  importance  of  histology  for  physiolog}'; 
on  the  contrary,  I  would  recommend  that  in  the  study  of  a  text-book  of 
this  science  a  text-book  of  histology  (and  one  of  anatomy)  be  always  at  hand 
in  order  to  combine  the  physiological  facts  with  the  histological  and  ana- 
tomical facts. 

Physiological  chemistry  also  has  developed  so  far  that  more  and  more  it 
can  claim  the  right  to  be  regarded  as  an  independent  science.  On  the  other 
hand  it  is  not  possible  to  present  the  physiological  facts  without  reference  to 
the  chemical  processes  of  the  body.  While  therefore  I  am  compelled  to  touch 
upon  the  facts  of  physiological  chemistry,  I  have  limited  the  discussion  to 


vi  ritKF.U'K  TO  Tin;  i  ii;sr  i:i)iii(».\ 

the  mo.-l  imporiaiu  huls  of  all,  li'aviii;:  iiiallcrs  ol'  dt'tail  and  cnntrovortcd 
tjuestions  to  tlu'  ti'xt-l>ooks  of  ])liysiol()i:ical  rluMiiistrv.  In  ])n'|)arin<x  ilicsc 
s<.»ctions  of  the  hook  1  have  ivt-i'ived  vcrv  vaiiiahk'  advit-i'  from  my  di>liii- 
guished  friend  Ileir  Professor  Dr.  K.  A.  II.  Miirner. 

I  may  say  further  that  the  discussion  of  the  elu'inieal  processes  of  llie 
body  is  based  in  the  main  upon  the  text-books  of  llammarsten  and  Ncumeistcr. 
The  experienced  reader  will  find  also  that  I  have  made  frequent  use  of  the 
pliysiological  monoirrai)hs  which  have  appeared  within  recent  years.  Espe- 
cially to  be  mentioned  are  the  "  Ali-remeine  Physiologic"  of  \'erworn  anil 
"Die  Zelle  und  die  Gewehe '"  of  ().  llertwig,  which  constitute  the  chief 
sources  of  the  chapter  on  the  cell. 

With  regard  to  the  physiology  of  the  sense  organs  1  may  state  that  J 
have  treated  them  in  this  book  chiefly  from  the  point  of  view  of  the  prac- 
ticing physician.  For  this  reason  the  physical  conditions  of  sensation  have 
been  discussed  rather  fully,  while  those  investigations  on  sense  perception 
falling  within  the  borderland  common  to  physiology  and  psychology,  and  of 
themselves  so  extremely  imjiortaiit.  have  been  discussed  only  in  roughest 
outline,  an  exhaustive  discussion  being  (piite  beyond  the  scope  of  the  book. 

In  the  citation  of  authorities  1  have  tried  to  hold  a  middle  course  betwei'U 
the  very  numerous  references  found  in  many  text-books  and  the  entire  ab- 
sence of  them  found  in  others.  I  must  acknowledge,  however,  that  I  have 
not  in  all  cases  succeeded  in  finding  the  proper  middle  course. 

The  few  references  given  will  direct  the  reader's  attention  to  only  the 
more  recent  monographic  discussions  of  the  a])proj)riate  sections.  Probably 
I  should  have  referred  throughout  to  the  ''  llandbiuh  der  Physiologic"  edited 
by  Hermann.    I  must  content  myself,  however,  with  citing  it  here  once  for  all. 

Among  the  many  beautiful  illustrations,  which  I  owe  to  the  liberality 
of  my  puldisher,  the  majority  have  been  taken  from  the  original  papers  of 
the  authors  cited  in  the  figures.  Figs.  3,  fi,  7,  55,  fil,  80,  .S;3,  80,  87,  88,  121 
have  been  Itorrowed,  with  the  courtesy  of  the  publishers,  from  "  Physiolo- 
gischen  Graphik  "  of  Langendorff. 

KOUEUT    TlGEKSTEDT. 
Stockholm,  May  1,  l.S'J7. 


PREFACE   TO   THE   THIRD  EDITION 


While  adhering  to  the  same  principles  which  I  have  followed  in  previous 
editions  of  this  Ijook,  I  have  in  the  present  edition  thoroughly  revised  almost 
all  the  chapters.  In  this  work  of  revision  the  monographic  discussions  con- 
tained in  the  "  Ergehnissen  der  Physiologic  "  have  been  of  very  great  service 
to  me,  and  I  would  especially  direct  the  reader  who  may  be  interested  in  a 
deeper  study  of  modern  physiology  to  this  collective  work. 

The  more  recent  literature  bearing  on  the  subjects  contained  in  Chapters 
I  to  XIV  inclusive  could  for  the  most  part  be  brought  up  only  to  the  end  of 
1903.  In  the  revision  of  the  remaining  chapters  I  have  been  able  to  make 
use  of  the  literature  of  the  first  half  of  the  present  year. 

Egbert  Tigerstedt. 

Helsixgfors,  October  1,  1904. 


TRANSLATOR'S   PREFACE 


Ix  preparing  this  abridged  udition  of  Professor  Tigerstedt's  well-knovrn 
"  Lehrbuch  der  Physiologie  des  Menschens  "  it  has  been  my  endeavor  to  bring 
the  Ijook  within  the  reach  of  the  second-year  medical  student  in  this  country. 
Believing  that  those  who  would  make  use  of  the  more  highly  technical  parts  of 
the  book,  as,  for  example,  the  mathematical  considerations  affecting  the  d}Tiam- 
ics  of  the  circulation  and  the  optics  of  vision,  already  have  access  to  these 
very  valuable  discussions  in  the  German,  I  have,  with  the  author's  permis- 
sion, omitted  these  parts.  All  other  omissions  and  condensations  have  been 
made  with  the  single  idea  alread}'  named.  I  shall  not  here  enumerate  these 
changes,  because,  with  the  exception  of  a  very  few  minor  ones,  which  in  the 
interest  of  clearness  it  has  seemed  necessary  to  make  in  the  proofs,  all 
abridgments  have  received  the  author's  expressed  approval.  Professor  Tiger- 
stedt  has  placed  me  under  very  great  obligations  for  the  readiness  he  has 
shown  Ijoth  to  adopt  my  suggestions  and  to  make  others  of  his  o\vn  motion. 

In  the  actual  work  of  translation  I  have  labored  throughout  to  give  the 
author's  thought  a  clear  and  accurate  expression.  While  feeling  my  obliga- 
tions to  the  author,  therefore,  I  have  endeavored  (not  always  with  success) 
to  leave  as  little  resistance  to  the  thought  in  the  form  of  German  idiom  and 
construction  as  possible. 

Following  in  jeneral  the  author's  usage,  I  have  employed  italics  for  three 
purposes:  for  generic  and  specific  names,  for  emphasis,  and  for  indicating 
the  key  word,  phrase,  or  clause  of  a  paragraph.  In  this  latter  use  they 
serve  the  purpose  of  subordinate  headings. 

The  few  additions  to  the  text  which  I  have  ventured  to  make  and  for 
which  I  assume  entire  responsibility,  have  l)een  selected  from  the  most  recent 
literature  and  will  be  found,  either  enclosed  in  brackets  or  in  the  form  of 
foot-notes,  bearing  the  customary  signature. 

After  examining  a  number  of  the  additional  illustrations  which  I  pro- 
posed be  introduced  for  the  benefit  of  American  students,  Professor  Tiger- 
stedt  gave  me  his  entire  authorization  to  make  such  additions  as  I  might 
deem  suitable.  The  authors  from  whose  works  these  illustrations  Avere  orig- 
inally taken  are  indicated  in  the  several  legends  which  accompany  them  and 


X  TRANSLATOR'S  PREFACE 

the  iiiuiu'diati'  soiircos  from  wliicli  1  have  ohtaiued   Iheiii  are  mentioned  in 
the  List  of  Illustrations. 

Finally,  I  wish  to  express  my  sincere  thanks  to  Professor  Graham  Lusk 
for  many  suggestions  by  which  I  have  profited  in  my  editorial  capacity,  and 
to  Professor  Percy  M.  Dawson  of  the  Johns  Hopkins  Medical  School  for 
reading  the  entire  proof. 

J.  K.  M. 
New  York,  1906. 


INTEODUCTION  TO   THE   AMERICAN   EDITION 


"  Tigerstedt's  Physiology  "  has  been  the  standard  text-book  of  German 
students  ever  since  its  first  publication  in  1897.  The  preparation  of  a 
third  German  edition  afforded  an  opportunity  of  translating  the  work  into 
English  as  the  new  proof  was  delivered  from  the  foreign  presses.  Dr.  Murlin 
presents  the  result  of  this  task  in  the  following  careful  and  accurate  repro- 
duction of  the  original. 

The  biological  introduction  is  an  admirable  chapter  of  the  book,  affording 
as  it  does  a  broad  insight  into  the  processes  of  the  hund^ler  forms  of  living 
things.  In  view  of  the  large  participation  in  this  department  of  physiology 
by  workers  in  our  own  country,  this  feature  of  the  book  will  be  especially 
welcomed. 

Tigerstedt  early  wrote  a  monogi-aph  on  the  circulation  of  the  blood  which 
to-day  stands  unrivaled,  and  in  this  important  section  of  physiology  the 
present  text-book  is  of  commanding  authority.  He  later  established  a  respira- 
tion apparatus  for  experiments  on  the  metabolism  of  men,  and  this  he  used 
not  only  in  health  but  also  for  determinations  of  the  life  processes  in 
diseased  conditions.  Tigerstedt  is  the  only  author  of  a  general  text-book 
of  physiology  who  has  had  any  experimental  knowledge  in  this  branch  of 
science.  His  chapter  on  metabolism  is  the  most  complete  general  account 
given  in  any  text-book  in  any  language,  and  it  is  certain  to  have  a  wide 
influence  among  the  many  in  this  country  who  are  striving  to  obtain  a 
knowledge  of  those  inner  processes  of  the  body  which  determine  dietary 
recjuirements  in  health  as  well  as  in  disease. 

The  treatment  of  the  subject  of  the  central  nervous  system,  and  the  gen- 
eralizations regarding  its  functions,  is  a  masterpiece  of  its  kind.  In  the 
other  parts  of  the  book  a  wide  range  of  knowledge  is  presented  with  a 
sustained  excellence  of  arrangement,  and  with  that  catholicity  of  selection 
which  has  made  the  book  so  successful  in  other  lands. 

It  has  been  said  that  good  physiology  is  the  best  preventive  of  bad 
medicine.  Tigerstedt's  physiology  is  essentially  good  physiology,  presenting 
a  picture   of   the   modern   scientific   structure   upon   which    modern   medical 


xii  INTRODUCTION   TO  THE   AMERICAN   EDITION 

practice  is  based.  It  must  be  ^"ranted  that  some  of  tlie  jjheiioiiiena  of  life 
are  to  be  explained  only  by  theoretical  induction.  But  this  is  the  daily 
experience  of  every  physician  as  regards  his  patient,  for  he  is  called  upon 
to  interpret  disease  caused  by  processes  which  he  cannot  see.  Tigerstedt's 
judicious  selection  of  the  facts  of  physiology,  and  their  interpretation  along 
lines  of  modern  critical  research,  afford  to  the  student  of  medicine  an  oppor- 
tunity for  that  kind  of  intellectual  training  which  best  fits  him  to  interpret 
phenomena  both  of  health  and  of  disease. 

The  book  may  be  earnestly  commended  to  the  medical  student  and  to 
the  practitioner. 

Graham  Lusk. 
University  axd  Bellevue  Hospital  Medical  College, 
New  Yokk. 


TABLE   OF   CONTENTS 


PAGE 

Introduction 1 

Chapter  I. — General  Physiological  Method 4  , 

§  1.     Physical,  Chemical,  and  Histological  Methods 4 

§  2.     Experiments  on  Living  Animals 5 

§  3.     Experiments  on  Surviving  Organs 6 

§  4.     The  Graphic  Method 6 

A.  The  Kymograph 7 

B.  Time  Recorders 10 

C.  Recording  by  Air-transmission 11 

D.  Registration  by  Photography 13 

Chapter  II.— The  Cell 15 

§  1.     General  Considerations 15 

A.  The  Cell  as  an  Elementary  Organism 15 

B.  The  Reciprocal  Relations  between  the  Nucleus  and  Protoplasm  .        .17 

C.  Physical  and  Chemical  Properties  of  Protoplasm 19 

D.  Morphology  of  the  Cell  Contents 20 

§  2.     The  Vital  Phenomena  of  Cells 22 

A.  Introductory  Survey 22 

B.  The  Ingestion  of  Food 30 

C.  Digestion 38 

D.  The  Oxidative  Processes 39 

E.  Elimination  of  Decomposition  Products 40 

F.  Secretion 41 

G.  Motility 42 

H.     Production  of  Light 45 

I.      Formation  of  Heat 46 

J.      Generation  of  Electricity 46 

§  3.     The  Effect  of  External  Influences  on  Cells 50 

A.  On  Stimuli  in  General 50 

B.  Automatic  Excitation 52 

C.  Chemical  Stimulation 52 

D.  Mechanical  Stimulation 56 

E.  Stimulation  by  Means  of  Light 66 

F.  Stimulation  by  Means  of  Heat 58 

G.  Electrical  Stimidation 59 

H.     Cosmic  Influences 61 

I.      Conductivity 62 

J.      The  Assimilative  Processes  Induced  by  Stimulation        ...  62 

K.     Paralysis  and  Fatigue 65 

§  4.     Death 66 


xiv  TABLE   OF  CONTENTS 

PAGE 

Chaptkr  III. — The  Chemical  Constituents  of  the  Body 68 

§  1.     The  Nitrogenous  Substances 68 

A.  The  Simple  Proteids 68 

B.  The  Compound  Proteids 75 

C.  Substances  Resembling  Proteids 77 

D.  Other  Nitrogenous  Substances 78 

§  2.     The  Nonnitrogenous  Substances 79 

A.  Fats 79 

B.  Cholesterin 80 

C.  Carbohydrates 80 

Chapter  IV. — Metabolism  and  Nutrition 83 

First  Section:  Metabolism 83 

§  1.     On  the  Method  of  Metabolism  Experiments 83 

A.  The  Ingesta 83 

B.  Determination  of  the  Excreta 84 

C.  Apportionment  of  the  Individual  Elements  to  the  Different  Excreta  .  89 

D.  Example  of  a  Metabolism  Experiment 91 

§  2.     Potential  Energy  of  the  Foodstuffs 92 

§  3.     Metabolism  in  Fasting 95 

A.  The  General  Condition  in  Fasting 95 

B.  Character  of  the  Metabolism  in  Fasting 96 

C.  Loss  of  Substance  from  the  Different  Organs 97 

§  4.     Influence  of  Food  on  the  Metabolism 98 

A.  Influence  of  the  Quantity  of  Proteid  in  the  Food  on  Proteid  Metabolism  99 

B.  The  Total  Metabolism  after  Ingestion  of  Proteid 102 

C.  Metabolism  after  Ingestion  of  Fat 104 

D.  Metabolism  after  Ingestion  of  Carbohydrates 105 

E.  Summary  and  Discussion 107 

F.  Metabolism  after  Ingestion  of  Albumoses.  Fatty  Acids,  Gelatin,  Alcohol, 

etc 108 

§5.     Influence  of  Muscular  Work  on  Metabolism 110 

§  6.     Influence  of  the  Surrounding  Temperature  on  Metabolism  .         .         .         .114 

§  7.     Metabolism  in  Animals  of  Different  Size 117 

§  8.     Retention  of  Proteid  in  the  Body 120 

§  9.     Storage  of  Carbohydrates  in  the  Body 124 

§  10.     Storage  of  Fat  in  the  Body 129 

§  11.     The  Inorganic  Foodstuffs 131 

A.  General 131 

B.  Phosphorus 132 

C.  Calcium  and  Magnesium 133 

§  12.     Flavors 133 

§13.     On  the  Theory  of  Metabolism 134 

Second  Section:  Nutrition  of  Man 137 

§  1.     Utilization  of  Foodstuffs 138 

A.  Proteid 137 

B.  Fat  and  Carbohydrates 137 

C.  Mixed  Diet 138 

§  2.     The  Energy  Requirements  of  an  Adult 140 

§3.     Nutrition  of  the  Young 143 

§  4.     Construction  of  the  Diet  from  the  Different  Articles  of  Food      .        .        .  145 


TABLE   OF  CONTENTS  XV 

PAGE 

Chapter  V. — The  Blood 147 

§  1.     The  Amount  of  Blood  in  the  Body 148 

§  2.     The  Formed  Constituents  of  the  Blood 148 

A.  The  Red  Blood  Corpuscles 148 

B.  The  White  Corpuscles .  153 

C.  The  Blood  Platelets 153 

§  3.     The  Plasma 154 

A.  Chemical  Constitution  of  the  Plasma 154 

B.  Coagulation  of  Blood 157 

Chapter  VI. — Circulation  of  the  Blood 161 

First  Section:  General  Surv^ey  of  the  Blood's  Movements IGl 

Second  Section:  The  Movements  of  the  Heart 162 

§  1.     The  Form  Changes  of  the  Heart  in  Systole 162 

A.  Structure  of  the  Ventricular  Wall 162 

B.  The  Form  Changes  of  the  Heart 163 

§  2.     Regulation  of  the  Blood  Flow  through  the  Heart 165 

A.  The  Atrio-ventricular  Valves 165 

B.  The  Semilunar  Valves 167 

§  3.     The  Heart  Sounds 167 

§  4.     Pressure  Changes  in  the  Heart  During  Its  Activity 168 

A.  Technique 168 

B.  Pressure  Variations  in  Different  Chambers  of  the  Heart         .        .        .  169 

§  5.     The  Apex  Beat 172 

§  6.     Time  Relations  of  the  Cardiac  Events 176 

§  7.     Filling  of  the  Heart  in  Diastole         .                 176 

§  8.     Power  and  Work  of  the  Heart  .        .                177 

A.  Power 177 

B.  Work 178 

§  9.     Properties  of  Heart  Muscle 179 

A.  The  Nature  of  the  Cardiac  Contraction 179 

B.  Nutrition  of  the  Heart 180 

C.  The  Behavior  of  Heart  Muscle  under  Direct  Stimulation        .        .        .  182 

§  10.     The  Cause  of  the  Rhythmical  Activity  of  the  Heart 185 

§  11.     The  Efferent  Cardiac  Nerves 188 

A.  The  Inhibitory  Nerves 188 

B.  The  Accelerator  Nerves 191 

§  12.     The  Heart  Reflexes 193 

§  13.     The  Cardiac  Nerve  Centers 195 

§  14.     Rate  of  the  Heart  Beat 196 

Third  Section:  The  Blood  Flow 198 

§1.     The  Flow  of  a  Liquid  in  Rigid  Tubes 198 

§  2.     The  Flow  of  a  Liquid  in  Elastic  Tubes 199 

§  3.     The  Flow  of  Blood  in  the  Arteries 200 

A.  Elasticity  of  Arterial  Wall 200 

B.  Methods  for  the  Determination  of  Blood  Pressure 202 

C.  Height  of  the  Blood  Pres.su re 204 

D.  Velocity  of  the  Blood  in  the  Arteries 209 

§  4.     The  Arterial  Pulse 212 

A.  The  Movement  of  Waves  in  Elastic  Tubes 212 

B.  The  Pul.se 214 

§  5.     Final  Survey  of  the  Movements  of  the  Blood  m  the  Arteries      .        .        .  218 


xvi  TABLE   OF  COXTENTS 

PACE 

§  G.     The  Flow  of  Blood  in  the  Capillaries 219 

§  7.     The  Flow  of  Blood  in  the  Veins 223 

A.  Pressure  and  Velocity 223 

B.  Aids  to  the  Blood  Flow  in  the  Veins 224 

§  8.     The  Lesser  Circulation  and  the  Respirator}^  Variations  of  Blood  Pressure  227 

A.  The  Pulmonarj'  Circulation 227 

B.  Respirator}'  Variations  of  Blood  Pressure 229 

§  9.     Vasoconstrictor  Nerves 231 

§  10.     Vasodilator  NerA'es 234 

§  11.     Vasomotor  Reflexes 235 

J  12.     The  Vasomotor  Centers 237 

§  13.     General  Considerations  on  the  Distribution  of  Blood  in  the  Body      .        .  239 

A.  Mechanical  Influences 239 

B.  The  Influence  of  Vasomotor  Ner^'es 240 

Chapter  VII. — Digestion 242- 

First  Section:  The  Digestive  Fluids  242 

§  1.     General  Sur\'ey 242 

§  2.     Saliva 245 

§  3.     Gastric  Juice 246 

A.  The  Acid  of  the  Gastric  Juice 247 

B.  Pepsin 248 

C.  Rennm 250 

D.  Gastric  Steapsin 250 

§  4.     Pancreatic  Juice 251 

A.  The  Amylolytic  Enzymes 251 

B.  The  Proteolytic  Enzyme,  Trypsin 252 

C.  Lipolytic  Enzyme,  Steapsin 253 

§  5.     Bile 253 

§  6.     Intestinal  Juice 255 

Second  Section:  Secretion  of  the  Digestive  Fluids 256 

§  1.     General  Sur^'ey 256 

§  2.     The  Salivary  Glands 257 

A.  Secretory  Ner\'es 257 

B.  Morphological  Changes  During  Secretion 261 

§  3.     The  Glands  of  the  Stomach 263 

A.  Secretory  Nerves 263 

B.  The  Gastric  Glands 266 

C.  Why  Does  the  Stomach  not  Digest  Itself? 269 

§  4.     Secretion  of  Pancreatic  Juice 269 

A.  Secretory  Nerves 269 

B.  Morphological  Changes  in  the  Pancreas 272 

§  5.     The  Liver  and  the  Secretion  of  Bile 272 

A.  General  Phenomena  of  Hepatic  Secretion 272 

B.  Dependence  of  the  Secretion  of  Bile  upon  the  Blood  Supply         .        .  273 

C.  The  Discharge  of  Bile  in  Digestion 275 

§  6.     The  Glands  of  the  Intestine 276 

A.  Glands  of  the  Small  Intestine 276 

B.  The  Glands  of  tjie  Large  Intestine 277 

Third  Section :  Movements  of  the  Alimentary  Canal 278 

§  1.     Mastication 278 

§  2.     Sucking 279 


TABLE   OF  CONTEXTS  xvii 

PAGE 

§  3.     Deglutition 279 

§  4.     Movements  of  the  Stomach 283 

A.  Kneading  Movements 283 

B.  Evacuation  of  the  Stomach 285 

C.  Vomiting 286 

§  5.     Movements  of  the  Intestine 286 

Fourth  Section:  Digestion  in  the  Different  Divisions  of  the  Alimentary  Canal       .  290 

§  1.     Digestion  in  the  Mouth 290 

§  2.     Digestion  in  the  Stomach 291 

§  3.     Digestion  in  the  Intestine 294 

§  4.     Formation  of  Fseces  and  Defecation 298 

Chapter  VIII. — Absorption 301 

§  1.     Absorption  in  General 301 

§  2.     Absorption  of  Carbohydrates 303 

§  3.     Absorption  of  Fat 304 

§  4.     Absorption  of  Proteid 305 

§  5.     Absorption  of  Mineral  Substances 307 

Chapter  IX. — Respiration 310 

First  Section:  Movements  of  Respiration 310 

§  1.     Elasticity  of  the  Lungs  and  Intrathoracic  Pressure 310 

§  2.     Inspiration 312 

A.  Registration  of  Respiratory  Movements 312 

B.  Movements  of  the  Ribs 314 

C.  Movements  of  the  Diaphragm 316 

§  3.     Expiration 317 

■    §4.     The  Number  of  Respiratory  Movements 318 

§  5.     Exchange  of  Air  in  the  Lungs 319 

§  6.     Concomitant  Respiratory  Movements 321 

§  7.     Special  Forms  of  Respiratory  Movements 321 

§  8.     Pressure  Changes  in  the  Respiratory  Passages 321 

§  9.     The  Respiratory  Sounds 322 

§  10.     Means  of  Protection  for  the  Lungs 323 

Second  Section:  Innervation  of  Respiration 323 

§  1.     The  Efferent  Nerves 323 

§  2.     The  Respiratory  Center 325 

§  3.     Respiratory  Reflexes 327 

A.  Reflexes  through  the  Vagi 327 

B.  Fibers  from  Anterior  Parts  of  the  Brain  to  the  Medulla         .        .        .  329 

C.  Other  Respiratory  Reflexes 330 

§  4.     Normal  Stimulation  of  the  Respiratory  Center 331 

Third  Section:  The  Blood  Gases 333 

§  1.     Absorption  of  Gases  in  Liquids 334 

§  2.     The  Blood  Gases 335 

A.  Nitrogen  and  Argon 335 

B.  Oxygen 335 

C.  Carbon  Dioxide 337 

D.  The  Quantity  of  Blood  Gases 339 

E.  The  Distribution  of  Blood  Gases  between  Corpuscles  and  Plasma        .  340 
Fourth  Section :  The  Respiratory  Exchange  of  Gases 340 

§  1.     Mechanism  of  Exchange  between  Blood  and  Alveolar  Air  ....  340 
2 


xviii  TABLE   OF  CONTENTS 

PAGE 

§  2.     Exchange  of  Gases  between  Blood  and  T.ymph 342 

§  3.     Changes  Produced  in  the  Respired  Air 342 

§  4.     The  Absolute  Amount  of  Kespiratorj-  Exchange 345 

Chapter  X. — The  Ljanph  and  Its  Movements 347 

§  1.     Chemical  Properties  of  the  Lymph 347 

§  2.     Movements  of  the  Lymph 348 

§  3.     The  Forpiation  of  Ljaiiph 349 

§  4.     The  Lymph  Glands 352 

§  5.     Absorption  from  Serous  Cavities 353 

Chapter  XL — The  Lifluence  of  the  Organs  on  One  Another 355 

§  1.     The  Osmotic  Phenomena 355 

§  2.     Internal  Secretions 356 

A.  General 356 

B.  The  Testes 357 

C.  The  Ovaries 358 

D.  The  Thyroid  Gland 358 

E.  The  Pancreas 362 

F.  The  Adrenal  Bodies 364 

G.  The  Pituitary  Body       .        .        .        . 367 

H.    The  Kidneys 367 

I.      The  Spleen 368 

Chapter  XII. — The  Final  Decomposition  of  Foodstuffs  in  the  Body      ....  369 

§  1.     The  Final  Destruction  of  Proteid 369 

§  2.     The  Decomposition  of  Carbohydrates 374 

§3.     The  Decomposition  of  Fat 376 

Chapter  XIII. — The  Excretions  of  the  Body 378 

First  Section:  The  Urine  and  Its  Excretion 379 

§  1.     The  U  ine 379 

A.  The  General  Properties  of  the  Urine 379 

B.  Composition  of  LIrine 381 

§  2.     The  Excretion  of  Urine 384 

A.  Structure  of  the  Kidneys 384 

B.  Mechanism  of  the  Excretion  of  Urine 386 

§  3.     Micturition 390 

A.  The  Ureters 391 

B.  The  Urinary  Bladder 391 

Second  Section:  Excretion  through  the  Skin 394 

§  1.     The  Sebaceous  Glands 394 

§  2.     Excretion  of  Sweat 395 

A.  Composition  and  Properties 395 

B.  The  Excretory  Process 396 

§  3.     The  So-called  Insensible  Perspiration 397 

Chapter  XIV. — Animal  Heat  and  Its  Regulation 398 

§  I.     The  Temperature  of  the  Human  Body 398 

§  2.     The  Source  of  Animal  Heat 402 

§  3.     Loss  of  Heat  from  the  Body 403 

§  4.     Protection  against  Loss  of  Heat 404 

§  5.     Regulation  of  the  Body's  Temperature 406 

A.  Regulation  of  Heat  Loss 407 

B.  Centers  for  Heat  Regulation 408 


TABLE   OF   CONTENTS  xix 

PAGE 

Chapter  XV. — Functions  of  Cross-striated  Muscles 410 

First  Section:  General  Physiology  of  Muscle  and  Nerve 410 

§  1.     Fundamental  Laws  of  Ner\^ous  Activity 410 

§  2.     The  Properties  of  Resting  Muscles 412 

A.  Elasticity 412 

B.  Chemistry  of  Muscle 413 

§  3.     Stimulation  of  Muscles  and  of  Nerves 414 

A.  The  Muscle  Cur^e 414 

B.  Rate  of  Transmission  of  a  Nerve  Impulse 417 

C.  Mechanical  Stimulation  of  Nerves 418 

D.  Electrical  Stimulation  of  Muscle  and  Nerve 418 

E.  Effect  of  a  Rapid  Series  of  Stimuli 428 

F.  Voluntary  Contractions 430 

§  4.     Signs  of  Activity  in  Muscle  and  Ner\'e 431 

A.  Electrical  Phenomena 431 

B.  The  Muscle  Tone 434 

C.  The  Chemical  Alterations  in  Muscle  Due  to  Its  Activity        .                 .  434 

D.  Mechanical  Work 435 

E.  Heat  Formation  in  Muscle 439 

§  5.     The  Central  Innervation  of  a  Skeletal  Muscle 440 

§  6.     Fatigue  and  Recovery  of  Muscles  and  Ner\'es 441 

A.  General  Phenomena 441 

B.  Fatigue  of  Human  Muscles  and  Nerves 443 

§  7.     Rigor  Mortis 447 

§  8.     Smooth  Muscles 447 

Second  Section:  Reciprocal  Relations  between  the  Muscles  and  Other  Organs  of 

the  Body 448 

Chapter  XVI. — On  Sensations  in  General 451 

First  Section:  Qualitative  Relations  between  Stimulus  and  Sensation     .        .        .  451 

Second  Section :  The  Quantitative  Relations  between  Stimulus  and  Sensation       .  455 

§  1.     Weber's  Law 450 

Chapter  XVII. — The  Sensory  Functions  of  the  Skin 458 

§  1.     Sensations  of  Temperature 458 

§  2.     Pressure  and  Touch 461 

§  3.     The  Local  Sign 463 

§  4.     Pain 465 

Chapter  XVIII. — Organic  Sensations 469 

§  1.     Motor  Sensations 469 

§  2.     Physiological  Significance  of  Motor  Sensations 472 

§  3.     The  Semicircular  Canals  and  the  Otolith  Sacs  of  the  Inner  Ear          .        .  473 

A.  Anatomical 473 

B.  Experimental  Suppression  of  the  Semicircular  Canals    ....  476 

C.  Artificial  Stimulation  of  the  Semicircular  Canals 479 

D.  The  OtoHth  Sacs 481 

E.  Observations  on  Men 481 

Chapter  XIX.— Taste  and  Smell 483 

§  1.     Sen.sations  of  Taste 483 

§  2.     Sensations  of  Smell 486 


XX  TABLE   OF  CONTENTS 

PAGE 

Chapter  XX. — Hearing,  Voice,  and  Speech        ....<,....   489 

First  Section:  Auditory  Sensations 489 

§  1.     Stimuli  Appropriate  for  the  Organ  of  Hearing 489 

A.  Loudness 489 

B.  Pitch 489 

C.  Timbre 491 

§  2.     Transmission  of  Sound  in  the  Ear 493 

A.  The  External  Ear 494 

B.  The  Middle  Ear 494 

§  3.     Excitation  of  the  Auditory  Nerve 498 

A.  The  Resonators  in  the  Cochlea 498 

B.  Objections  to  the  Resonator  Theory  . 501 

Second  Section:  Physiology  of  Voice  and  Speech 502 

§  1.     Action  of  the  Laryngeal  Muscles 502 

§  2.     Voice  Production 504 

§  3.     Registers  of  Voice 504 

§  4.     Elements  of  Speech 506 

A.  Vowels 506 

B.  Consonants 507 

Chapter  XXL— Vision 508 

First  Section:  The  Eye  as  an  Optical  Instrument 508 

§  1.     The  Optical  Constants  of  the  Eye 508 

§  2.     Images  upon  the  Retina 513 

A.  Direct  and  Indirect  Vision 514 

B.  The  Light-perceiving  Layer  of  the  Retina 514 

C.  Visual  Angle  and  the  Limits  of  Vision 517 

§  3.     Static  Refraction  in  the  Eye 519 

§  4.     Optical  Defects  of  the  Eye 520 

A.  Transparency  of  the  Media  of  the  Eye 521 

B.  Form  of  the  Refracting  Surfaces 522 

C.  Astigmatism 522 

D.  The  Angle  between  the  Line  of  Vision  and  the  Optical  Axis  .  525 

E.  Chromatic  Aberration  in  the  Eye 526 

F.  Summary 527 

§  5.     The  Iris 527 

§  6.     Accommodation 529 

A.  Range  of  Accommodation 529 

B.  Mechanism  of  Accommodation 530 

Second  Section:  Excitation  of  the  Retina  and  Visual  Sensations     ....   536 

§  1.     Light  Rays 536 

§  2.     The  Phenomena  of  Excitation 537 

A.     Fatigue  and  Recovery  of  the  Visual  Organ 539 

§  3.     Sensations  of  Color 541 

A.  Relations  of  the  Properties  of  Light  to  the  Different  Constituents  of  the 

Retina 541 

B.  Successive  Color  Induction 542 

C.  Color  Mixture 542 

D.  On  the  Theory  of  Color •        .544 

E.  Simultaneous  Contrast 547 


TABLE   OF  CONTENTS  xxi 

PAGE 

Third  Section:  Movements  of  the  Eyes  and  Visual  Perceptions        ....  549 

§  1.     Action  of  the  Eye  Muscles 549 

A.     Limits  of  the  Eye  Movements 551 

§  2.     Significance  of  the  Eye  Movements  for  the  Outward  Projection  of    Vis- 
ual Perceptions 552 

§  3.     Binocular  Vision 555 

A.  Correspondence  of  the  Two  RetinjB 555 

B.  Single  Vision  with  Two  Eyes 555 

C.  Perception  of  Depth 556 

Chapter  XXII. — The  Physiology  of  the  Nerve  Cell  and  of  the  Spinal  Cord  .                .  559 
§  1.     General  Considerations  Concerning  the  Finer  Structure  of  the  Nervous 

System 559 

§  2.     The  Structure  of  the  Spinal  Cord 562 

§  3.     Kinds  of  Nerves 564 

A.  Classification  According  to  Function 564 

B.  Special  Properties  of  Different  Kinds  of  Nerve  Fibers     ....  565 

C.  Magendie's  Doctrine 565 

§  4.     Functions  of  the  Nerve  Cell 566 

A.  The  Nutritive  Functions  of  Nerve  Cells 567 

B.  Physiological  Stimuli  of  Nerv^e  Cells .        .  569 

C.  Mode  of  Reaction  of  Nerve  Cells  to  Stimulation 570 

D.  Dependence  of  the  Nerve  Cell  upon  the  Blood  Supply,  and  the  Effects 

of  Poisonous  Substances 572 

E.  Morphological  Changes  in  the  Nerve  Cell.    Reproduction  and  Regener- 

ation       574 

§  5.     Reflex  Processes 575 

A.  Segmentation  in  the  Central  Nervous  System 575 

B.  General  Features  of  Reflexes 576 

C.  Inhibition  of  Reflexes 577 

D.  Augmentation  of  Reflexes 579 

E.  Reflex  Responses  to  Different  Stimuli 580 

§  6.     Automatic  Excitation 580 

§  7.     Tonus 581 

§  8.     Central  Functions  of  Peripheral  Nerve  Cells 582 

§  9.     Centers  in  the  Spinal  Cord 585 

A.  Control  of  Skeletal  Muscles 586 

B.  Influence  of  the  Spinal  Cord  on  the  Vegetative  Functions     .        .        .  587 
§  10.     Conducting  Pathways  in  the  Spinal  Cord 588 

A.  Electrical  Stimulation  of  the  Cord 588 

B.  Methods  of  Determining  the  Conducting  Pathways  in  the  Spinal  Cord.  589 

C.  Anatomical  Data  Concerning  the  Conducting  Pathways  of  the  Cord    .  591 

D.  Experimental  and  Clinical  Observations  on  the  Conducting  Pathways 

in  the  Spinal  Cord 595 

Chapter  XXIII.— Physiology  of  the  Brain-stem 599 

§  1.     General  Surv^ey 599 

A.  Method 599 

B.  Divisions  of  the  Brain 601 

§  2.     The  Medulla  Oblongata,  or  After-brain 602 

§  3.     The  Cerebellum 605 


xxii  TABLE   OF   CONTEXTS 

PAGE 

§  4.     The  Mesencephalon,  or  Midbrain .       .        .613 

A.  The  Corpora  Quadrigemina 613 

B.  The  Crura  Cerebri 614 

§  5.     The  Diencephalon   or  Tweenbrain 617 

§  6.     Functions  of  the  Brain-stem  as  a  Whole 618 

Chapter  XXIV. — Physiology  of  the  Cerebrvun 629 

First  Section:  The  Motor  and  Sensory  Areas  of  the  Cortex 632 

§  1.     The  Motor  Areas 632 

A.  General  Survey 632 

B.  Stimulation  of  the  Motor  Cortical  Areas  in  Different  ilammals  .   633 

C.  Direct  and  Crossed  Effects  of  Stimulation  of  the  Motor  Cortical  Areas  640 

D.  The  Commissures  between  the  Cortical  Areas  of  the  Two  Hemispheres  641 

E.  Cortical  Epilepsy 641 

F      Suppression  of  the  Motor  Cortical  Areas 643 

G.     The  Course  of  the  Conducting  Pathways  from  the  Motor  Cortical  Areas 

to  the  X'uclei  of  the  Motor  Xerves 647 

H.  Development  of  the  Motor  Areas  of  the  Cortex  .  .  .  .  .  648 
§  2.  Influence  of  the  Cerebral  Cortex  on  the  Vegetative  Processes  of  the  Body  649 
§  3.     The  Sensory  Cortical  Areas 650 

A.  Area  of  General  Sensation  and  Touch 651 

B.  The  Cortical  Areas  of  Taste  and  Smell 653 

C.  The  Auditory  Area 654 

D.  The  Visual  Area 655 

E.  Recapitulation 658 

Second  Section:  Psycho-physical  Functions  of  the  Cerebrum 658 

§  1.     The  Significance  of  the  Motor  and  Sensory  Cortical  Areas  ....   659 

§  2.     The  Language  Faculties 661 

§  3.     The  Association  Centers  of  Flechsig 665 

A.  Anatomical 666 

B.  The  Anterior  Association  Center 668 

C.  The  Posterior  Association  Center 669 

D.  Final  Survey 670 

§  4.     The  Time  Consumed  by  Psycho-physical  Processes 673 

Appendix:  X'ourishment  of  the  Brain 676 

Chapter  XXV. — Physiology  of  Special  X'erves 680 

§  1.     Cranial  Xerves 680 

§  2.     Spinal  Xerves 682 

A.  Sensory  Xerves 682 

B.  Motor  Xerves 682 

§  3.     The  Sympathetic  X'er\'es 685 

A.  Relations  of  the  Sympathetic  X'erves  to  the  Central  X^ervcus  System.  685 

B.  Course  of  the  SjTnpathetic  Fibers 687 

C.  Regeneration  in  the  Sympathetic  System 689 

D.  Afferent  X'erves  in  the  SjTnpathetic  System 689 

Chapter  XXVI. — Reproduction  and  Growth 691 

First  Section:  Reproduction 691 

§  1.     The  Male  Sexual  Organs 691 

A.  The  Testes 692 

B.  The  Accessory  Sexual  Glands 692 

C.  Erection  and  Ejaculation 693 


TABLE   OF  CONTENTS  xxiii 

PAGE 

§  2.     The  Female  Sexual  Organs        .....,,...  695 

A.  The  Ovaries  and  Oviducts 695 

B.  The  Uterus 696 

C.  Pregnancy  and  Birth 697 

D.  Inners'ation  of  the  Sexual  Organs 700 

§  3.     Secretion  of  Milk 700 

A.  The  Milk 700 

B.  Secretion  of  Milk 703 

Second  Section:  Growth  of  the  Human  Body 705 


LIST   OF   ILLUSTPwVTIONS' 


FIG.  P'^«f^ 

1. — Illustrating  the  use  of  the  graphic  method  in  recording  the  contraction  of  a  frog's 

muscle  (drawn  for  this  edition) 6 

2. — Muscle  curves  recorded  on  the  same  drum 7 

3. — The  mercury  manometer 8 

4. — Blood  pressure  curve  of  rabbit 8 

5. — Membrane  manometer  (courtesy  of  Prof.  W.  T.  Porter) 9 

6. — Kymograph  with  "endless"  paper 9 

7. — Electric  signal  used  as  time  marker 10 

8. — Curves  of  blood  pressure  in  left  ventricle  and  aorta  of  the  dog        .        .        .        .11 

9. — Recording  tambour  of  Marey 11 

10. — Receiving  tambour  for  pulse  record 12 

11. — Pulse  curve  from  carotid  of  man 12 

12. — Capillary  electrometer 13 

13. — Action  currents  of  dog's  heart 13 

14. — PolystomeUa  vennsta 17 

15. — Thalassicola  nucleata 18 

16. — Parenchyma  cells  from  root  cortex  of  Frittilaria 21 

17. — Leaf  showing  starch  formation 23 

18. — Root  of  bean  with  Bacteria  tubercles 23 

19. — Gromia  ovijormis 35 

20. — Amoeba  polypodia 35 

21. — Phases  in  the  life  history  of  Amoeba  (from  Mill's  "Animal  Physiology")        .        .  36 

22. — White  blood  corpuscle  of  frog  with  bacillus  Ingested 37 

23. — Vampyrella  spirogyroe 37 

24. — Frontana  leucas  (courtesy  of  Prof.  Gary  N.  Calkins) 41 

25. — Chlorophyll  bodies  in  Lemna  triscula 42 

26. — Mode  of  movement  of  Amoeba 43 

27. — Amoeboid  movements  of  white  blood  corpuscles 43 

28. — VortiVe//a  (from  Mill's  "Animal  Physiology") 44 

29. — Demarcation  current  in  a  muscle 47 

30.— Electric  apparatus  of  cramp  fish  (from  Mill's  "Animal  Physiology")      ...  49 

31. — Illustrating  chemotaxis 54 

32. — Motor  response  in  Paramoecium  (courtesy  of  Prof.  Gary  X.  Calkins)      ...  55 

33. — Distribution  of  Bacteria  in  sunlight                                        57 

34. — Effects  of  constant  current  on  the  shrimp,  Palcemonetes 60 

35 — Opalina  ranarum "1 

36. — Cross  section  of  intestinal  musculature  of  cat 62 

37. — A  shoot  of  Antcnniilaria  antennina 64 

38. — Crystals  of  serum  albumin 69 

39. — Face  mask  for  respiration  experiments 85 

>  Unless  otherwise  stated  the  illustrations  in  this  edition  are  the  same  as  in  the  third  German  edition. 


XXVI 


LIST   OF    ILLUSTRATIUXS 


(horse) 


40. — Schema  of  Atwater-Benedict  respiration  caloriniettT  (courtesy  of  Prof.  P>ancis 

G.  Benedict) 

41. — Respiration  apparatus  of  Pettenkoffer  and  Voit  (drawn  for  this  edition) 

42. — Respiration  apparatus  of  Sonden  and  Tigerstedt 

43. — Three  experiments  on  ehmination  of  urea  by  fasting  dogs 

44. — Ehmination  of  X  in  urine  of  man 

45. — Preparations  from  the  Hver  (normal  and  diabetic)  of  man 

46. — Blood  crystals 

47. — .\bsorption  spectrum  of  oxyha>moglobin 
48. — Absorption  spectrum  of  haemoglobin     . 

49. — Hsemin  crystals 

50. — Schema  of  the  circulation 

51. — Cross  section  through  a  fully  contracted  human  heart 

52. — "Krehl's  cone"  of  fibers  in  the  left  ventricle 

53. — Casts  of  ventricular  cavities  of  ox  heart  in  rigor  mortis 

54. — Position  of  atrio-ventricular  valves  when  closed. 

55. — Cardiographic  sound 

56. — Intracardial  pressure  curv'es  of  horse     .... 

57. — Pressure  curs'es  of  right  ventricle,  left  ventricle,  and  aorta  of  hors 

58. — Pressure  cur\'es  from  left  ventricle  and  aorta  of  horse 

59. — Schema  illustrating  Ludwig's  theory  of  the  apex  beat 

60. — Pressure  curves  in  right  auricle,  right  ventricle,  and  of  apex  beat 

61. — Receiving  tambour  of  Marey's  cardiograph 

62. — Curves  of  apex  beat  and  carotid  pulse  of  man 

63. — Variations  of  electrical  potential  in  human  heart 

64. — Action  current  of  human  heart       .... 

65. — Direct  stimulation  of  isolated  cat's  heart 

66. — Influence  of  temperature  on  isolated  heart  of  the  cat 

67. — Cardiac  nerves  of  dog       .... 

68. — Representation  of  pulse  rate   . 

69. — Depressor  nerse  of  rabbit 

70. — Behavior  of  blood  pressure  on  stimulation  of  depressor  nerve 

71. — Pulse  rate  in  man  at  different  ages 

72. — Flow  of  liquid  through  rigid  tube  of  uniform  diameter 

73. — Flow  of  liquid  through  rigid  tube  of  varj'ing  diameter 

74.— Artificial  schema  of  mechanics  of  circulation  (courtesy  of  Prof.  W. 

75. — Cubic  enlargement  of  aorta  of  rabbit,  increasing  internal  pressure 

76. — Erlanger's  apparatus  for  determination  of  blood  pressure  in  man  (courtesy  of 

Prof.  Joseph  Erlanger) 

77. — Blood  pressure  curve,  feeble  stimidation  of  vagus 
78. — Blood  pressure  curve,  medium  stimulation  of  vagus 
79. — Blood  pressure  curve,  strong  stimulation  of  vagus 

80. — Current  clock 

81. — Ha^madomograph  with  air-transmission 

82. — Velocity  and  pressure  curves  in  carotid  of  horse 

83. — Plethysmograph 

84. — Plethysmographic  cur\-c 

85. — Schema  iUustrating  Weber's  theorj'^  of  pulse 
86. — Spring  of  Marey's  sphygmograph  . 
87. — Marey's  sphygmograph  as  used 

88. — Radial  pulse  curs^e 

89. — Contractile  cells  embracing  wall  of  capillary 


T.  Porterj 


86 
87 
88 
101 
102 
126 
150 
151 
1.51 
153 
162 
163 
163 
164 
166 
168 
169 
170 
171 
172 
173 
174 
175 
179 
180 
183 
184 
191 
192 
193 
194 
197 
198 
199 
200 
201 

203 
205 
206 
207 
209 
209 
210 
211 
212 
213 
214 
215 
216 
220 


LIST   OF   ILLUSTRATIONS 


xxvu 


Dr. 


Ed 


ar  F. 


90. — Capillary  constricted  by  vasomotor  influence      .... 

91. — Apparatus  for  determining  blood  pressure  in  capillaries 

92. — Cubic  enlargement  of  inferior  vena  cava  of  cat   . 

93. — Position  of  human  body  in  which  veins  are  stretched  most 

94. — Position  of  human  body  in  which  veins  are  relaxed  most 

95. — Variations  of  aortic  pre.ssure  in  dog 

96. — Respiratory  variations  of  blood  pressure,  rabbit 

97. — Reflex  rise  of  blood  pressure  in  rabbit 

9S. — Reflex  fall  of  blood  pressure  in  rabbit 

99. — Section  of  hepato-pancreas  of  an  isopod  crustacean  (courte.sy  o 
Nolan,  Philadelphia  Academy  of  Natural  Sciences) 

100. — Parotid  gland  of  rabbit 

101. — Parotid  gland  of  cat 

102. — Parts  of  a  tongue  gland  of  the  frog 

10.3. — Hourly  course  of  secretion  of  gastric  juice  in  dog's  stomach  . 
104. — Hourly  course  of  the  digestive  action  of  gastric  juice  on  proteid 
105. — Secretion  capillaries  surrounding  parietal  cells  of  gastric  glands 
106. — The  course  of  pancreatic  secretion  in  man  .... 

107. — ^The  course  of  secretion  in  the  pancreas  of  the  dog   . 
108. — Enzymes  of  pancreatic  juice,  relative  rate  of  activity  of 
109. — Pancreas  of  rabbit  as  observed  in  living  animal 
110. — Hourly  course  of  discharge  of  bile  into  the  intestine  of  the  dog 

111. — Glands  of  large  intestine  of  rabbit 

112. — Sagittal  optical  sections  of  floor  of  mouth  and  neck 

113. — Motor  nerv'es  of  throat  and  palate  of  monkey   .... 

114. — Nerves  of  stomach  musculature 

115. — Schema  to  illustrate  relation  of  longitudinal  muscular  flbers  of  intestine 

116. — Schema  illustrating  rhythmical  segmentation  of  small  intestine  (courtesy  of  Dr, 

W.  B.  Cannon) 

117. — Schema  illustrating  antiperistalsis  (courtesy  of  Dr.  W.  B.  Cannon) 
118. — Successive  stages  in  absorption  of  fat  in  epithelial  cells  of  frog's  intestine 
119. — Duodenum  of  mouse  showing  absorption  of  iron       .... 
120. — Experiment  on  expansion  of  lungs  of  rabbit  (drawn  for  this  edition) 

121. — Pneumographic  curve  of  man 

122. — Apparatus  for  registering  volume  of  the  respired  air 

123. — Respiratory  curve  of  rabbit 

124. — ^Thorax  as  seen  from  the  right  side 

125. — Schema  of  movements  of  the  diaphragm,  liver,  stomach,  and 
tion 

-Diaphragmatic  and  thoracic  types  of  respiration 

-Number  of  respirations  per  minute  in  persons  of  different  ages 

-Spirometer 

-Respiratory  curve  of  rabbit 

130 — Schema  of  Ltidwig's  pump  for  extraction  of  blood  gases. 
131. — Absorption  of  oxygen  by  horse's  blood  .... 
132. — Absorption  of  carbon  dioxide  in  solution  of  hsemoglobin 

133. — Lung  catheter 

134. — Amount  of  carbon  dioxide  expired,  measured  in  two-hour  periods 
135. — Elimination  of  carbon  dioxide  on  ordinary  diet  and  in  fiisting 

136. — Elimination  of  carbon  dioxide  by  a  boy 

137. — A  mj'TccBdematous  woman 

138. — A  cretinous  child  (from  Holt's  "Diseases  of  Children")  . 


126.- 
127.- 
128.- 
129.- 


spleen  in  respira 


P.VGE 

220 
221 
223 
226 
226 
229 
2.30 
2.36 
237 


244 
260 
261 
262 
265 
265 
267 
270 
270 
271 
272 
275 
277 
281 
282 
284 
287 

288 
289 
304 
307 
311 
313 
313 
314 
315 

316 
318 
319 
320 
328 
.334 
337 
339 
341 
343 
344 
345 
359 
360 


xxviii  LIST   OF   ILLUSTRATIONS 

FIG.  PAGE 

139.— Crystals  of  urea 382 

140.— Crystals  of  uric  acid 382 

141. — Other  forms  of  uric-acid  crystals 383 

142. — Hippuric-acid  crystals 383 

143. — Schema  representing  blood  vessels  of  the  kidney 385 

144. — Schema  representing  tubules  of  the  kidney 385 

145.— The  nerves  of  the  bladder 392 

146. — Portion  of  the  preputial  gland  of  the  mouse 394 

147. — The  normal  diurnal  variations  of  temperature  in  man 399 

148. — The  elimination  of  carbon  dioxide  in  man  determined  every  two  hours                .  400 

149. — The  temperature  of  the  body  after  death 401 

150. — Curves  of  extension  and  elastic  shortening  of  muscle 412 

151. — Apparatus  of  Blix  and  Loven  for  recording  the  elasticity  curve  of  a  muscle        .  412 

152. — Extension  and  elasticity  curves  of  the  frog's  gastrocnemius 413 

153. — Fick's  apparatus  for  recording  variations  in  the  length  and  in  the  tension  of  a 

muscle ...  414 

154. — Simple  contraction  curve  of  the  frog's  gastrocnemius 415 

155. — Curves  illustrating  the  method  of  determining  the  rate  of  conductivity  in  the 

sciatic  nerve  of  a  frog  (from  a  student's  note-book) 417 

156. — Schema  representing  the  rheocord  of  Du  Bois-Reymond 418 

157. — Nonpolarizable  electrodes  (courtesy  of  Prof.  W.  T.  Porter) 419 

158.— Induction  coil  (courtesy  of  Prof.  W.  T.  Porter) 420 

159. — Details  of  the  Wagner  hammer,  or  interrupter  of  the  induction  coil  .  421 
160. — Arrangement  of  apparatus  for  sending  induction  shocks  through  a  muscle  (drawn 

for  this  edition) 422 

161. — Catelectrotonus 424 

162. — Anelectrotonus 425 

163. — Stimulation  of  a  nerv^e  by  ascending  make  and  descending  break  induction 

shocks 426 

164. — Distribution  of  an  electric  current  in  a  human  arm 427 

165. — Entrance  into  and  exit  from  a  nerve  of  an  electric  current  applied  to  the  skin 

over  the  nerve 428 

166. — Tetanus  curve  of  the  frog's  gastrocnemius 429 

167. — Tetanus  curves  of  the  white  and  red  muscles  of  the  rabbit 430 

168. — Schema  representing  a  rheotome  experiment 431 

169. — Rheotome  of  Bernstein 432 

170. — Schema  representing  the  spread  of  an  excitation  causing  an  action  current          .  433 

171. — Illustrating  the  theory  of  electro  tonic  currents 433 

172. — Relation  of  work  to  size  of  stimulus 435 

173. — Isotonic  and  simple  projectile  contractions 436 

174. — Relation  of  the  form  of  contraction  curve  to  load 436 

175. — Veratrin  curve  of  frog's  gastrocnemius 437 

176.— Isotonic  and  isometric  contractions 438 

177. — Fatigue  curv'es 441 

178. — Fatigue  curv^es  (courtesy  of  Prof.  F.  S.  Lee) 442 

179. — Ergograph  of  Mosso 444 

180. — Fatigue  tracings  obtained  w^ith  Mosso's  ergograph 444 

181. — Fatigue  tracings  with  different  rates  of  stimulation 445 

182. — Arrangement  of  cold,  heat,  and  pressure  spots  on  the  skin  of  the  wrist        .        .  459 

183. — Topographical  distribution  of  cold  and  heat  senses 460 

184. — The  semicircular  canals  of  the  pigeon,  laid  bare 474 

185. — Relation  of  the  planes  of  the  semicircular  canals  to  each  other      ....  475 


LIST   OF   ILLUSTRATIONS 


XXIX 


186. — Distance  of  the  anterior  and  posterior  canals  (prolonged)  from  each  other 

187. — Pigeon  with  membranous  labyrinths  removed 

188. — Pigeon  five  days  after  removal  of  the  right  membranous  labyrinth 

189. — Pigeon  twenty  days  after  removal  of  the  right  membranous  labyrinth 

190. — The  taste  zone  of  the  upper  surface  of  the  human  tongue 

191. — Course  of  the  gustatorj'  nerve  fibers  (from  Leube's  "Special  Medical  Diagnosis") 

192. — Olfactometer  of  Zwaardemaker 

193. — Seebeck's  siren 

194. — Schema  representing  the  relations  of  overtones  to  their  fundamental 

195. — Resonator  of  Helmholtz 

196. — Transverse  section  through  the  left  auditorj'  canal  and  tympanic  membrane 
197. — Horizontal  section  through  the  tympanic  cavity 

198. — -Hammer  and  anvil 

199. — The  organ  of  Corti  of  the  human  ear 

200. — Action  of  the  posterior  crico-arj'tenoid  muscle  .... 
201. — Action  of  the  lateral  crico-arytenoid  muscle       .... 
202. — Larj'ngoscopic  picture  during  quiet  respiration 
203. — Appearance  of  the  vocal  cords  while  producing  a  chest  tone  . 
204. — Position  of  the  vocal  organs  in  producing  the  sound  of  broad  A 
205. — Position  of  the  vocal  organs  in  producing  the  sound  of  long  E 

206. — Illustrating  the  refractive  index 

207. — Illustrating  the  refracting  surfaces  of  the  eye 

208. — Illustrating  a  simple  refracting  system 

209.— Illustrating  the  nodal  points  in  a  complex  system 

210. — Position  of  the  cardinal  points  in  the  schematic  eye 

211. — Section  through  the  retina  of  a  full-grown  dog 

212. — Illustrating  the  blind  spot  in  the  eye   .... 

213. — View  of  the  rods  and  cones  from  the  outer  surface  of  the  retina 

214. — Diagram  showing  the  visual  angle        .... 

215. — The  static  refraction  of  a  hypermetropic,  an  emmetropic 

216. — Method  of  demonstrating  entoptic  phenomena 

217. — Entoptic  particle  in  the  vitreous  body 

218. — Illustrating  spherical  aberration 

219. — Refraction  of  light  rays  in  regular  astigmatism  (from 

Ophthalmology") 

220. — Astigmatism  chart 

221. — Diagram  illustrating  chromatic  aberration 

222. — The  iris  of  a  cat  at  rest  and  on  stimulation 

223. — The  iris  of  a  cat  with  a  sector  isolated 

224. — Method  of  demonstrating  accommodation  in  the  eye 

225. — Reflection  of  images  from  the  eye  in  accommodation 

226. — The  protrusion  of  the  iris  in  accommodation 

227. — Meridional  section  through  the  ciliarj'  body 

228. — Zonule  of  Zinn  of  an  adult  man 

229. — Schema  of  the  mechanism  of  accommodation  according  to  Schon 

230. — Schematic  representation  of  the  optic  tracts  (modified  from  Fuchs'   "Text 

of  Ophthalmology,"  drawn  for  this  edition) 

231. — Optogram  formed  in  the  visual  purple 

232. — Morphological  changes  produced  in  a  frog's  eye  by  light 

233. — Disk  with  white  and  black  sectors 

234 — Illustrating  the  excitation  of  the  retina  successively  by  white  and  black  sectors 
235. — Excitation  of  the  retina  as  a  function  of  the  time  exposed 


and  a  myopic  ey 


Fuchs'   "Text-book  of 


P.\GE 

475 
476 
476 
477 
483 
484 
487 
490 
492 
493 
494 
495 
496 
500 
503 
503 
504 
505 
505 
506 
509 
510 
511 
511 
513 
515 
516 
517 
518 
519 
521 
522 
523 


book 


XXX  LIST   OF    ILLUSTRATIONS 


FIG 


PAGE 

236. — Illustrating  successive  color  induction .')-42 

237. — Excitation  of  the  different  components  of  the  visual  organ  by  light  rays  of  dif- 
ferent wave  lengths 5-1^ 

238. — Excitation  of  the  different  components  in  eyes  of  KiJnig  and  Dieterici  by  dif- 
ferent wave  lengths ^■^•^ 

239. — Illustrating  simultaneous  contrast 548 

240.^The  extra-ocular  muscles  and  their  axes  of  rotation  (from  B^ox's  "Diseases  of 

the  Eye") 550 

241. — Rotation  of  the  eye  about  the  separate  axes 551 

242. — ^The  field  of  vision  projected  on  a  distant  plane  perpendicular  to  the  line  of 

vision 552 

243. — Illustrating  Scheiner's  experiment 553 

244. — Illustrating  optical  delusion  in  judgment  of  distances 554 

245. — Illustrating  optical  delusion  in  judgment  of  distances 554 

246. — Illustrating  optical  delusion  in  judgment  of  distances 554 

247. — ^The  rivalry  of  the  two  retina> 555 

248. — Illustrating  the  simultaneous  formation  of  images  of  an  oblique  line  in  the  two 


eyes 


556 


249. — Showing  the  positions  of  these  images  on  the  retinae 557 

250. — Stereoscopic  vision 557 

251. — Brewster's  stereoscope 558 

252  — Ganglion  cell  of  a  leech  showing  intracellular  networks 560 

253. — Pericellular  network  of  Golgi,  nucleus  dentatus  of  the  dog 561 

254. — Semidiagrammatic  section  of  the  spinal  cord 562 

255. — Schema  of  connections  in  the  cord 563 

256. — Reflex  contractions  of  the  frog's  leg,  illustrating  summation  in  the  nerv^e  cells 

of  the  cord 571 

257. — The  relative  resistance  of  several  different  nerve  centers  to  asphyxiation  573 

258. — Schema  of  an  axon  reflex  through  peripheral  ganglion  cells 584 

259. — Schema  of  a  reflex  through  several  peripheral  ganglion  cells 584 

260. — Illustrating  a  possible  explanation  of  an  axon  reflex 585 

261. — Cro.ss  section  at  different  levels  of  the  spinal  cord 589 

262. — Secondary  descending  degeneration  in  the  cord 590 

263. — Illustrating  method  of  stimulating  the  cord  electrically 590 

264. — Sections  through  the  cervical  and  lumbar  parts  of  the  cord 591 

265. — Diagram  of  the  course  of  the  sensory  conducting  pathways  (from  Striimpell's 

"A  Text-book  of  Medicine") 592 

266. — Diagram  of  the  upper  and  lower  motor  conducting  pathways  (from  Barker's 

"Nervous  System") 594 

267. — Median  section  through  the  brain,  showing  divisions 600 

268. — Transverse  section  of  the  meduUa  oblongata 602 

269. — Position  of  the  nuclei  of  the  cranial  nerves 603 

270. — Brain  of  a  dog  with  the  cerebellum  removed 606 

271. — Diagram  showing  paths  connecting  the  cerebellum  and  pons  with  the  cerebnim 

(from  Barker's  "Nervous  System") filO 

272. — Frontal  section  through  the  anterior  quadrigeminal  body  of  a  human  foetus  .  615 
273.— Schematic  representation  of  the  nucleus  of  the  oculo  motor  ner\'es  .616 

274. — The  brain  of  Squalius  cephahis,  a  bony  fish 618 

275. — The  brain  of  ScyUium  canicula,  a  dog-shark 619 

276.— The  brain  of  a  frog 620 

277.— The  brain  of  Hatteria  punctata,  a  hzard  (from  Wiedersheim's  "Anatomic  der 

Wirbeltiere") 621 


LIST  OF  ILLUSTRATIONS  xxxi 

FIG.  PAGE 

278. — Brain  of  a  pigeon  (from  Wiedersheim's  "Anatomie  der  Wirbeltiere")  .        .   622 

279. — Brain  of  a  rabbit  (from  Wiedersheim's  "Anatomie  der  Wirbeltiere")  .  .  .  623 
280. — Lateral  view  of  a  dog's  brain  (from  Ellenberger  and  Baum's  "Anatomie  des 

Hundes") 624 

28L — ^The  remainder  of  the  brain  of  Goltz'  dog  after  removal   of  the  cerebral  hemi- 
spheres   625 

282. — Dorsal  surface  of  the  dog's  brain,  with  excitation  points  indicated  according  to 

Fritsch  and  Hitzig's  early  experiments 632 

283. — Latent  period  of  muscular  contraction  induced  by  stimulation  of  the  cortex  and 

by  stimulation  of  the  underlying  white  matter 633 

284. — Structure  of  the  cortex  of  the  convolutions  bordering  on  the  fissure  of  Rolando  634 
285. — Motor  cerebral  localization  in  the  monkey,  outer  surface  of  left  hemisphere 

(from  Barker's  "Xerv'ous  System") 635 

286. — Motor  cerebral  localization  in  the  monkey,  inner  surface  of  left  hemisphere 

from  Barker's  "Nervous  System") 635 

287. — Motor  cortical  areas  in  the  monkey  (from  Barker's  "Ner\'ous  System")      .        .   637 

288. — The  motor  cortical  areas  of  the  chimpanzee 638 

289. — Diagram  of  the  external  surface  of  the  left  cerebral  hemisphere  of  man  .  .  639 
290. — Diagram  of  the  internal  surface  of  the  right  cerebral  hemisphere  of  man  .   639 

291. — The  course  of  an  epileptic  attack  induced  by  stimulation  of  the  motor  cortical 

zone 642 

292. — The  motor  tract  at  various  levels  of  the  internal  capsule  (from  Barker's  "Ner- 
vous System") 647 

293. — Sensory  areas  on  the  outer  surface  of  the  right  cerebral  hemisphere     .  .   654 

294. — Sensory  areas  on  the  inner  surface  of  the  left  cerebral  hemisphere  .        .   654 

295. — Schematic  representation  of  the  optic  tracts  (modified  from  Fuchs,  drawn  for 

this  edition) 656 

296.— Diagram  of  the  speech  tract  together  with  various  centers  of  the  cerebral  cor- 
tex concerned  in  speech  (from  Leube's  "Special  Medical  Diagnosis")       .        .   662 

297. — The  myelogenetic  areas  of  the  human  brain,  outer  surface 666 

298. — The  myelogenetic  areas  of  the  human  brain,  inner  surface 667 

299. — Curve  representing  the  depth  of  sleep 677 

300. — Distribution  of  the  superficial  areas  ser\'ed  by  the  differerit  sensory  roots  (from 

Striimpell's  "A  Text-book  of  Medicine") 683 

301. — Schematic  representation  of  the  connections  of  the  sympathetic  fibers  .   686 

302. — Normal  curve  of  contraction  of  the  uterus 698 

303. — Pressure  curve  of  the  last  contraction  of  the  uterus  in  parturition  .  .  699 
304. — Curves  representing  the  height  and  weight  of  boys  and  girls  of  different  ages  .  709 
305. — Variations  in  the  height  of  military  recruits  in  Sweden 710 


A   TEXT-BOOK    OF    PHYSIOLOGY 


INTRODUCTION 

The  aim  of  .scientific  physiology  is,  to  determine  the  functions  of  the  animal  body  and  to 
derive  them  strictly  from  the  elementary  conditions  of  animal  life  (Ludwig). 

The  animal  l)oc\y  is  composed  of  a  large  number  of  different  organs.  The 
first  task  therefore  is  to  find  out  what  functions  are  performed  by  each  indi- 
vidual organ,  to  learn  how  these  functions  may  be  influenced  by  different 
conditions,  and  to  determine  as  exactly  as  possible  the  intensity  with  which 
each  function  may  be  performed  under  different  circumstances. 

Of  all  the  varying  conditions,  whose  influence  on  the  functions  of  the 
organs  we  shall  have  to  investigate,  there  is  none  so  important  as  the  action 
of  the  organs  themselves  upon  one  another,  and  the  consequent  manifold 
interdependence  among  them.  It  is  only  by  giving  attention  to  this  inter- 
action of  the  organs  that  we  can  arrive  at  any  real  determination  of  their 
functions,  or  make  any  satisfactory  progress  toward  understanding  how  the 
existence  and  capabilities  of  the  body  as  a  whole  result  from  the  collective 
activity  of  the  individual  organs. 

In  most  of  the  functions  the  activity  of  the  elementary  constituents  of  the 
body,  the  cells  and  tissues,  is  to  be  reckoned  as  a  fundamental  condition.  And 
the  farther  modern  physiology  progresses,  the  more  clearly  does  it  appear 
that  the  cell,  or  as  Briicke  appropriately  calls  it,  the  elementanj  organism, 
represents  the  real  unit  of  the  Ijody,  not  only  in  the  morphological  sense,  but 
in  the  physiological  sense  as  well.  The  remarkable  properties  of  the  living 
substance,  as  exhibited  in  most  of  the  fundamental  processes  going  on  in  the 
living  body,  are  dependent  upon  much  more  complicated  conditions  than  the 
exact  scientific  investigations  of  our  time  have  been  able  to  explain :  but  in 
most  physiological  problems  where  research  has  progressed  far  enough  to 
warrant  theoretical  conclusions  to  any  degree  well  founded,  it  has  been  shown 
that  the  fundamental  conditions  for  the  functions  of  the  organs  and  tissues 
are  precisely  those  conditions  which  determine  the  vital  activity  of  the  cells. 
It  need  scarcely  be  emphasized  here  that  in  so  saying  I  have  meant  to  give 
no  actual  theory,  that  is  to  say,  no  mechanical  explanation,  of  the  phenomena 
in  question.  If  we  trace  the  functions  of  the  organs  back  to  the  vital  activity 
of  the  cell,  we  have  done  nothing  more  than  point  out  where  the  solution  of 
the  prol)lem  is  ultimately  to  be  sought,  without  having  thereby  entered  more 
deeply  into  the  problem. 

3  1 


2  INTRODUCTION 

I  wisli  expressly  to  state  that  lliis  coiucplion  does  not  at  all  imply  that  in 
the  livincr  body  forces  are  to  he  found  ..f  an  essentially  different  kind  from 
those  which  rule  in  the  inanimate  world.  The  fundamcnial  point  of  view 
of  all  modern  natural  science  is  this,  that  every  ])henomenon  is  the  necessary 
consequence  of  certain  active  causes,  wliich  when  they  .cooperate  under  the 
same  circumstances  always  produce  the  same  phenomenon.  The  energy  which 
represents  the  active  cause  of  any  natui-al  jn-ocess  is  never  destroyed  and  is 
never  created  anew :  it  may  assume  various  forms,  it  may  pass  from  one  form 
to  another,  but  in  its  quantitative  relations  it  is  never  changed. 

This  principle  of  the  conservation  of  energy,  which  was  first  enunciated 
by  J.  R.  Mayer,  J.  P.  Joule,  L.  A.  Colding,  and  H.  Helmholtz  (1842-1847), 
in  physiologi/,  as  in  other  fields,  is  the  foundation  of  all  scientific  thinking. 
We  maintain  that  in  those  processes  which  take  place  in  the  living  body 
and  which  together  make  up  our  conception  of  life,  the  principle  of  the 
conservation  of  energy  holds  good ;  and  in  so  doing  we  place  physiological 
investigation  on  the  firm  basis  of  exact  natural  science,  even  though  we  are  not 
yet  in  position  to  follow  out  this  view  to  the  phenomena  of  life  in  all  their 
details,  or  to  conjecture  what  is  the  real  cause  of  the  activity  of  living  sub- 
stance. This  conception  of  the  living  world  and  of  its  ruling  forces  is  quite 
different  from  the  ancient  vitalism,  now  finally  abandoned.  That  doctrine 
relied  upon  a  capricious  phantom  of  vital  force,  which,  entirely  unfettered 
by  natural  law,  at  times  was  responsible  for  the  most  unheard  of  results,  and 
at  others  vanished  completely  from  the  field. 

All  animals  throughout  tlie  whole  vast  series,  from  the  lowest  to  the  highest, 
are  the  proper  subject  of  physiological  research.  Wiile  it  is  true  that  the 
close  relation  of  physiology  with  medicine  has  given  man  and  the  animals 
which  stand  next  to  him  in  the  scale  an  exceptionally  predominant  place  in 
research  as  well  as  in  education,  physiology  does  not  seek  to  know  the  func- 
tions of  the  body  and  the  fundamental  conditions  of  existence  in  the  human 
species  alone.  Philosophically  all  animals  possess  an  equal  Interest  for  physi- 
ology; and  in  studying  the  fundamental  conditions  of  life  (cell  activity  and 
its  dependence  upon  different  varial)les)  we  are  compelled  to  widen  the  prov- 
ince of  our  rci^earch  still  more  and  to  draw  upon  the  other  large  groups  of 
living  beings,  the  unicellular  organisms  and  plants,  for  data  looking  to  the 
explanation  and  completion  of  the  results  ol)tained  from  higher  animals. 

Moreover,  it  is  incumbent  upon  physiology  to  study  the  development  of 
vital  phenomena  both  in  the  individual  and  in  the  animal  kingdom  as  a  whole. 
Thiis  it  is  placed  side  l)y  side  with  comparative  anatoniy  whose  province  it  is 
to  investigate  the  development  of  all  organic  forms  from  the  lowest  to  the- 
highest.  We  are  not  to  forget,  however,  that  physiology  is  an  exact  natural 
science.  It  is  not  sufficient  to  demonstrate  how  a  definite  function  appears 
first  in  its  simplest  form  and  then  becomes  more  and  more  manifold  and 
complicated :  physiology  must  give  also  a  mechanical  explanation.  Investi- 
gation of  the  elementary  mechanism  of  the  phenomenon  is  therefore  the  chief 
and  all-important  thing  in  physiology,  and  if  we  were  to  name  the  ultimate 
goal  of  the  science,  we  should  say  it  is  to  furnish  a  mechanical  explanation 
of  the  origin  of  living  beings  and  of  their  progressive  development  to  higher 
and  higher  forms.     Within  the  province  of  physiology  would  thus  fall   the 


INTRODUCTION  3 

mechanical  explanation  of  morphological  results,  and  according  to  this  con- 
ception physiology  would  constitute  the  very  summit  of  all  biological  investi- 
gation. It  is  scarcely  necessary  to  remark  that  in  the  present  state  of  our 
knowledge  we  cannot  yet  forecast  how  this  far-distant  goal  shall  be  reached, 

Eeferences. — Helmholtz,  "  Uber  die  Wechselwirkung  der  Naturkrafte  und 
die  darauf  beziiglichen  neuesten  Ermittlungen  der  Physik  "  (1854).  "Uber  die 
Erhaltung-  der  Kraft  "  (1862) — in  "  Vortrage  uud  Reden  "  by  Hermann  v.  Helm- 
holtz.    I.   Braunschweig,  1884. 


CHAPTER    I 

GENERAL    PHYSIOLOGICAL    METHOD 

§  1.    PHYSICAL,  CHEMICAL,  AND   HISTOLOGICAL   METHODS 

Physiology  makes  use  of  all  the  modern  aids  to  research  in  natural 
science.  We  have  not  infrequently  to  employ  the  finest  instruments  of  pre- 
cision and  the  highest  mathematical  analysis.  The  physiology  of  the  two 
highest  sense  organs,  the  eye  and  the  ear,  has  progressed  so  far  that  every 
fact  which  relates  not  to  our  owti  perceptions  and  interpretations,  hut  to  the 
purely  physical  conditions  of  their  origin,  can  he  treated  wdth  a  discrimination 
and  exactness  of  experimentation  which  place  this  portion  of  physiology  on  a 
plane  with  the  most  exact  of  all  natural  sciences,  namely,  physics.  The  same 
holds,  for  the  most  part  also,  in  the  general  physiology  of  cross-striated  muscle 
and  nerve.  Here  electrical  science  and  several  other  hranches  of  physics  have 
found  wide  application. 

The  study  of  the  circulation  of  the  blood  presents  an  extraordinarily 
complicated  problem  in  hydraulics;  the  study  of  equilibrium  and  locomotion 
of  the  body  is  to  be  treated  from,  a  purely  mechanical  point  of  view;  in  the 
discussion  of  the  respiratory  exchange  of  gases  in  the  lungs  and  in  the  tissues 
physiology  turns  to  account  both  theoretically  and  experimentally  the  physical 
theory  of  gases ;  and  the  doctrine  of  heat  regulation  is  hased  naturally  on 
the  physical  theory  of  heat.  In  short,  almost  every  division  of  physics  has 
some  direct  bearing  upon  our  study  of  the  functions  of  the  body. 

In  the  same  way  chemistry  is  of  far-reaching  importance  in  physiological 
research.  The  chemical  nature  of  the  substances  contained  in  or  formed  in 
the  animal  body  is  one  of  the  first  things  to  be  considered.  Besides  this, 
chemical  physiology  has  to  investigate  also  the  changes  which  the  ingested 
substances  undergo  in  the  vital  processes  of  the  body. 

Microscopical  investigation  furnishes  us  valuable  data  with  regard  to  the 
activity  of  the  cells,  and  histological  methods  have  therefore  very  wide  appli- 
cation in  physiology. 

The  physiology  of  the  sense  organs  and  of  the  central  nervous  system 
stands  in  very  close  relation  with  psychology  and  the  theory  of  knowledge, 
or  to  put  it  more  strongly,  a  thoroughgoing  study  of  this  branch  of  physiology 
is  impossible  without  a  knowledge  of  these  sciences. 

Finally,  physiology  must  take  into  account  also  the  discoveries  of  pathology 
and  of  pharmacodynamics.  For  however  the  functions  of  the  body  are  influ- 
enced by  the  different  abnormal  changes,  or  by  poisons,  they  are  not  altered 
in  nature ;  and  the  study  of  these  changes  must  evidently  throw  light  on  the 
normal  processes. 
4 


EXPERIMENTS  OX   LIVING   ANIMALS  5 

As  for  the  rest,  physiology  must  create  its  o^ii  methods  according  to  the 
nature  of  the  problems  to  be  solved;  and  in  the  following  presentation  of  the 
functions  of  the  body  we  shall  discuss  as  far  as  may  be  necessary  for  our 
present  purposes  the  methods  in  use.  There  are  however  some  general  methods 
of  physiological  teclinique  which  it  will  be  appropriate  to  discuss  in  this  place. 

§2.    EXPERIMENTS   ON   LIVING  ANIMALS 

It  is  true  that  one  can  obtain  important  information  concerning  the 
functions  of  the  organs  and  of  the  entire  body  ivithout  any  operative  inter- 
ference— indeed,  all  of  our  direct  observations  on  man  have  been  made  under 
such  circumstances.  But  it  is  often  necessary  to  make  the  organs  accessible 
to  immediate  observation.  We  are  therefore  often  compelled  to  perform  on 
living  animals  many  kinds  of  operations,  some  of  which  put  the  skill  and 
inventive  genius  of  the  operator  to  a  severe  test.  In  these  operations  the 
animals  are  as  a  rule  ancesthetized  with  ether,  chlorofonn,  chloral,  morphine 
or  some  other  narcotic.  Only  if  the  purpose  of  the  experiment  makes  it  neces- 
sar}'  is  the  operation  performed  on  un-ana^sthetized  animals.  For  many  physi- 
ological purposes  the  animal  must  be  observed  for  a  long  time  after  the  end  of 
the  operation,  and  in  such  cases  it  is  necessary  to  use  the  antiseptic  and  aseptic 
methods  of  surgery  with  every  possible  care.  Furthermore,  it  is  many  times 
of  advantage  in  the  experiment  to  sujjpress  the  voluntary  movements  of  the 
animal,  and  this  is  done  by  administering  the  American  arrow  poison,  curare. 
Since  this  drug  paralyzes  the  respiratory  muscles  along  with  others  it  is 
necessary  to  resort  to  artificial  respiration,  which  is  usually  accomplished  by 
rhythmically  forcing  into  the  lungs  with  a  bellows  a  quantity  of  air  suitable 
to  the  size  of  the  animal.  The  air  is  introduced  through  the  trachea  by 
means  of  a  cannula  connected  with  the  bellows.  In  all  operations  where 
the  pleural  cavities  must  be  opened  artificial  respiration  is  indispensable 
(Vesalius,  about  1540). 

After  the  animal  has  been  prepared  in  this  way,  the  particular  experiment 
follows.  It  would  be  impossible  to  describe  here  even  in  condensed  form  the 
different  principles  of  experimentation  which  must  be  observed  if  perfectly 
unequivocal  results  are  to  be  obtained.  The  following  may  be  given  as  an 
illustration : 

There  are  in  general  only  two  ways  of  discovering  the  influence  of  the 
central  nervous  system  on  a  given  organ  or  function :  either  the  nerve  supply- 
ing that  organ  may  be  cut  and  the  effects  on  the  behavior  of  the  organ  noted, 
or  the  nerve  may  be  stimulated  artificially  and  the  resulting  action  of  the 
organ  be  determined.  In  most  cases  the  latter  method  gives  the  clearer  results, 
for  mere  section  of  the  nerve  cannot  give  us  any  definite  conclusions,  unless 
the  nerve  at  the  moment  it  was  cut  was  actually  transmitting  impulses  from 
the  central  system,  which  of  course  is  by  no  means  always  the  case. 

It  is  often  of  great  profit,  in  determining  the  physiological  importance 
of  an  organ,  to  extirpate  it,  and  to  maintain  the  animal  alive.  The  resulting 
absence  of  certain  phenomena  frequently  permits  of  very  valuable  conclusions. 
Especially  is  this  true  in  the  case  of  organs  like  the  thyroid  gland  and  the 
adrenal  bodies,  which  to  direct  observation  disclose  no  sign  of  their  func- 


6 


GENERAL  PHYSIOLOGICAL  METHOD 


tious.  Extirpation  and  transscction  represent  important  methods  of  research 
in  studying  the  functions  of  the  central  nervous  system.  It  cannot  be  denied 
however  that  the  resuUs  of  excision  methods  are  unfortunately  too  often 
very  ditlicult  of  exjilanation.  and  that  their  interpretation  is  not  infrequently 
made  still  more  ditlicult  by  unintentional  lesions. 

§3.    EXPERIMENTS   ON   SURVIVING   ORGANS 

In  the  cold-blooih'd  aiiinidls  niani/  onjans  remain  alire  for  a  long  time 
after  the  death  of  ^he  organism,  even  when  they  have  been  cut  out  of  the  body. 
By  virtue  of  this  property  it  has  been  possible  to  collect  a  great  mass  of  most 
important  facts.  Our  knowledge  of  the  general  properties  of  nerve  and  muscle 
rests  for  the  most  part  on  experiments  with  exsected  organs.    Organs  removed 


Fig.    1. — Illustrating   ttie  u.se  of  the  graphic  method  in  recording  the  simple  contraction  of  a 
frog's  muscle.      For  description,  .see  text. 

from  the  Ijody  remain  still  longer  alive  if,  as  was  first  done  by  Ludwig  and  his 
school,  they  be  artificially  nourished  with  blood.  Under  such  conditions  it  is 
))Ossible  also  to  maintain  organs  of  warm-blooded  animals  alive  for  a  consid- 
(•ral)le  time  after  death  of  the  body  as  a  whole.  Organs  removed  from  the 
Ijody  which  remain  capable  of  activity  are  called  surviving  organs. 


§  4.    THE    GRAPHIC   METHOD 

Functions  of  organs  are  not  infrequently  expi'essed  by  outward  move- 
ments of  some  kind,  which  as  a  rule  are  so  rapid  that  their  details  cannot  be 
followed  by  the  naked  eye.  They  can  be  studied  very  exactly,  however,  if 
one  can  hit  upon  a  method  by  which  the  movements  record  themselves  upon  a 
moving  surface  (graphic  method,  Ludwig,  1847). 

Since  this  method  finds  very  wide  application  in  most  branches  of  physiol- 


THE   GRAPHIC  METHOD 


ogy,  it  is  necessary  to  describe  it  here  somewhat  fully.  The  apparatus  em- 
ployed for  recording  movements  by  the  graphic  method  consists  essentially 
of  two  parts:  (o)  the  surface  upon 
which  the  movement  is  traced,  and 
(b)  the  mechanism  by  which  the 
movement  is  transferred  to  the  re- 
cording surface. 

A.    THE   KYMOGRAPH 

[A  very  simple  illustration  of  the 
graphic  method  is  given  in  Fig.  1,  where 
the  simple  contraction  of  a  frog's  mus- 
cle is  being  recorded  on  a  moving  sur- 
face— an  application  of  the  method  first 
made  by  Helmholtz  in  18.52.  In  such 
an  apparatus  ^  the  surface  consists  of  a 
glazed  paper  covered  evenly  with  the 
soot  from  a  gas-flame  and  attached  to 
the  surface  of  the  drum  (D)  of  an  in- 
strument called  the  kymograph.  The 
drum  is  caused  to  revolve  in  the  direc- 
tion of  the  arrow  by  a  clockwork  (CW) 
inclosed  in  the  base  of  the  kymograph. 
The  clockwork  is  propelled  by  a  strong 
spring  which  is  wovnid  by  means  of  the 
lever  at  the  left.  By  means  of  the 
thumbscrews  (AS)  and  fans  (F)  of 
different  sizes,  the  gearing  of  the  clock- 
work may  be  so  adjusted  as  to  revolve 
the  drum  at  any  desired  speed. 

The  recording  lever  (RL)  termi- 
nates in  a  fine  point  which  bears  on  the 
smoked  surface,  and,  as  the  drum  re- 
volves, scratches  a  tracing  in  the  soot. 
The  muscle,  the  gastrocnemius  of  a  frog, 
is  so  prepared  that  its  tendon  of  Achilles 
is  free  to  be  attached  to  the  hook  on 
the  lever.  The  other  end  of  the  muscle  is 
still  attached  to  the  femur,  a  stump  of 
which  is  left  to  be  fastened  in  the  clamp. 
In  order  to  imitate  as  nearly  as  i)()s- 
sible  the  action  of  the  muscle  in  its 
normal  relations,  it  is  necessary  that 
it    be   made   to    lift   some   weight    (W) 

— i.  e.,  to  do  a  certain  amount  of  work.  This  weight,  however,  has  considerable 
inertia  compared  with  the  lever  itself,  and  in  order  that  this  may  influence  the 
character  of  the  contraction  as  little  as  possible,  the  weight  is  fastened  to  the  lever 
quite  close  to  its  axis,  the  muscle  itself  being  fastened  somewhat  farther  from  the 
axis.    Electrical  connections  are  made  so  as  to  send  a  shock  through  the  muscle. 


Fig.  2. — Muscle  curves  recorded  one  above 
the  other  on  the  same  drum ;  to  be  read 
from  right  to  left.  The  vertical  line  marks 
the  moment  of  stimulation. 


'  For  the  sake  of  simplicity  the  recording  surface  in  the  figure  is  shown  white,  and  the 
tracing  black. 


GENERAL   THYSIOLUUICAL   METHOJJ 


When  the  muscle  is  thus  caused  to  contract,  it 
lifts  the  lever  and  a  "  muscle  cui"ve,"  or  myogram, 
the  proportions  of  which  are  determined  by  the 
extent  of  the  contraction  and  the  si)eed  of  the 
drum,  is  recorded. — Ed.] 

When  it  is  desired  to  compare  with  one  an- 
other several  successive  contractions  of  the  same 
or  of  different  muscles,  the  curves  may  be  recorded 
one  above  another  by  simply  lowering  the  drum  on 
its  supporting  axis  to  different  levels.  Such  a 
series  is  shown  in  Fig".  2. 

Tracings  made  in  this  way  are  preserved  for 
future  study  by  immersing  the  smoked  paper  for 
a  moment,  after  it  has  been  cut  loose  from  tlie 
drum,  in  a  solution  of  shellac  in  wood  alcohol. 
The  alcohol  evaporates  quickly,  leaving  a  perma- 
nently hard  varnish  over  the  soot. 

The  graphic  method  is  adapted  for  recording 
a  great  many  other  physiological  phenomena. 
The  first  use  made  of  it  on  an  extensive  scale 
was  that  of  recording  the  blood  pressure  and  its 
variations   (Ludwig,  1847). 


The  blood  pressure  in  an  artery  may  be  deter- 
mined by  tying  a  cannula  into  the  central  cut-end 
of  an  artery  and  connecting  it  with  a  U-shaped 
tube  containing  mercury  (mercury  manometer, 
Fig.  3).  When  the  connections  are  properly 
made  and  the  artery  is  undamped,  the  blood  pres- 
sure is  brought  to  bear  on  the  mercui-y  column  in  the  limb  (a)  of  the  tube,  and  the 
column  in  the  other  limb  (b)  is  forced  upward.    This  difference,  however,  is  never 


Fig.  3. — Tlie  mercviry  manome- 
ter, provided  with  a  writing 
point  for  recording  tlie  level 
of  the  mercury  in  the  limb 
(6)  of  the  tube. 


Fig.  4. — Blood  pressure  curve  taken  from   a  rabbit.     .4,  the  line  of  no  pressure;    T,  the  time 
recorded  in  seconds;   D,  the  pressure  tracing.     To  be  read  from  right  to  left. 


THE  GRAPHIC  METHOD  9 

constant  but  shows  incessant  variations  corresponding  to  the  heart  beats,  respira- 
tory movements,  etc.  These  variations  produce  osciUations  in  the  mercury  col- 
umn, which  are  recorded  by  placing  on  the  free  surface  of  the  mercury  a  float  (s) 
to  which  is  attached  a  light  rod  carrying  at  its  upper  end  a  writing  point.  The 
writing  point  is  adjusted  so  as  to  scratch  a  tracing  on  a  lightly  smoked,  revolving 


Fig.  5. — A  membrane  manometer,   after  Porter. 

drum.     Fig.  4  represents  a  tracing  (D)  of  the  blood  pressure  in  a  rabbit  recorded 
in  this  way.      (For  further  explanation  of  this  experiment,  see  Chapter  V.) 

Owing  to  the  inertia  of  the  mercury  column,  the  actual  variations  of  pres- 
sure are  not  exactly  reproduced  by  this  method.  They  may  be  more  faithfully 
portrayed  if  the  blood  pressure  can  be  brought  to  bear  on  an  elastic  membrane 


Fi< 


A  kymograph  with  "cn(llt\ss"  paper,  after  Liulwig  and  Hahzar. 


or  spring  (elastic  manometer).  [Fig.  5  shows  such  a  manometer.  A  small 
chamber  about  7  mm.  in  diameter  is  provided  with  two  stopcocks,  one  of  which 
is  connected  with  the  artery  the  pressure  ih  which  is  to  be  measured,  while  the 
other  opens  to  the  atmospheric  air.    This  chamber  is  closed  above  by  an  elastic 


10  GENERAL  PHYSIOLOGICAL  METHOD 

nieinbrane  (not  shown)  upon  which  is  fastened  by  means  of  cement  a  small  disk 
supporting-  a  rod  which  carries  a  magnifying  lever.  The  height  of  the  writing 
point,  which  is  fastened  to  the  lever,  may  be  varied  by  means  of  the  thumb- 
screw at  the  top.  Errors  due  to  inertia  of  the  blood-column  itself  may  be  still 
further  diminished  by  damping'  its  movements  with  the  stopcock  between  the 
chamber  and  the  artery.  A  thumbscrew  at  the  right  enables  one  to  graduate 
this  resistance  as  required. — Ed.] 

In  case  it  is  desired  to  continue  the  record  of  the  blood  pressure  or  of 
other  physiological  movements  uninterruptedly  for  a  long  time,  a  kymograph 
carrying  two  drums,  placed  at  some  distance  from  each  other  and  so  arranged 
that  the  smoked  paper  extends  around  both,  may  be  employed,  and  a  longer 
recording  surface  is  thus  obtained.  A  still  longer  record  can  be  made  in  ink 
on  a  white  surface  by  means  of  a  kymograph  carrying  "  endless  "  paper  (Fig.  6). 
By  means  of  a  "  pen  "  of  suitable  construction,  a  record  can  be  continued  for 
days,  the  paper  being'  unrolled  from  one  spool  and  rolled  onto  another  at  the 
proper  rate  of  speed,  after  the  ink  has  had  time  to  dry. 


B.    TIME   RECORDERS 

It  is  often  necessary  to  know  the  speed  at  which  the  revolving  surface 
passes  the  writing  point.  This  may  be  determined  roughly  by  regulating  the 
revolutions  of  the  drum  to  a  certain  uniform  speed ;  but  if  the  exact  temporal 


Fig.   7. — An  electric  signal  used  as  a  time  marker,  after  Deprez. 

relations  of  the  events  which  are  being  recorded  nuist  he  known,  it  is  necessary 
to  employ  a  time  marker.  This  instrument  commonly  takes  the  form  of  an 
electric  signal. 

A  convenient  form  is  that  represented  in  Fig.  7.  An  electro-magnet  (?n) 
bears  on  its  armature  a  recording  lever  (s)  which  can  be  arranged  so  as  to  write 
on  a  smoked  surface.  The  movements  of  the  armature,  and  hence  those  of  the 
lever,  are  determined  by  making  and  breaking  the  current  to  the  magnet  at 
regular  intervals  of  time.  If  it  is  desired  to  mark  seconds,  as  in  Fig.  4,  a  clock 
beating  seconds  may  be  so  arranged  as  to  make  and  break  the  current.  If  small 
fractions  of  a  second  are  required  as  in  Fig.  8,  a  tuning  fork  vibrating  the 
desired  number  of  times  per  second  may  be  made  to  dip  a  platinum  wire  in  and 
out  of  mercury  with  each  vibration  and  so  interrupt  the  current. 

The  tuning  fork  itself  may  also  be  employed  as  the  time  marker  by  attach- 
ing a  very  light  writing  point  to  one  of  its  prongs  and  arranging'  this  so  that 
it  will  make  a  light  tracing  on  the  recording  surface  while  the  tuning  fork  is 
in  vibration. 

It  will  be  apparent:  (1)  that  the  time  interval  to  be  employed  must  be 
adapted  to  the  speed  of  the  drum  and  this  in  turn  to  the  rapidity  of  the  events 


THE  GRAPHIC  METHOD 


11 


to  be  recorded;  and  (2)   that  while  it  is  not  necessary  to  have  the  drum  move 
at  a  uniform  speed,  if  the  time  record  is  made  simultaneously  with  the  physio- 


FiG.   8. — Curves  of  blond  pressure  in  the  left  ventricle  (V)  and  in  the  aorta  (A)  of  the  dog,  after 
Hiirthle.      ,S',  the  time-record  in  iJotiis  of  a  second.      To  be  read  from  left  to  right. 

logical  record,  much  more  satisfactory  results  will  be  obtained  if  it  does  move 
both  uniforndy  and  steadily. 


C.    RECORDING   BY  AIR-TRANSMISSION 

The  method  of  air-transmission  for  the  registration  of  physiological  events, 
first  introduced  into  physiology  by  Buisson  (1861)  and  later  brought  to 
perfection  by  Marey,  has  also  found  wide  application.  The  ])rinciples  of  this 
method  may  be  understood  from  the  following : 

When  two  thin-walled  rubber  bulbs  are  connected  with  each  other  by  means 
of  a  rubber  tube  having  fairly  rigid  walls,  and  pressure  is  exerted  on  the  one. 


Fig.  9. — Recording  tambour  of  Marey,  actual  size,  a,  metallic  case;  6,  thin  India-rubber  mem- 
brane; c,  thin  disk  of  aluminium  supjjorting  the  lever  d  (a  small  portion  of  which  only  is 
represented);  e,  screw  for  placing  support  of  lever  vertically  over  c;  /,  metallic  tube  com- 
nmnicatii.g  with  cavitv  of  tambour  for  attaclmient  to  an  India-rubber  tube. 


the  other  will  of  course  bo  dilated.  Now  if  a  writing  lever  be  connected  with 
one  of  the  bulbs  it  can  be  made  to  record  any  such  variations  in  pressure  taking 
place  in  the  other.    The  apparatus  necessary  for  registration  by  air-transmission 


12 


GENERAL  PHYSIOLOGICAL  METHOD 


consists  therefore  of  two  parts:  a  receiving  bulb  or  tambour,  and  a  recording 
bulb  or  tambour. 

A  very  simple  form  of  recording  tambour  is  shown  in  Fig.  9.  A  hollow 
aluminium  tube  (f)  conveys  the  air-waves  to  the  elastic  membrane  (b)  fitting 
over  the  chamber.     A  small  metallic  disk  (c)  is  cemented  to  the  membrane  and 

on  the  upright  bar  as  a  fulcrum  rests  the  writ- 
ing lever  (d).  The  axle  of  the  lever  is  held 
in  a  yoke,  the  distance  of  which  from  the  ful- 
crum can  be  readily  adjusted  and  the  excur- 
sions of  the  writing  point  be  thereby  varied 
as  desired. 

The  second  part  of  the  apparatus  or  receiv- 
ing tambour  is  usually  in  the  form  of  a  small 
rubber  balloon  or  of  a  small  metallic  box  cov- 
ered with  a  rubber  membrane.  The  form  of 
the  recording  tambour  can  be  the  same  for  a 
great  many  kinds  of  physiological  movements, 
but  the  form  of  the  receiving  tambour  must  be 
adapted  to  the  special  form  of  experiment  in 
which  it  is  being  used. 

The  receiver  shown  in  Fig.  10  is  adapted 

for  transmitting  movements  of  the  wall  of  the 

carotid   artery,  for  the  purpose  of  securing   a 

pulse-tracing.     It  consists  of  a  small  metallic 

box    containing    three    small    spiral    springs, 

which  serve  to  give  the  membrane  covering  it 

a  certain  tension.     The  membrane  bears  on  its 

outer  side  a  small  button  or  plunger  which  can 

be  applied  to  the  skin  over  the  artery.     The 

pulsatory  movements   of  the  arterial  wall  are 

taken  up  by  the  plunger  and  are  conveyed  by  the  tube  leading  from  the  chamber 

of  the  box  to  the  recording  tambour.     The  whole  apparatus  is  fastened  to  the 

neck  by  means  of  the  hoop  and  screw. 

With  well-constructed  apparatus  this  method  of  registration  has  been  found 
to  be  very  exact.  But  not  all  tambours  are  so  constructed,  and  it  is  necessary 
before  undertaking  any  exact  determinations  to  prove  the  apparatus.     A   very 


Fig.  10. — Receiving  tambour  adapt- 
ed for  taking  a  pidse-record  from 
the  carotid  artery  of  man. 


Fig.   11. — Pulse  curve  from  tlie  carotid  artery  of  man,  after  Edgren.     To  be  read  from  left  to 

right. 


good  test  for  a  recording  tambour  is  that  of  registering  a  pulse  curve,  the  pulse- 
beat  being  received  from  the  carotid  artery  by  an  apparatus  of  given  form. 
With  the  receiver  shown  in  Fig.  10  the  tracing  given  by  the  carotid  should  be 
essentially  like  that  shown  in  Fig.  11. 


THE  GRAPHIC  METHOD 


13 


D.    REGISTRATION   BY   PHOTOGRAPHY 

Even  the  most  delicately  constructed  writing  lever  has  some  weight,  and 
hence,  because  of  its  inertia,  may  give  an  incorrect  form  to  the  curve.  The 
ideal  recorder  would  be  entirely  without  mass.     We  have  such  a  recorder  in 


HJ 


Fig.   12. — Capillarj'  electrometer,  after  Loven.     The  instrument  is  mounted  so  that  it  can  be 
placed  on  the  stage  of  a  compound  microscope. 

a  beam  of  light,  provided  the  experiment  can  ])e  so  arranged  that  the  move- 
ment to  be  recorded  is  transmitted  directly  to  a  small  mirror  which  reflects 
the  beam  of  light,  and  the  reflected  beam  can  then  be  made  to  fall  on  a 
moving  surface  which  is  sensitive  to  light. 

But  the  photographic  method  is  of  much  greater  importance  for  recording 
movements  which  cannot  be  recorded  in  any  other  way. 

This  is  the  case,  for  example,  with  the  excursions  of  the  capillary  electrom- 
eter. This  instrument  (Fig.  12)  consists  of  a  fine  capillary  tube  partially 
filled  with  mercury  and  dipping  into  a 
dilute  solution  of  sulphuric  acid  so 
that  the  mercury  comes  in  contact 
with  the  acid  in  the  tube.  When  elec- 
tricity from  any  source  is  led  into  the 
instrument  by  connectiug  one  pole 
with  the  Hg  and  the  other  with  the 
H.SO,,  the  mercury  meniscus  in  the 
capillarv  tube  will  move  in  the  direc- 
tion of  the  current.  Such  movements 
can  be  magnified  by  a  microscope  and 
bo  recorded  on  a  moving  photograjihic 
plate.  Since  many  forms  of  activity 
in  the  animal  body  are  accompanied 
by  electrical  changes  of  potential 
which  cannot  be  demonstrated  in  any 
other  way  than  by  a  very  sensitive 
electrometer,  this  mode  of  registra- 
tion is  very  valuable  for  the  study  of  such  phenomena.  Fig.  13  represents  the 
photographic  curve  of  the  electrical  variations  (action  currents)  appearing  during 
the  cycle  of  events  in  the  dog's  heart. 


Fig.  13. — .\ction  currents  of  the  dog's  heart  as 
recorded  by  photographing  the  excursions 
of  the  mercury  column  in  the  capillary 
electrometer,  after  v.  Kries.  Electrical 
connection  was  made  with  the  base  and 
apex  of  the  heart.  First  pha-se:  ba.se  nega- 
tive to  the  apex.  Second  pha.^e:  apex 
negative  to  the  base.  The  upper  line  rep- 
resents the  time  in  fifths  of  a  second.  To 
be  read  from  left  to  right. 


14  GENERAL  PHYSIOLOGICAL  METHOD 

Refkrexcks. — CI.  Bernard,  "  Legons  dc  pliysiolofjie  operatoire,"  Paris,  1879. — 
T.  G.  Brodie,  "  The  P^ssciitials  of  Experimnital  Physiology,"  New  York  and  Lon- 
don, 1898. — E.  Cyon,  "  Methodik  der  i)hysiol(;gisehen  Exporimenten  und  Vivisek- 
tionen,"  Giessen,  1876. — W.  S.  Hall,  "A  Manual  of  Experimental  Physiology," 
Philadelphia,  1904. — 0.  Langendorff,  "  Physiologische  Graphik,"  Leipzig  und 
\Vien,  1891.— ir.  T.  Porter,  "  An  Introduction  to  Physiology,"  Boston,  1906.— 
E.  A.  Schcifer,  "  Class-\Vork  in  Practical  Physiology,"  London  and  New  Y^ork, 
1901.— F.  Schenck,  "  Physiologisches  Practicum,"  Stuttgart,  1895.-4.  D.  Waller, 
"  Exercises  in  Practical  Physiology,"  London  and  New  Y'"ork,  1896. 


CHAPTEE    II 

THE    CELL 

§  1.    GENERAL   CONSIDERATIONS 

A.    THE   CELL  AS  AN   ELEMENTARY   ORGANISM 

The  remarkable  substance  whose  activity  is  the  l)asis  of  all  vital  phenom- 
ena in  both  animals  and  plants,  and  which  we  call  therefore  the  living  sub- 
stance, occurs  not  in  a  homogeneous  aggregation  but  in  the  form  either  of 
discrete  masses  called  cells  or  of  small  bodies  which  represent  transformed 
cells  (Schleiden,  1838;  Schwann.  1839).  Every  living  being  and  every  sepa- 
rate cell  arises  from  a  preexisting  cell  (omnis  celhda  e  ceJlula.  Yirchow,  1855). 
Many  animals  and  plants  throughout  their  lives  consist  of  but  one  cell.  In 
others,  from  the  original  cell  new  ones  arise;  these  in  their  turn  multiply, 
are  transformed  into  a  variety  of  shapes,  and  thus  become  adapted  for  special 
purposes.  In  this  way  the  independence  which  characterizes  the  single-celled 
creatures  is  reduced  to  a  considerable  extent,  so  that  cells  detached  from  the 
parent  organism  are  as  a  rule  unal^le  to  maintain  themselves. 

The  cell  is  therefore  the  beginning  and  the  source  of  the  entire  body,  and 
the  formed  elements  of  which  the  body  is  constructed  are  each  and  all  nothing 
else  than  cells  or  cell  derivatives.  Correspondingly  we  may  say  that  the 
powers  of  the  body  as  a  whole  represent  the  sum  of  the  powers  resident  in 
the  individual  cells  and  the  cell  descendants. 

In  the  study  of  vital  processes  we  have  thus  in  the  first  place  to  consider 
the  activity  of  cells.  The  discoveries,  however,  which  have  been  made  by  direct 
observation  upon  cells  (especially  those  that  are  free-living)  are  not  by  any 
means  sufficient  to  serve  as  the  basis  for  a  complete  presentation  of  the  general 
vital  phenomena.  Besides,  there  take  place  in  the  many-celled  organisms,  owing 
to  the  differentiations  occurring  in  them,  many  kinds  of  phenomena  which  do 
not  take  place  in  the  elementary  organism,  or  which  at  least  with  our  present 
means  cannot  be  demonstrated,  and  at  all  events  can  be  investigated  much  more 
thoroughly  in  the  organs  of  the  many-celled  animals.  In  any  general  discussion 
of  vital  phenomena,  therefore,  one  should  give  the  results  obtained  in  the  different 
provinces  of  general  physiology  each  its  proper  share  of  attention.  Since,  how- 
ever, this  text-book  has  for  its  special  subject  the  physiology  of  man,  I  must 
limit  myself  in  the  present  chapter  to  the  boldest  outlines  of  general  physiology. 
Elsewhere  the  general  vital  phenomena  will  be  discussed  from  time  to  time  in 
connection  with  the  facts  of  special  physiology. 

15 


16  THE  CELL 

Wo  know  nolliing  at  all  ahnut  how  life  first  appeared  on  the  earth,  and  we 
are  unahle  to  attach  any  great  importance  to  the  hypotheses  which  have  heen 
put  forward  concerning  its  origin.  For  a  long  time  it  was  imagined  that 
many  kinds  of  living  creatures  arose  directly  from  dead  matter  by  spontaneous 
generation.  But  the  more  deeply  studies  in  this  direction  were  followed,  the 
more  improbable  this  view  became,  and  at  last  it  was  held  only  with  reference 
to  the  lowest  organisms;  until  finally  Pasteur  (18G1)  by  his  ingenious  re- 
searches incontestably  established  the  fact  that  spontaneous  generation  does 
not  take  place  at  all. 

Within  the  cell  the  living  substance  is  divided  between  the  nncleus  and 
the  surrounding  protoplasm.  The  protoplasm  may  be  manifoldly  differenti- 
ated into  contractile  fibers,  cilia,  etc.  Besides,  the  cell  contains  in  greater 
or  less  quantity  nonliving  substances  of  the  most  different  kinds,  some  of 
which  appear  clearly  as  specialized  contents — e.  g.,  the  cell-sap  of  plant 
cells  and  the  fat  of  fat  cells — while  some  are  intimately  mixed  with  the 
nucleus  or  protoplasm  and  are  therefore  not  to  be  distinguished  from  living 
substance. 

Some  cells  are  surrounded  by  a  specialized  cell  membrane,  while  others  have 
none ;  hence  it  is  not  an  essential  constituent  of  a  cell.  Almost  all  plant  cells  have 
even  in  their  early  stages  a  specialized  membrane  which,  increases  in  thickness 
as  the  cell  grows  in  size.  According  to  present  views  it  represents  either  a 
transformation  product  of  the  outer  layer  of  the  protoplasm  or  a  secretion 
product  of  the  cell.  Only  a  few  animal  cells  have  an  actual  membrane.  The 
zona  pellucida  of  the  egg  cell,  the  membrane  of  fat  cells  and  probably  the 
sarcolemma  of  muscle  fibers  are  about  all  that  can  be  named.  In  other  animal 
cells  however  the  outermost  layer  of  the  cytoplasm  is  often  firmer  and  more 
elastic  than  the  inner  parts,  and  is  therefore  able  to  protect  the  cell  to  a  certain 
extent  in  the  same  manner  as  a  true  membrane. 

Cells  differ  greatly  in  external  form.  The  spherical  form  which  we  regard 
as  the  type  is  by  no  means  general :  we  find  on  the  contrary  a  great  variety 
of  forms,  not  only  in  the  many-celled  organisms,  where  the  shape  of  the  cell 
is  influenced  by  its  position  with  reference  to  other  cells,  but  also  in  free 
living,  isolated  cells.  Cells  likewise  vary  in  size,  all  the  way  from  that  which 
is  perceptible  only  with  the  highest  magnification  of  the  microscope  to  that 
of  the  giant  cells  of  certain  algae,  many  meters  in  length. 

The  nucleus  occurs  usually  as  a  spherical  or  oval  body  in  the  middle  of 
the  cell ;  but  it  may  take  many  other  forms.  As  a  rule  the  size  of  the  nu- 
cleus bears  a  direct  proportion  to  the  size  of  the  cell.  The  larger  the  cell  is, 
the  larger  is  the  nucleus.  However,  there  are  many  exceptions  to  this  rule 
also.  Most  cells  contain  but  a  single  nucleus,  although  not  infrequently  two 
or  more  may  be  present.  Indeed,  in  the  giant  cells  of  the  bone-marrow,  in 
several  of  the  lowest  organisms,  and  in  some  other  cells,  as  many  as  one 
hundred  nuclei  have  been  observed. 


GENERAL  CONSIDERATIONS 


17 


B,    THE   RECIPROCAL   RELATIONS   BETWEEN   THE   NUCLEUS 
AND    PROTOPLASM 

Most  animal  and  plant  cells  are  nucleated.  Only  in  the  Bacteria  is  the 
presence  of  a  nucleus  doubtful.  Some  authors  claim  indeed  that  these  organ- 
isms also  are  to  be  added  to  the  general  cell  scheme;  but  the  facts  which 
have  been  brought  forward  in  support  of  this  view  are  far  from  sufficient 
to  constitute  actual  proof.  Although  the  red  blood  corpuscles  of  tlie  ^lam- 
malia  contain  a  nucleus  at  an  early  stage  of  their  development,  in  their  mature 


Fig.    14. — Pohjstomella  vcnusta,  a  microscopic  organism  surrounded  by  a  calcareous  shell,  after 

Max  Schultze. 


state  they  are.  so  far  as  we  know,  without  nuclei.  If  so.  they  are  scarcely  to 
be  regarded  as  cells,  since  having  lost  the  nucleus  they  are  no  longer  capable 
of  reproduction. 

}Yhcrevpr  it  occurs  the  nucleus  represents  a  necessary  constituent  of  the 
cell.  Single-celled  forms  may  be  divided  by  a  sharp  cut  or  by  other  means 
into  a  nucleated  and  a  nonnucleated  part.  The  former  is  soon  regenerated 
to  a  complete  cell  even  if  it  contain  but  a  portion  of  the  nucleus ;  while  the 
nonnucleated  part  invariably  dies  after  a  short  time,  for  although  it  may 
move  about  quite  normally,  may  ingest  foreign  bodies  (Infusoria),  and  even 
kill  them,  no  digestion,  or  at  best  only  a  partial  digestion,  can  take  place 
(Nussbaum). 

The  production  of  certain  siihstances  on  the  part  of  the  protoplasm  is 
likewise  stopped  by  the  removal  of  the  nucleus.  A  nonnucleated  portion  of 
Polystomella  (Fig.  14)  is  no  longer  able  to  elaborate  calcium  carbonate,  while 
a  nucleated  piece  at  once  makes  good  any  defect  in  its  calcareous  shell  by  the 
deposit  of  new  carl)onate  at  the  injured  place  (Verworn).  In  plants  it  has 
been  observed  that  an  isolated  piece  of  protoplasm  is  unable  to  construct  a 
new  cellulose  membrane  (Klebs). 


IS 


THE  CELL 


Bv  the  influonce  of  a  low  tern  pent  hire  on  the  cell  of  Sj)irog!/ra  caught  in 
the  act  of  division.  Gerassimow  succeeded  in  driving  all  the  nuclear  substance 
into  one  daughter  cell,  leaving  the  other  quite  devoid  of  a  nucleus.  In  a 
series  of  such  experiments  it  was  seen  that  in  twenty-one  days  the  growth 
of  the  enucleated  cells  amounted  to  0.4-4.5  per  cent  of  the  average  growth 
of  the  normal  cell,  while  the  growth  of  the  cells  with  a  surplus  of  nuclear 
material  exceeded  that  of  the  normal  cells  by  as  much  as  seventy-eight  per 


Fig.  15. — A  radiolarian,  Thalassirola  nucleata,  after  Verworn.  Cross  section  of  a  normal  indi- 
vidual. The  layer.s  from  without  inward  are:  the  corona  of  radial  pseudopodia,  the  gelat- 
inous layer,  va.scular  layer,  pigmented  sheath  about  the  central  capsule,  and  the  central  cap- 
sule (in  the  center). 

cent.  At  the  same  time  the  solution  of  starch  in  the  enucleated  cells  either 
did  not  take  place  at  all  or  proceeded  very  feebly;  tlie  outer  cell  membrane 
was  less  extensible  than  usual ;  the  color  of  the  chiorophvll  bands  became 
constantly  ])aler  and  their  contour  less  clear. 

While  the  nucleus  is  tluis  of  the  greatest  importance  for  the  normal  activity 
of  tlie  protoplasm,  it  cannot  maintain  an  independent  existence.  When  the 
protoplasm  is  paralyzed  with  narcotics  the  nucleus  may  indeed  continue  its 
movements  (Demoor),  showing  itself  quite  as  independent  of  the  protoplasm 
as  the  protoplasm  is  of  the  nucleus.  Nevertheless,  if  removed  entirely  from 
the  protoi)lasm,  even  if  it  be  entirely  uninjured  by  the  manipulation  and 
be  protected  from  all  external  disturbances,  as  has  been  done  in  the  case  of 
the  great  radiolarian.  Thnlassicola  (Fig.  15,  Verworn),  the  nucleus  invariably 
perishes  without  exhibiting  any  trace  of  regeneration.     Xor  do  nuclei  ever 


GENERAL  CONSIDERATIONS  19 

occur  in  nature  without  a  protoplasmic   sheath;   it  may  be  extreme!}'  thin 
in  certain  cells,  but  it  is  never  entirely  wanting. 

Many  ■  hypotheses  have  been  advanced  to  explain  the  influence  of  the 
nucleus  and  the  nature  of  its  reciprocal  relations  with  the  protoplasm,  but 
they  are  yet  rather  more  of  a  speculative  than  of  an  exact  scientific  nature. 
The  only  conclusion  which  can  be  dra^vn  with  certainty  from  the  discoveries 
thus  far  made  is  that  the  metabolic  processes  of  the  cell  go  on  normally  only 
under  the  mutual  influence  of  both  nucleus  and  protoplasm,  which  after  all 
is  only  a  bare  statement  of  the  facts  in  the  case.^ 


C.    PHYSICAL  AND   CHEMICAL   PROPERTIES  OF  PROTOPLASM 

Protoplasm  appears  as  a  viscous,  usually  colorless  substance  which  is  not 
miseible  with  water,  and  which  always  contains  a  varying  number  of  very 
small,  punctiform  granules.  The  distribution  of  the  granules  in  the  cell 
body  is  seldom  uniform,  for  one  finds  as  a  rule  an  outermost  layer  of  greater 
or  less  thickness  free  from  them.  Since  this  layer  is  firmer  than  the  inclosed 
protoplasm  containing  granules,  it  is  designated  as  the  hyaloplasm  (Leydig) 
in  contradistinction  to  the  granular  spnngio plasm. 

In  general  it  is  assumed  that  resting  protoplasm  has  an  alkaline  reaction. 
This  appears  to  be  true  however  only  with  indicators  which  are  not  sensitive 
to  COo :  for  with  indicators  which  respond  to  CO,,  neither  animal  nor  plant 
cells  in  the  resting  state  show  the  alkaline  reaction  (Friedenthal).  But  in 
the  case  of  some  lowly  organisms — e.  g.,  the  fission-fungi  and  the  Ama?boe — 
the  true  reaction  of  the  living  substance  must  still  appear  doubtful,  since 
these  are  able  to  live  in  strongly  alkaline  nutrient  media — a  circumstance 
which  does  not,  however,  constitute  conclusive  proof  of  an  alkaline  reaction 
for  the  interior  of  the  cell. 

In  the  gelatinous,  colloidal  substances  (e.  g.,  a  solution  of  gelatin  which 
is  drying  up  through  loss  of  water)  with  which  from  a  purely  physical  point 
of  view  protoplasm  exhibits  a  close  agreement,  all  possil)le  gradations  are 
met  with  from  the  fluid  to  the  solid  state,  and  for  such  substances  the  terms 
"  fluid  "  and  "  solid  "  may  have  within  wide  limits  a  purely  relative  signifi- 
cance. Hence  it  is  not  difficult  to  understand  that  views  regarding  the  state 
of  aggregation  of  protoplasm  are  very  divergent,  it  being  regarded  by  some 
authors  as  solid,  by  others  as  fluid.  Moreover,  it  is  not  to  l)e  overlooked  that 
in  the  endless  varieties  of  differentiations  met  with  in  different  orders  of 
living  beings  the  state  of  aggregation  may  present  not  insignificant  differ- 
ences. For  the  cells  which  exhibit  protoplasmic  currents  (cf.  page  21)  as  well 
as  for  the  auKeboid  cells  (cf.  page  42)  and  the  og^  and  early  embryonic  cells, 
Rhumbler,  with  strict  regard  to  the  laws  which  apply  to  fluids,  has  adduced 
weighty  reasons  for  the  view  that  the  protoplasm  possesses  in  fact  a  fluid  state 
of  aggregation,  and  has  the  mechanical  peculiarities  of  a  foam  the  individual 
alveoli  of  which  are  locallv  of  different  constitution. 


*  Spitzer,  Loeh  and  R.  S.  Lillie  have  brought  forward  considerable  evidence  that  the 
nucleus  is  the  chief  agency  in  the  activation  of  oxygen  within  the  cell. — Ed. 
4 


20  THE  CELL 

Water  is  an  integral  constituent  of  living  substance  and  on  drying  the 
cell  either  die.s  or  it  becomes  apparently  dead  ("dry  rigor"),  and  resumes 
its  vital  activities  again  on  the  addition  of  water. 

We  do  not  know  aiiythin^r  definite  about  the  manner  in  which  water  is 
combined  with  the  real  livinfir  substance.  That  it  is  not  held  in  pores  of  the 
protoplasm  as  in  a  si)on{i:e  ai)pears  from  the  fact  that  water  cannot  be  pressed 
out  by  mechanical  means.  Xo  more  can  the  water  here  be  regarded  as  an 
analofrue  of  the  water  of  cr;s'stallization  in  inorp:anic  salts.  It  seems  more  likely 
that  it  is  held  in  interstices  between  the  molecules  or  combinations  of  molecules 
whieh  make  up  the  livinp:  substance.  It  is  not  impossible  also  that  at  the  death 
of  the  protoplasm  a  part  of  the  water  constitutes  a  product  of  disintegration. 

The  .specific  gravitij  of  ])r()toplasm  is  somewhat  greater  than  that  of  water. 
It  refracts  light  more  strongly  than  water,  is  transparent  in  thin  layers, 
opaque  in  thick  layers.  Some  forms  of  living  matter  are  doubly  refractive. 
Tins  property  was  first  observed  in  cross-striped  muscle  (Boeck)  ;  but  since 
that  time  it  has  been  found  that  practically  all  contractile  substance  differ- 
entiated into  fibers,  such  as  smooth  muscle  cells,  cilia,  etc.,  is  positively  donblv 
refractive  in  such  a  way  that  the  optical  axis  coincides  with  the  direction  of 
the  fibers  (Engelmann).  This  fat>t  is  evidence  that  the  structures  in  ques- 
tion have  a  different  molecular  arrangement  from  that  of  other  living 
structures. 

We  know  nothing  concerning  the  chemical  constitution  of  living  substance. 
Chemical  investigation  of  dead  animal  and  plant  bodies  has  made  us  ac- 
quainted with  a  very  large  number  of  different  organic  and  inorganic  com- 
pounds :  but  not  even  the  delicate  micro-chemical  reactions  have  been  able  to 
furnish  any  information  on  the  chemical  nature  of  living  substance.  We  can 
only  say,  therefore,  that  wlien  the  living  substance  dies  we  are  able  to  demon- 
strate proteid  bodies  of  different  kinds  as  the  chief  constituents,  and  that 
in  (inimaJs  at  least  the  living  substance  can  he  formed,  as  it  appears,  only  from 
proteid  bodies  (cf.  Chapter  III). 


D.    MORPHOLOGY  OF  THE   CELL  CONTENTS 

Everywhere,  in  plants  as  well  as  in  animals,  protoplasm  has  the  same 
appearance,  just  as  it  is  everywhere  essentially  the  same  ^Wth  respect  to  its 
fundamental  vital  properties.  Even  with  the  highest  possible  magnification 
we  are  unable  to  distinguish  the  protoplasm  of  a  plant  cell  from  that  of  an 
animal  cell.  This  similarity  is  of  course  only  apparent,  for,  since  the  life 
process  in  every  particular  organism  takes  place  in  a  way  peculiar  to  itself, 
and  since  the  protoplasm— outside  the  nucleus— represents  the  theater  of 
different  vital  activities,  these  outstanding  differences  must  be  conditioned  bv 
a  difference  in  the  quality  of  the  protoplasm   (0.  TIertwig). 

Leaving  out  of  account  the  apparent  similarity  of  the  protoplasm,  different 
cells  may  as  a  whole  present  a  very  different  appearance.  This  is  due  partly 
to  the  externa]  form  of  the  cell  and  its  envelope,  which  must  be  regarded  as 
something  secondary  at  least,  partly  to  differentiations  inside  the  cell   (cilia 


GENERAL  CONSIDERATIONS 


21 


contractile  fibers),  and  partly  to  different  substances  deposited  within  the 
cell.  Sometimes  the  last  are  present  in  such  quantity  that  on  first  sight  the 
cell  appears  to  consist  only 
of  sub.-tances  foreign  to  pro- 
toplasm, as  it  is  here  defined. 

These  cell  contents  vaiy  a 
great  deal  in  kind :  substances 
which  are  taken  up  from  out- 
side by  the  cell  to  be  further 
elaborated  in  it,  substances 
stored  in  the  cell  as  reserve 
material,  substances  formed  in 
the  cell  by  its  own  activity  to 
be  given  out  again  under  ap- 
propriate circumstances,  etc. 

In  most  plant  cells  the 
protoplasm  fills  but  a  small 
part  of  the  cell  body  (Fig.  1(5). 
Only  those  cells  which  lie  close 
to  the  growing  tip  consist  en- 
tirely of  protoplasm.  In  their 
growiih  the  wall  of  the  cell  in- 
creases in  size  much  more  rap- 
idly than  the  protoplasm,  and 
as  a  result  vacuoles  are  fomied 
filled  with  cell-sap.  The  nu- 
cleus then  lies  embedded  in  a 
mass  of  protoplasm,  which  is 
connected  by  means  of  proto- 
plasmic strands  with  a  layer 
inside  the  cell  walls.  The  pro- 
toplasm of  such  cells  streams 
back  and  forth  within  the  cell 
wall,  carrying  with  it  the  gran- 
ules embedded  therein  and  oft- 
times  the  nucleus  as  well. 

In  the  protoplasm  of  green 
plant  cells  are  contained  spe- 
cially differentiated  chloro- 
phyll bodies  (cf.  Figs.  25  and 
31)    to  which  these   cells   owe 

their  green  color,  and  which  are  of  very  great  importance  in  the  vital  activities 
of  plants  (cf.  page  23).  Among  the  inclosures  contained  by  the  plant  cell  outside 
the  cell-sap,  the  starch  granules  are  to  be  especially  mentioned,  since  they  repre- 
sent the  first  visible  product  of  the  assimilative  activity  of  the  plant  cell. 

Animal  cells  as  a  rule  consist  almost  entirely  of  protoplasm  and  contain 
foreign  substances  only  in  relatively  small  quantities :  they  are  therefore  essen- 
tially like  young  plant  cells  (Fig.  16).  There  are  some  animal  cells  also  in 
which  the  protoplasm  is  almost  entirely  displaced  by  foreign  substances.  This 
is  the  case  for  example  with  fat  cells  in  which  the  major  part  of  the  fat  in 


Fig.  16. — Parenchj-ma  cells  from  the  middle  layer  of 
the  root-cortex  of  Frittilaria  imperialis;  longitudinal 
section,  after  Sachs.  -4,  portion  of  the  section  close  to 
the  root-ape.x,  very  young  cells,  without  cell-sap;  B, 
cells  of  the  same  layer  about  2  mm.  from  the  root- 
apex;  cell-sap  (.•?)  is  forming  in  the  protoplasm  (p) ; 
C,  cells  of  the  same  layer  7-8  mm.  from  the  apex. 
The  cell  at  the  right  above  has  been  rupturetl  by  the 
razor;  its  nucleus  (.ri/)  is  seen  much  swollen  by  absorjj- 
tion  of  water;  k.  nucleus;  kk,  nucleolus;  h,  cell-mem- 
brane. 


22  THE  CELL 

the  body  is  deposited.     Eggs  likewise  contain  an  abundant  su])|)ly  of  proteid, 
lecithin  and  fat  which  are  to  serve  as  nourishment  for  tiie  developing  embryo. 

Oiher  inclosures  which  occur  in  greater  or  less  abinulaiK'(^'  in  animal  cells, 
are:  fat  droplets  in  the  cells  of  the  maniniary  glands  and  of  the  intestinal  mucosa 
during  absorption;  pigment  g:ranules  in  the  pigment  cells  of  the  skin  and  of 
the  choroid  coat  in  the  eye;  glycogen  granules  in  the  liver  cells,  etc.  In  the 
naked  cells  which  are  able  to  take  up  solid  particles  from  the  surrounding 
medium  we  observe  often  small  Algae,  Bacteria,  Infusoria  and  the  like  (Figs. 
19,  20,  21  and  22),  which  serve  as  nourishment  for  the  cell,  and,  after  digestion 
is  completed,  indigestible  shells,  skeletons,  envelopes,  etc.  Again  small  cavities 
filled  with  fluid  (vacuoles)  are  present  in  the  protoplasm  of  certain  animal  cells. 
Among  these  are  to  be  mentioned  especially  the  so-called  contractile  vacuoles, 
i.  e.,  drops  of  fluid  which  are  pressed  out  of  the  protoplasm  by  the  contraction 
of  a  surrounding  sheath,  only  to  be  re-collected  from  the  protoplasm  in  the  same 
place  again  when  the  contraction  ceases  (Figs.  21,  24,  2S). 

Finally,  there  are  found  within  the  protoplasm  of  animal  cells  certain  plant 
cells,  Algje.  which  do  not  serve  their  host  as  nutritive  material,  but  merely  live 
in  company  with  it  (symbiosis).  They  are  of  the  greatest  importance  to  the 
life  of  the  animal  cell  in  which  they  occur,  since  through  the  activity  of  their 
chlorophyll  bodies,  they  supply  it  with  the  necessary  oxygen,  thereby  rendering 
it  independent  of  the  oxygen  contained  in  the  surrounding  medium.  We  have 
the  most  beautiful  instance  of  symbiosis  in  a  lichen,  which  is  nothing  more  than 
an  aggregate  individual  consisting  of  a  fungus  and  an  alga. 

Reference  must  be  made  to  works  on  cytology  and  histology  for  a  discussion 
of  the  ultimate  structure  of  the  protoplasm,  nucleus  and  centrosome,  as  well  as 
for  the  changes  in  these  accompanying  cell  division. 


§  2.    THE   VITAL    PHENOMENA    OF    CELLS 
A.    INTRODUCTORY    SURVEY 

The  vital  activity  of  all  cells,  both  plant  and  animal,  consists  of  two  oppo- 
site processes,  assimilation  and  dissimilation.  We  include  under  assimilation 
all  the  synthetic  processes,  of  whatever  kind,  going  on  in  the  cell  or  under 
its  influence;  under  dissimilation  all  the  disintegration  processes  going  on  in 
the  cell  or  under  its  influence. 

A.  Assimilation  is  of  two  kinds,  namely  growth  of  protoplasm,  i.  e.,  for- 
mation of  living  substance,  and  syntheses  of  new  substances  not  living. 

Our  knowledge  of  the  growth  of  protoplasm  is  still  very  meager.  We 
can  observe  how  the  cell  increases  in  size,  and  how  it  multiplies  after  it  has 
reached  a  certain  size,  hut  the  inner  mechanism  of  these  processes  is  still  quite 
obscure.  Somewhat  more  satisfactory  is  our  knowledge  of  the  syntheses  of 
organic  nonliving  substances  accomplished  by  cells.  In  fact  the  synthesis 
which  is  quite  the  most  impo-tant  of  all,  namely,  the  formation  of  starch  in 
the  green  parts  of  plants,  is  known  with  tolerable  exactness,  and  may  be 
described  briefly  as  follows: 

There  always  occur  in  the  neighborhood  of  the  nucleus  of  plant  cells  small, 
colorless,  highly  refractive  bodies,  for  the  most  part  oval  or  elliptical  in  form,' 
which  are  called  trophohlaats  and  which  arise  always,  like  the  nucleus  and  the 


THE  VITAL  PHENOMENA  OF  CELLS 


23 


centrosome,  by  division  of  preexisting  trophoblasts.    These  structures  generate 
within  themselves  the  chlorophyll. 

The  property  of  plants  discovered  by  lugenhousz  (1TT9),  Senebier  (1782- 
1800),  and  Th.  de  Saussure  (1804),  of  reducing  carbon  dioxide,  depends  upon 
this  chlorophyll.  The  reduction  takes  place  under  the  in- 
fluence of  the  sun's  ra^'s,  and  starch  appears  as  the  first 
visible  product  of  the  resulting  synthesis.  It  is  deposited 
in  the  chlorophyll  bodies  in  the  form  of  small,  highly  re- 
fractive granules  (Julius  Sachs,  1862).  At  the  same  time 
the  plant  gives  off  the  oxygen  set  free  by  the  reduction 
of  carl)on  dioxide,  and  if  it  grows  in  a  closed  room  the 
quantity  of  CO,  in  the  confined  air  constantly  decreases, 
while  the  quantity  of  0,  is  correspondingly  increased. 

Starch  serves  as  the  starting  point  for  all  further  syn- 
thetic processes  in  the  plant  body.  By  its  cleavage  and 
hydration   different   kinds  of   sugars   are  produced,   and. 

this  being  the  form  in  which 
carbohydrates  are  transported, 
they  are  of  great  importance  in 
the  further  synthetic  processes 
within  the  plant  body.  Vege- 
table oils  are  also  formed  from 
starch;  and  it  participates 
finally  in  the  synthesis  of  pro- 
teids  in  plants. 

Besides  the  elements  found 
in  starch  (carbon,  hydrogen 
and  oxvgen),  proteids  contain 
nitrogen  and  sulphur  (some 
also  phosphorus).  The  plant 
obtains  these  elements  from 
the  soil  principally  in  the  form 
of  nitrates,  sulphates,  phosphates  and  ammonia 
compounds.  It  obtains  on  the  other  hand  only  an 
insignificant  part  of  its  nitrogen  from  the  ammonia 
and  nitric  acid  in  the  air.  The  nitrogen,  sulphur 
and  phosphorus  are  liberated  from  their  compounds 
by  processes  of  reduction  and  they  together  with 
the  elements  contained  in  starch  are  synthetized 
into  proteids.  It  is  very  probable  that  the  amino 
acids  and  their  amides — e.g.,  asparagin  (amino- 
succinamic  acid,  C^HgX.O.,) — represent  intermedi- 
ate stages  in  this  synthesis;  but  how  such  processes 
take  place  we  do  not  yet  know.  Finally  from  the  pro- 
teids thus  formed,  living  protoplasm  is  constructed. 
Certain  plants  are  able  to  absorb  free  atmospheric  nitrogen  and  to  com- 
bine it  into  organic  compounds.  A  species  of  bacterium,  Clostridium  Pas- 
teurianum,  which  lives  in  the  soil,  is  an  example  (Winogradsky).     Kriiger 


Fig.  17.— This  leaf, 
which,  in  the  liv- 
ing condition,  had 
been  partially  cov- 
ered with  a  strip 
of  tin  foil,  was  sub- 
sequently treated 
with  iodine  for  the 
starch  reaction. 
The  area  which 
had  been  shaded 
remains  colorless, 
showing  that 
starch  cannot  be 
formed  without 
the  direct  action 
of  sunlight,  after 
Noll. 


Fig.  is.— The  root  of  the 
field  bean  {Vicia  Faba) 
thickly  beset  with  bacteria 
tubercles,  after  Noll. 


24  THE  CELL 

and  SclintMdowind  isolated  a  X-coniltininsi-  BdciUus  wliicli  in  sixty-two  days 
translencd  -l.(!-S.r)  iiii;.  of  atinosplit'iic  nitrogen  to  prolcid  nitroircn.-  Accord- 
ing: to  Kulin  one  licktar  of  his  cxpcriiiicnt  licld  in  one  year  would  cxjierience 
through  the  agency  of  inicroltcs  alone  an  increase  in  nitrogen  of  (iti  kg.  Other 
microorganisms  capable  of  iixing  nitrogen  are  the  Azobacteria  studied  by 
Beverinek.  Still  others  which  form  on  roots  of  certain  species  of  Leguminosfe 
peculiar  excrescences,  called  root  tubercles,  have  the  power  of  transforming 
free  nitrogen  into  such  compounds  (amides?)  as  are  able  to  serve  not  only 
themselves  but  also  their  hosts  as  the  immediate  source  of  nitrogenous  food 
(Hellriegel)  (Fig.  18). 

Several  other  mineral  constituents  are  needed  in  the  development  of  plants, 
notably :  iron,  which  is  necessary  for  the  formation  of  chlorophyll ;  potassium 
and  magnesium,  which  it  is  believed  play  an  important  role  in  assimilation  and 
the  syntheses  of  the  body:  calcium,  which  is  very  important  in  the  transporta- 
tion and  combination  of  the  harmful  products  of  metabolism  (oxalic  acid),  etc. 
On  the  other  hand,  the  plant  does  not  require  any  organic  foodstuffs.  If  the 
root  of  a  maize  plant  which  has  been  germinated  in  water  be  placed  in  a  vessel 
with  an  artificial  nutrient  solution  (one  per  cent  potassium  nitrate,  0.5  per 
cent  each  of  sodium  chloride,  calcium  sulphate,  magnesium  sulphate,  and  cal- 
cium phosphate,  and  0.005  per  cent  ferrous  sulphate)  while  the  foliar  part  is 
exposed  to  the  air,  the  plant  grows  quite  perfectly,  develops  into  a  large  maize 
stalk,  puts  forth  leaves  and  brings  forth  seed. 

Only  the  plants  containing  clironiophyll'^  have  the  power  of  feedino-  ex- 
clusively on  purely  inorganic  substances.  The  parts  of  the  plant  devoid  of 
chlorophyll  receive  their  carbohydrates  from  the  parts  which  contain  chloro- 
phyll. Those  plants  which,  like  the  Fungi,  contain  no  chlorophyll  at  all  must 
obtain  substances  already  completely  organized  for  their  food;  and  this  is 
likewise  the  case  with  the  whole  animal  kingdom. 

The  beginning  of  the  organic  syntheses  going  on  in  nature  is  therefore 
the  formation  of  starch  in  the  green  parts  of  plants  under  the  influence  of 
sunlight.  The  energy  stored  up  by  this  means  is  used  in  all  the  further  proc- 
esses of  the  plant  body.  In  plants  and  plant  parts  lacking  chlorophyll  as 
well  as  in  animals  all  the  life  processes  take  place  at  the  expense  directly 
or  indirectly  of  the  substances  formed  in  the  green  parts  of  plants.  The 
green  plants  therefore  constitute  a  necessary  condition  for  the  life  of  all  other 
living  beings  on  the  earth.  But  since  carbon  dioxide,  the  nitrates  and  sul- 
phates required  by  plants  are  present  on  the  earth  and  in  the  atmosphere 
entirely  independent  of  the  life  processes  of  animals,  plants  can  ^et  along 
without  the  aid  of  animals.  ^ 

We  are  not  to  suppose,  however,  that  synthetic  processes  do  not  take  place 
in  animals.  It  is  true  that  animals  cannot  form  complex  compounds  out  of 
completely  oxidized  carbon  (CO,)  and  hydrogen  (H,0)  and  that  the  animal 
body  can  utilize  as  raw  material  only  compounds  of  relatively  complex  consti- 


This  term,  employed  by  Engelmann,  and  adopted  by  the  author,  includes  all  the 
colonng  matters  m  plants  capable  of  exercising  an  assimilative  function.  Since  however 
by  far  the  most  abundant  coloring  matter  is  chlorophyll,  it  will  avoid  confusion  pcrhaos 
to  use  only  the  one  term  hereafter.— Ed.  ^ 


THE  VITAL  PHENOMENA  OF  CELLS  25 

tution,  chief  among  them  being  proteids.  fats  and  carltohydrates.  But  from 
this  raw  material  the  animal  body  has  the  power  of  forming  many  new  sub- 
stances, notably  living  protoplasm,  by  a  true  synthesis. 

Besides  the  substances  Just  mentioned  the  animal  cell,  like  the  plant  cell, 
requires  certain  mineral  compounds  in  order  that  it  may  develop  fully  and 
accomplish  its  functions  in  a  normal  manner.  Thus  observation  on  the  Meta- 
zoa  has  proved  that  the  animal  body  is  continually  giving  off  such  substances 
in  its  excretions,  and  would  necessarily  become  impoverished  in  this  respect 
if  the  supply  were  not  sufficient.  Even  in  grown  animals  very  profound 
disturbances  ensue  as  a  consequence  of  such  failure  of  mineral  substances, 
which  ultimately  end  in  death.  The  growing  body  has  a  relatively  much 
greater  need  of  inorganic  compounds,  for  such  substances  are  absolutely 
necessary  for  the  construction  of  its  organs. 

x\mong  the  mineral  substances  contained  in  the  fluids  of  the  animal  Ijody 
common  salt  (NaCl)  comes  first  in  order  of  quantity.  A  solution  of  common 
salt  alone,  of  a  strength  corresponding  to  its  concentration  in  these  fluids 
(0.6-0.9  per  cent),  is  in  fact  sufficient  to  maintain  a  frog's  muscle  or  a  frog's 
heart  in  functional  condition  for  a  long  time  after  its  removal  from  the  body, 
whereas  an  exsected  heart  will  not  beat  in  a  solution  where  XaCl  is  wanting 
(Lingle). 

In  a  solution  containing  only  XaCl,  however,  the  contractions  of  the  heart 
gradually  cease,  although  they  may  be  roused  again  by  the  addition  of  CaCU 
in  small  quantity.  The  addition  of  KCl  is  likewise  beneficial ;  but  whereas 
the  Ca  salt  is  favorable  to  the  contraction  of  the  heart,  the  K  salt  appears 
to  be  important  for  its  relaxation.  The  heart  beats  best,  therefore,  in  a  nutri- 
ent fluid  in  which  are  contained  Ca  and  K  as  well  as  Xa  (Ringer,  Howell  and 
several  other  authors).^ 

Analogous  phenomena  appear  in  other  organs.  A  skeletal  muscle  of  the  frog 
remains  alive  outside  the  body  longer  if  CaCL  is  added  to  the  XaCl  solution. 
It  is  asserted,  at  least  for  smooth  muscles,  that  the  Ca  salt  favors  the  contrac- 
tion process,  and  KCl  the  relaxation,  just  as  in  the  heart.  The  egg  of  Fundulus 
develops  in  XaCl  solution  only  when  CaCL  is  added  (Loeb). 

In  the  present  state  of  our  knowledge  of  this  subject  it  would  be  premature 
to  conclude  that  the  metals  just  discussed  have  the  same  sweeping  importance 
for  all  animal  cells.  As  a  matter  of  fact  data  are  at  hand  which  show  that  such 
a  generalization  is  not  warranted.  Thus  the  vibration  of  flagella — e.  g.,  in  the 
spermatozoa— and  cilia  of  both  vertebrates  and  invertebrates,  is  entirely  inde- 
pendent of  XaCl  in  the  surrounding  fluid.  The  same  is  true  of  the  contractile 
stalk  of  Vorticella  (Fig.  28)  and  related  Protozoa  (Overton).  In  very  young 
larva"  of  Arenicola  cristata  solutions  containing  CaCL  favor  muscular  move- 
ments, while  solutions  containing  MgCL  favor  ciliary  movements.  Pure  XaCl 
solutions  are  much  more  harmful  for  the  latter  than  for  muscular  movements; 
Xa-free  solutions  stop  muscular  movements,  whereas  cilia  remain  active  in 
these,  and  are  quite  unaffected  by  pure  CaCL  or  MgCL  (Lingle).  In  this  con- 
nection should  be  mentioned  also  the  facts  brought  out  by  Goldberger  that  cer- 

>  A  solution  especially  well  adapted  for  feeding  an  excised  mammalian  heart  is  the  fol- 
lowing: eight  per  cent  NaCl,  0.075  per  cent  KCl,  0.1  per  cent  CaCL,  01  per  cent  NHCO3, 
and  saturated  with  oxygen.     (Compare  the  composition  of  the  blood  ash,  Chapter  V.) 


26  THE  CELL 

tain  Ca  salts  \vhi('h  have  so  favorable  an   influence  in  the  hiprher  animals,  are 
poisonous  for  the  Protista,  while  other  Ca  salts  are  harmless  for  them. 

Besides  the  elements  just  mentioned  (Xa,  Ca,  K  and  CI)  and  those  con- 
tained in  the  proteids,  fats  and  carbohydrates  (C,  H,  O,  N,  S,  P),  there  are 
still  a  few  others  which  are  just  as  necessary  for  the  animal  body.  First  among 
these  are:  Mg,  contained  with  the  Ca  in  the  solid  framework  of  the  bones;  Fe, 
which  is  necessary  for  the  formation  of  the  coloring  matter  in  the  red  cor- 
puscles; and  I,  which  is  a  necessarj'  constituent  of  the  secretion  of  the  thyroid 
gland.  J 

In  all  processes  of  assimilation  in  nature,  whatever  their  kind,  energy  is 
stored  up.  As  a  measure  of  the  energy  contained  in  a  substance  we  use  the 
amount  of  heat  developed  by  its  combustion.  Carbon  dioxide  and  water  are 
not  combustible  substances,  but  starch  produced  from  them  generates  a  con- 
siderable quantity  of  heat  when  it  is  burned — possesses  therefore  a  certain 
quantity  of  potential  energy,  amounting  in  fact  to  about  4.1  Cal.^  per  gram. 
This  potential  energy  is  derived  from  the  sunliglit.  whoso  kinetic  energy  has 
been  transformed  under  the  influence  of  chlorophyll  to  the  potential  energy 
of  starch. 

When  a  synthesis  takes  place  in  a  living  cell,  if  the  necessary  energy  is  not 
supplied  from  without  as  in  starch  formation,  the  synthesis  can  only  be 
carried  out  at  the  expense  of  potential  energy  stored  in  the  cell  itself.  In  other 
A,vords :  in  all  synthetic  processes  taking  place  in  plant  or  animal  cells  without 
the  agency  of  sunlight,  the  potential  energy  at  the  disposal  of  the  cell  is 
transformed  in  one  way  or  another  into  the  potential  energy  of  the  newly 
formed  substance. 

The  assimilative  functions  of  cells  are  closely  bound  up  with  dissimilative 
functions — i.  e.,  if  the  cell  has  not  the  power  to  develop  kinetic  energy  within 
itself  no  new  formation  of  substance  appears  to  take  place — and  conversely, 
the  more  rapid  the  dissimilative  process,  the  more  active  is  the  assimilative 
process.  Neither  plants  nor  the  eggs  of  animals  can  develop  continuously  without 
oxygen,  as  was  determined  successively  by  Spallanzani,  Dutrochet,  De  Saussure 
and  Schwann.  In  the  egg  of  Ctenolahrus,  a  marine  bony  fish,  the  cleavage  cells 
undergo  partial  solution  and  fuse  together  when  oxygen  is  withdrawn,  but  are 
reformed  when  oxygen  is  again  supplied  (Loeb).  Possibly  in  this  connection 
belong  also  the  facts :  that  growth  is  always  accompanied  Ly  dissimilation,  and 
that  skeletal  muscles  increase  in  size  only  under  the  influence  of  work  (involving 
dissimilation,  cf.  page  63). 

B.  The  (Jissiniilative  processes  constitute  the  source  of  the  kinetic  energy 
developed  in  the  cells.  These  processes  in  plant  as  well  as  in  animal  cells  are 
everywhere  essentially  similar,  and  consist  in  a  destruction  of  complex  mole- 
cules. Whether  this  destruction  involves  the  living  substance  of  the  cell,  or 
only  the  nonliving  cell  contents  cannot  yet  be  definitely  decided.  Under  the 
general  subject  of  metabolism  we  shall  find  opportunity  to  discuss  this  question 
somewhat  more  exhaustively.    Here  we  must  limit  ourselves  to  the  following : 

'  1  Cal.  (Calorie)  =  the  amount  of  heat  necessary  to  raise  1  kg.  of  water  from  0° 
tol°C. 


THE  VITAL  PHENOMENA  OF  CELLS  27 

1.  The  above-mentioned  destruction  in  a  majority  of  cases  is  an  oxidation, 
that  is,  a  combustion  of  the  substances  called  organic  foodstuffs — proteid,  fat 
and  carbohydrate — at  the  disposal  of  the  cell  (Lavoisier,  17?7).  This  is 
proved  by  the  fact  that  all  animals  produce  carbon  dioxide,  and  that  they 
succumb  in  a  short  time  in  the  absence  of  oxygen.  Since  a  plant  under  the 
influence  of  sunlight  has  the  power  to  reduce  carbon  dioxide  and  set  oxygen 
free,  it  follows  that  under  suitable  circumstances  plants  and  animals  can  live 
if  they  be  kept  together  in  a  closed  room;  for  the  carbon  dioxide  formed  by 
the  animals  is  reduced  by  the  plants  with  the  liberation  of  oxygen;  and  thus 
each  receives  the  gas  most  useful  in  its  life  processes. 

And  yet  we  are  not  to  suppose  that  the  plant  does  not  form  any  carbon 
dioxide.  On  the  contrary  the  plant  protoplasm  in  its  production  of  kinetic 
energy  behaves  exactly  like  the  animal  protoplasm  and  produces  carbon  dioxide 
in  the  same  way.  The  production  of  carbon  dioxide  in  green  plants  in  the 
light  is  masked  by  the  much  more  abundant  reduction  of  carbon  dioxide  going 
on  at  the  same  time;  in  the  dark,  however,  where  the  reduction  processes  are 
checked,  it  is  plainly  perceptible. 

In  the  decomposition  brought  about  by  the  vital  activity  the  combustible 
substances  are  not  broken  down  immediately  into  their  end  products ;  but  the 
complex  organic  molecules  are  split  up  gradually  into  less  and  less  complex 
ones,  oxidation  and  reduction  processes  probably  taking  place  in  rapid  suc- 
cession (Drechsel).  Finally,  these  intermediate  decomposition  products  are 
transformed  into  substances  which  leave  the  body  as  the  end  products  of 
metabolism. 

2.  The  living  cell  itself  regulates  the  amount  of  oxygen  consumed,  combus- 
tion in  the  body  being,  within  wide  limits,  entirely  independent  of  the  partial 
pressure  of  the  uncombined  oxygen  (Pfliiger). 

In  addition  protoplasm  has  the  power  to  store  up  oxygen  in  compounds  in 
which  it  is  loosely  held,  and  from  which  it  may  be  withdrawn  again  in  case  of 
need.  This  is  witnessed  by  the  fact  that  cells  can  develop  kinetic  energy, 
though  in  general  only  for  a  relatively  short  time,  without  a  supply  of  free 
oxygen  from  outside.  In  certain  cases  this  happens  even  at  the  expense  of 
compounds  which  contain  oxygen  firmly  bound  up  chemically  and  which  cannot 
be  deoxidized  with  our  strongest  reducing  agents.  We  have  examples  of  such 
phenomena  in  the  Myxomycetes  which  continue  their  movements  for  three  hours 
in  an  oxygen-free  medium;  in  ciliated  cells  which  can  live  still  longer  without 
oxygen;  in  the  skeletal  muscles  which  contract  and  give  off  carbon  dioxide  even 
in  a  vacuum.  The  mawworm,  Ascaris,  can  live  five  days  without  a  supply  of 
oxygen  (Bunge).  In  this  case  there  occurs  in  the  body  of  the  animal  a  process 
of  fermentation  by  which  CO,  and  a  mixture  of  valerianic  acid,  caproic  acid, 
etc.,  are  formed  from  the  glycogen  stored  in  the  animal's  tissues  (Weinland). 
Here  should  be  mentioned  also  the  liberation  of  oxygen  by  hen's  eggs  during  the 
first  five  hours  of  their  incubation  (Ilasselbalch). 

A  very  pretty  experiment  on  the  life  of  higher  animals  in  the  absence  of 
oxygen  is  the  following  which  we  owe  to  Pfliiger.  At  2.44  o'clock  two  frogs 
were  placed  in  an  atmos])here  cooled  to  about  0°  C.  from  which  every  trace  of 
oxygen  had  been  carefully  removed.  At  three  o'clock  they  showed  the  most 
pronounced  dyspna?a  but  no  convulsions.  They  soon  became  motionless,  as  if 
they  wished  by  suppression  of  their  movements  to  obviate  the  need  for  oxygen. 


28  THE  CELL 

From  time  to  time  they  wandered  about  the  cage,  raisetl  their  heads  and  occa- 
sionally gasped.  At  eight  o'clock  they  had  become  still  more  quiet  and  were 
visibly  very  much  exhausted,  but  on  pricking  them  with  a  wire  they  still  showed 
indubitable  signs  of  physiological  integrity.  On  the  following  morning  at  nine 
the  frogs  lay  quite  motionless.  Even  the  most  vigorous  stimulus  failed  to  pro- 
duce any  trace  of  reaction  and  there  were  no  signs  of  respiratory  movements. 
At  ten  after  a  duration  of  seventeen  hours  the  confinement  was  terminated  and 
oxygen  was  admitted.  When  after  two  hours'  exposure  to  the  atmospheric  air, 
and  after  repeated  inflation  of  the  lungs  there  was  no  sign  of  returning  life, 
Pfliiger  opened  the  body  cavity  of  one  frog  and  found  the  heart  still  heating 
with  great  energy  and  the  arteries  full  of  remarkably  bright  red  blood.  In  spite 
of  this  there  were  no  muscular  movements  for  five  or  six  hours.  Keflex  irrita- 
bility gradually  returned,  and  spontaneous  respiratory  movements;  but  coordi- 
nated movements  such  as  are  mediated  only  by  the  higher  nerve  centers  did  not 
reappear  at  all. 

3.  Finally,  certain  organisms  of  the  lowest  order,  especially  some  of  the 
Bacteria,  can  maintain  life  permanently  only  in  the  absence  of  oxygen  (anaero- 
bic Bacteria.  Pasteur).  The  yeast  cell  furnishes  us  some  information  concern- 
ino-  the  wav  in  which  the  enero^v  necessary  for  the  functions  of  these  ortranisms 
is  liberated.  This  organism  can  maintain  life  for  a  long  time  without  air 
and  can  develop  considerable  activity  which  displays  itself  notably  in  the 
alcoholic  fermentation  of  sugar — i.e..  by  splitting  grape  sugar  into  2(C02) 
and  ^(C^HgO).  Since  now  the  calorific  energy  of  the  alcohol  formed  is  less 
than  that  of  the  sugar  destroyed,  a  certain  quantity  of  energy  is  developed 
and  is  placed  at  the  disposal  of  the  3'east  plant  (Hermann,  Kiihne). 

In  the  dissimilatory  processes  of  the  cell  the  nutrient  substances  at  its 
disposal  are  gradually  consumed,  and  if  no  supply  from  outside  is  kept  up 
the  cell  must  of  course  die  of  hunger. 

.  The  changes  appearing  in  the  cell  body  when  it  is  deprived  of  nourishment 
have  been  closely  followed  by  Wallengren  on  the  ciliate  infusor  Paramecium. 
During  the  first  days  of  starvation  all  the  food  vacuoles  and  food  masses  dis- 
appear. Thereupon  the  small  granules  present  in  the  protoplasm  are  consumed, 
and  the  endoplasm  consequently  decreases  in  quantity.  At  the  end  of  this 
period  the  living  substance  of  the  endoplasm  is  itself  probably  consumed  in 
part.  In  spite  of  the  more  or  less  profound  changes  in  the  form  of  the  body 
thereby  produced,  the  ectoplasm,  the  contractile  vacuoles  and  the  cilia  are  still 
not  influenced  in  any  noticeable  way.  During  this  period  the  activity  of  the 
last-named  structures  is  maintained  by  material  supplied  by  the  endoplasm.  With 
further  inanition  the  endoplasm  becomes  much  vacuolated,  the  ectoplasm,  as 
well  as  a  large  number  of  the  cilia  become  more  and  more  absorbed,  and  the 
macronucleus  is  finally  attacked,  while  the  micronucleus  remains  comparatively 
untouched.  At  last  the  point  is  reached  where  everything  which  the  cell  body 
can  furnish  as  nutrient  material  is  consumed,  the  living  substance  remaining 
is  itself  exhausted,  and  the  cell,  fallen  into  granular  disintegration,  perishes. 

C.  Temperature. — Since  temperature  exercises  a  very  profound  influence 
on  the  varions  activities  of  cells,  it  will  be  appropriate  to  consider  it  in  this 
preliminary  survey.  We  may  safely  assert  that  for  every  cell  there  is  a  definite 
temperature  which  is  most  favorable  to  its  life  processes.  The  cell  perishes 
if  the  temperature  passes  beyond  certain  limits,  although  these  limits  differ 


THE  VITAL  PHENOMENA  OF  CELLS  29 

with  different  cells  and  may  be  gradually  changed  more  or  le.ss  for  each 
particular  cell  by  training. 

For  most  animal  and  plant  cells  the  upper  limit  of  temprrnhtre  compatible 
with  life  is  from  40°  to  47°  C.  They  die  if  they  be  subjected  even  for  a  short 
time  to  a  temperature  a  little  higher  than  this,  owing  partly  at  least  to  the 
coagulation  which  takes  place  at  this  temperature.  And  yet  there  are  cells 
which  are  able  to  endure  a  considerably  higher  temperature.  In  the  hot 
springs  of  Ischia,  Alg^  live  at  a  temperature  of  53°  C,  and  it  is  said  that 
between  the  filaments  of  OsciUarin,  ciliate  Infusoria  and  Rotatoria  survive  a 
temperature  of  81°  to  85°  C.  (Ehrenberg).  Many  Bacteria  thrive  at  a  tem- 
perature of  50°-55°  C.  or  even  as  high  as  72°  C. ;  and  still  more  resistant 
against  heat  are  their  spores,  a  dry  heat  of  140°  C.  maintained  for  at  least 
three  hours  being  necessary  to  destroy  life  in  them  with  absolute  certainty. 

With  regard  to  the  lower  limit  of  temperature  compatible  with  life,  it  has 
been  found  that  Amoebae  placed  upon  ice  will  cease  all  movements  and  remain 
quiescent  until  the  temperature  is  raised.  If  however  they  be  frozen  up  in 
drops  of  water,  warming  fails  to  revive  them. 

A  temperature  below  0°  C.  is  not  necessarily  fatal  for  the  cell.  Pictet 
observed  with  certainty  that  fish  which  had  been  cooled  in  a  block  of  ice  to 
— 15°  C.  survived  after  carefully  raising  the  temperature,  although  their 
companions  while  frozen  could  be  reduced  to  powder  like  ice.  Fish  which 
were  cooled  to  —  20°  C.  could  not  be  revived.  Frogs  survived  a  temperature 
of  —  28°  C,  and  myriopods  —  50°  C.  Seeds  of  cereals  do  not  lose  their  power 
of  germination  if  they  be  subjected  for  a  long  time  to  a  temperature  of 
-42°  C.  (C.  de  Candolle).  Cholera  spirilla  and  anthrax  spores  can  be  kept 
alive  for  from  twenty  hours  to  seven  days  at  the  temperature  of  liquid  air 
(  -  183°  to  —  192°  C).  Indeed  one  species  of  Bacterium  (B.  phosphorescens) 
survived  a  period  of  ten  hours  at  —252°  C.  (McFadayen). 

One  would  suppose  a  priori  that  at  a  temperature  so  low  that  the  protoplasm, 
becomes  rigid,  life  must  be  temporarily  suspended.  According  to  the  experi- 
ment with  the  fish  stated  above  this  does  not  appear  to  be  correct,  for  in  this 
case  it  would  be  a  matter  of  indifference,  so  far  as  external  signs  go,  whether 
the  temperature  of  a  frozen  fish  were  —  15°  or  -  20°  C,  and  yet  after  cooling 
to  —  20°  it  dies.  If  life  were  actually  suspended  at  —  15°  it  would  be  ditficult 
to  understand  why  a  further  lowering  of  the  temperature  has  any  effect.  In 
any  case  we  may  say  that  at  these  low  temperatures  life  processes  are  reduced 
to  the  minimum. 

If  the  chemical  constitution  or  the  temperature  of  the  surrounding  mcclium 
be  altered  and  the  cells  continue  to  live,  various  changes  in  their  properties 
may  be  induced,  which,  especially  in  the  pathogenic  microorganisms,  are  of 
great  importance,  because  the  degree  of  their  virulence  may  be  thereby  in- 
creased or  diminished  (Pasteur).  The  protective  inoculation  introduced  by 
Pasteur  is  based  upon  these  facts. 

After  this  general  discussion  we  shall  now  proceed  to  tlie  different  mani- 
festations of  life,  taking  up  in  order  the  ingestion  of  food,  digestion,  the 
oxidative  processes,  the  elimination  of  decomposition  products,  the  secretions, 
and  finally  the  phenomena  of  motility,  production  of  light,  formation  of  heat 
and  the  generation  of  electricity. 


30  THE  CELL 

B.    THE   INGESTION  OF  FOOD 

It  is  self-evident  tlial  tlie  mediuiu  in  whicli  elementary  organisms  live 
must  contain  all  the  nutrient  substances,  including  oxygen  and  water,  neces- 
sary for  their  subsistence.  Besides,  different  cells  have  very  different  require- 
ments with  respect  to  the  chemical  constitution  of  the  medium,  and  these 
peculiarities  are  conditioned,  in  part  at  least,  upon  the  hereditary  traits  of 
the  species. 

Certain  unicellular  organisms  are  adapted  for  life  in  fresh  water,  others 
for  life  in  salt  water.  Most  of  them  die  if  they  be  placed  in  distilled  water. 
Likewise  if  the  chemical  composition  of  the  medium  in  which  the  cells  live  be 
changed  suddenly,  they  die;  but  if  the  change  take  place  gradually  and  slowly, 
they  can  adapt  themselves  to  the  altered  nature  of  the  medium  and  continue 
to  live.  How  great  a  change  may  be  made  before  disturbances  in  the  vital 
activities  of  the  cell  appear,  depends  partly  upon  the  nature  of  the  cell  and 
partly  upon  the  substance  added  to  the  medium. 

That  even  in  the  higher  animals  and  man  the  properties  of  the  cells  are 
altered  by  a  changed  composition  of  the  lymph  follows  directly  from  observa- 
tions on  diseases  characterized  by  chronic  intoxication  (e.  g.,  alcoholism, 
morphinism). 

In  multicellular  animals  the  cells  are  bathed  by  a  fluid,  the  lymph,  which 
represents  the  medium  in  tvhich  they  live.  If  the  lymph  is  to  be  adapted 
to  its  purpose,  it  must  contain  in  the  first  place  all  the  substances  necessary 
for  the  nourishment  of  the  cells,  and  must  possess  also  the  other  necessary 
chemical  and  physical  properties. 

Lymph  is  distinguished  from  those  media  in  which  unicellular  organisms 
live,  by  l^eing  inclosed  within  the  body  and  by  being  formed  essentially  through 
the  activity  of  the  cells  themselves.  The  quantity  of  lymph  is  not  unlim- 
ited, for  the  supply  of  nutrient  materials  and  oxygen  which  it  contains  at  any 
-  given  time  is  soon  used  up,  and  their  place  is  taken  by  decomposition  prod- 
ucts which  are  harmful  to  the  body.  But  in  order  to  maintain  life  in  the 
Metazoa  it  is  necessary  in  the  first  place  that  the  lymph  shall  be  always  of 
normal  constitution.  To  this  end  many  organs  of  the  hody  cooperate,  each 
being  adapted  for  a  special  purpose. 

Experience  teaches  us  that  in  general  a  special  function  cannot  be  carried 
out  by  a  single  organ,  but  requires  the  cooperation  of  several.  All  those  organs 
which  together  accomplish  a  definite  purpose  are  designated  as  an  organ  system 
or  apparatus. 

In  order  that  the  lymph  may  serve  as  the  medium  for  the  vital  activities 
of  the  cells,  it  must  contain  besides  water  certain  combustible  substances  and 
certain  mineral  constituents  (all  of  which  are  comprehended  under  the  name 
foodstuffs)  and  oxygen.  Neither  the  foodstuffs  nor  the  oxygen  come  directly 
into  the  lymph;  to  bring  them  there  not  less  than  three  organ  systems  must 
cooperate:  namely,  (1)  the  circulatory  system,  (2)  the  digestive  system,  and 
(3)  the  respiratory  system. 

The  object  of  the  circulatorij  system  is  to  supply  the  lymph  with  nutrient 
snbstances  and  with  oxygen.  The  object  of  the  digestive  system  is  to  take  up 
the  foodstuffs  necessary  to  the  maintenance  of  the  body  and  to  change    them 


THE  VITAL  PHENOMENA  OF  CELLS  31 

so  that  they  may  be  transferred  to  the  blood.  The  respiratory  si/stem  supplies 
the  blood  with  the  oxygen  necessary  for  combustion  in  the  body. 

The  decomposition  products  arising  from  combustion  must  not  remain  in 
the  lymph,  because,  if  they  did,  they  would  finally  poison  the  cells.  They  must 
therefore  be  removed  by  passage  first  into  the  blood  and  thence  out  of  the  body 
through  the  excretory  organs. 

In  order  that  these  necessary  functions  shall  be  directed  to  the  proper  end 
of  maintaining  life,  they  are  all  subordinated  to  the  influence  of  the  nervous 
system  whose  important  object  it  is  to  control  the  organs  and  to  regulate  their 
functions.  In  addition  to  this,  in  the  warm-blooded  animals  a  constant  body 
temperature — i.  e.,  a  constant  temperature  of  the  lymph  is  maintained  through 
the  influence  of  the  nervous  system. 

1.  Cells  completely  surrounded  by  membranes  can  take  up  only  gaseous 
and  dissolved  substances.  The  processes  concerned  in  the  absorption  of  gases 
by  the  elementary  organisms  are  but  little  known,  and  the  phenomena  accom- 
panying these  processes  in  the  higher  animals  are  fully  discussed  in  Chapter 
IX.  Our  knowledge  has  progressed  somewhat  further  concerning  the  absorp- 
tion of  fluids  and  compounds  in  solution,  and  since  the  phenomena  of  osmosis 
figure  prominently  in  this  connection,  it  seems  best  to  discuss  them  here 
somewhat  in  detail. 

Osmosis. — When  a  layer  of  pure  water  is  carefully  stratified  upon  a  solu- 
tion— e.  g.,  sugar  in  water — the  layers  do  not  remain  separate.  The  sugar  begins 
at  once  to  rise  in  spite  of  the  force  of  gravity  and  to  diffuse  into  the  water;  and 
the  movement  ceases  only  when  the  sugar  is  distributed  uniformly  throughout 
the  whole  volume  of  water.  The  same  thing  occurs  if  the  water  and  the  sugar 
solution  are  separated  by  a  partition  which  is  equally  permeable  for  both.  The 
dissolved  substance  passes  from  the  place  of  higher  concentration  to  the  place 
of  lower  concentration  just  as  if  no  separating  membrane  were  present. 

Quite  a  different  order  of  things  prevails  if  between  the  water  and  the 
solution  a  partition  is  interposed  which  allows  the  water  but  not  the  dissolved 
substance  to  pass  through.  Such  "  semipermeable  "  walls  are  obtained  by  soak- 
ing a  porous  clay  cell  in  a  solution  of  copper  sulphate,  carefully  pouring  this 
out  and  filling  the  cell  with  a  solution  of  potassium  ferrocyanide.  There  is  then 
foi-med  within  and  upon  the  clay  wall  a  coherent  layer  of  copper  ferrocyanide 
through  which  water  can  be  filtered;  but  if  one  attempt  to  filter  through  it  a 
sugar  solution,  a  much  higher  pressure  is  required,  and  what  finally  comes 
thi'ough  is  not  the  sugar  solution  at  all  but  pure  water. 

If  a  cell  prepared  in  this  way  be  filled  with  a  sugar  solution  and  be  closed 
by  means  of  a  stopper  through  which  connection  is  made  with  a  manometer, 
and  the  cell  then  be  placed  in  pure  w^ater,  an  increase  in  pressure  inside  the 
cell  is  noticed,  which  finally  rises  to  a  definite  maximum  value.  This  value 
represents  the  osmotic  pressure  of  the  fluid  inside  the  cell,  and  is  equal  to  the 
gas  pressure  which  would  be  exerted  by  the  same  quantity  of  sugar  in  the  form 
of  a  vapor  inclosed  within  the  same  space  at  the  same  temperature.  For  a  one- 
per-cent  solution  of  cane  sugar  at  13.7°  C.  the  osmotic  pressure  amounts  to 
0.691  atmospheres.  A  four-per-cent  sugar  solution  raises  the  pressure  to  2.74 
atmospheres. 

Since  there  is  no  membrane  w^hich  is  semipermeable  for  all  substances,  it  is 
necessary  to  resort  to  indirect  methods  of  determining  the  osmotic  pressure  of 
some  solutions.  One  such  method  which  has  found  wide  application  both  in 
physiology  and  medicine  is  based  upon  the  fact  that  in  a  watery  solution  the 


32  THE  CELL 

dissolved  substance,  e.g.,  salt,  exercises  a  restraining  influence  on  the  freezing 
of  the  water  and  consequently  lowers  the  freezing  point.  The  cause  of  this 
restraining  influence  is  that  the  particles  of  salt  by  means  of  the  attraction 
they  exercise  on  the  particles  of  water  tend  to  prevent  the  latter  from  cohering 
with  one  another,  i.  e.,  from  passing  into  the  solid  state.  The  greater  this 
attraction,  the  more  difficult  is  it  for  the  water  to  be  solidified,  and  the  lower 
must  be  the  temperature  before  this  change  of  state  can  be  brought  about. 

The  lowering  of  the  freezing  point,  which  is  designated  with  "  A,"  is  there- 
fore a  measure  of  the  osmotic  pressure  (P)  of  the  salt,  calculated  in  atmospheres 
according  to  the  formula  P  =  12.03  A.  A  one-per-cent  solution  of  NaCl  freezes 
at  — -0.606°  C. :  the  lowering  of  the  freezing  point  is  therefore  0.606.  If  one 
finds  for  an  unknown  fluid  A  =  0.606,  its  osmotic  pressure  corresponds  to 
that  of  the  one-per-cent  NaCl  solution,  and  amounts  to  12.03  X  0.606  =  7.29 
atmospheres. 

When  equimolecular  quantities  of  diiferent  substances  (i.  e.,  quantities  pro- 
portional to  their  molecular  weights)  are  brought  into  solution  in  the  same 
solvent,  and  solutions  which  have  the  same  number  of  molecules  of  the  dissolved 
substances  in  equal  volumes  are  thus  obtained,  these  solutions  have  at  any  given 
temperature  the  same  osmotic  pressure. 

We  have  in  the  electrolytes  an  apparent  exception  to  this  law.  The  os- 
motic pressure  is  higher  than  it  ought  to  be  according  to  this  general  state- 
ment. This  is  due  to  the  fact  that  the  substances  in  question  are  partially 
dissociated  in  water  into  electrically  charged  atoms  or  ions — e.  g.,  HCl  into 
+  H  and  -  CI,  KCl  into  +  K  and'  -  CI,  l^aOU  into  +  Na  and  -  OH,  etc. 
In  this  way  the  number  of  effective  molecules  in  a  solution  is  increased  and 
in  consequence  the  osmotic  pressure  is  raised — in  perfect  agreement  with  the 
general  law. 

The  degree  of  dissociation  depends  primarily  upon  the  concentration  and 
upon  the  nature  of  the  dissolved  substance.  The  more  dilute  the  solution  the 
more  complete  is  the  dissociation  with  one  and  the  same  electrolyte — i.  e.,  the 
greater  is  the  relative  (not  the  absolute)  number  of  free  ions.  In  different 
electrolytes  dissociation  presents  certain  variations  into  which  we  cannot  enter 
at  this  time.  It  will  suffice  here  to  say  that  the  most  important  salts  in  the 
body,  those  formed  by  the  alkalies  with  monobasic  acids,  are  dissociated  in 
dilute  solutions  of  equivalent  concentration  to  a  very  considerable  extent,  and 
are  dissociated  equally. 

The  combined  osmotic  pressure  of  several  substances  in  the  same  solution 
is  equal  to  the  sum  of  the  pressures  of  the  separate  substances. 

When  two  solutions  of  different  osmotic  pressure  are  separated  from  each 
other  by  a  semipermeable  membrane,  water  passes  from  the  one  of  less  pressure 
to  the  one  of  higher  pressure  until  the  two  are  of  equal  pressure — i.  e.,  are  isotonic. 
With  reference  to  each  other  these  solutions  are  said  to  be  hypotonic  and  hyper- 
tonic respectively. 

Dead  animal  and  plant  membranes  are  as  a  rule  permeable  to  water  and, 
though  in  less  degree,  to  substances  soluble  therein.  When  such  a  membrane 
separates  water  from  an  aqueous  salt  solution,  the  foi*mer  passes  into  the  solu- 
tion and  the  salt  passes  out  until  the  osmotic  pressure  on  both  sides  of  the 
membrane  is  the  same.  This  is  the  case  also  when  two  isotonic  solutions  of 
different  salts — e.  g.,  NaCl  and  NaNO,,  are  separated  by  the  membrane.  The 
common  salt  passes  from  one  to  the  other  and  vice  versa,  so  that  the  two  solu- 
tions remain  isotonic.  If  they  are  of  unequal  osmotic  pressure — i.  e.,  anisotonic — 
to  begin  with,  an  exchange  of  water  and  salt  molecules  takes  place  until  a  con- 
dition of  equilibrium  is  established. 


THE   VITAL   PHENOMENA  OF  CELLS  33 

From  these  discoveries  on  the  phenomena  of  osmosis  it  follows  that  even- 
change  in  the  constitution  of  the  medium  surrounding  the  cell  or  of  the  fluid 
contained  within  it  will  have  power  to  effect  a  change  in  the  osmotic  pressure 
prevailing  in  the  cell.  This  would  mean  also  a  change  in  the  quantity  of  fluid 
(degree  of  turgescence)  as  well  as  in  the  chemical  constitution  of  the  fluid 
contained  in  the  cell,  or  indeed  in  the  constitution  of  the  protoplasm  itself, 
according  as  the  limiting  layer  of  the  protoplasm  is  permeahle  or  not  to  the 
substances  present. 

Plant  cells  afford  us  the  simplest  examples  of  the  influence  of  osmosis. 
The  cell  membrane  is  permeable  to  gas,  water  and  solutions.  In  the  living 
cell  the  membrane  is  impregnated  with  water ;  hence  all  substances  which  are 
dissolved  in  the  water  can  penetrate  the  membrane  and  thus  come  into  contact 
with  the  outer  layer  of  the  protoplasm  (primordial  sheath)  just  inside  the 
membrane  (cf.  Fig.  16). 

Within  the  plant  cell  and  surrounded  by  the  primordial  sheath  we  find 
the  cell  sap,  which  is  a  watery  solution  of  various  salts,  carbohydrates,  etc. 
The  primordial  sheath  is  permeable  to  water,  but  prevents  entirely  the  en- 
trance of  certain  compounds,  behaves  toward  them  in  other  words  exactly  like 
a  semipermeable  membrane. 

If  therefore  the  cell  is  bathed  by  a  solution  of  a  compound  whose  osmotic 
pressure  is  greater  than  that  of  the  cell  sap,  water  passes  out  of  the  cell,  the 
primordial  sheath  is  loosened  and  shrinks  away  from  the  cell  membrane  (plas- 
7nolijsis).  But  if  the  cell  is  bathed  by  pure  water,  the  water  can  pass  through 
the  primordial  sheath  in  the  reverse  direction  and  raise  the  internal  pressure 
above  its  usual  level,  whence  we  have  the  condition  of  cell  turgor. 

The  primordial  sheath  permits  the  entrance  of  certain  other  substances 
more  or  less  easily,  and  in  the  commerce  between  the  cells,  where  transporta- 
tion and  exchange  occur  freely,  it  has  the  power  to  change  its  permeahility 
according  to  circumstances.  From  this  it  follows  that  neither  absorption  nor 
excretion  on  the  part  of  plant  cells  is  to  be  described  as  a  simple  osmotic 
process. 

In  the  cells  of  the  animal  body,  both  the  cell  body  and  the  nucleus  permit 
certain  substances  dissolved  in  water  to  pass  through,  Init  exclude  others ;  they 
behave  toward  these  substances  like  semipermeable  memljranes  (Hamburger, 
Hedin).  To  one  and  the  same  substance  the  permeability  of  different  kinds 
of  cells  may  be  considerably  different,  and  it  appears  to  vary  with  the  same 
kind  of  cells  under  different  physiological  conditions   (Hamburger). 

From  the  investigations  of  Hamburger,  Hedin,  Koeppe  and  GrjTis  on  the 
permeahility  of  red  blood  corpuscles  to  different  substances,  one  may  gather 
that  the  K,  Na,  Ca,  Sr,  Ba,  Mg  ions,  the  different  kinds  of  sugar,  arabite  and 
mannite  do  not  penetrate  them  at  all;  and  that  they  are  but  slightly  penneable  to 
amino  acids  (glycocoll,  asparagin,  etc.).  In  fact  they  appear  to  offer  a  power- 
ful resistance  to  the  amido  group  in  the  amino  acids,  but  toward  the  amido 
group  in  the  acid  amides  (acetamide,  etc.)  the  resistance  is  not  so  groat.  The 
red  blood  corpuscles  are  permeable  to  NH«  ions,  to  free  acids  and  alkalies, 
and  to  alcohols  in  inverse  proportion  to  the  number  <jf  hydroxyl  ions  in  the  mole- 
cule; also  to  aldehydes,  ketones,  ethers,  esters,  antipyrin,  amide,  urea,  urethan, 
bile  acids  and  bile  salts.     The  leucocytes  of  the  blood  and  of  the  lymph  glands. 


34  THE  CELL 

so  far  as  this  property  has  yot  been  studied,  are  shown  to  be  permeable  to 
chlorine,  snljihuric  acid,  carbon  dioxide,  iodine,  bromine,  oxalic  acid,  phosphoric 
acid,  salicylic  acid,  benzoic  acid,  and  arsenic  acid  (Hamburger  and  v.  der 
Sehroeff). 

Overton  has  studied  the  permeability  of  cross-striated  muscle  to  a  large 
number  of  organic  compounds,  and  has  come  to  the  conclusion  that  toward  the 
same  substances  they  behave  just  as  do  plant  cells.  All  compounds  which  are 
plainly  soluble  in  water  and  are  also  soluble  in  ethyl-ether,  in  the  higher  alco- 
hols, in  olive  oil  and  similar  organic  solvents,  or  which  at  least  are  not  much 
more  difficultly  soluble  in  these  than  in  water,  penetrate  living  muscle  fibers  and 
other  animal  and  plant  cells  very  easily.  But  the  more  the  solubility  of  a  com- 
pound in  water  exceeds  its  solubility  in  one  of  the  organic  solvents,  the  more 
slowly  does  it  penetrate  these  structures.  For  explanation  of  this  peculiar 
behavior,  Overton  has  put  forward  the  hypothesis  that  the  limiting  layers  of 
the  protoplasm  are  impregnated  with  a  fatty  substance,  a  mixture  of  lecithin 
and  cholesterin,  and  that  the  elective  solvent  power  of  this  mixture  for  definite 
substances  governs  the  pure  osmotic  permeability  of  the  cells. 

Out  of  some  75,000  organic  compounds  known  at  present  more  than  G0,000, 
to  accept  Overton's  rough  estimate,  can  penetrate  the  cell.  Among  these  how- 
ever are  found  neither  the  carbohydrates  nor  a  number  of  other  substances  par- 
ticipating actively  in  the  metabolism  of  plants  and  animals.  Overton  remarks 
that  so  far  as  the  constitution  of  these  compounds  is  known,  derivatives  of  them 
can  always  be  found  which  do  penetrate  the  cells  very  easily.  How  far  his 
explanation  applies  to  the  living  body  we  do  not  know. 

It  has  been  found  that  different  Infusoria  are  to  a  great  extent  independent 
of  the  osmotic  pressure  of  the  solution,  since  they  can  exist  for  days  at  a  time  in 
distilled  water,  without  suffering  noticeably  and  without  exhibiting  any  very 
striking  changes  in  form  (Goldberger).  The  eggs  of  Fundulus  also  do  not 
swell  if  they  are  suddenly  brought  from  sea  water  into  distilled  water;  and  they 
do  not  shrink  if  the  reverse  change  is  made  (Loeb).  McCallum  found  in  the 
case  of  the  medusa,  Anrelia,  that  the  salt  content  of  the  surrounding  medium 
can  vary  within  wide  limits  without  materially  affecting  the  body  fluid.  The 
fluid  pressed  out  of  the  body  contains  less  SO3,  MgO,  and  Na.O,  and  more  CI, 
Fe,  and  especially  K  than  the  sea  water;  the  depression  of  the  freezing  point 
also  was  less  for  the  latter  than  for  the  body  fluid.  While  the  salt  content  of 
the  blood  of  the  green  crab  increases  and  decreases  with  that  of  the  sea  water, 
the  relation  in  the  crayfish  is  just  the  reverse :  here  the  depression  of  the  freezing 
point  of  the  blood  is  0.8°  C,  while  in  the  surrounding  water  it  is  only  0.02°- 
0.03°  C.  (Fredericq).  Frogs  kept  for  weeks  in  distilled  water  give  up  only  a 
part  of  their  salt  to  the  water,  notwithstanding  that  between  them  and  the  water 
there  is  a  difference  of  osmotic  pressure  amounting  to  about  two  atmospheres 
(Durig). 

In  the  different  tissues  of  any  given  animal  also  there  are  noteworthy  differ- 
ences with  respect  to  osmosis.  Membranes  consisting  of  only  a  single  layer  of 
connective  tissue  coated  with  a  single  layer  of  smooth  muscle  cells,  like  the 
peritoneum  and  the  mesentery,  offer  very  little  resistance  to  the  passage  of  dif- 
ferent ions;  and  their  pernieability  is  not  noticeably  changed  after  the  death  of 
the  cells  by  chloroform.  But  living  membranes  constructed  of  specifically  dif- 
ferentiated epithelial  cells  behave  differently:  their  ability  to  oppose  or  to  facili- 
tate the  passage  of  ions  corresjjonds  to  the  physiological  functions  devolving 
upon  them,  and  disappears  with  the  death  of  the  cell,  at  which  time  also  the 
pernieability  rises  significantly  (Galeotti). 


THE  VITAL  PHENOMENA  OF  CELLS 


35 


The  fact  demonstrated  by  Schiicking  in  the  case  of  the  snail,  Aphjsia,  that 
long-continued  stimulation  of  the  dermal  musculature  can  more  than  compen- 
sate the  effects  of  osmotic  pressure,  and  the  discoveries  on  absorption  from  the 
alimentary  canal  (cf.  Chapter  VIII).  together  with  the  facts  summarized  above, 
go  to  show  that  the  osmotic  processes  cannot  he  the  only  factors  at  work  in 
the  absorption  of  substances  by  animal  cells.  The  outer  limiting  membrane 
of  the  cell  behaves  in  many  respects  as  a  semipermeable  meml)rane,  but,  so 
far  as  we  can  grasp  the  matter  at  present,  it  appears  to  differ  in  many 
respects  from  such  a  membrane.  Just  as  the  cell  itself  regulates  the  extent 
of  the  oxidation  processes  taking  place  within  it  or  inaugurated  by  it,  so 
within  certain  limits,  and  independently  of  the  quantitive  composition  and 
the  osmotic  pressure  of   the   surrounding   medium,   it   regulates   its   absorp- 


FiG.  19. — Gromia  ovijormis,  after  Max  Schultze.  Some 
of  the  pseuclopodia  have  caught  a  diatom,  which  by 
gradual  shortening  of  the  contractile  threads  will 
be  taken  into  the  interior  of  the  organism.     20/1. 


Fig.  20. — Amoeba  polypo- 
dia, after  Max  Schultze. 
A  small  organism  has 
been  engulfed.     330/1. 


tion  and  elimination  of  sulistance.  It  is  possible  that  this  is  duo  to  the 
specific  affinities  of  the  living  bodies  which  constitute  the  protoplasm.  Just 
as  gelatin  plates  and  agar  plates  take  up  substances  from  solution,  whether 
the  solution  is  isotonic,  hypotonic,  or  hypertonic,  until  their  affinity  for  the 
substance  is  satisfied,  so  the  living  substance  might  take  up  or  give  off  sub- 
stances according  to  its  affinities,  independently  of  the  osmotic  pressure.  Just 
what  weight  this  hypothesis,  developed  bv  Friedlander  and  Durig,  may  have 
we  cannot  say  definitely  at  present. 

In  connection  with  the  investigations  here  discussed  opportunity  has  often 
been  afforded  to  determine  the  osmotic  tension  inside  animal  cells.  It  is  found 
to  correspond  to  a  XaCl  solution  of  0.7  to  0.9  per  cent,  and  amounts  to  about 
5  to  6.5  atmospheres.  In  order  that  the  aqueous  content  of  animal  cells  may 
be  preserved,  it  is  necessary  therefore  that  the  surrounding  medium  have  a 
corresponding  osmotic  pressure. 


36 


THE  CELL 


Since  XaCl  i)la.vs  the  most  iniiKHtaul  rule  in  niaiiitaiiiiiit!:  tliis  pressure,  one 
might  sui)pose  that  this  is  the  only  special  physiolojiical  signiticance  of  common 
salt.  That  is  not  the  case  however,  as  appears  from  the  fact  that  a  frog's  mus- 
cle which  remains  excitable  for  a  long  time  in  a  O.G-per-cent  NaCl  solution  very 
soon  loses  its  excitability  in  an  isotonic  solution  of  cane  sugar  (Overton). 

2.  Xaked  elementary  organisms  have  tlic  power  also  of  ingesting  solid  par- 
ticles.    In  many  cases  this  takes  place  in  a  vury  simj)le  manner.     The  ele- 


vc 


E 


c^f 


Fig.  21. 


-AH,  Several  successive  phases  in  the  life  history  of  an  Amneha,  kept  under  constant 
observation  for  tliree  days;    /,  anotlicr  indivickial  eiicy.sted. 


A,  locomotor  pha'-e:  the  ectoplasm  is  seen  extending  to  form  a  pseudopocHum,  into  which  the 
endoplasm  passes;  B,  a  stage  in  the  ingest ive  phase;  fp,  a  vegetable  organism  being  in- 
gested; C,  a  portion  of  the  Amoeba  represented  in  b,  after  complete  ingestion  of  the  food- 
particle;  D,  E,  successive  stages  in  the  assimilative  and  excretory  processes;  F.  G,  H, 
successive  stages  in  the  reproductive  process  of  the  same  individual.  It  will  be  noticed 
{F)  that  the  nucleus  divides  first;  re,  contractile  vacuole;  nc,  nucleus;  p.s,  pseudopodium ; 
dt,  diatom;    jp,  food  particle. 


mentary  organism  puts  ont  processes,  psoudopodia.  which  apply  themselves  to 
the  particles  of  food,  then  gradually  flow  around  it  until  it  comes  to  lie 


THE  VITAL  PHENOMENA  OF  CELLS 


37 


within  the  protoplasm.  Examples  of  this  are  found  in  the  Amoeba?  and  other 
Khizopoda  (Figs.  19  to  23).  and  in  the  leucocytes  of  all  classes  of  animals, 
which  very  closely  resemble  Ama'ba^  with  respect  to  their  structure. 

This  ability  of  the  leucocytes  is  of  great  importance  to  the  body  as  a  whole, 
for  wherever  a  destruction  of  tissues  takes  place  either  from  normal  or  patho- 


FiG.  22. — A  white  blood  corpuscle  of  the  frog,  contaniing  an  anthrax  bacillus.     The  two  figures 
were  drawn  from  the  same  cell  at  different  times,  after  Metschnikoff. 

logical  causes,  the  dfliris  is  taken  up  In'  the  leucocytes  and  is  removed.  The 
leucocytes  play  an  imjmrtant  role  also  in  disposing  of  the  pathogenic  Bacteria 
which  find  their  way  into  the  body,  since  they  are  aide  to  eat  and  to  digest 
such  organisms  (Fig.  22),  and  thereby  to  afford  the  body  substantial  pro- 
tection against  infection  (Metschnikoff'). 

The  more  highly  organized  elementary  organisms  provided  with  cilia  and 
a  cell  mouth,  such  as  the   ciliate  Infusoria  (Figs.  24  and  28),  ingest  solid 


Fig.  23. — VampyrcUa  spirmjrircc,  a  rhizopodous  unicellular  organism,  ingesting  the  contents  of 

an  alga  cell,  after  Cienkowski. 


particles  liy  creating  with  their  cilia  a  vortex  so  directed  that  the  particles 
are  driven  into  the  mouth.  In  this  and  other  similar  ways  of  taking  up  solid 
particles  the  organism  can  exercise  an  actual  choice  of  nourishment;  certain 
Khixopoda  for  example  eat  only  certain  alga  cells  (cf.  Fig.  23). 


38  THE  CELL 


C.    DIGESTION 


J 


Tlie  solids  taken  up  in  this  way  by  tlic  cells  must  unders^o  various  change.^ 
in  order  that  they  may  be  of  use  to  the  cell.  Oltcii  this  is  true  also  with 
the  dissolved  foods.  All  such  processes  l)y  which  the  foods  arc  chanj^ed  so 
that  they  may  be  assimilated  or  further  elal)oratcd  by  the  cell  are  included 
under  the  term  digedion. 

The  digestion  accomplished  by  the  cell  is  either  extra-  or  iutracclhihir. 
In  the  former  case  digestion  takes  place  under  the  influeuce  of  special  sub- 
stances, the  enzymes,  formed  by  the  cell.  These  substances,  like  catalytic 
agents,  have  the  property  when  present  in  very  small  quantity  of  producing 
chemical  changes  in  great  quantities  of  complex  molecules,  thereby  splitting 
them  into  simpler  compounds,  which  in  their  turn  reduce  the  activity  of  the 
enzymes.  By  the  action  of  enzymes  proteid  is  split  into  albumoses  and  ])ep- 
tones,  starch  into  sugar,  and  fat  into  glycerin  and  free  fatty  acids  (cf.  C'hajiter 
VII).  It  should  be  noted  further  that  every  special  enzyme  acts  only  upon 
a  definite  compound  or  group  of  compounds.  The  proteid-splitting  en- 
zyme therefore  does  not  act  upon  starch,  nor  the  starch-splitting  enzyme 
on  fats.  etc. 

It  is  quite  possible  that  the  enzymes  can  produce  their  effects  inside  the 
cell  just  as  well  as  in  the  surrounding  medium,  and  it  is  very  doubtful  whether 
an  intracellular  digestion  takes  place  anywhere  without  the  help  of  enzymes, 
though  such  participation  cannot  be  definitely  asserted. 

Enzymes  which  have  the  property  of  dissolving  proteids  just  like  the 
corresponding  enzymes  in  the  digestive  fluids  have  been  ol)tained  from  finely 
minced  organs — spleen,  lymph  glands,  kidneys,  liver,  heart,  etc.  It  is  assumed 
that  they  are  present  in  the  living  cells,  though  this  has  not  been  finally 
proved.  Nothing  definite  can  be  said  at  this  time  with  regard  to  the  impor- 
tance of  such  enzymes  in  the  normal  processes  of  the  body.  It  is  possible  that 
in  starvation  they  may  effect  the  solution  of  the  tissue  proteids.  also  that  the 
autolytic  processes  which  take  place  after  death  are  initiated  and  carried  on 
by  such  enzymes. 

The  enzymes  are  products  of  cell  activity,  but  once  they  are  formed  they 
act  entirely  without  the  help  of  the  cell  and  are  nonliving  sul)stances.  In 
general  it  is  supposed  that  they  are  proteid  in  nature,  and  in  fact  Pekel baring 
has  prepared  from  the  stomach  of  the  dog  a  very  pure  enzyme  (pepsin)  which 
was  free  of  phosphorus  and  had  the  constitution  of  proteid.  But  it  would 
be  premature  to  draw  any  general  conclusions  from  a  single  observation. 

Enzymes  occur  in  the  cells  for  the  most  part  in  the  form  of  precursors, 
known  as  zymogens.  Often  the  zymogen  is  changed  into  the  active  enzyme 
in  the  act  of  secretion :  or  its  activation  may  be  brought  about  under  the 
influence  of  another  enzyme. 

Enzymes  are  only  slightly  diffusible,  but  they  pass  through  a  porcelain 
filter  and  can  be  separated  in  this  way  from  the  cell  fragments  of  an  extract 
or  juice.  In  the  dissolved  state  they  withstand  heating  up  to  70°  C;  in  the 
dry  state  many  enzymes  are  not  destroyed  by  a  temperature  of  over  100°  C. 
In  general  they  are  most  powerfully  active  at  35°  to  45°  C. ;  at  a  lower  tem- 


THE  VITAL  PHENOMENA  OF  CELLS  39 

perature  they  act  more  feebly,  but  if  warmed  again  will  regain  their  activity 
even  after  having  been  reduced  to  a  temperature  as  low  as  —  192°  C.  They 
are  destroyed  by  mineral  acids  and  alkalies  of  sufficient  strength.  With  some 
enzymes  also  the  decomposition  products  formed  ])y  them  exert  an  inhibiting 
influence  on  their  further  activit3^  On  the  other  hand  their  activity  is  but 
slightly  affected  by  the  protoplasmic  poisons. 

Various  facts  favor  the  view  that  enzymes  exercise  their  specific  effects 
only  after  uniting  with  the  substance  acted  upon.  Thus  pepsin  for  example 
unites  with  the  proteid  filjrin  so  firmly  that  it  cannot  be  removed  by  washing 
with  water.  The  fact  also  that  when  mixed  with  the  appropriate  substances 
enzymes  endure  a  higher  temperature  than  otherwise  gives  a  certain  support 
to  this  conception. 

Recently  Croft  Hill  has  shown  that  the  enz3'me  formed  in  the  yeast  cell 
by  which  maltose  is  changed  into  dextrose,  has  the  power  in  concentrated  solu- 
tions of  sugar  (over  four  per  cent)  of  changing  dextrose  back  into  maltose; 
that  what  takes  place  is  therefore  a  reversible  process.  Similar  phenomena 
have  since  been  ol)served  with  other  enzymes.  Pancreas  extract  effects  a  par- 
tial synthesis  of  ethyl  butyrate  from  ethyl  alcohol  and  butyric  acid  (Kastle 
and  Loevenhart).  By  means  of  a  lactose-splitting  enzyme  E.  Fischer  and 
Armstrong  prepared  isolactose  from  galactose  and  glucose  in  equal  quanti- 
ties, etc. 

It  is  very  probable  that  this  reversil)ility  of  enzyme  action  is  of  very 
great  importance  in  the  transformations  taking  place  in  the  body,  although 
we  are  not  yet  able  to  foresee  its  entire  range. 

D.    THE   OXIDATIVE   PROCESSES 

Attempts  have  been  made  to  give  an  exhaustive  theoretical  explanation 
of  the  oxidative  processes  going  on  in  the  tissues,  and  several  hypotheses  have 
been  put  forward.  Some  of  these  suppose  that  the  influence  of  the  animal 
tissues  on  the  physiological  oxidations  consists  of  an  increase  in  the  oxidizing 
activity  of  oxygen;  some  assume  that  the  tissues  in  mediating  oxidations  do 
not  influence  the  oxygen  itself,  but  act  on  the  oxidizable  substances  making 
them  more  accessible  to  the  oxygen. 

We  cannot  here  enter  into  the  development  of  these  theories  since,  as  they 
stand  to-day,  they  are  not  by  any  means  able  to  explain  the  facts.  We  may 
say  only  that  from  both  fresh  and  dead  organs  hardened  in  alcohol,  it  is 
possible  to  extract  with  water  a  substance  which  oxidizes  certain  substances 
like  benzyl  alcohol,  salicvl  aldehyde  and  glucose  (Jacquet).  According  to 
Spitzer  this  substance  is  an  iron-containing  nucleo-proteid  derived  from  the 
nucleus.  Whether  it  has  any  special  significance  in  the  physiological  proc- 
esses of  the  cell  cannot  be  said  definitely  as  yet.  because  of  the  possibility 
that  it  is  set  free  only  by  the  destruction  of  tissue  elements.  That  in  any 
case  its  ])hysiological  importance  is  only  secondary,  would  appear  to  be  suffi- 
ciently sliown  by  tbe  fact  that  its  ((uantity.  or  more  correctly,  its  oxidizing 
function  as  determined  in  the  manner  above  mentioned  is  considerably  greater 
in  the  glandular  organs  (spleen,  liver,  thyroid,  kidneys,  etc.)  than  in  the 
muscles,  where  combustion  takes  place  most  extensively. 
5 


40  THE  CELL 

The  following  discoveries  appear  to  aft'ord  a  wider  outlook.  In  the  alco- 
holic fermentation  ett'ected  by  the  yeast  plant,  maltose  dissolved  in  water  is 
changed  under  the  influence  of  an  enzyme  formed  by  the  yeast  cells  into  grape 
sugar,  and  this  is  split  into  carbon  dioxide  and  alcohol.  Until  recently  it 
■was  supposed  that  the  latter  cleavage  could  only  be  accomplished  by  the  vital 
activity  of  the  yeast  cells  themselves,  which  appeared  in  fact  to  follow  from 
a  number  of  experiments.  By  trituration  of  the  yeast  cells  and  subsequent 
compression  with  a  pressure  of  4UU-500  atmospheres,  how^ever,  E.  Buchner 
(1897)  succeeded  in  obtaining  a  sap,  which  after  being  filtered  through  steril- 
ized "  infusorial  earth  "  and  thus  being  freed  entirely  of  yeast  cells,  was 
still  able  to  split  sugar  into  alcohol  and  carbon  dioxide.  The  active  substance 
contained  in  the  sap  Buchner  named  zymaze. 

This  discovery  opens  up  new  prospects  for  our  whole  conception  of  the  mode 
of  decomposition  in  the  animal  body.  It  makes  possible  the  assumption  that 
not  only  the  yeast  cell  but  all  other  cells  carry  out  the  chemical  work  charac- 
teristic of  their  vital  activities  by  means  of  substances  analogous  to  the  enzymes 
and  capable  of  being-  isolated  which  are  foimed  within  the  cells  and  are  given  off 
by  them.  It  would  be  premature  however  from  the  present  standpoint  of  science 
to  make  such  a  genei'alization  even  hypothetically.  For  the  substances  formed 
in  the  processes  under  consideration  are  so  manifold,  and  the  essence  of  the 
processes  is  still  so  obscure  that  immediate  dissimilation  effected  by  the  vital 
activity  of  the  cells  cannot  without  further  information  on  the  subject  be  com- 
pletely excluded.  Moreover,  the  oxidation  processes  of  the  body  are  so  well  regu- 
lated in  relation  to  the  amount  of  work  to  be  done  and  the  time  of  doing  it, 
that  it  is  difficult  to  imagine  how  they  could  be  brought  about  exclusively  by 
ferment  action. 

Any  dissimilation  accomplished  by  the  direct  action  of  the  cell,  in  contra- 
distinction to  the  effect  of  the  enzymes  and  zymaze,  is  designated  as  ferment 
action,  and  the  cells  participating  are  known  as  organized  ferments.  Sub- 
stances resulting  from  such  action  represent  decomposition  products  formed 
directly  by  the  vital  activity  of  the  cell.  Carbon  dioxide  which  is  produced 
in  every  living  being  belongs  (at  least  in  part)  in  this  category,  as  do  other 
substances  wdiich  especiall}^  characterize  the  different  organisms,  e.  g.,  the 
peculiar  metabolic  products  of  different  Bacteria  (toxins). 

It  is  generally  true  for  all  cells  that  the  substances  prochired  in  their 
metabolism  are  harmful  to  the  organisms  themselves,  and  if  retained  in  large 
quantities  they  are  fatal.  Hence  neither  yeast  cells  nor  Bacteria  can  live 
continuous!}^  in  the  same  solution,  even  though  there  is  no  lack  of  nourish- 
ment, unless  provision  is  made  for  the  removal  of  the  products  of  decomposi- 
tion from  the  solution. 


E.    THE   ELIMINATION   OF   DECOMPOSITION  PRODUCTS 

The  cells  of  course  cannot  remove  the  waste  products  from  the  medium 
in  which  they  live.  They  can  do  no  more  than  remove  the  products  from 
their  own  bodies.  The  indigestible  residues  of  the  solid  food  such  as  walls 
of  Alga?,  cases  of  diatoms,  the  chitin  of  rotifers,  etc.,  are  egested  from  the 


THE  VITAL  PHENOMENA  OF  CELLS 


41 


free-living  cell  body  in  a  manner  exactly  the  reverse  of  their  ingestion.     The 
remnant  is  brought  to  the  surface  of  the  cell,  the  protoplasm  gives  way  in 
this    particular    place,    the    body    to    be 
eliminated    is    extruded,    and    the    cell 
withdraws  from  it. 

The  gaseous  excretions,  carbon  diox- 
ide and  oxygen,  are  probably  eliminated 
according  to  the  laws  of  diffusion  (cf. 
Chapter  IX). 

We  have  as  yet  but  little  reliable  in- 
formation as  to  how  dissolved  substances 
leave  the  cell.  To  reason  by  analogy 
with  the  manner  of  their  absorption  we 
ought  to  find  at  work  besides  the  osmotic 
processes,  an  active  influence  on  the  part 
of  the  cell  itself.  If  the  products  can- 
not be  removed  immediately  they  are 
sometimes  rendered  harmless  by  a  com- 
bination of  some  sort.  For  example,  ox- 
alic acid,  which  is  poisonous,  is  bound 
up  with  calcium  in  the  insoluble  and 
therefore  harmless  compound  calcium 
oxalate.  In  Chapter  XIII  we  shall  dis- 
cuss a  number  of  analogous  processes  in 
the  higher  animals.  A  highly  special- 
ized mode  of  removing  fluid  waste  from 
the  body  of  an  Infusorian  is  shown  in 
Ficr.  24. 


--'N 


--71 


Fig.  24. — Frontana  leucas,  after  Schewia- 
koff.  A",  macronucleus ;  n,  micronu- 
cleus;  c,  one  of  several  excretory  canals 
leading  into  the  excretorj'  vacuole;  v, 
by  contraction  of  wliich  the  fluid  contents 
are  ejected.  Several  ingested  diatoms  are 
to  be  seen. 


F.     SECRETION 

In  unicellular  as  well  as  in  multicel- 
lular organisms,  though  in  the  latter 
probably  to  a  much  greater  extent,  the 

cells  by  their  own  activity  form  various  substances  which  either  serve  the 
purposes  of  the  cell  itself,  or,  in  the  multicellular  forms,  are  essential  to 
the  purposes  of  the  entire  body.  We  include  all  such  substances  under  the 
head  of  Secretions. 

To  the  secretions  belong  the  enzymes  and  analogous  compounds,  such  as  the 
products  of  the  so-called  internal  secretions  (cf.  Chapter  XI).  also  most  of 
the  skeletal  substances,  as  the  chitinous  cases  of  insects,  the  calcareous  shells 
of  Foraminifera,  the  cell  membranes,  etc.;  and,  finally,  the  intercellular  sub- 
stances such  as  occur  in  the  fibrillar  connective  tissue,  cartilage  and  bone.  How 
far  these  substances  arise  by  transformation  of  the  living  protoplasm,  or  are 
only  produced  by  its  activity  cannot  be  regarded  as  settled.  But  it  is  probable 
that  the  latter  alternative  holds  in  the  case  of  those  structures  which  are  formed 
of  silicic  acid  or  calcium  carbonate  or  phosphate;  for  it  can  scarcely  be  sup- 
posed that  structures  of  this  kind  arise  directly  from  protoplasm. 


42 


THE  CELL 


G.    MOTILITY 

It  has  alreadv  Ijcen  necessary  to  refer  briefly  to  the  movements  of  the  ele- 
mentary organisms,  but  since  motility  is  one  of  the  most  important  functions 
of  living  substance,  we  must  study  it  here  in  its  different  manifestations. 

1.  llie  protoplasm  of  a  plant  cell  inclosed  within  the  membrane  exhibits 
diiferent  forms  of  motility.  Some  of  these,  as  for  example  tlie  migration  of 
chlorophyll  bodies,  take  place  very  slowly  (Fig.  25).     In  diffuse  daylight  the 

chlorophyll  bodies  are  so  placed  that  they  pre- 
sent their  greatest  surface  to  the  light  (T)  \ 
in  direct  sunlight  they  are  so  placed  that  their 
narrow  edge  is  turned  toward  the  incident  rays 
(S)  ;  while  in  windows  a  third  position  (N) 
may  be  taken.  The  purpose  of  these  move- 
ments is  doubtless  to  protect  the  plant  in 
strong  illumination  from  a  too  intense  effect 
of  the  light,  and  in  moderate  illumination  to 
secure  the  plant  as  great  an  effect  as  possible. 
We  observe  in  plant  cells  also  streamings  of 
protoplasm  which  can  be  followed  by  the  mi- 
gration of  the  granules.  In  these  movements 
the  protoplasmic  particles  either  flow  in  dif- 
ferent directions,  often  in  great  confusion 
(circulation),  or  the  protoplasm  collected 
along  the  wall  is  caught  in  a  rotatory  move- 
ment all  in  the  same  direction,  in  which  the 
nucleus  and  often  the  chlorophyll  bodies  are 
dragged  along  (rotation)    (Fig.  16). 

2.  The  simplest  kind  of  protoplasmic  move- 
ment in  the  naked  cells  proceeds  in  a  manner 
similar  to  that  just  mentioned,  as  may  be  ol)- 
served  in  the  xlmrebte  (Figs.  30,  21,  26),  and 
in  the  leucocytes  of  multicellular  animals 
(Figs.  22,  27).  During  rest  the  Am.o'ba  is 
spherical.  When  it  begins  to  move  one  or 
more  processes  protrude  from  the  periphery  of 
its  body.  By  a  kind  of  streaming  movement 
the  protoplasm  of  the  cell  body  then  flows  into 
this  process  or  processes  and  the  position  of  the 
entire  mass  of  the  animalcule  is  there])y  changed.  The  protrusions  are  not 
preformed  structures,  for  the  cell  has  the  power  to  put  out  such  a  process 
from  any  point  of  its  surface  and  to  withdraw  it  again.  It  is  on  account 
of  their  transitory  character  that  they  are  called  pseudopodia.  or  false  feet. 

The  appearance  of  the  pseudo])odia  in  different  species  of  elementary  organ- 
isms is  very  different.  In  unicellidar  animals  provided  with  an  external  skeleton 
they  arc  modified  according  to  the  character  of  the  openings  in  the  skeleton 
through  which  they  protrude  (cf.  e.g.,  Fig.  14).  We  meet  with  short  and  thick, 
or  long  and  slender,  threadlike  or  thorn-shaped  pseudopodia ;  or  again  with  those 


Fig.  25. — Varying  positions  of  the 
chlorophyll  bodies  in  the  cells 
of  Lemna  triscula,  according  to 
the  direction  of  the  incident 
light  rays,  after  Stalil. 


THE  VITAL  PHENOMENA  OF  CELLS 


43 


Fig.     26.  - 

movement  of  an 
Amoeba.  The  arrows 
indicate  the  direction 
and  strength  of  the 
protopla-smic  c  u  r  - 
rents ;  the  crosses,  the 
resting  places.  For 
the  instant  the  prin- 
cipal line  of  move- 
ment is  from  H  to- 
ward V,  but  at  any 
other  moment  it  may 
turn  toward  L  or  J{. 


which  project  quite  independently  of  each  other,  or  which 
unite  in  the  most  complex  sort  of  a  network  (Figs.  19,  20, 
21,  26). 

Both  phase.s  of  the  movement  of  pseudopodia  in 
Amceba,  namely  expansion  and  contraction,  are  to  be  re- 
garded as  active  processes,  and  the  two  are  of  equal  im- 
portance in  ingesting  food  or  in  locomotion.  In  other 
kinds  of  movement  the  most  important  phase  consists  in 
a  reduction  of  the  surface  of  the  cell — i.  e.,  in  contraction. 
To  this  category  belong  especially  the  movements  of  the 
smooth  and  cross-striated  muscles,  to  which  we  shall  de- 
vote proper  attention  in  Chapter  XY. 

3.  The  cell  body  of  certain  unicellular  organisms  ))re- 
sents  specially  differentiated  contractile  elements.  .^7^^/?- 
tor,  for  example,  has  in  its  outer  sheath  of  protoplasm 
smooth  muscle  fibrils  running  almost  parallel ;  VorticetJa 
(Fig.  28)  contains  only  a  single  smooth  muscle  fiber 
composed  of  several  fibrils.  This  leaves  the  body  as  a 
thick  cord,  and  is  surrounded  by  an  elastic  membrane 
to  the  inner  side  of  which  it  adheres  along  a  .-spiral  course 
from  one  end  to  the  other.  It  .serves  as  a  stalk  for  the 
attachment  of  the  organism.  If  these  contractile  fibers 
are  roused  to  activity,  they  become  shorter  and  thicker 

just  like  true  muscles,  and  thereljy  change  the  form  of  the  cell  in  a  corre- 
sponding wa}'. 

4.  In  numerous  unicellular  organisms  and   in   numerous  cells  of  multi- 

cellular organisms,  we  find  cilia 
or  ftagella  as  special  differen- 
tiations of  the  cell  body.  These 
are  not  temporary  like  p.seu- 
dopodia,  but  permanent  struc- 
tures of  greater  or  less  length 
attached  to  the  outer  surface 
of  the  cell.  They  are  in  con- 
stant motion  and  occur  on 
every  cell  or  on  a  great  ma- 
jority of  the  cells  forming  a 
ciliated  surface.  If  the  cell 
bears  only  a  few  (1  to  4 )  such 
structures,  they  are  called  fla- 
gella ;  if  a  larger  number,  they 
are  called  cilia.  In  certain  or- 
ganisms they  can  be  counted 
by    the    hundreds    and    thou- 

FiG.  27. — ^\^lite  blood  corpuscles  at  38°  performing  Sands. 

amcpboid  movements,  after  Max   Schultze.     The  _,.        ,.  <r>       i     •  i 

different    figures  are  all    drawn    from    the    same  F  lagella  are  affixed  either  to 

corpuscle.  the  anterior  or  the  posterior  end 


44 


THE  CELL 


of  the  coll  body.  The  former  arrangement  is  found  in  the  Flagellata,  in  the 
spermatozoids  of  plants,  many  Bacteria,  and  in  the  swarm  spores  of  many  Algae 
and  Fungi.     In  locomotion  the  flagella   precede  and  pull  the  body  after  them. 

The  latter  arrangement  is  found  in  the  spermatozoa 
of  most  animals,  where  the  flagellum  drives  the  cell 
body  forward  after  the  manner  of  a  propeller. 

If  the  cilia  should  beat  back  and  forth  in  both 
directions  with  equal  force,  only  a  to-and-fro 
movement  would  result,  and  no  locomotion  would 
be  possible.  Careful  investigation  of  both  flagella 
and  cilia  has  shown  that  tiiey  always  strike  more 
forcibly  in  one  direction  than  in  the  other,  a  fact 
which  at  once  makes  clear  the  mechanical  re- 
sults of  their  movements. 

In  the  freely  motile  cells  the  object  accom- 
plished by  the  ciliary  movement  is  locomotion.  In 
addition  to  this,  if  the  cell  is  swimming  in  a  fluid 
specifically  lighter  than  itself,  motion  of  the  cilia 
prevents  it  from  sinking  to  the  bottom.  Again  in 
certain  unicellular  animals  they  participate  in  the^ 
ingestion  of  food,  being  arranged  in  a  circle  around 
the  mouth,  and  when  in  motion  creating  a  vortex 
in  the  water  which  sucks  suspended  particles  into 
the  mouth  (Fig.  28). 

The  ciliated  cells  covering  the  surface  of  the 
mucous  membranes  in  Metazoa  drive  such  particles 
as  may  happen  to  be  on  the  surface  in  a  given 
direction,  and  thus  play  a  role  in  many  ways  very 
important  to  the  animal. 

Cilia  are  always  fastened  to  a  protoplasmic 
substratum  and  are  never  outgrowths  of  a  firm 
cell  membrane.  Very  often,  however,  they  are 
not  immediate  extensions  of  the  protoplasm,  but 
rest  directly  upon  a  thin  layer  of  transparent 
substance  which,  though  very  closely  resembling 
the  substance  of  the  cilia,  appears  not  to  ])e  con- 
tractile but  to  lie  as  a  kind  of  coat  on  the  naked 
surface  of  the  cell  protoplasm.  The  coats  of  the 
adjacent  cells  are  so  closely  connected  that  in 
many  cases  a  considerable  patch  of  this  layer  can 
l)e  lifted  up  as  one  piece. 

Certain  cilia  continue  to  move  even  if  they 
be  separated  entirely  from  the  protoplasm  or  the 
basal  part  of  the  cell.  Since  both  cilia  and  flagella  can  of  themselves  perform 
many  complicated  movements  we  must  assume  that  they  consist  of  a  contractile 
substance.  If  in  addition  we  assume  that  they  contain  also  a  noncontractile 
supporting  substance,  we  should  have  a  somewhat  satisfactory  explanation  of 
the  different  forms  of  movement  of  these  structures  (Putter). 


Fig.  28. — Vorticella. 

A,  a  group  of  individuals  as 
seen  under  the  low  power; 
B,  a  single  vorticella  with 
stalk  extended  and  beside 
it  another  with  stalk  con- 
tracted; d,  denotes  disc;  p, 
peristome  ;  vc,  contractile 
vacuole  ;  vs,  ^•estibule  ;  cf, 
contractile  fiber;  nc,  nucleus; 
d,  cilia. 


THE  VITAL  PHENOMENA  OF  CELLS  45 

In  most  cases  ciliarj'  movement  is  not  influenced  in  any  manner  by  the 
adjacent  or  by  the  distant  cells,  and  in  the  mucous  membranes  of  the  vertebrates 
it  appears  to  be  entirely  independent  of  nerves;  for  ciliated  cells  continue  to 
move  after  they  are  cut  out  of  the  body,  and  in  the  human  body  for  as  much 
as  three  days  after  death  (Valentin).  Hence  it  is  the  more  remarkable  that  in 
a  row  of  cells  the  cilia  always  move  in  complete  harmony  even  if  the  cilia  are 
not  in  contact  with  each  othei-.  This  and  the  further  fact  that  a  stimulus, 
applied  to  a  portion  of  the  epithelium  where  ciliary  motion  has  ceased,  can  be 
transmitted  to  a  portion  where  it  is  still  active,  go  to  show  that  the  basal  part 
of  the  cell  must  have  something  to  do  with  the  regulation  of  ciliary  movements. 
Xevertheless  much  here  remains  to  be  explained. 

5.  Still  other  forms  of  movement  than  those  already  discussed  occur  in 
the  animate  world.  The  following  may  be  briefly  mentioned.  Various  uni- 
cellular animals  (Radiolaria,  Rhizopoda)  can  raise  or  lower  themselves  in  the 
water  where  they  live  hy  changes  in  their  specific  gravity.  Arcellge  and  Difflu- 
gife  rise  by  developing  a  bubble  of  carbon  dioxide  in  their  cell  body.  Thalassi- 
cola  (Fig.  15)  swims  at  the  surface  of  the  sea  because  its  vacuoles  contain  a 
fluid  specifically  lighter  than  sea  water.  Under  certain  conditions  it  can  sink 
itself  by  rupturing  the  sheaths  of  the  vacuoles  which  then  fuse  together.  When 
the  vacuoles  are  reformed  the  animalcule  once  more  mounts  upward.  Finally, 
in  plants  a  great  many  movements  occur  through  strelling  of  the  cell  wall, 
and  through  changes  of  turgor,  which  we  cannot  discuss  in  this  book. 

H.    PRODUCTION  OF  LIGHT 

Certain  putrefactive  Bacteria  which  live  on  decaying  flesh  of  marine 
fishes  and  on  meat,  as  well  as  certain  Fungi  and  a  few  insects  have  the  power 
of  producing  light.  In  certain  places  where  the  sea  water  glows  it  is  found 
on  filtration  that  the  glowing  substance  remains  on  the  filter  and  is  not  founc^r 
in  the  filtrate;  the  cause  of  the  light  is  therefore  an  insoluble  substance. 
Microscopical  examination  of  the  residue  on  the  filter  reveals  millions  of 
phosphorescent  organisms  belonging  to  all  classes  of  the  invertebrates. 

That  the  phosphorescence  of  these  animals  is  not  due  to  previous  exposure 
to  the  sun's  rays  follows  from  the  fact  that  even  when  they  are  kept  for  a  long 
time  in  complete  darkness,  they  glow  just  as  strongly  as  their  companions  which 
have  been  in  the  sunlight.  The  phosphorescence  ceases  however  when  the  ani- 
mals are  brought  into  a  medium  unsuitable  for  respiration;  it  therefore  repre- 
sents a  true  oxidation  process. 

Closer  investigation  of  this  phenomenon  proves  that  it  is  initiated  by  the 
activity  of  the  living  protoplasm,  for  the  organisms  produce  light  only  so  long 
as  they  are  alive.  In  the  case  of  Pholas  (a  mussel),  the  phospliorescent  sub- 
stance can  be  thrown  out  of  tlie  body,  hut  it  is  formed  only  l)y  the  activity 
of  the  living  protoplasm.  Tlie  phosphorescence  arises  through  the  action 
of  a  special  enzyme  on  this  substance  (E.  Dubois).  In  the  "lightning  bug," 
Lampyris,  nerve  fibers  have  been  demonstrated  running  to  the  light-producing 
organ.  The  animal  suppresses  its  light  when  there  is  a  noise;  the  darken- 
ing then  begins  at  the  proximal  end  and  spreads  to  the  distal  end  of  the 


46  THE  CELL 

organ.  It  is  worthy  of  note  also  that  the  li<rht  produced  hy  the  "lightning 
bug"  is  dcficiont  at  both  ends  of  the  spoctruiu.  We  have  here  in  other  words 
a  source  of  light  which  is  devoid  or  almost  devoid  of  the  ultra-red  and  ultra- 
violet rays   (Langley  and   Very). 

1.    FORMATION   OF  HEAT 

Heat  is  foriued  in  all  dissimilative  processes,  and  since  processes  of  this 
kind  occur  everywhere  in  animate  nature,  we  may  say  that  the  generation  of 
heat  is  universal.  This  cannot  always  be  demonstrated;  for  in  the  isolated 
elementary  organisms  the  quantity  formed  is  so  small  that  it  cannot  be  meas- 
ured with  our  instruments.  In  plants  as  a  rule  heat  is  formed  so  slowly 
that  as  fast  as  it  is  generated,  it  is  radiated  to  the  surrounding  medium; 
consecjuently  the  temperature  of  the  plant  cannot  be  elevated  perceptibly  above 
the  medium.  It  should  be  said  also  that  the  abundant  transpiration  occur- 
ring in  plants  has  much  to  do  with  keeping  down  their  temperature.  The 
same  is  true  and  for  the  same  reason  in  most  of  the  so-called  ruld-blooded  or 
poikjJothermos  animals,  that  is,  animals  in  which  the  body  temperature  rises 
and  falls  with  the  temperature  of  the  surrounding  medium.  In  dry  air/,  on 
account  of  evaporation  from  the  surface  of  the  body,  the  temperature  of  a 
cold-blooded  animal  is  usually  lower  than  that  of  its  medium.  In  a  moist 
or  water-saturated  atmosphere  the  body  temperature  may  rise  some  tenths  of 
a  degree.  This  is  true  likewise  of  cold-l)looded  animals  which  live  in  water. 
Only  in  the  so-called  wann-hJooded  or,  more  correctly,  homoiothernios  animals 
(birds  and  mammals) — i.  e.,  animals  whose  body  temperature  remains  con- 
stant in  spite  of  the  variations  of  the  surrounding  temperature — can  the 
production  of  heat  be  demonstrated  directly  and  without  difficulty.  In  these 
animals  the  temperature  of  the  body  is  almost  always  higher  than  that  of 
the  medium  in  which  they  live. 

I  nder  certain  circumstances  it  can  be  shown  very  clearly  that  in  plants  as 
well  as  in  cold-blooded  animals  heat  is  actually  formed.  With  peas  which  have 
been  allowed  to  germinate  in  a  funnel  under  a  bel]  jar  a  rise  in  the  temperature 
of  1.5°  C.  has  been  observed.  In  the  spadix  of  the  Aracete  (e.  g.,  "  skunk- 
cabbage ")  a  temperature  of  15°  C.  higher  than  that  of  its  surroundings  has 
often  been  witnessed.  Likewise  in  the  fermentation  of  sugar  solutions  by  the 
yeast  plant  elevations  of  temperature  of  about  the  same  extent  may  occur. 

With  regard  to  the  body  temperature  of  the  cold-blooded  animals,  the  fol- 
lowing data  on  the  excess  of  the  animal's  temperature  over  that  of  its  sur- 
roundings have  been  gathered:  various  invertebrates  in  water  0.21°-0.60  C. ; 
earthworms  in  a  glass  vessel  1.4°  C. ;  bees  in  a  beehive  21°  C:  moving  butter- 
flies 14°  C. 

The  animal  heat  of  warm-blooded  animals  will  be  more  fully  discussed  in 
Chapter  XIV. 

J.    GENERATION   OF   ELECTRICITY 

The  enormous  number  of   investigations   on   animal   electricity   beo-ins 

if  we  except  the  electrical  fishes — with  the  pregnant  observation  of  Galvani 
that  a  frog's  thigh  contracts  when  it  is  touched  in  two  places  with  the  ends  of 
a  metallic  arc  (September  JiO,  1786).    From  this  observation  Galvani  thou^^ht 


THE  VITAL  PHENOMENA  OF  CELLS 


47 


himself  justified  in  concluding  that  animals  have  a  peculiar  kind  of  elec- 
tricity and  that  it  is  of  very  great  importance  in  the  functions  of  the  animal 
body;  in  fact,  physiologists  of  that  time  thought  their  dream  of  a  vital  force 
was  at  last  to  be  realized. 

It  was  reserved  for  the  discriminating  insight  of  Yolta  to  show  that  these 
contractions  are  conditioned  upon  the  dissimilarity  of  the  two  ends  of  the 
metal  touching  the  moist  conductor,  and  upon  the  production  thereby  of  a 
galvanic  arc.  Further  investigation  proved,  however,  that  electrical  differ- 
ences of  potential  do  occur  in  the  animal  body.  The  events  historically  most 
important  from  this  point  of  view  are:  the  discovery  of  the  so-called  frog 
current — i.  e.,  of  a  current  running  from  the  feet  to  the  head  of  the  frog 
(Xobili,  1827)  ;  the  demonstration  that  the  isolated  muscle  under  definite 
circumstances  gives  a  regular  current  (Matteuci  and  Du  Bois-Keymond, 
1840-1843 ) ;  the  discovery  of  the  electrical  variations  in  muscular  activity 


Fig.  29. — Schema  representing  the  current  of  injury,  or  demarcation  current,  in  a  muscle,  after 

Foster. 

(Matteuci   and  Du   Bois-Reymond,   1842);  and   the   discovery   of  the   nerve 
current  and  its  variations  (Du  Bois-Reymond.  1843). 

The  object  most  used  in  these  investigations  is  cross-striated  muscle.  If 
two  points  of  an  exsected  muscle  be  connected  with  a  galvanometer  an  excur- 
sion of  the  needle  nearly  always  occurs;  between  tlie  two  points  of  the  muscle 
there  is,  therefore,  a  difference  in  tension.  More  detailed  study  has  shown  that 
these  tension  differences  are  perfectly  regular,  and  in  muscles  with  parallel 
fibers  they  have  been  found  to  take  the  following  form  (Du  Bois-Reymond) 
(cf.  the  schema  in  Fig.  29).  If  a  hmgitudinal  surface  and  a  transversely  cut 
surface  of  such  a  muscle  be  connected  with  a  galvanometer,  a  current  is 
obtained,  which  in  the  muscle  is  directed  from  the  transverse  to  the  longi- 
tudinal surface,  and  which  reaches  its  greatest  intensity  (0.06  to  0.08  volt) 
if  the  leading-off  electrodes  are  placed  in  the  middle  of  the  two  surfaces. 
If  two  asymmetrical  points  of  the  longitudinal  surface  be  led  off  weaker  cur- 
rents are  obtained,  which  in  the  muscle  are  directed  from  the  periphery 
toward  the  middle.  With  two  asymmetrical  points  of  the  cross  section  a 
current  is  olitained  whicli  passes  from  the  middle  toward  the  periphery. 
Finally,  if  symmetrical  points  of  the  cross  section  or  of  the  longitudinal  sur- 


48  THE  CELL 

face  be  connected,  no  differences  of  tension  are  shown  (Fig.  29.  dotted  lines). 
From  these  facts  it  follows  that  the  entire  lotujitiulinal  surface  of  the  mus- 
cle possesses  a  positire  tension,  every  cross  section  a  negative  tension. 

It  has  been  shown  by  Hermann  (1867)  that  in  an  entirely  uninjured,  rest- 
ing muscle  there  are  no  such  diflferences  of  tension.  If  the  skin  be  removed 
very  carefully  from  the  gastrocnemius  of  a  frog  and  great  pains  be  taken  that 
it  does  not  come  in  contact  with  the  secretion  of  the  skin,  no  current  at  all,  or 
only  the  very  weakest  one,  is  obtained  when  the  muscle  is  connected  with  the 
galvanometer.  If  on  the  other  hand  the  muscle  be  injured  in  any  way  in  the 
neighborhood  of  one  electrode,  a  strong  current  appears.  The  uninjured,  resting 
hea'rt  also  gives  no  current  (Engelmann). 

These  and  other  discoveries — among  which  should  be  mentioned  the  fact 
that  the  current  of  injuiy  does  not  appear  in  its  full  strength  immediately  but 
develops  gradually — induced  Hermann  to  propound  the  following  theory  in 
explanation  of  the  current  of  rest,  which  at  this  time  is  the  one  most  acceptable 
to  physiologists.  The  cause  of  the  diiference  of  electrical  tension  in  the  resting 
muscle  lies  in  the  injury  which  it  receives.  In  a  partially  injured  muscle  every 
point  of  the  injured  portion  is  negative  to  every  point  of  the  uninjured  part. 
The  facts  may  be  expressed  in  the  following  general  proposition:  in  every 
injtired  muscle  fiber  the  demarcation  surface  heticeen  the  living  and  the  dead 
contents  of  the  fiber  is  the  seat  of  an  electromotive  force  directed  toward  the 
living  part.  On  this  account  Hermann  designated  the  current  of  rest  as  the 
demarcation  current. 

Exactly  the  same  electrical  phenomena  as  in  the  resting  muscle  appear  in 
resting  nerve. 

Electrical  currents  appear  also  when  a  muscle  or  a  nerve  is  active,  and 
these  currents  are  intimately  connected  with  the  functional  condition  of  the 
tissue.  The  general  law  of  these  currents  {action  currents)  may  be  com- 
prehended in  the  following  statement:  Every  active  portion  of  muscle  or  of 
nerve  maintains  a  negative  relation  toward  the  resting  part  (Bernstein, 
1867).  We  can  therefore  condense  the  law  for  the  rest  current  and  the 
action  current  into  the  following  simple  formulation :  In  muscle  and  in  nerve 
every  active  or  injured  part  maintains  a  negative  electrical  relation  toward 
every  other  part  which  at  that  time  is  at  rest  or  is  uninjnred. 

Further  study  of  the  action  current  will  be  postponed  to  the  discussion 
of  the  general  physiology  of  muscles  and  nerves  (Chapter  XY). 

W  e  meet  with  analogous  electrical  phenomena  in  many  other  tissues.  The 
currents  present  in  glands  are  of  special  interest.  Du  Bois-Re.ymond  proved  that 
the  skin  of  the  Amphibia  is  the  seat  of  a  current  directed  from  without  inward 
which  he  ascribed  to  the  secretion  of  the  skin  peculiar  to  these  animals.  Later 
investigations  have  made  us  acquainted  with  similar  currents  in  many  other 
objects  (mucous  membrane  of  the  frog's  tongue,  of  the  pharynx  and  cloaca  of 
the  frog,  skin  of  the  Amphibia  and  fishes,  and  of  the  leech,  etc.),  and  have 
shown  that  they  are  generated  by  the  mucus-forming  epithelia  composed  of 
single-celled  glands,  as  well  as  by  other  epithelia  not  glandular  (Reid).  Both 
the  strength  and  the  direction  of  the  current  of  action  may  be  modified  by  such 
agencies  as  pilocarpine,  which  stimulates  secretion,  by  excitation  of  the  mucosa 
or  of  the  glandular  nerves,  by  changes  of  temperature,  of  the  blood  supply  and 
of  the  water  content. 


THE  VITAL  PHENOMENA  OF  CELLS 


49 


nV 


We  find  similar  skin  currents  in  all  ^lammalia  including  man.  If  the 
two  hands  or  the  two  feet  of  a  man  be  led  off  symmetrically  to  the  gal- 
vanometer and  one  arm  or  one  foot  be  moved  voluntarily  the  needle  makes 
an  excursion,  which  is  not  caused  by  the  muscular  contraction  in  itself  but 
by  the  process  of  secretion  going  on  at  the  same  time  in  the  sweat  glands  of 
the  contracted  extremity.  This  current  passes  from  the  outside  to  the  inside 
of  the  skin.  A  very  similar  skin  current  has  been  observed  in  the  sweating 
of  different  mammals. 

Biedermann  observes  that  one  cannot  draw  a  sharp  line  of  separation  between 
current  of  rest  and  current  of  action  in  epithelial  and  glandular  cells,  for  -the 
reason  that   the  differences  of  tension  met  with  e 

are  always  the  expression  of  differences  in  the 
chemical  relations  of  the  neighboring  parts.  From 
this  point  of  view  it  appears  quite  arbitrary,  or 
incorrect  indeed,  to  speak  of  the  current  of  rest 
in  contradistinction  to  the  current  of  action  of  a 
glandular  structure,  since  in  both  cases  one  deals 
with  the  effects  of  certain  metabf)lic  processes 
going  on  in  detinite  parts  of  the  cell  body,  which 
by  direct  or  indirect  stimulation  are  only  changed 
in  one  direction  or  another.  It  is  better,  there- 
fore, to  say  that' the  ordinary  skin  current  is  pro- 
duced by  the  negativity  of  that  portion  of  the  cell 
which  is  being  transformed  into  mucus,  toward 
the  protoplasmic  portion  (Hermann). 

As  above  remarked,  this  inwardly  directed 
current  may,  under  certain  circumstances,  un- 
dergo a  complete  reversal.  To  explain  this  we 
can  make  only  one  assumption,  namely,  that  the 
same  epithelial  cell  has  the  power  to  act  electi'i- 
cally  sometimes  in  one  sense,  sometimes  in  the 
other.  This  is  borne  out  by  the  fact  that  each 
cell  is  the  seat  of  two  different  chemical  processes 
(assimilation  and  dissimilation),  which,  going  on 
at  the  same  time,  give  rise  to  opposite  tensions. 
The  deviation  occasionally  observed  would,  ac- 
cording to  this,  always  be  the  resultant  of  the 
two   antagonistic  forces    (Hering,   Biedermann). 

It  is  possible  that  a  relationship  similar  to  this  exists  between  the  chemical 
processes  underlying'  the  secretion  of  water  on  the  one  hand  and  the  seci'etion 
of  organically  specific  constituents  on  the  other  (Biedermann).  Perhaps  from 
this  point  of  view  are  to  be  explained  certain  results  obtained  with  the  digestive 
glands,  of  which  more  in  Chapter  VTT. 

Electrical  currents  have  been  demonstrated  even  in  plants,  where,  just  as 
in  the  animal  tissues,  an  injured  ])lace  is  found  to  be  electro-negative  to  an 
uninjured  place.  Electrical  effects  appear  'also  under  a|)propriate  circum- 
stances in  certain  parts  of  plants  which  are  entirely  uninjured.  Thu<.  differ- 
ences of  tension  are  obtained  between  cells  or  cell  territories  of  an  organ  or 
of  a  whole  plant  which  maintain  different  chemical  relations  to  each  other. 

For  example,  according  to  Waller,  the  processes  taking  place  in  the  forma- 


FlG 


30. — The  cramp  fish,  Torpedo, 
dissected  to  sliow  electric  ap- 
paratus, after  Huxley;  b,  gills; 
c,  brain;  c,  electric  organ;  y, 
cranium;  ine,  spinal  cord;  np, 
branches  of  pneumogastric 
nerves  to  electric  organs ;  o,  eye. 


50  THE  CELL 

tion  of  starch  are  hound  up  witli  elect romotive  phenomena.  If  a  shaded  and 
an  exposed  part  of  a  green  leaf  (Fig.  17)  be  connected  with  a  galvanometer, 
when  the  light  falls  on  the  exposed  part,  an  electric  current  is  ()l)served  which 
runs  in  the  leaf  itself  from  the  insolated  to  the  shaded  part.  The  deflec- 
tion begins  after  some  three  to  ten  seconds  and  lasts  as  long  as  the  illumina- 
tion continues,  if  that  time  does  not  amount  to  more  than  about  five  min- 
utes. The  effect  is  least  in  diffuse  daylight,  greatest  in  direct  sunlight  and 
is  abolished  by  boiling  the  leaves.  All  such  effects  are  absent  in  flower  parts 
devoid  of  chlorophyll. 

Whether  these  electrical  variations  have  any  general  significance  for  the 
cells  exliibiting  them,  or  for  the  individuals  containing  the  cells  we  cannot 
sa}'  definitely.  But  the  matter  is  clearer  in  the  case  of  the  well-known  elec- 
tric fishes,  of  which  there  are  many  different  species.  Tn  most  of  these 
fishes  the  electrical  organs  are  metamorphosed  muscles,  but  in  Malapferurus 
it  represents  a  transformation  of  the  glands  of  the  skin.  Jn  rest  the  organ 
shows  no  current ;  but  under  the  influence  of  the  specific  nerves,  as  well  as 
by  direct  stimulation  it  develops  very  strong  electric  currents,  the  force  of 
which  in  the  cramp  fish  (Fig.  30)  amounts  to  thirty-one  volts.  That  such 
currents  must  be  of  great  service  for  these  animals  in  their  struggle  for  exist- 
ence is  at  once  perfectly  obvious. 


§  3.    THE   EFFECT   OF   EXTERNAL   INFLUENCES   ON   CELLS 
A.    ON   STIMULI   IN  GENERAL 

The  fundamental  property  to  which  we  trace  the  total  activity  of  the  liv- 
ing substance  is  its  irritability — i.  e.,  its  ability  under  the  influence  of  all 
kinds  of  agents  to  change  its  metal)olism,  and  therefore  to  change  its  trans- 
formation of  energy,  in  one  direction  or  another.  All  those  agents  which 
have  the  power  to  evoke  a  change  of  this  kind  are  called  stimuli.  Among 
them  are  to  be  included  difl:erent  chemical  reagents,  mechanical  agents  of  all 
kinds,  heat,  light  and  electricity. 

The  change  in  metabolism  produced  by  a  stimulus  is  either  dissimila- 
tive  or  assimilative  (cf.  supra  page  32).  In  the  former  there  is  a  produc- 
tion of  l-inetic  energy  and  the  process  taking  place  in  the  cell  is  described  as 
an  excitation.  In  the  latter  we  have  a  storing  of  potential  energy,  and  the 
change  is  often  described  as  a  trophic  effect.  The  stimulus  may  however 
check  metabolism  for  a  longer  or  shorter  time,  may  bring  it  to  a  standstill 
momentarily,  or  stop  it  altogether.  We  speak  then  of  a  paralysis  of  the  cell. 
Paralysis  represents  a  negative  condition  with  respect  either  to  the  assimilative 
or  the  dissimilative  responses. 

By  stimulation  of  certain  nerves  the  dissimilative  action  of  the  innervated 
org-an  may  be  abolished.  Of  such  phenomena,  described  as  inhibition,  the  influ- 
ence of  the  vagus  on  the  heart  has  been  most  closely  studied.  When  the  vagus 
is  stimulated  artificially  the  heart  beats  more  slowly,  and  with  a  stimulus  strong 
enough  it  stops  in  diastole  (the  brothers  Weber,  1846).  This  inhibition  is  not 
a  kind  of  paralysis,  for  phenomena  to  be  described  later  (Chapter  VI)  show  that 
while  the  heart  in  vagois  standstill  is  inexcitable,  it  is  not  paralyzed. 


THE  EFFECT  OF  EXTERNAL  INFLUENCES  ON  CELLS  51 

The  a>similative  and  di.ssimilative  processes  often  go  on  side  1)V  side  in 
the  same  cell.  Since  the  latter  are  best  known  it  will  he  well  to  discuss  them 
first.  We  shall  make  five  general  observations,  which  apply  to  all  dissimila- 
tive  processes. 

1.  The  production  of  energy  is  many  times  as  great  as  the  energy  of  the 
stimulus  employed,  which  will  appear  for  example  in  the  following  experi- 
ment :  A  frog's  gastrocnemius  is  fastened  in  a  clamp  by  the  femur  and  a 
weight  of  48.5  gm.  is  suspended  from  its  lower  end.  The  nerve  attached  to 
the  muscle  is  laid  upon  a  solid  block.  If  now  a  weight  of  0.485  gm.  be  allowed 
to  fall  upon  the  nerve  from  a  height  of  10.1  mm.  the  muscle  contracts  and 
lifts  the  weight  3.8  mm.  high.  The  work  done  by  the  muscle  is  48.5  x  3.8 
=  184.3  gm.  mm.;  while  the  active  force  of  the  stimulus  is  equivalent  to  only 
0.485  X  10.1  =  4.9  gm.  mm.  of  work.  The  mechanical  work  of  the  muscle 
called  forth  is  therefore  about  thirty-eight  times  the  active  force  of  the  stimu- 
lus, taking  no  account  of  the  heat  developed  by  the  muscle  at  the  same  time. 

All  other  cells  conduct  themselves  just  like  the  muscle  cells  in  this  ex- 
periment, when  they  develop  energy  through  dissimilative  processes.  We 
meet  with  numerous  analogies  also  in  inanimate  nature.  For  example,  a 
weight  of  10  kg.  suspended  liy  a  cord  10  m.  al)ove  the  floor,  represents  a 
potential  energy  of  100  kg.  m.  In  order  to  change  this  potential  energy  to 
kinetic  we  have  only  to  cut  the  cord,  which  of  course  does  not  call  for  an 
effort  of  100  kg.  m.    The  same  is  true  when  powder  is  exploded  by  a  match,  etc. 

In  all  such  cases  we  speak  of  energy  having  been  libera  fed,  a  term  which 
conveys  to  our  minds  the  idea  of  an  impetus  by  which  a  transformation  from 
potential  to  kinetic  energy  is  produced,  where  in  the  nature  of  the  case  the 
size  of  the  impetus  need  be  only  very  insignificant. 

2.  Generally  speaking,  in  order  to  call  forth  a  demonstrable  effect  in  living 
substance,  the  stimulus  is  effective  only  from  a  certain  minimum  onward.  If 
the  stimulus  is  increased  above  this  by  uniform  increments,  the  response 
usually  increases,  but  the  increase  becomes  less  the  stronger  the  total  stimu- 
lus, until  finally  the  maximum  response  is  reached,  beyond  which  it  cannot 
rise  however  much  the  stimulus  is  strengthened. 

3.  Another  property  characteristic  of  the  behavior  of  living  protoplasm, 
which  is  developed  to  different  degrees  in  different  cells,  is  its  power  fo 
summate  the  effects  of  stimuli.  If  a  loaded  muscle  be  affected  by  a  maxi- 
mal stimulus,  it  contracts  to  a  certain  extent ;  but  if  it  be  affected  by  another 
stimulus  before  this  contraction  ceases,  it  contracts  still  further.  With  a 
sufficiently  rapid  succession  of  stimuli  contractions  may  be  obtained  which 
are  very  much  stronger  than  that  obtained  by  a  single  stimulus  with  the  same 
load. 

4.  All  excitation  processes  are  accompanied  by  the  development  of  heat 
and  electricity.  The  other  forms  in  which  the  dissimilative  processes  manifest 
themselves  differ  with  different  kinds  of  cells;  toward  every  effective  stimu- 
lus, a  cell  alwai/s  reacts  in  a  way  which  is  characteristic  for  its  kind.  Thus 
whatever  the  stimulus  employed,  a  muscle  cell  always  responds  with  a  con- 
traction;  a  salivary  gland  cell,  when  stimulated,  always  secretes  saliva,  etc. 
In  the  following  discussion  of  the  different  stimuli  it  will  not  be  necessary 
to  enter  specifically  into  the  various  forms  of  activity  of  the  different  cells. 


52  THE  CELL 

5.  Those  agents  which  evoke  a  response  as  a  rule  also  aJlcr  the  excitability 
of  the  living  substance — i.  e.,  under  their  influence  a  given  .stimulus  pro- 
dut-es  a  stron<rer  or  weaker  rcsjwnse  than  if  it  were  acting  alone.  We  must 
therefore  make  a  distinction  between  excitation  and  the  alterations  of  excita- 
bilitii  (positive  or  negative).  An  excitation  may  he  said  to  have  taken  place 
if  a  given  stimulus  can  be  shown  to  have  started  a  dissimilative  process.  If, 
however,  the  stimulus  produces  no  effect  of  this  kind,  but  a  second  stimulus 
under  the  influence  of  the  first  produces  a  response  stronger  or  weaker  than 
it  otherwise  would,  then  the  first  stimulus  has  increased  or  diminished  the 
exeital)ility  of  the  cells  stimulated.  If  the  stimulus  becomes  too  strong,  the 
functional  powers  of  the  living  substance  may  be  either  reduced  or  destro3'ed. 

B.  AUTOMATIC   EXCITATION 

When  protoplasm  is  protected  from  all  possible  external  influences,  it 
still  exhibits  the  functions  which  we  have  learned  to  regard  as  essential: 
absorption  of  food,  motility,  digestion,  heat  formation,  etc.  There  must  be 
therefore  inside  the  cell  something  which  calls  forth  its  activities,  and  from 
all  that  is  known  to  us  on  this  sul)ject,  we  may  assume  with  a  high  degree 
of  probability,  that  the  excitation  is  caused  by  the  products  of  metabolism 
formed  in  the  activity  of  the  cell. 

The  sigrnificance  of  stimuli  arising  in  the  body  itself  appears  from  dis- 
coveries which  have  been  made  concerning  the  activity  of  the  central  nervous 
system  in  the  higher  animals.  If  for  example  a  rabbit  be  choked  by  compression 
of  the  trachea,  within  a  short  time  there  appear  powerful  respiratory  move- 
ments, convulsions  of  the  whole  body  musculature,  contractions  of  the  vascular 
walls,  etc.  In  this  case  the  decomposition  products  normally  eliminated  in  the 
expired  air  are  retained  in  the  body  and  bring  about  the  powerful  stimulation 
of  the  central  nervous  system  in  the  manner  observed  (ef.  Chapter  XXII). 
Similar  phenomena  appear  when  by  extirpation  of  the  kidneys  the  fluid  decom- 
position products  otherwise  removed  from  the  body  by  them,  are  allowed  to 
collect  in  the  body  in  large  quantity. 

The  direct  excitation  produced  by  metabolic  products  is  called  automatic 
excitation,  because  the  exciting  substances  are  formed  by  the  activity  of  the 
protoplasm  itself.  That  is  to  say,  in  this  case  the  cells  develop  within  them- 
selves the  stimuli  ivhich  rouse  them  to  continued  activity. 

C.  CHEMICAL  STIMULATION 

Automatic  excitation,  as  it  is  here  defined,  is  a  kind  of  chemical  stimu- 
lation, and  fundamentally  is,  so  far  as  we  can  judge,  of  exactly  the  same 
nature  as  the  excitation  which  we  can  produce  artificially  by  various  kinds  of 
chemical  su1)stances. 

Unicellular  organisms,  Amoeb»  and  other  Rhizopoda,  are  made  to  con- 
tract by  contact  with  a  one-  to  two-per-cent  sodium  chloride  solution,  0.1-per- 
cent hydrochloric  acid,  one-per-cent  potassium  hydrate  or  weak  solutions  of 
other  acids,  alkalies  and  salts;  they  draw  in  their  pseudopodia  and  assume 
a  spherical  form.    The  same  substances  quicken  the  movements  of  the  flagel- 


THE  EFFECT  OF   EXTERNAL  INFLUENCES  ON  CELLS  53 

lated  and  ciliated  cells  sonietinics  in  a  very  high  degree.  Xerves  and  rau.-cles 
of  the  Metazoa  as  well  as  the  contractile  fibers  of  the  single-celled  organisms 
behave  in  a  similar  manner.  As  regards  muscle  Hering  has  shown  that  vari- 
ous substances  which  for  a  long  time  were  supposed  to  stimulate  chemically, 
in  fact  stimulate  by  closing  the  demarcation  current  of  the  muscle.  Here 
belong  the  so-called  physiological  salt  solution  (0.6  per  cent),  solutions  of 
fixed  alkalies  up  to  0.1  per  cent,  and  diiferent  salt  solutions.  Solutions  also, 
which  stimulate  chemically,  may  cause  muscular  contractions  in  this  way,  if 
they  are  good  conductors.  A  purely  chemical  stimulation  of  the  muscle  takes 
place  therefore  only  by  means  of  fluids  which  do  not  conduct  electricity  or 
do  so  very  poorly,  or  by  means  of  substances  applied  only  to  the  uninjured 
longitudinal  surface  of  the  muscle. 

As  Biedermann  has  shown,  the  cross-striated  muscles  of  the  frogc  fall  into 
rhythmical  contractions,  if  they  are  placed  in  weak  solutions  of  Xa-^HPO^, 
JSTa.rO^,  jSTa.SO,,  jSTaOH.  Loeb  has  studied  these  contractions  further  in  the 
light  of  the  dissociation  theory,  and  has  come  to  the  conclusion  that  they  are 
produced  only  by  certain  ions  (e.g.,  Na,  CI,  Li,  F,  Br,  I),  but  are  impeded  or 
rendered  impossible  by  others  (e.  g.,  Ca,  K,  Mg,  Be,  Sr,  Co,  Mn) — the  excita- 
bility of  the  muscle  not  being  changed  in  either  ease.  Hydro xyl  and  hydrogen 
ions  hasten  the  appearance  of  the  contractions  without  being  able  directly  to 
call  them  forth.  Solutions  which  do  not  contain  electrolytes  produce  no  such 
contractions. 

The  theoretical  significance  of  these  and  related  facts  cannot  be  discussed 
here  because  we  cannot  yet  adequately  survey  the  field  recently  opened  up  by 
these  investigations.  We  may,  however,  expect  from  this  quarter  very  valuable 
results  on  the  chemical  relations  of  the  living  being  in  the  near  future. 

Chemical  stimuli  which  have  a  higher  osmotic  tension  than  that  of  the  struc- 
tures to  be  stimulated,  may  exei-cise  an  exciting  influence  or  may  alter  the 
excitability  by  the  extraction  of  water,  as  probably  occurs  in  many  cases  with 
the  nerves. 

That  this  is  not  the  only  determining  factor  however,  and  that  the  peculiar 
properties  of  the  chemical  substance  exercise  an  essential  influence,  appears  from 
the  fact  that  equimolecular  solutions  in  general  stimulate  more  powerfully  the 
higher  the  molecular  weight  (Griitzner).  Thus  sodium  iodide  for  example 
stimulates  more  powerfully  than  the  bromide  and  chloride,  whereas  the  osmotic 
tensions  of  all  these  is  equal. 

Besides  these  direct  responses  to  stimuli  and  the  alterations  of  excitability, 
wliich  we  must  pass  over,  certain  substances  exercise  a  very  remarkabh^  influ- 
euce  '  on  the  movements  of  free-living  cells  by  attracting  or  repelling  them. 
These  phenomena  are  designated  by  the  term  chemotaa:is  and  are  described  in 
the  one  case  as  positive,  in  the  other  as  negative.  Difl'erent  substances  exer- 
cise different  influences  on  various  cells,  and  the  same  substance  in  different 
concentrations  may  produce  different  effects  on  the  same  organism. 

Some  examples  of  chemotaxis  may  be  cited  here.  Certain  forms  of  Bac- 
teria are  attracted  by  oxygen,  and  in  a  microscopical  preparation  which  contains 
these  Bacteria  together  with  some  alga  cells  one  may  observe  how  they  gather 

*  First  demonstrated  by  Engelmann  on  the  Bacteria. 


54  THE  CELL 

iUduiul  the  alpa  drawn  by  the  oxygen  wliich  is  set  free  by  the  chlorophyll  (Fig. 
31,  Engchnann). 

If  a  eapillaVy  tnbe.  fnscd  at  one  end,  be  filled  with  a  0.05-per-cent  solution 
of  malie  acid  and  the  open  end  of  it  be  placed  in  a  drop  of  water  containing 
the  spennatozoids  of  a  fern,  so  that  the  acid  can  diffuse  gradually  into  the  water, 


Fig.  31. — Illustratinp;  chcmotaxi.s.  The  chloropliyll  bodies  in  the  cells  of  Mesocarpus  scalaris 
under  the  influence  of  light  liberate  oxygen:  the  bacteria  are  most  abundant  where  the  chlo- 
rophyll bodies  lie  nearest  the  surface — i.  e.,  where  the  hberation  of  oxygen  is  nio.st  active, 
after  Engelmann. 

the  spennatozoids  begin  at  once  to  move  toward  the  opening  of  the  tube  and  to 
wander  into  it.  The  same  phenomenon  may  be  observed  indeed  with  a  much 
weaker  solution  (0.001  per  cent,  PfefFer). 

It  has  been  observed  that  the  uterus  and  Fallopian  tubes  of  rabbits  and  rats 
exercise  a  positive  chemotactic  influence  on  the  spermatozoa  of  the  correspond- 
ing species,  but  that  the  ovary  itself  is  entirely  indifferent  in  this  respect.  Chemo- 
taxis  is  of  the  utmost  importance  in  the  following  connection  also.  We  have  seen 
how  the  leucocytes  have  the  power  to  seize  and  consume  Bacteria  which  find 
their  way  into  the  body.  They  are  attracted  to  the  Bacteria  by  substances  given 
off  by  those  organisms.  If  a  capillaiy  tube,  containing  a  sterilized  culture  of, 
say  Staphylococcus  pyogenes  alhiis,  be  introduced  under  the  skin  of  a  rabbit, 
after  a  few  hours  it  is  filled  with  leucocytes.  The  same  culture  fluid  by  itself 
exercises  no  sxich  influence  on  the  leucocytes. 

Likewise  when  the  leucocytes  assemble  in  a  certain  place  for  the  purpose 
of  carrying  away  the  products  of  normal  or  pathological  tissue  destruction,  their 
migration  is  caused  by  chemotaxis  (cf.  page  37).  In  short,  as  far  as  our  present 
information  goes,  we  may  say  that  the  migrations  of  the  leucocytes  are  con- 
trolled, quite  independently  of  the  nervous  system,  essentially  by  chemotaxis. 

From  these  examples  it  ought  to  be  apparent  tliat  chemotaxis  plays  a  very 
great  role  in  the  processes  of  the  living  world,  since  by  it  the  migrations  of 
free-living  cells  are  often  controlled  according  to  their  momentary  needs.  It 
is  therefore  unnecessary  to  invoke  any  psychical  properties  in  explanation  of 
such  phenomena. 

In  the  higher  animals  the  sense  of  smell  has  been  developed  as  a  special 
chemical  sense.  It  is  true  that  many  of  the  movements  taking  place  under 
its  influence  are  to  be  regarded  as  conscious;  but  in  many  other  cases  they 
run  the  course  of  pure  reflexes,  and  if  we  may  extend  the  notion  of  chemo- 
taxis to  all  movements  which  either  directly  or  indirectly  are  inaugurated 
and  controlled  by  chemical  stimuli  without  the  participation  of  consciousness, 


THE   EFFECT  OF  EXTERNAL  INFLUENCES  ON  CELLS 


55 


these  may  l)e  regarded  as  to  a  certain  extent  chemotactic.  Thus  according  to 
the  thorough  analysis  of  Bethe,  a  whole  order  of  complicated  habits  of  the 
ants  might  be  explained  as  chemotactic  reactions,  and  in  the  bees  several  habits 
are  undoubtedly  of  this  origin. 

Jennings  has  shown  that  there  is  nothing  specifically  directive  about  the 
chemotactic  effects  of  chemical  substances  on  Infusoria  and  Bacteria.  If,  for 
example,  Bacillum  volutans  be  placed  in  a  preparation  with  a  green  alga<  they 
are  uniformly  distributed  at  first  throughout  the  preparation.  When  the  alga  be- 
gins to  give  off  oxygen  and  the  bacilli  come  by  chance  into  this  zone  rich  in  O,, 
they  swim  through  it  to  the  opposite  side,  turn  and  swim  again  to  the  border, 
and  so  on  incessantly,  but  they  do  not  adhere  to  any  definite  orientation  with 
respect  to  the  middle  point  of  the  oxygen  zone. 

[The  behavior  of  an  Infusorian  under  chemical  stimulation  may  be  illus- 
trated, according  to  Jennings,  as  follows:  the  usual  motor  response  of  a  Paramce- 
cium  to  any  kind  of  an  obstruction  is  to  reverse  its  cilia  and  swim  backward, 
then  turn  toward  the  side  containing  the  peristome  and  swim  forward  again 
(Fig.  32).  When  in  its  wanderings  the  Paramecium  enters  a  drop  of  dilute  acid, 
the  chemical  change  of  the  medium  does  not  cause  the  reaction,  but  whenever 
the  organism  attempts  to  leave  the  drop  the  chemical  change  experienced  consti- 
tutes a  stimulus  which  evokes  the  usual  motor  response,  and  the  organism  remains 
entrapped.  Coming  in  contact  with  an  alkali  produces  the  same  response  and 
the  organism  turns  so  as  to  avoid  the  substance.  The  result  is  that  the  organ- 
isms collect  in  dilute  acids,  including  carbon  dioxide  (positive  chemotaxis),  and 
refuse  to  do  so  in  alkalies  (negative  chemotaxis).    But  the  acid  can  scarcely  be 


:$^- 


Fig.  32. — Motor  re.spon.se  in  Paramaecium,  after  Jennings,     a-j,  succes.sive  positions  after  meet- 
ing an  obstruction,  .4. 

said  to  attract  the  organisms  in  any  proper  sense  of  the  term,  nor  the  alkali  to 
repel  them.  They  remain  in  the  acids  doubtless  because  the.se  substances  are 
favorable'  to  their  life  processes  and  avoid  the  alkalies  because  the  latter  are 
harmful. — Ed.] 


'  Jennings  recognizes  this  selection  by  random  movements  of  conditions  not  interfering 
with  the  physiologieal  processes  as  a  fixed  principle  of  behavior,  not  only  in  the  Bacteria 
and  Lifusoria  but  in  higher  animals   as  well.— Ed. 


5d  the  cell 


D.    MECHANICAL   STIMULATION 

lu  a  great  manv  ditlVront  kinds  of  colls  the  production  of  energy  may  be 
aroused  by  shocks  of  a  purely  mechanical  nature.  Agencies  of  this  kind  may 
exercise  also  an  important  influence  upon  the  locomotion  of  many  organisms. 

In  so  far  as  they  are  due  to  gravitation  these  agencies  are  designated 
as  geotactic. 

The  collection  of  Infusoria  at  the  central  end  of  a  centrifuge  (Jensen)  ;  the 
movement  of  Parama'ciinn  downward  in  its  medium  in  condition  of  hung-er  and 
of  low  temperature,  but  upward  under  opposite  circumstances;  the  vertical 
climbing  of  Cucumaria,  Actinia,  Asterina,  Peripleneta,  etc.;  the  orientation  of 
fishes;  and  the  behavior  of  a  decerebrated  frog  are  instances  of  geotaxis. 
Changes  of  position,  changes  of  attitude,  etc.,  taking  place  among  the  Metazoa 
are  to  be  regarded  as  reflexes  of  a  complex  order,  analogous  to  those  initiated 
by  chemical  stimulation  (cf.  page  54).  It  is  probable  that  they  are  brought 
about  according  to  the  attitude  of  the  animal  by  the  stimulation  of  the  end 
organs  of  different  nerves  (of  the  skin,  joints,  etc.)  through  the  pressure  of  the 
body  or  through  the  pull  which  is  exerted  by  unsupported  parts.  Finally,  we 
should  mention  the  otolith  apparatus  as  a  seat  of  peripheral  stimulation  (cf. 
Chapter  XVIII). 

A  second  form  of  movement  produced  by  mechanical  influence  is  rheotaxis 
— i.  e.,  changes  of  position  induced  by  flowing  water  or  currents  of  air. 

In  microscopical  preparations  it  may  be  shown  that  spermatozoa  move 
against  the  current  (Roth),  and  it  has  long  been  known  that  once  these  ele- 
mentary organisms  enter  the  oviduct  they  strive  to  reach  the  very  end  of  the 
tube,  forcing  their  way  against  the  current  produced  by  the  ciliated  epithelium. 
Wheeler  has  directed  attention  to  the  fact  that  air  in  motion  influences  the 
movements  of  insects  in  a  similar  way. 

Another  group  of  phenomena  conditioned  by  mechanical  stimulation  is  the 
following.  Frog's  spermatozoa  when  mounted  on  a  slide  bore  into  all  the  little 
scratches  and  crevices  of  the  glass  surface.  These  cells  have  therefore  a  decided 
inclination  to  be  in  contact  with  solid  bodies  (ihif/tnofaxis).  In  line  with  this 
Jennings  has  found  that  Paramcpcium  aurelia  will  attach  itself  to  solid  particles 
in  the  preparation,  and  Piitter  has  demonstrated  that  thigmotaxis  represents 
probably  a  quite  general  phenomenon  widely  distributed  among  all  classes  of 
the  Protista. 

Thigmotaxis  is  exhibited  also  by  many  higher  animals.  There  are  animals 
such  as  the  ants,  which  always  seek  out  the  concave  corners  and  edges  of  cavities, 
while  other  animals  as  constantly  establish  themselves  on  the  convex  edges  and 
corners  of  bodies. 

E.    STIMULATION   BY   MEANS  OF  LIGHT 

Light,  if  we  include  only  the  so-called  illuminating  ra3's,  stimulates  directly 
only  a  few  kinds  of  cells.  In  higher  animals  it  acts  only  upon  the  visual  cells 
of  the  retina,  on  the  musculature  of  the  iris,  and,  if  it  be  concentrated 
enough,  upon  the  end  organs  of  the  heat  nerves.  Likewise  the  skin  (of 
certain  invertebrates  at  least)  is  sensitive  to  light  rays.  In  some  unicellular 
organisms  movements  have  been  observed  which  are  undoubtedly  induced  by 


THE   EFFECT  OF   EXTERNAL   IXFLUENCES  OX  CELLS 


57 


light.  The  red  rays  are  said  to  exercise  the  most  powerful  influence  on 
Amoebae  (Harrington  and  Leaming).  In  frog  and  triton  embryos  both  in 
the  egg  and  in  the  young  larval  stage,  light  calls  forth  pronounced  move- 
ments, and  in  this  case  the  blue  and  violet  rays  are  most  powerful  (Finsen). 
The  Ehizopod  PeJomyxa  contracts  on  sudden  illumination.  A  species  of 
Bacterium  {photometriciim)  is  stimulated  to  active  movements  by  light,  while 
in  the  dark  it  lies  perfectly  still.  In  the  microspectrum  (Fig.  33)  the  major- 
ity of  these  Bacteria  wander  into  the  ultra  red,  while  another  collection  is 
formed  in  the  orange  and  yellow  (Engelmann). 

The  effects  on  the  direction  of  movements  produced  l)y  the  light  are 
designated  by  the  term  [jhototaxis. 

Free-living  unicellular  organisms,  inclosed  in  a  drop  of  water^  collect  on 
the  side  of  the  drop  turned  toward  the  light  (positive  phototaxis),  if  the  illumi- 
nation is  moderate.  They  flee  from  this  side  and  collect  on  the  opposite  edge 
(negative  phototaxis)   if  the  illumination  is  strong.     Thus  we  have  in  different 


:         1 
i 

'             1                      '              I                                               i 
,11                                       1          1 

Ml 

1 

•V;:    '         •.  *j        *         J 

'§:'  ,.'    •^''  .'.'*.  ' 

1                           1 

1        !          ,                                                            —                                                                                                                      1 

a    B     C  U  £   b  r  g 

Fig.  33. — The    distribution  of    Bacteria   (Bacterium   photometriciim)    in  the  microspectrum  of 

direct  sunhght,  after  Engelmann. 

degrees  of  illumination  the  same  difference  with  which  we  have  become  ac- 
quainted under  chemotaxis.  In  general  the  short-waved  rays  of  the  spectrum, 
the  blue  and  violet,  are  the  most  important  in  this  directive  influence.' 

Loeb,  Finsen.  Adams.  Yerkes.  and  others  have  described  simihir  phenom- 
ena among  the  Metazoa.  Earthworms  exposed  to  a  light  varying  in  strength 
from  192  to  0.012  candle  jjower  exhibit  negative  phototaxis,  which  dimin- 
ishes with  the  intensity  of  the  light:  in  0.011  candle  power  they  exhibit  posi- 
tive phototaxis.  In  diffuse  daylight  the  frog  is  positively  phototactic:  in 
direct  sunlight  it  shows  at  first  positive,  then  negative  phototaxis. 

The  movements  of  the  pigment  cells  of  the  retina  by  which  their  processes 
become  longer  and  the  inner  ends  of  the  cones  shorter  may  be  cited  as  an  unmis- 
takable example  of  phototaxis  (cf.  Chapter  XXI).  Even  the  unconscious  reflex 
movements  of  the  eyes,  of  the  head  and  of  the  body  as  a  whole,  which  are  pro- 
duced by  stimulation  of  the  visual  cells  of  the  retina  by  light  may  be  regarded  as 
in  a  certain  measure  a  kind  of  phototaxis  (cf.  page  54). 

The  ultra-violet  rays  exercise  a  very  marked  influence  on  cells.  On  the 
anterior  portion  of  the  eye  they  produce  an  excitation  which  is  characterized  by 

*  See  note  page  59. 


58  THE  CELL 

catarrhal  symptoms  of  the  conjunctiva  palpehralis,  inflammation  and  swelling 
of  the  conjunctiva  oculi.  descjuanuition  of  the  ei)itheliuni  and  clouding  of  the 
cornea,  as  well  as  contraction  of  the  pupil  and  discoloration  of  the  iris.  Similar 
effects  appear  on  the  skin :  it  becomes  red  and  swollen ;  l)urning  sensations 
and  sensitiveness  to  touch  distinguish  the  affected  portions;  after. some  days 
the  epidermis  begins  to  peel  off  in  the  form  of  large  scales,  and  in  about 
fourteen  days  the  skin  becomes  normal  again.  There  usually  remains  for 
a  long  time,  however,  a  light  coloration  of  the  affected  part,  which  is  sharply 
marked  off  from  the  surrounding  skin  (Widmark).  With  sufficient  concen- 
tration of  the  light,  the  l)lue-violet  rays  also  are  said  to  exercise  a  similar 
influence  ( Finsen ) . 

The  X  rays  discovered  by  Rontgen  produce  in  the  skin  similar  but  even 
more  powerful  effects  than  those  discussed  alwve.  Possibly  the  ultra-violet 
rays  contained  in  the  cathode  rays  contribute  in  some  degree  to  this  effect. 
Certain  Bacteria  (the  cholera,  anthrax,  diphtheria,  and  tubercle  bacilli)  are 
killed  by  the  X  rays,  and  cells  of  higher  plants  siiffer  a  reduction  of  their 
activities.  Different  Protozoa  exhibit  a  very  different  power  of  resistance 
toward  the  X  rays  (of  fourteen  hours'  duration) :  some  forms  appear  not  to  be 
affected  by  them  at  all,  others  slightly,  some  very  powerfully.  In  general  it 
appears  that  forms  which  have  vacuolated  protoplasma  react  more  quickly 
than  those  of  firmer  structure.  The  presence  or  absence  of  memln'anes  and 
shells  may  also  be  significant  (Schaudinn). 

With  respect  to  the  Becquerel  rays  (radium)  Aschkinass  and  Caspari 
have  found  that  they  weaken  markedly  the  Bacillus  prodigiosus  in  from  two 
to  four  hours.  With  a  longer  exposure  to  radium  (twenty-four  and  sixteen 
hours  respectively)  typhoid  and  cholera  bacilli  were  killed  (Pfeiffer  and 
Friedberger).  Schwarz  has  shown  further  from  researches  on  the  hen's  egg 
that  these  rays  destroy  albuminoid  bodies  by  a  kind  of  dry  distillation,  that 
they  decolorize  lutein  and  act  upon  the  lecithin  of  the  cell  substance.  In  these 
effects  he  finds  the  explanation  of  the  peculiar  cell  necrobiosis  observed  by 
Becquerel  himself.  Becquerel  once  carried  in  his  vest  pocket  for  only  two 
hours  a  well-wrapped  but  highly  active  radium  preparation.  Fourteen  days 
later  he  observed  on  the  abdominal  skin  opposite  the  pocket  a  small  burn 
which  became  larger  and  larger  and  finally  developed  into  a  deep  wound 
which  did  not  heal  for  months. 


F.    STIMULATION  BY  MEANS  OF  HEAT 

Only  in  relatively  few  cases  does  heat  appear  to  exercise  a  direct  stimu- 
lating effect  on  living  cells.  In  the  higher  animals  only  the  end  organs  of 
certain  afferent  nerve  fibers  are  really  roused  to  activity  by  heat.  Heat,  as 
already  remarked  above,  exercises  a  more  powerful  influence  on  the  excita- 
hility  of  the  cells.  In  all  cells  we  find  that  the  life  processes  increase  in 
intensity  with  the  temperature  up  to  certain  limits  (cf.  supra  page  29),  and 
likewise  that  with  a  lowering  of  the  temperature  they  are  depressed  at  least, 
if  not  brought  to  a  complete  standstill.  It  is  not  easy  in  any  given  case  to 
separate  clearly  the  actually  stimulating  effect  from  the  heightening  influence 


THE  EFFECT  OF  EXTERNAL  INFLUENCES  ON   CELLS  59 

on  the  excitability,  and  the  phenomena  just  mentioned  are  regarded  by  some 
as  the  expression  of  actual  stimulation. 

As  an  example  of  the  directive  ^  influence  of  heat  on  the  movements  of 
cells  {thermotaxu)  the  behavior  of  the  ciliate  Infusorian,  Paramcecium.  may 
be  mentioned.  If  the  vessel  in  which  they  are  contained  is  warmed  on  one 
side  to  about  34°-28°  C.  the  animalcules  withdraw  to  the  other  side,  while 
with  a  temperature  below  this  limit  they  wander  to  the  warmer  side — opposite 
movements  therefore  according  as  the  same  stimulus  is  strong  or  weak. 


G.    ELECTRICAL   STIMULATION 

Because  they  are  the  most  easily  manipulated  and  most  easily  graduated, 
electrical  stimuli  have  been  studied  with  very  great  exactness.  Since  their 
effects  are  investigated  chiefly  on  nerves  and  muscles  of  the  vertebrates,  we 
shall  deal  with  them  at  some  length  in  presenting  the  physiology  of  nerves 
and  muscles.  Suffice  it  for  the  present  to  state  that  it  has  been  found  in 
nerves  and  muscles  that  the  electrical  current  stimulates  only  at  one  pole  or 
the  other,  at  the  negative  pole  on  closing  the  current,  and  at  the  positive  on 
hreaking  it  (Pfliiger).  Between  the  two  poles  it  acts  to  change  the  excita- 
bility, but  not  to  stimulate. 

In  Paramcecium,  excitation  is  said  to  take  place  with  the  closing  of  the 
current  at  the  anode  (Verworn).  And  there  are  other  exceptions  to  the  law 
as  it  applies  to  nerve  and  muscle.  Carlgren  has  shown  with  regard  to  Paramce- 
cium, that  lifeless  individuals,  immediately  after  the  closing  of  a  sufficiently 
strong  constant  current,  show  at  the  anode  a  shrinking  up  and  at  the  cathode 
bending  movements,  both  of  which  are  the  consequence  of  the  so-called  cata- 
phoric effect  of  the  constant  current  [i.  e.,  the  tendency  which  this  current  has 
to  sweep  substances  in  solution  along  with  it — Ed.]  ;  and  it  is  not  at  all  improb- 
able that  similar  phenomena  in  the  living'  Paramcecium  are  of  the  same  origin. 

The  following  phenomenon  might  be  presented  as  a  secondary  effect  of 
the  electric  current.  If  a  salamander  {Amhh/stoma)  be  traversed  longitu- 
dinally by  an  electric  current,  the  skin  glands  of  the  animal  begin  to  produce 
a  copious  secretion,  which  appears  only  on  the  side  of  the  anode.  The  same 
occurs  also  with  isolated  pieces  of  the  animal  in  which  the  spinal  cord  has 
been  destroyed.  But  this  secretion,  as  Loeb  has  shown,  is  not  excited  by  the 
current  itself,  but  by  the  electro-positive  ions  liberated  by  the  current.  For 
if  the  animal  is  immersed  in  a  NaCl  solution,  the  electro-positive  ions  in  their 
migration  toward  the  cathode  are  set  free  on  the  skin  of  the  animal  and  are 
combined  with  the  hydroxyl  of  water  into  XaOH.  As  direct  experiments  have 
proved,  this  alkali  exercises  a  powerful  stimulating  effect  on  the  skin  glands; 

1  Jennings  is  of  the  opinion  that  these  so-called  "directive  influences"  of  light  and  of 
heat  are  merel}^  other  instances  of  the  selection  by  random  movements  of  conditions  favor- 
able to  the  life  processes.  Taking  Paramcecium  as  an  example  we  find  that  when  it  wanders 
into  a  degree  of  illumination  or  of  temperature  which  is  unfavorable,  the  organism  is  stim- 
ulated by  the  change  and  reacts  by  making  the  usual  motor  response  for  avoiding  an  ob- 
stacle. The  total  eflfect  of  many  such  responses  is  to  carrj'  the  organism  out  of  the  field  of 
unfavorable  influences  or  to  keep  it  in  the  field  of  favorable  ones. — Ed. 
6 


60 


THE  CELL 


the  phenomenon  is.  therefore,  only  a  secondary  effect  of  the  current.  It 
should  be  remarked  further  that  neither  weak  acids  nor  electro-negative  ions 
exercise  such  an  intluenco. 

Electrical  stimuli  like  other  stimuli  exercise  a  directing  influence  on  Loco- 
motor movements.  If  a  constant  current  be  passed  through  a  vessel  in  which 
are  frog  tadpoles  or  fish  embryos,  the  animals  orient  themselves  with  their 
long  axes  in  the  direction  of  the  current,  and  with  the  head  directed  toward 
the  cathode.  They  remain  in  this  position  as  long  as  the  current  is  closed; 
when  the  current  is  reversed  the  animals  turn  as  if  by  command  (Her- 
mann). 

Hermann  explained  this  form  of  galvanotaxis  by  supposing  the  central 
nervous  system  to  be  excited  by  the  ascending  current,  but  to  be  unaffected  or 
even  paralyzed  by  the  descending  current,  so  that  the  larvae  and  embryos  either 
instinctively  or  reflexly  take  the  position  in  which  they  are  stimulated  least. 
Loeb  on  the  contrarj'  has  made  it  quite  probable  by  experiments  on  shrimps  and 

Amhlystoma  larvae  that  the  current 
produces  parallel  changes  of  tension 
and  energy  production  in  associated 
groups  of  muscles,  the  result  of  which 
is  that  the  movement  toward  one  pole 
is  facilitated,  but  movement  toward 
the  opposite  pole  is  impeded.  Thus 
with  the  shrimps  the  tension  of  the 
flexors  predominates  on  the  side  of 
the  anode,  while  the  tension  of  the 
extensors  predominates  on  the  side  of 
the  cathode.  With  a  current  of  me- 
dium strength  the  animals  always 
move  toward  the  anode;  if  when  the 
current  is  turned  on  the  head  end  is 
already  near  the  anode,  the  change 
in  position  is  effected  by  a  forward 
movement ;  if  the  tail  end  lies  nearer 
the  anode,  it  is  effected  by  a  back- 
ward movement. 

The  following  examples  of  gal- 
vanotaxis may  be  mentioned.  Cer- 
tain echinoderms  in  their  youngest 
and  oldest  stages  (free-swimming 
gastrulae  and  the  creeping  mature 
animals)  exhibit  no  galvanotaxis, 
while  in  the  intermediate  stages 
(free-swimming  plutei  and  bipen- 
naria)  they  exhibit  very  marked  gal- 
vanotaxis, and  wander  to  the  cathode 
(Carlgren).  The  majority  of  ciliate  Infusoria  and  Amoebae  assemble  at  the 
cathode,  if  an  electric  current  is  conducted  through  the  vessel  in  which  they  are 
contained.  Many  flagellate  Infusoria  show  the  opposite  reaction  by  moving  to 
the  anode.  Finally,  it  has  been  observed  that  the  ciliate  Infusorian  Spirostomum 
places  itself  v.'ith  its  long  axis  at  right  angles  to  the  current  (Verworn).  All 
these  differences  find  an  explanation  according  to  Wallengren  in  the  general  fact 


Fig.  34. — Showing  the  effects  of  a  constant  cur- 
rent on  the  shrimp  PoUi-ivonetes,  when  the 
current  passes  trans\'ersely  through  the  ani- 
mal's body,  after  Loeb  and  Maxwell.  The 
legs  on  the  side  of  the  anode  are  strongly 
flexed,  those  on  the  side  of  the  cathode  are 
strongly  extended. 


THE  EFFECT  OF  EXTERNAL  INFLUENCES  ON  CELLS 


61 


that  in  all  ciliate  Infusoria  the  cilia  on  the  side  of  the  cathode  beat  toward  the 
anterior  end,  those  on  the  side  of  the  anode,  toward  the  posterior.  For  example, 
as  long  as  its  anterior  end  is  directed  toward  the  cathode,  Opalina  ranarum 
(Fig.  35)  always  turns  toward  the  right  as  indicated  by  the  arrow. 


Organisms  are  killed  by  strong  electric  currents.  Concerning  the  changes 
effected  by  such  currents  on  the  higher  animals,  Prevost  and  Battelli  especially 
have  made  extensive  investigations,  of  which  the  following,  relating  to  the 
dog  only,  will  be  mentioned  here.  With  an  induc- 
tion current  of  lower  tension  (up  to  120  volts) 
death  results  from  fibrillary  contractions  of  the 
heart  produced  by  the  current,  in  consequence  of 
which  the  circulation  is  ultimately  stopped  (cf. 
Chapter  VI).  The  disturbances  in  the  nervous 
system  coming  on  at  the  same  time,  indicated  by 
convulsions  and  the  like,  have  relatively  little  im- 
portance. Respiration  is  resumed  after  a  tem- 
porary pause,  and  may  even  continue  for  two  or 
three  minutes  after  the  inception  of  fibrillar}^  con- 
tractions of  the  heart. 

With  induction  currents  of  higher  tension 
(more  than  1,200  volts)  death  occurs  as  a  result 
of  paralysis  of  respiration,  while  the  ventricles 
beat  rapidly  and  powerfully  and  the  auricles  stop 
in  diastole.  Indeed  by  means  of  currents  of  high 
tension  one  may  even  restore  a  heart  seized  with 
fibrillary  contractions  to  its  former  functional 
power,  when  it  cannot  be  restored  to  its  normal 
action  in  any  other  way. 


Fig 


35. — Opalina  ranarum, 
a  ciliated  organism  from 
the  intestine  of  the  frog, 
seen  from  above,  after 
Wallengren.  Dr,  the  cilia 
used  by  the  organism  in 
changing  direction  to  the 
right. 


Strong    induction    shocks    (Rhumkorff,    45    cm. 
spark,  twenty  interruptions  per  second,  primary  cur- 
rent twenty-five  volts)   can  be   conducted   from  mouth  to  rectum  for  one   and 
one-half  minutes  without  danger  to  the  animal.     In  two  and  one-half  minutes 
he  dies  in  convulsions  produced  by  failure  of  respiration ;  if  artificial  respiration 
is  maintained  the  animal  can  survive  such  currents  acting  for  ten  minutes. 


The  effect  of  the  electric  current  is  dependent  not  only  upon  its  tension, 
but  also  upon  its  duration  and  the  place  of  its  application,  as  well  as  upon 
contact  between  the  electrodes  and  the  body.  The  different  animal  species 
also  exhibit  differences  in  sensitivity :  the  dog  appears  to  be  the  most  sensitive, 
the  horse  less  so,  still  less  the  guinea  pig,  rabbit  and  mouse. 


H.    COSMIC  INFLUENCES 

It  has  long  been  firmly  established  by  general  experience  that  cosmic  forces 
exercise  a  marked  influence  upon  organisms ;  and  to  convince  ourselves  of 
such  influence  we  have  only  to  be  reminded  of  the  pains  affecting  gouty  and 


62 


THE  CELL 


rheumatic  individuals  with  different  conditions  of  weather.  We  know  very 
little  at  this  time  about  the  real  nature  of  these  agents.  Recently  Arrhenius 
has  sought  to  bring  various  physiological  processes,  notably  menstruation,  into 
relation  with  electrical  variations  of  the  atmosphere  and  the  chemical  changes 
thereby  effected.  But  the  results  thus  far  obtained  on  this  subject  appear  to 
be  too  limited  to  justify  a  fuller  presentation  in  this  book. 


I.    CONDUCTIVITY 

Besides  these  artificial  stimuli  which  are  able  to  excite  the  cells  or  to 
increase  their  excitability,  there  occurs  in  the  Metazoa  a  form  of  stimulus 
which  belongs  to  the  body  itself,  namely,  the  stimulation  of  one  cell  hy  an- 
other. It  is  in  this  connection  that  the  nerves 
are  of  the  very  greatest  importance ;  they  trans- 
fer their  excitations  to  the  end  organs,  the  mus- 
cle cells,  gland  cells,  etc. ;  or  they  are  themselves 
stimulated  by  other  cells,  as  when  the  sensory 
nerve  fibers  are  roused  to  activity  by  their 
peripheral  end  organs,  or  when  a  nerve  cell  by 
means  of  its  processes  arouses  another  cell  to  a 
state  of  activity.  Here  belongs  also  the  case 
of  the  stimulation  of  a  smooth  muscle  cell  by 
its  neighbor,  which  in  all  proliability  is  accom- 
plished by  means  of  the  protoplasmic  connec- 
tions (intercellular  bridges)  which  have  been 
demonstrated  between  these  as  well  as  between 
other  kinds  of  cells  (cf.  Fig.  36).  This  form 
of  stimulation  represents  one  of  the  most  im- 
portant mechanisms  by  which  the  different 
parts  of  the  Metazoan  body  are  made  to  coop- 
erate harmoniously. 

The  stimulus  is  transmitted  from  one  part 
to  the  other  also  in  a  single  cell.  The  clearest  example  of  this  we  have  again 
in  the  nerves,  which  are  nothing  else  than  long  processes  of  nerve  cells,  and 
they  propagate  a  stimulus  directly  transmitted  to  them  by  passing  it  along 
from  one  section  to  the  next  throughout  its  entire  length.  We  meet  with  the 
same  mode  of  transmission  wherever  a  cell  is  stimulated  at  one  definite  point 
and  the  excitation  extends  throughout  the  entire  cell  body. 


Fig.  36. — Cross  section  of  the  in- 
testinal musculature  of  the  cat, 
after  Boheman.  The  dotted 
areas  represent  cross  sections 
of  muscle-cells,  the  black  lines 
between  them  represent  inter- 
cellular bridges. 


J.    THE  ASSIMILATIVE  PROCESSES  INDUCED  BY  STIMULATION 

Our  knowledge  of  the  assimilative  processes  induced  by  different  stimuli 
is  still  very  imperfect. 

With  respect  to  the  question  of  most  interest  to  us,  namelv,  the  influence 
of  stimuli  upon  the  formation  of  living  substance,  we  know  that  the  Bacteria 
and  Infusoria  multiply  rapidly  as  the  result  of  increasing  the  supply  of  nour- 
ishment, and  that  the  sunlight  gives  the  impetus  for  the  formation  of  the 


THE  EFFECT  OF   EXTERNAL   INFLUENCES  ON  CELLS  63 

green  coloring  matter  of  plants;  for  germinating  seeds  develop  in  the  dark 
into  a  white  or  whitish  seedling  which  becomes  green  only  when  it  is  exposed 
to  the  light.  Since  the  chlorophyll  bodies  are  to  be  regarded  as  composed 
of  living  substance,  we  have  in  the  latter  instance  a  case  where  an  external 
stimulus  actually  effects  the  formation  of  living  substance.  As  regards  the 
first  example,  one  might  say  that  the  abundant  supply  of  nourishment  had 
given  the  impetus  for  a  more  active  formation  of  living  substance;  but  the 
matter  is  not  entirely  clear,  for  it  might  also  be  that  the  impulse  to  mul- 
tiply in  these  organisms  is  just  as  great  with  scanty  as  with  abundant 
nourishment,  only  with  a  deficiency  of  nutrient  substances  it  cannot  be 
manifested. 

From  observations  on  the  storage  of  substance  in  the  bodies  of  young 
animals  it  appears  that  the  inherent  groivth  energy  is  of  much  greater  im- 
portance than  any  form  of  external  stimulation.  But  in  mature  animals, 
if  any  increase  in  the  living  substance  takes  place  under  normal  circumstances, 
we  think  of  it  at  once  as  being  caused  by  some  agency  outside  the  cells  them- 
selves; and  hence  its  consideration  properly  belongs  under  the  present  topic. 
Now  results  of  metabolism  experiments  show  that  ordinarily  the  cells  (of 
the  higher  animals  at  least)  destroy  practically  all  of  their  daily  supply  of 
proteid  nourishment,  but  that  under  certain  circumstances  (not  too  great 
age,  and  great  excess  of  potential  energy  in  the  food,  cf.  page  120)  they  store 
some  of  the  proteid.  It  appears  in  fact  that  in  spite  of  their  inner  propensity 
to  destroy  proteid,  an  abundant  supply  of  nourishment  in  some  way  makes  it 
possible  for  the  cells  to  change  dead  proteid  into  living  protoplasm.  If  this 
is  correct — and  the  question  can  scarcely  be  regarded  as  finally  settled — this 
storage  would  be  the  consequence  of  a  chemical  stimulation  brought  about 
by  the  excess  of  proteid. 

However  this  may  be,  the  only  really  effective  way  known  to  us  of  increas- 
ing the  living  substance  in  the  mature  higher  animals  is  ivorl- ;  and  it  is 
possible  to  conceive  of  this  also  as  a  special  form  of  chemical  stimulation.  A 
grown  man  may  eat  ever  so  much  food,  his  diet  may  be  adapted  perfectly  to 
the  purpose,  but  no  significant  increase  of  muscle  substance  will  take  place  if 
the  muscle  does  not  accomplish  suthcient  work;  whereas  a  working  muscle 
increases  both  in  power  and  in  volume — i.  e.,  the  work  has  called  forth  an 
increase  of  living  substance.  Since  now  every  muscular  movement  is  orig- 
inated by  the  motor  nerves,  and  since  experience  shows  that  a  nonworking 
muscle  always  decreases  in  volume,  and  a  muscle  paralyzed  by  cutting  its 
motor  nerves  undergoes  atrophy  and  degeneration  in  a  relatively  short  time, 
it  follows  that  some  Jcind  of  a  nutrient  or  trophic  influence  on  the  muscle 
must  be  exercised  hy  the  central  nervous  system  through  the  motor  nerves. 
What  the  nature  of  this  influence  is,  we  cannot  say  definitely.  Since,  how- 
ever, the  stimuli  originating  in  the  body  itself  are  in  general  of  a  chemical 
nature,  we  may  perhaps  conclude  that  the  trophic  influence  mediated  by  the 
nerves  is  a  chemical  stimulus.  Other  facts  which  we  shall  discuss  somewhat 
in  detail  in  what  follows  show  that  an  influence  of  a  similar  nature  is  exerted 
on  other  organs  by  the  nerves  belonging  to  thcin.  If  the  cerebral  secretory 
nerve  of  the  submaxillary  gland  be  cut,  the  gland  atrophies.  This  nerve  is 
therefore  of  great  importance  for  the  maintenance  of  this  part  of  the  body, 


64 


THE  CELL 


\ 


\ 


/ 


\ 


\j 


althougli  it  does  not  follow  with  certainty  from  the  foregoing  that  it  has 
contributed  also  to  the  formation  of  living  substance.^ 

With  regard  to  the  original  formation  of  cells  and  tissues,  there  are 
numerous  data  which  go  to  show  that  the  most  widely  different  stimuli  can 
effect  an  essential  modification  of  the  growth  process. 

Here  belong  the  effects  of  gravitation  {geotropism).  and  other  mechanical 
agencies  {rheotropism,  thigmotropism) ,  of  light  {helio- 
tropism),  and  of  galvanism  (gahanotropism)  upon  the 
orientation  of  plants  and  of  various  sessile  animals.- 

The  following  may  be  mentioned  as  examples.  The 
stems  of  plants  grow  away  from  the  center  of  the  earth 
(negative  geotropism),  the  roots  toward  the  center  of  the 
earth  (positive  geotropism).  If  germinating  seeds  be  placed 
on  a  wheel  rotating  rapidly  in  a  vertical  plane  so  that  the 
influence  of  gravitation  is  overcome,  the  stem  grows  toward 
the  middle  point  of  the  wheel,  the  roots  turn  away  from  it 
i.  e.,  the  stem  grows  in  the  direction  of  least  pressure,  the 
root  in  the  direction  of  the  greatest  (Kiiight). 

The  hydroid  polyp  (Antennnlaria  antennina)  consists  of 
a  central  stem  of  1-2  mm.  thickness,  and  often  moi'e  than 
20  cm.  in  length,  which  generally  grows  perfectly  straig'ht 
up  from  a  tangle  of  very  thin  filamentous  rootlets.  If  now 
an  Antennnlaria  whose  stem  is  in  process  of  growth  be 
brought  into  a  position  deviating  from  the  vertical,  the 
growing  tip  bends  until  it  finds  the  vertical  direction  again, 
and  then  grows  directly  upward.  The  root  on  the  other 
hand  grows  vertically  downward  but  not  in  so  straight  a 
line  as  the  stem  (cf.  Fig.  37). 

Rheotropism. — Seedlings  of  maize  and  other  plants  ger- 
minated in  a  tub  of  flowing  water  grow  with  roots  paral- 
lel to  the   surface  of  the  water  and  against  the  current. 

The  hydroid  polyp,  Eudendrium,  also  bends  in  its  growth  against  the  current 

(Loeb). 

Thigmotropism. — Numerous  plants  twine  around  the  vertical  stems  of  other 

plants  and  so  climb  upward. 

Heliotropism. — The  growing  parts  of  a  plant  always  turn  toward  the  light. 


Fig.  37. — A  .shoot  of 
Antennnlaria  an- 
tennina, a  small 
hydroid  animal, 

exhibiting  negative 
geotropism,  after 
Loeb. 


^  Perhaps  a  clearer  case  of  the  influence  of  nervous  tissue  on  the  formation  of  living 
substance  is  that  of  the  regeneration  of  a  "  head  "  in  a  simple  worm.  C.  M.  Child  has 
shown  that  if  the  anterior  end  of  the  flatworm  Lepfoplana  be  cut  off'  in  such  a  way  as  to 
leave  the  collection  of  ganglion  cells  which  serves  the  animal  as  a  '"  brain,"  the  animal  will 
regenerate  a  new  "  head  ";  but  if  the  cephalic  ganglia  be  removed  with  the  anterior  end  no 
"  head  "  is  regenerated,  because  in  this  instance  the  anterior  end  is  no  longer  capable  of 
functioning  as  a  "  head."  In  other  words,  the  determining  factor  in  the  formation  of  the 
living  substance  here,  as  in  the  mammalian  mu.scle,  is  the  motor  activity  dependent  upon 
the  nervous  system,  or,  as  we  have  just  learned,  a  special  kind  of  chemical  stimulus. — Ed. 

^  With  Herbst  I  employ  the  term  geotaxis,  galvanotaxis,  etc.,  for  the  effects  on  the 
movements  of  free-living  organisms  brought  about  by  external  stimuli,  and  the  terms 
geotropism,  galvanotropism,  etc.,  for  the  changes  in  growth  brought  about  by  external 
stimuli.  The  former  phenomena  are  purely  dissimilative,  the  latter  are  essentially  assim- 
ilative. These  phenomena  could  only  bo  produced  by  the  constant  effect  of  these  stimu- 
lating agents  acting  in  a  perfectly  definite  manner. 


THE  EFFECT  OF  EXTERNAL   INFLUENCES  ON  CELLS  65 

Indeed,  in  many  plants  one  may  observe  that  on  a  sunny  day  the  whole  course 
of  the  sun  is  followed  by  appropriate  movements  of  the  plant.  This  effect  is 
brought  about  chiefly  by  the  more  strongly  refractive  rays  of  the  spectrum. 

Galvanotropum. — With  long  exposure  to  a  constant  current  root  tips  turn 
toward  the  cathode. 

Even  in  the  highest  animals  we  meet  with  extensive  regenerative  proc- 
esses which,  in  part  at  least,  are  caused  by  a  kind  of  chemical  stimulation. 
Thus  if  a  large  part  of  the  liver  be  cut  away,  a  considerable  regeneration  of 
liver  tissue  follows  (Ponfick,  Podw}'ssozki).  After  extirpation  of  one  kidney, 
the  remaining  kidney  increases  considerably  in  volume  by  new  formation 
of  kidney  tissue.  Xunierous  discoveries  of  the  pathologists  on  abnormal 
growths  belong  here  also. 

Among  the  Mammalia,  however,  the  powers  of  regeneration  are  relatively 
small  in  comparison  with  those  of  the  lower  vertebrates  and  especially  of 
certain  invertebrates  and  of  plants,  for  in  the  former  the  tendency  to  regen- 
eration is  limited  to  certain  tissues,  while  in  the  latter  whole  organs  may  be 
formed  anew. 

The  tendency  to  the  syntheses  of  nonliving  substatices  in  the  organism 
appears  to  be  favored  to  a  certain  extent  by  a  rich  supply  of  food.  In  an 
atmosphere  rich  in  CO,,  under  otherwise  similar  conditions,  plants  show  a 
greater  production  of  starch;  and  with  an  abundant  supply  of  carbohj'drates 
animal  cells  form  fat  which  is  stored  up  in  the  fat  cells.  Animal  cells 
carry  on  also  a  multitude  of  other  syntheses  the'  stimulus  to  which  might  well 
be  sought  for  in  a  chemical  excitation  effected  by  the  substances  supplied  them. 
Anything  more  exact  than  this  is  quite  beyond  our  knowledge  at  this  time. 


K.    PARALYSIS  AND   FATIGUE 

We  meet  with  a  true  case  of  paralysis  when  a  dissimilative  stimulus  is 
carried  beyond  a  certain  strength.  This  is  true  of  all  kinds  of  stimuli  and 
for  all  kinds  of  cells,  in  so  far  as  they  can  be  roused  to  a  state  of  activity 
by  the  particular  stimulus.  If  the  strength  of  the  stimulus  be  not  too  great, 
nor  its  duration  too  long,  complete  restoration  may  take  place  after  its 
cessation.  But  if  the  stimulus  be  too  strong  or  if  it  last  too  long,  it  has  a 
fatal  effect  on  the  protoplasm. 

Certain  chemical  substances — e.  g.,  the  narcotics,  to  which  belong  alcohol, 
ether,  chloroform,  morphine,  cocaine,  paraldehyde  etc. — are  characterized  by 
their  paralyzing  effects,  obtained  even  with  small  doses.  After  a  short  period 
of  excitation,  the  protoplasm  exposed  to  these  substances  loses  to  a  greater  or 
less  extent  its  vital  activity.  With  small  doses  and  short  exposure  the  paral- 
ysis passes  off,  but  with  large  doses  or  long  exposure  the  paralysis  becomes 
more  and  more  profound  until  death  finally  ensues. 

Fatigue  may  be  considered  as  a  special  kind  of  paralysis.  In  all  living 
beings  (though  in  different  genera  and  individuals  in  different  degree)  there 
always  occurs  after  a  sufficiently  intense  dissimilative  activity  a  reduction 
of  the  functional  power,  as  a  consequence  of  which  the  same  strength  of 
stimulus  produces  a  much  weaker  effect  than  before.     If  the  stimulation  be 


66  THE  CELL 

eontiniR'd  loiiij  oiioiii,rli.  tho  excitability  may  be  entirely  destroyed.  All  these 
phenomena  which  are  best  known  in  man  from  his  subjective  experience  of 
the  results  of  severe  muscular  work  are  included  under  the  term  fatigue. 

Now  it  has  been  shown  that  fatigue,  for  the  most  part  at  least,  is  caused 
hi/  the  products  formed  in  nictaholism  (J.  Kanke).  as  may  be  seen  from 
such  facts  as  the  following:  if  the  blood  of  an  exhausted  dog  be  injected  into 
a  vein  of  a  fresh  dog,  the  latter  immediately  exhibits  very  evident  signs  of 
fatigue. 

If  a  fatigued  organ  be  allowed  to  rest  for  a  long  time  a  remarkable  thing 
occurs:  the  organ  completely  recovers — i.e.,  its  former  functional  power  has 
returned.  This  is  not  difficult  to  explain  for  the  free-living  unicellular 
organisms;  for  they  give  off  the  decomposition  products  to  the  surround- 
ing medium  in  a  very  simple  manner.  And  even  in  the  higher  animals  the 
recovery  after  fatigue  presents  no  great  difficulties,  for  the  waste  products 
are  carried  away  from  the  organ  by  the  circulation  of  the  blood  and  lymph, 
and  at  the  same  time  the  blood  places  new  nutrient  material  at  its  disposal. 
The  same  phenomenon  is  observed  however  in  the  organs  of  cold-blooded 
animals  which  have  been  cut  out  of  the  body.  A  frog's  muscle  which  by 
repeated  stimulation  has  been  brought  to  a  condition  where  it  cannot  contract 
at  all,  recovers  and  becomes  functional  again  in  spite  of  the  fact  that  there  is 
no  circulation  to  carry  away  waste  products.  It  follows  therefore  that  recov- 
ery is  not  conditioned  solely  upon  the  removal  of  waste  products,  but  that 
other  factors  also  must  be  taken  into  account,  w^ith  which  we  are  not  yet  thor- 
oughly acquainted. 

§4.    DEATH 

We  have  seen  that  the  most  widely  different  external  agencies  of  suffi- 
cient intensity  and  sufficient  duration  have  the  power  to  check  life  and  to 
bring  on  death.  Changes  also  which  are  going  on  in  the  cells  without  any 
such  external  influences  can  reduce  their  functional  powers.  In  the  course 
of  life  these  alterations  come  on  gradually,  in  some  beings  more  rapidly  than 
others,  but  always  inevitably.  They  are  known  by  the  term  senescence.  If 
they  progress  far  enough,  death  ensues  as  the  result  of  old  age.  This  form 
of  death  is,  in  man  at  least,  only  rarely  to  be  considered ;  for  the  body  is  sub- 
jected to  many  external  accidents  of  all  kinds,  and  only  in  the  most  excep- 
tional cases  does  it  escape  all  of  them.  The  senescent  changes,  however,  play 
an  important  role  even  here,  for  by  their  influence  the  power  of  resistance  of 
the  organism  to  the  accidents  which  it  must  encounter  is  more  and  more 
reduced. 

After  death  the  body  is  destroyed  as  a  rule  within  a  short  time,  partly  by 
autolysis  of  the  organs  (ef.  page  38),  partly  by  processes  of  decomposition  and 
putrefaction  which  are  carried  on  by  the  lowest  organisms.  The  carbon  and 
hydrogen  of  the  body  pass  off  in  the  atmosphere  as  carbon  dioxide  and  water 
vapor;  and  the  nitrogen  and  sulphur,  after  a  series  of  transformations  taking 
place  under  the  influence  of  Bacteria,  are  combined  with  metals  in  the  form  of 
nitrates  and  sulphates  which  are  taken  up  by  the  water  of  the  soil.  These  sub- 
stances, carbon  dioxide,  water,  nitrates  and  sulphates  are  the  normal  food  of 
green  plants,  and  by  the  synthetic  processes  going  on  within  them  are  combined 


DEATH  67 

again  into  starch,  fat  and  proteid.  Thus  they  are  in  condition  once  more  to 
serve  as  food  for  animals  and  thus  the  organic  elements  complete  a  circulation 
between  animals  and  plants,  which  is  interrupted  by  the  circumstance  that  the 
synthesis  going  on  in  plants  can  take  place  only  under  the  influence  of  sun- 
light. The  entire  living  world  represents,  therefore,  a  collective  whole  in  which 
every  living  being  fulfills  its  special  purpose  as  a  link  in  the  chain. 

Eeferences. — W.  Biedermann,  "  Electrophysiologic,"  Jena,  1895. — G.  N.  Cal- 
kins, "  Protozoa,"  New  York,  1901. — //.  J.  Hamburger,  "  Osmotischer  Druck 
und  lonenlehre  in  den  medizinischen  Wissenschaften,"  I-II,  Wiesbaden,  1902- 
1904.— L.  Felix  Hennegmj,  "  Legons  sur  La  Cellule,"  Paris,  1896.— 0.  Hertwig, 
"  Die  Zelle  und  die  Gewebe,"  I-II,  Jena,  1892-98.— i?.  *S'.  Jennings,  "  Behavior  of 
Lower  Organii^ms,"  Carnegie  Institution  Publications,  Xo.  16,  Washington,  1905. 
• — t/.Loe6,"  Studies  in  General  Physiology,"  I-II,  Chicago,  1905. — C.Oppenheimer, 
"  Die  Fermente  und  ihre  Wirkungen :  translated  by  C.  Ainsworth  Mitchell,"  Lon- 
don and  Philadelphia,  1901. — W.  Pfeffer,  "  Pflanzenphysiologie :  translated  by  A. 
J.  Ewart,"  Oxford,  1900.—^.  Strashurger,  F.  Noll,  H.  Schenk,  G.  Karsten,  "  Lehr- 
buch  der  Botanik,"  6th  edition,  Jena,  1904. — M.  Verworn,  "  Allgemeine  Physiolo- 
gic: translated  by  F.  S.  Lee,"  New  York,  1899.—^.  B.  Wilson,  "The  Cell  in 
Development  and  Inheritance,"  2d  edition,  Xew  York,  1900. 


CHAPTER   III 

THE   CHEMICAL   COXSTITUENTS    OF    THE   BODY 

As  already  observed  at  page  20  we  know  nothing  at  all  concerning  the 
chemical  nature  of  the  living  protoplasm.  And  yet  from  the  dead  body  we 
are  able  to  isolate  a  number  of  substances  derived  from  the  living  proto- 
plasm.^ The  most  important  of  these  are  the  simple  and  the  compound  pro- 
teids.  ^Many  substances  occur  also  as  nonliving  cell  contents  and  as  special- 
ized products  or  as  assimilative  products,  part  of  which  are  closely  related 
to  the  proteids,  while  part  have  an  entirely  different  constitution.  Here 
belong  the  gelatin-forming  substances,  fats,  carbohydrates,  the  enzvmes,  the 
products  of  internal  secretions  (cf.  Chapter  XI),  etc.  Finally  there  are  found 
in  the  body  itself  as  well  as  in  its  secretions  and  its  excretions,  numerous 
substances  which  owe  their  origin  to  the  dissimilative  processes  of  the  body. 
These  latter  substances,  as  well  as  the  enzymes  and  the  products  of  the  in- 
ternal secretions,  will  be  discussed  later  in  connection  with  the  physiological 
processes  involved,  but  it  will  be  appropriate  to  treat  here  the  products  of  the 
assimilative  activity  of  the  cells,  and  the  final  decomposition  products  of  pro- 
toplasm so  far  as  they  are  yet  known  to  us. 

§  1.    THE   NITROGENOUS    SUBSTANCES 

A.    THE  SIMPLE  PROTEIDS 

In  the  purest  state  obtainable  proteids  are  colloidal,  slightly  or  not  at  all 
diffusible,  Isevo-rotatory  bodies  of  high  molecular  weight,  without  'imell,  with- 
out taste,  and  as  a  rule  amorphous.  In  the  dry  condition  they  are  either 
white  or  yellowish  powders,  or  are  made  up  of  solid  yellowish  disks  trans- 
parent in  thin  layers.  Crystallized  proteid  has  I)een  obtained  from  plant  seeds 
and  from  egg  albumin  (Hofmeister),  from  whey  (Wichmann),  and  from 
serum  albumin  (Griiber)  (Fig.  38). 

Proteids  exhibit  great  differences  with  respect  to  their  solubility:  some 
are  soluble  in  water,  others  in  solutions  of  neutral  salts,  others  again  in  weak 
alkaline  or  weak  acid  solutions,  and  some  are  not  soluble  in  any  of  these 
fluids. 

The  last  mentioned  can  be  dissolved,  in  part  at  least,  by  means  of  strong 
acids  or  bases,  but  they  at  the  same  time  undergo  a  transformation,  and  in- 
stead of  the  original  proteid  substances  we  then  have  what  are  kno\^Ti  as 
modified  proteids. 

68 


THE  NITROGENOUS  SUBSTANCES 


69 


Fig.    38.- 


Proteids  which  are  dissolved  by  means  of  the  above-named  indifferent 
solvents  can  be  isolated  from  the  tissues  and  fluids  of  the  body  probably 
unchanged,  and  are  therefore  designated  as  native  proteids. 

The  solubility  of  these  substances  is  intimately  related  to  their  acidic  or 
basic  character.  Proteids  react  with  both  acids  and  bases  forming  salt.s,  and 
themselves  therefore  partake  of  the  nature  of  both  bases  and  acids.  The  acidic 
and  basic  characters,  however,  are  not  equally  developed  in  all  proteids.  Those 
in  which  the  two  are  approximately  equal  have  a  neutral  reaction  and  are 
soluble  in  water  and  in  solutions  of  neutral  salts.  Others  react  as  weak  acids, 
are  insoluble  in  neutral  fluids,  but  are  solu- 
ble in  weak  alkaline  solutions,  and  are  pre- 
cipitated from  the  latter  by  weak  acids. 
Others  again  react  as  weak  bases,  are  solu- 
ble in  weak  acids  and  are  precipitated  by 
weak  bases. 

The  proteids  are  precipitated  from  their 
solutions  by  various  reagents,  the  reactions 
being  for  the  most  part  traceable  to  their 
double  character  as  acids  and  bases.  As 
acids  they  form  with  the  salts  of  the  heavy 
metals    precipitates    of    insoluble    proteid- 

metal  salts.  As  bases  they  form  insoluble  salts  with  numerous  weak  acids, 
such  as  tannic  acid,  phospho-tungstic  acid,  hydroferrocyanic  acid  (the  so- 
called  alkaloid  reagents).  Proteids  cannot  be  recovered  unchanged  from  these 
precipitates;  they  have  been  modified  by  the  reactions. 

Proteids  are  precipitated  and  at  the  same  time  modified  by  strong  mineral 
acids  (e.  g..  Heller's  test  with  HXO3)  and  by  alcohol.  They  are  modified 
also  by  heating  their  solutions.  If  a  proteid  in  solution  is  treated  with  a 
concentrated  solution  of  certain  neutral  salts  of  the  alkalies  or  metallic  earths 
— particularly  ammonium,  magnesium  or  sodium  sulphate — or  with  these  salts 
in  substance,  it  separates  out  unmodified — i.  e..  is  "  salted  out."'  The  con- 
centration of  the  neutral  salt  necessary  for  salting  out  varies  greatly  for 
different  proteids,  and  we  have  in  this  circumstance  a  method  of  separating 
different  proteids  in  the  same  solution  from  one  another. 

The  chemical  elements  characteristic  of  simple  proteids  are  C,  IST,  S,  H 
and  0.  A  compound  in  which  no  S  is  found  ought  not  to  be  described  as  a 
true  proteid. 

Tbe  percentage  composition  of  the  proteids,  which  consist  of  these  five 
elements  onlv.  varies  within  rather  narrow  limits: 


Crystals   of   serum-albumin, 
after  Wichmann. 


C  50.6-55.0  per  cent average,  52  per  cent. 

H    6.5-  7.7        "        "  7 

N  15.0-18.5        "         "         16 

S     0.3-  2.2        "        "  2 

0  20.5-23.5        "        "         23 


On  burning  proteid,  various  mineral  constituents  remain  as  the  ash.     These 
it  appears  cannot   be  completely   removed   from   proteid   without   changing   its 


70  THE  CHEMICAL  CONSTITUENTS  OF  THE   BODY 

composition.     Yet  in  none  of  the  analyses  of  proteid  has  the  ash  been  taken 
into  account. 

Investigators  have  subjected  proteids  to  various  treatments,  particularly 
hA'droh'tic  cleavage,  and  have  sought  to  determine  the  resulting  cleavage  prod- 
ucts both  qualitatively  and  quantitatively,  hoping  thus  to  arrive  at  the  con- 
stitution of  the  proteid  molecule.  In  this  way  it  has  been  sho^\^l  that  certain 
groups  of  atoms  are  present  in  all  proteid  substances,  while  others  occur  only 
in  some  and  are  therefore  not  characteristic  of  the  proteids  as  a  group.  Such 
compounds  as  contain  the  smallest  number  of  atomic  groups  and  at  the  same 
time  give  all  of  the  general  proteid  reactions  would  l)e  classed  by  this  method 
as  simple  proteids.  The  compound  proteids  would  be  formed  by  addition 
of  new  groups  of  atoms  to  the  simple  proteid  molecule. 

The  atomic  groups  thus  far  known  as  characterizing  the  proteids  are  the 
following   (Ilofmeister). 

1.  The  guanidin  rest— CNH .  NH^. 

2.  Monobasic  a-monamino  acids  of  the  series  CnHan+iNO,,  such  as  amino- 
acetic  acid  (glycocoll,  CH.,(NH„) -COOH),  amino-propionic  acid  (alanin,  CH3. 
CH(NH,).COOH),  amino-butyrie  acid  (CH3.CH,.CH(NH,)  .COOH),  amino- 
valerianic  acid  (CH,.CIT.CIT.CH(NH,,).COOH),  amino-caproic  acid,  isobutyl- 
amino-acetic  acid  (leucin.  (CH3),.CH.CH,.CH(XIT)  .COOH).  Of  these  com- 
pounds leucin,  glycocoll  and  alanin  occur  most  abundantly,  amino-valerianic 
acid  and  amino-butyric  acid  less  frequently.  Certain  of  them  are  wanting-  in 
various  proteids. 

3.  Monobasic  a-co-diamino  acids  of  the  series  CoHan^aNjO-  :  e.  g.,  the 
a-S-diamino-valerianic  acid  (CH,(NH.,)  .CH.,.CH,.CH(NH,)  .COOH)  and  the 
a-e-diamino-caproic  acid  (lysin,  CH,(XH,)  .CH,.CH,.CH,.  CH(NH,)  .COOH). 
The  former  is  always  associated  with  the  guanidin  rest,  the  compound  being 

described  as  arginin:  NH^   •    ^^^^ „ 

C.NH.CH,.CH,.CIL.Cn(XK,).COOII. 

Arginin  and  lysin  occur  in  varj^ng  proportions  in  all  proteids  (Drechsel,  Hedin, 

Kossel),  although  as  an  exception  one  of  them  may  be  entirely  absent,  as  lysin 

from  zein.     They  are  particularly  abundant  in  the  protamins,  first  obtained  by 

Miescher  from  fish  sperm,  and  described  by  Kossel  as  the  simplest  proteid.    This 

designation,  however,  is  not  admissible  since  protamins  do  not  contain  sulphur. 

4.  A  monobasic  ^-oxy-a-monamino  acid,  namely,  the  /3-oxy-a-amino-propi- 
onic  acid  (serin,  CH,(OH)  .CH(NIT)  .COOH),  has  been  demonstrated  so  far 
in  serum  albumin,  globin  and  edestin,  and  probably  occurs  in  the  other  simple 
proteids,  since  it  was  found  in  casein  and  in  fibroin  of  silk  (Fischer). 

5.  A  monobasic  /3-tbio-a-monamino  acid :  namely,  the  0-thio-a-monamino- 
propionic  acid  (CH,(SH)  .CH(XH,)  .COOH),  corresponding  to  serin,  which 
probably  enters  into  proteids  as  the  disulphide  (cvstin,  C00H.CH(]SrH2) . 
CH,-S-S-CH,.CH(NH,).COOH)  (K.  A.  H.  Morner,  Embden).  Morner  finds 
that  the  total  sulphur  of  keratin  (cow's  horn,  human  hair),  serum  albumin,  and 
serum  globulin  might  occur  as  cystin  groups.  In  the  shell  membrane  of  the  hen's 
egg  as  much  as  three-fourths  of  the  sulphur  are  present  as  cystin,  in  fibrinog-en 
about  one-half,  and  in  egg  albumin  only  about  one-third.  How  the  remaining 
sulphur  is  combined  in  these  and  other  proteids,  we  do  not  know. 

6.  Dibasic  a-monamino  acids  of  the  series  C„H2„4_iN04.  namely,  amino- 
succinic  acid  (aspartic  acid,  COOH.CH,.CH(NH,)  .COOH)  and  amino-pyro- 
tartaric  acid   (glutamic  acid,  COOH.CH,.CR,.CH(NH,)  .COOH).     The  per- 


THE  NITROGENOUS  SUBSTANCES  71 

centage  of  monamino  acids  in  the  proteid  molecule  is  by  no  means  small:  60.2 
per  cent  of  the  total  nitrogen  in  crystallized  serum  albumin,  67.8  per  cent  in 
crystallized  egg  albumin,  55.0  per  cent  in  crystallized  edestin,  68.3  per  cent  in 
serum  globulin   (horse). 

^  7.  Carbohydrate  groups.  In  many  proteids,  but  not  in  all,  there  is  a  nucleus 
which  on  total  cleavage  appears  regularly  as  glucosamin  (CHj(OH)  .CH(OH) . 
CH(OH).CH(OH).CH(XH,).CH:0)  (F.  Miiller).  Besides  this  nucleus,  or 
in  its  place,  nitrogenous  or  nonnitrogenous  carbohydrate  complexes  may  also  be 
present. 

Among  the  simple  native  proteids  there  appears  to  be  only  one  thus  far 
kno\vn,  namely,  edestin,  which  contains  no  carbohydrate  group  in  its  molecule. 
In  the  others  the  number  of  these  groups  varies  considerably.  Crystallized  egg 
albumin  contains  at  least  10.0  to  11.0  per  cent  of  glucosamin,  submaxillary  mu- 
cin 20.8  per  cent  of  reducing  substance,  pseudomucin  from  ovarial  cysts  30.0 
per  cent,  egg  mucoid  34.9  per  cent,  and  the  mucin  of  sputum  36.9  per  cent.  In 
crystallized  serum  albumin  the  content  is  very  small. 

8.  A  monamino  acid  of  the  benzol   series,  namely,  the  para-phenyl-amino- 

propionic  acid  (phenylalanin,/\CH2.CH(NHj)  .COOH)  and 

I    I 

\/ 

9.  The  corresponding  para-oxy-compound,  p-oxy-phenyl-amino-propionic  acid 
(tyrosin,  /^CH,.CH(XHO  .COOH) 

In  most  proteids  tyrosin  occurs  in  far  greater  quantity  than  phenylalanin. 
The  maximal  yield  of  tyrosin  is  1.5  per  cent  in  crystallized  egg  albumin,  2.0 
per  cent  in  serum  albumin,  3.0  per  cent  in  fibrin,  6.3  per  cent  in  thymus  histon 
and  10.1  per  cent  in  zein. 

10.  From  numerous  observations  on  the  cleavage  products  formed  in  putre- 
faction of  proteid,  it  appears  that  an  indol  nucleus  is  present.  It  is  likely  that 
this  nucleus  in  very  small  quantities  is  changed  into  /3-methyl-indol-amino-acetic 
acid  (tryptophan, 

CII 
CH     ^C-CCH, 
CH      C    C.CH.(NHj.COOH 

CH  NH 

Hopkins  and  Cole). 

11.  The  heterocyclic  pyrrolidin  nucleus  is  represented  among  the  cleavage 
products  of  different  proteids  (edestin,  serum  albumin,  serum  globulin,  egg  albu- 
min, fibrin)  by  the  a-pyrrolidin-earboxylic  acid 

CH,-CH, 

CH,    CH.COOH 

NH 
and 

12.  By  the  oxy-a-pyrrolidin-carboxylic  acid 

CH,— CH.OH 

c'h,   c'hcooh 

NH 
(Fischer). 


72 


THE  CHEMICAL  CONSTITUENTS  OF  THE  BODY 


13.  In  many  proteids  the  presence  of  a  hexonc  base,  described  as  histidin, 
CgHgNjO,,   has   been   demonstrated.     It    appeal's   to   be    a    pyrimidin    derivative 

NH-CH, 

HC    CH 

N-C.CH(NH,).COOH. 

In  the  following  table  are  brought  together  after  Ehrstrom  the  most  impor- 
tant nuclei  occurring  in  the  proteid  molecule,  arranged  according  to  the  number 
of  carbon  atoms  which  they  contain. 

C. 


C  :  NH(NH,) 

Guanidin  rest. 


CH,(NH,) 
COOH 

GlycocoU. 


C.HgN.CHCNH,) 
COOH 

Tryptophan. 


C,H,N,.CH(NH,)  (?) 
COOH 

Histidin. 


C,        CH3 


CH(NH,) 
COOH 

Alanin. 


CH,(OH)       Cn,(SH)      C^H^.CH, 
CH(NHJ       CH(NHJ 


COOH 

Serin. 


COOH 

Cystein. 


CH(NH,) 
COOH 

Phenylalanin. 


C.H.O.CH, 

CH(NH,) 
COOH 

Tyrosin. 


c. 


CH, 
CH, 

CH(NH,) 
COOH 

Amino-butyric  acid. 


COOH 
CH, 

CH(NH,) 
COOH 

Aspartic  acid. 


C. 


CH3 

CH, 


CH, 


ch; 

CH(NH,) 
COOH 

Amino- 
valerianic 
acid. 


CH, 
•  CH 
CH, 

CH(NH,) 
COOH 

Leucin. 


COOH 

CH, 

CH, 

CH(NH,) 

COOH 

Glutamic 
acid. 


CH,(NH,) 
CH, 


CH, 
CH, 


CH, 

CH(NH,) 

COOH 

Diamino- 

valerianic 

acid. 


CH, 

CH(NH) 

COOH 

o-Pyrrolidin- 

carboxylic 

acid. 


CH,— 

CH, 

CH(OH) 


CH       (NH) 

COOH 

Oxy-a-Pyrrol- 

idiri-carboxylic 

acid. 


C,        CH,(NH,) 
CH, 
CH, 
CH, 

CH(NH,) 
COOH 

Lysin. 


CH,(OH) 

CH(OH) 

CH(OH) 

CH(OH) 

CH(NH,) 

CH:0 

Qlucosaniin. 


Certain  of  these  groups  can  be  recognized  by  characteristic  color  reactions. 
(1)  The  xanthroprote'ic  reaction  gives  a  yellow  color  with  strong  nitric  acid; 
after  neutralization  with  ammonia  or  a  caustic  alkali,  the  color  passes  over  to 
orange  or  reddish  brown.  The  reaction  depends  upon  the  presence  of  the  ben- 
zol ring  in  the  proteid  molecule  (phenylalanin,  tyrosin,  indol).  (2)  Millon's  reac- 
tion gives  a  red  coloration  to  the  precipitate  or  to  the  fluid,  when  a  solution 
of  mercuric  nitrate  containing  some  nitrous  acid  is  added  to  a  solid  proteid  or 
to   a  proteid  solution.      This    indicates   the  presence   of  the   oxyphenyl   group 


THE   NITROGENOUS  SUBSTANCES  73 

(tyrosin).  (3)  The  reaction  of  Adamhiewicz  gives  a  reddish  violet  color  with 
1  vol.  concentrated  HjSO^  and  9  vol.  acetic  acid  containing  some  glyoxylic  acid, 
and  characterizes  the  indol  group  (tryptophan).  (4)  By  means  of  MoliscWs 
reaction,  which  is  a  violet  color  with  concentrated  HoSO^  and  a-naphthol,  the 
carbohydrate  groups  are  demonstrated,  and  (5)  hy  boiling  with  alkali  and  a 
lead  salt  (formation  of  black  lead  sulphide)  the  cystin  groups  are  detected. 

The  biuret  reaction  gives  a  color  changing  from  red  through  reddish  violet 
to  violet  blue,  on  addition  of  dilute  solution  of  copper  sulphate  to  a  proteid 
solution  previously  alkalized  with  caustic  potash  or  soda  and  then  warmed.  It 
is  very  generally  regarded  as  specifically  characteristic  for  the  proteids.  This 
reaction,  according  to  11.  Schiff,  appears  with  those  substances  which  contain  two 
CO.NH,,  CS.NH,-,  C(NH).NH,-,  or,  under  certain  conditions,  -CH,.NH,- 
groups,  joined  together  by  their  own  C  atoms,  or  by  a  C  atom  in  a  CH-, 
CH(OH)-,  CO  group,  or  finally  by  a  N  atom  in  an  NH  group.  However,  this 
reaction  is  not  a  positive  criterion  of  the  proteid  nature  of  a  body,  for  on  the 
one  hand  substances  of  so  simple  a  structure  as  the  g'lycinamid  give  it,  and  on 
the  other,  it  is  wanting  with  the  desamido-albumin  (obtained  by  the  action  of 
nitrous  acid)  where  all  the  carbon  nuclei  of  the  proteid  are  present. 

As  a  matter  of  fact  there  is  at  this  time  no  physical  or  chemical  feature 
by  which  one  can  decide  positively  whether  a  compound  is  to  be  described  as 
a  proteid  or  not ;  and  for  this  reason  certain  substances  are  by  some  enumerated 
among  the  proteids,  while  by  others  their  proteid  nature  is  positively  denied. 

After  discussing  exhaustively  all  the  facts  obtained  from  the  cleavage 
products  of  proteids,  Hofmeister  reaches  the  conclusion  that  proteids  arise 
chiefly  by  condensation  of  the  a-amino  acids,  union  taking  place  regularly 
and  repeatedly  by  means  of  the  CO-NH-CH  =  groups.  He  remarks,  how- 
ever, that  this  conception  of  the  subject  does  not  explain  all  forms  of  linkage 
in  proteid  and  that,  considering  our  incomplete  knowledge  of  the  proteid 
molecule,  other  relations  are  by  no  means  excluded. 

A  rational  classification  of  the  simple  proteids  can  only  be  carried  out 
when  we  possess  more  exact  knowledge  of  their  constitution,  and  are  thus 
able  to  state  what  nuclei  occur  in  each  individual  proteid  and  in  what  quan- 
tity. This  is  far  from  possible  as  yet,  and  with  most  proteids  we  are  not 
even  in  position  to  say  whether  they  are  actually  chemical  individuals  or  are 
mixtures  of  different  substances.  We  are  compelled  therefore  to  classify  the 
proteids  according  to  their  relative  solubility  and  precipitative  reactions.  This 
is  by  no  means  a  scientific  principle  of  classification,  but  it  is  justifiable  on 
purely  practical  grounds. 

Accordingly  simple  proteids  have  been  divided  into  the  following  groups: 

A.  Native  proteids.  These  are  obtained  from  the  tissues  and  fluids  of  the 
body  by  neutral  chemical  reagents:  the  albumins,  globulins  and  mucins  are 
the  most  important. 

1.  Albumins:  soluble  in  water;  not  precipitated  from  aqueous  solutions  by 
small  quantities  of  acids  or  alkalies,  but  precipitated  by  larger  quantities  of 
certain  acids  and  metallic  salts.  On  boiling,  the  solutions  are  coagulated  if 
salts  are  present.  They  are  precipitated  by  XaCl  or  by  MgSO^  only  on  addition 
of  acetic  acid.  They  are  not  salted  out  by  half-saturation  of  their  solutions 
with  ammonium  sulphate,  but  are  so  separated  with  greater  concentration  of 
the  salt. 


74  THE  CHEMICAL  CONSTITUENTS  OF  THE  BODY 

Albumins  occur  chiefly  in  the  animal  fluids.  To  this  group  belong  serum 
albumin,  egg  albumin,  albumin  of  milk,  etc. 

2.  Globulins :  insoluble  in  water;  soluble  in  dilute  salt  solutions,  from  which 
they  are  precipitated  by  further  dilution.  Solutions  are  coagulated  by  boiling. 
Soluble  in  water  on  addition  of  very  small  quantities  of  acid  or  alkali,  whence 
they  are  precipitated  by  neutralization.  Likewise  when  solution  is  effected  by 
minimal  quantities  of  alkali,  they  are  precipitated  by  carbon  dioxide  and  are 
redissolved  by  excess  of  the  same.  Complete  precipitation  by  saturation  with 
MgSO^,  partial,  by  saturation  with  NaCl.  They  are  salted  out  by  half-satura- 
tion with  ammonium  sulphate. 

This  characterization  of  the  globulins  however  is  no  longer  sufiicient,  for 
it  appears  from  several  recent  researches  that  among  the  compounds  which  are 
precipitated  by  fractional  salting  out  of  the  globulins  in  the  blood,  there  occur 
substances  which  are  neither  insoluble  in  water  nor  precipitated  from  their 
solutions  with  carbon  dioxide.  The  only  positive  distinction  between  albumins 
and  globulins  therefore  consists  in  their  relation  to  neutralization,  and  especially 
to  ammonium  sulphate:  the  globulins  are  precipitated  by  half-saturation,  the 
albumins  are  not. 

The  globulins  also  occur  chiefly  in  the  fluids  of  the  animal  body;  but  they 
may  be  obtained  from  the  tissues.  To  this  group  belong  fibrinogen  and  serum 
globulin  of  the  blood,  myosin  and  myogen  of  the  muscles,  etc. 

3.  The  true  mucins  are  substances  insoluble  in  water  and  in  solutions  of 
neutral  salts,  but  soluble  with  very  little  alkali.  The  solutions  are  viscous,  and 
form  with  acetic  acid  a  precipitate  not  soluble  in  an  excess  of  the  acid.  Chem- 
ically the  mucins  are  characterized  by  their  high  content  of  the  carbohydrate 
groups.  The  true  mucins  occur  in  the  submaxillary  saliva,  in  the  umbilical  cord 
(Wharton's  jelly),  etc. 

The  so-called  mucoids  are  distinguished  from  the  true  mucins  in  certain 
respects  which  are  not  yet  definitely  understood.  They  are  obtained  from  the 
ovarial  fluids,  from  the  cornea,  the  vitreous  body,  the  urine,  etc. 

It  is  also  asserted  that  the  mucins  contain  fat.  If  the  submaxillary  mucin 
be  first  extracted  with  ether  and  be  then  digested  with  pepsin-HCl,  one  can 
later  extract  with  ether  more  than  three  per  cent  fat  from  the  substance 
(NerkingO. 

B.  Simple  proteids  which  can  he  split  off  from,  compound  proteids.  Here 
belong  globin  from  ha?nioglol)in,  the  proteids  from  the  mucins,  etc. 

C.  The  native  proteids  are  changed  by  the  action  of  alkalies  and  acids  in 
sufficient  concentration  into  alkali  and  acid  albuminates  (syntonin).  In  the 
formation  of  alkali  albuminates  some  nitrogen  is  split  off  from  the  proteid, 
and  with  stronger  action  of  the  alkali  some  sulphur  also  is  separated. 

In  spite  of  their  different  modes  of  formation,  and  in  spite  of  different 
chemical  constitutions,  the  alkali  and  acid  albuminates  are  very  closely  related 
to  each  other.  In  water  or  dilute  NaCl  solution  they  are  almost  insoluble,  but 
are  soluble  on  addition  of  small  quantities  of  acid  or  alkali.  Such  a  solution 
(even  if  neutral)  is  not  coagulated  on  boiling,  without  the  addition  of  sufficient 
quantity  of  neutral  salts.  Solutions  of  albuminates  are  precipitated  at  room 
temperature  by  neutralization,  by  excess  of  mineral  acids,  by  many  metallic 
salts.  An  acid  solution  of  albuminate  is  readily  precipitated  by  NaCl,  an  alka- 
line solution  only  with  difficulty. 

D.  Under  the  influence  of  the  digestive  fluids  there  are  formed  by  hydro- 
lytic  cleavage  of  the  proteids  a  number  of  new  substances,  the  so-called  albu- 


THE   NITROGENOUS  SUBSTANCES 


75 


moses  and  peptones  which  will  be  fully  treated  in  our  study  of  digestion 
(Chapter  VII). 

E.  Finally,  we  should  mention  the  compounds  arising  hy  coagulation  of 
the  soluble  proteids,  whose  properties  are  less  well  known  than  those  of  other 
proteid  substances.  To  this  group  belongs  also  the  fibrin  formed  in  the  coagu- 
lation of  the  blood  by  splitting  of  fibrinogen  (see  Chapter  V). 

In  order  to  give  a  more  exact  idea  of  the  quantitative  composition  of  the 
simple  proteids,  we  have  brought  together  in  the  following  table  the  results  of 
analyses  by  Aberhalden. 


Percentage  of 

In 
Casein. 

In 
Gelatin. 

In 

Elastin. 

In 

Globin  from 

Hsema- 

globin. 

In 
Edestin. 

Glycoeoll 

0 
0.9 

10.5 
3.1 
3.2 

10.7 
1.2 
0.065 
0.23 
0.25 
4.5 
1.0 
5.80 
2.59 
4.84 
1.5 

16.5 
0.8 
2.1 
5.1 
0.4 
0.88 
0.56 

s'.o" 

2!75 
7.62 
0.40 

25.75 
0.58 

21.38 
1.74 
3.89 
0.76 

i!6' 

6  ".34 

0 

4.19 
29.04 
2.34 
4.24 
1.73 
4.43 
0.31 
0.56 
1.04 
1.33 

4*.  28 
10  90 

5.42 
* 

3  8 

Alaniii 

3  6 

Leucin 

20  9 

o- Pyrrol idiii  carboxylic  acid  .... 
Phenvlalanin 

1.7 
2  4 

Glutamic  acitl 

6  3 

Aspartic  acid 

4  5 

C!vstin  ...   

0  25 

Serin 

0  38 

Oxy-a-PyrroIidiii  carboxylic  acid 

Tyrosiu 

Amino-valerianic  acid 

2.0 

2.13 
* 

Lysin 

Histidin 

2.0 

1  0 

Artrinin 

11  7 

Tryptophan  

* 

* 

Present. 

B.    THE   COMPOUND   PROTEIDS 

Simple  proteids  are  distinguished  largely  by  the  fact  that  they  can  unite 
with  each  other  as  well  as  with  other  substances  to  form  new  compounds. 
The  atomic  group  conjoined  with  the  proteid  in  the  latter  case  is  described 
by  Kossel  as  the  prosthetic  group.  Such  conjugated  proteids  can  be  isolated 
from  the  animal  fluids  and  tissues  in  great  numbers.  They  are  classified 
according  to  the  nature  of  the  conjugant  into  the  following  groups : 

A.  Hccmoglobins:  These  represent  compounds  of  a  basic  proteid  body, 
globin,  ^vith  the  acid,  iron-containing,  pigment  hgemochromogen,  and  will  be 
discussed  at  length  in  Chapter  Y. 

B.  NiirJco-albamins:  phosphorus-containing  proteids  which  are  character- 
ized by  the  fact  that  on  digestion  with  pepsin-HCl  a  portion  remains  tem- 
porarily insoluble.  This  portion,  like  the  soluble  portion,  contains  phosphorus, 
and  is  described  as  psendonuclein  or  paranuclein.  It  is  distinguished  from 
the  true  nucleins  (see  below)  by  not  containing  any  purin  bases. 

To  the  nueleo-albumins  belong  the  casein  of  milk,  whose  properties  will  be 
fully  considered  later  (Chapter  XXVI)  ;  vitellin  found  in  the  yolk  of  a  bird's 
ef^g;  various  proteids  of  the  bile,  the  kidneys,  the  mucous  membrane   of   the 
bladder,  etc. 
7 


76  THE  CHEMICAL  CONSTITUENTS  OF  THE  BODY 

Little  is  known  yet  with  regard  to  the  constitution  of  paranuclein,  or  the 
form  in  whicli  pliosphorus  is  found  either  in  it  or  in  the  nucleo-alburains 
in  general.  Levene  and  Alsberg  however  have  isolated  an  acid  (vitellinic 
acid)  from  vitellin  which  possibly  represents  a  compound  of  proteid  with 
phosphoric  acid  in  the  form  of  an  ester.  Like  the  corresponding  pseudo- 
nuclein  this  acid  contains  iron  in  organic  combination,  which,  as  Bunge  be- 
lieves, may  serve  for  the  formation  of  the  iron-containing  haemoglobin  of  the 
young  bird.  Likewise  from  casein  a  paranucleinic  acid  has  been  obtained  by 
Salkowski,  from  which  orthophosphoric  acid  can  be  split  off. 

Neither  casein  nor  vitellin  contains  any  carbohydrate  group.  Twenty-seven 
and  one-tenth  per  cent  of  the  total  nitrogen  in  cow's-milk  casein  occurs  as 
diamino-X,  and  sixty-two  per  cent  as  monamino-N.  The  maximal  yield  of 
tyrosin  from  casein  is  4.5  per  cent.  Only  about  one-tenth  of  the  sulphur  of 
casein  is  present  in  the  form  of  cystin  compounds  (Morner). 

C.  A^iicleins:  compounds  of  proteid  with  the  nucleic  acids. 

The  nucleic  acids  are  phosphorus-containing  substances  which  yield  on 
decomposition,  besides  phosphoric  or  metaphosphoric  acid :  different  charac- 
teristic purin  bases;  the  pyrimidin  derivatives  thymin,  uracil,  and  cytosin; 
and  finally  carbohydrates.  Moreover  they  are  dextro-rotatory,  notwithstand- 
ing that  nucleins  and  even  the  nucleo-proteids  (see  below)  are  laevo-rotatory. 

1.  The  purin  bases  (called  also  alloxuric,  xanthin,  or  nuclein  bases)  are 
derivatives  of  purin,  which,  according  to  Fischer,  consists  of  a  pyrimidin 
nucleus  and  a  glyoxalin  nucleus  joined  to  the  former  in  the  4,  5  position, 

(1)N==CH(6) 

(2)HC    (5)C-^NH(7) 
II  II  >CH(8) 

(3)N C(4)— N(9). 

Different  hydrogen  atoms  of  this  structure  may  be  replaced  by  hydroxyl,  amid, 
or  alkyl  groups.  The  purin  bases  are:  xanthin  (2.6.dioxypurin,  CsHjiN^iOj) ; 
guanin  (2.amino-6.oxypuriu,  C5H5X5O) ;  hypoxanthin  (G.oxypurin,  CjILX,©) : 
and  adenin  (G.amino-purin,  C-H5X5).  In  guanylic  acid  from  the  pancreas  only 
guanin  is  found.  Several  purin  bases  occur  in  the  other  nucleic  acids  and  in 
the  nucleic  acid  from  yeast  all  of  them  are  found. 

2.  Thymin,  discovered  by  Kossel  in  the  nucleic  acid  of  the  thymus,  is 
5.methyl-2.6.dioxy-pyrimidin, 

NH— CO 

OC     C-CH3 
NH— CH. 

It  has  been  found  also  in  the  nucleic  acids  of  the  spleen,  of  fish  sperm,  of  the 
brain,  liver  and  pancreas. 

3.  Uracil,  2.6-dioxy-pyrimidin, 

NH— CO 

OC     CH 

I       II 

NH— CH 

occurs  in  the  nucleic  acid  of  yeast  and  in  those  of  the  pancreas,  thymus,  herring 
sperm,  etc.  (Ascoli). 


THE  NITROGENOUS  SUBSTANCES  77 

4.  Cytosin,  6,amino-2.oxj--pyrimidin, 

NH— C.NH, 

OC    CH 

I      II 

NH— CH 

(Kossel)  has  an  equally  wide  distribution. 

5.  In  nearly  all  of  the  nucleic  acids  there  is  a  carbohydrate,  sometimes  a 
pentose  (1-xylose),  sometimes  a  hexose. 

Nothing  definite  is  known  concerning  the  manner  in  which  phosphorus  is 
combined  in  the  nucleic  acids. 

One  can  obtain  a  fair  idea  of  the  complexity  of  nucleic  acids  from  the  follow- 
ing structural  formula  for  a-guanylic  acid  given  by  Bang. 

OH    OH 
C,H,X -0-P-0-C,H,(OH).  C.H^O, 

Guanin  L  Glycerin        Pentose 

C,H,N,-0-P-0-C3H,(0H).  C,H,0, 

O   O 

C,H,N,-0-P-0-C3H,(0H).  C,H,0, 

6 

C,H,N -0-P-0-C3H,(0H).  C,H,0, 

OH^OH. 

The  simplest  nucleins  are  the  saltlike  compounds  of  nucleic  acids  with  the 
protamins  and  histons.  These  simple  proteids  are  closely  related  chemically,  and 
there  seems  to  be  a  close  relationship  physiologically  as  well;  for  whereas  one 
finds  histons  in  unripe  fish  sperm,  in  the  ripe  sperm  protamins  are  found. 

The  nucleins  finally  unite  with  proteid  to  form  nucleo-proteids,  which,  it 
appears,  occur  in  (dead)  cell  protoplasm  and  especially  in  the  (dead)  cell 
nucleus,  where  Miescher  first  demonstrated  them.  Their  composition  is  very 
complicated,  and  they  represent  the  first  decomposition  products  of  the  living 
substance  thus  far  known.    Some  of  them  appear  to  contain  iron. 

D.  Chondro-proteids.  Compounds  of  proteid  with  chondroitin-sulphuric 
acid  (CigH.-XSOi-  Schmiedeberg)  and  found  in  the  mucoid  of  cartilage, 
amyloid,  in  tendon  mucin,  and  presumably  in  other  mucous  substances. 


C.    SUBSTANCES   RESEMBLING   PROTEIDS 

The  following  substances  are  known  to  be  closely  related  to  proteids,  from 
the  fact  that  on  decomposition  they  yield  in  general  the  same  substances  as  do 
proteids.  It  is  possible  that  some  of  them  should  be  enumerated  among  the 
true  proteids. 

A.  Protamins  (see  page  TO). 

B.  Keratin,  a  substance  rich  in  sulphur  (2.5-5  per  cent)  ;  amorphous,  in- 
soluble in  water,  alcohol,  ether  and  the  digestive  fluids;  contained  in  horn, 
epidermis,  hair,  nails,  etc.  On  heating  with  water  in  closed  tubes  it  yields 
albumoses  and  peptones.  It  develops  the  characteristic  smell  of  burnt  horn 
when  ignited. 


78  THE  CHEMICAL  CONSTITUENTS  OF  THE  BODY 

About  the  same  products  (with  the  exception  of  carbohydrates)  have  been 
obtained  by  cleavag-e  of  the  keratin  molecule,  as  from  the  typical  proteids. 

C.  Albumoid,  a  substance  obtained  from  the  cartilage  of  the  trachea,  which 
stands  in  certain  respects  between  the  tnie  proteid  and  keratin.  Another  albu- 
moid occurs  in  the  fibers  of  the  crystalline  lens. 

D.  Elastin,  a  yellowish  white,  amorphous  substance  containing  only  a  small 
quantity  of  sulphur;  insoluble  in  water,  alcohol  and  ether;  and  attacked  by 
chemical  reagents  with  great  difficulty.  It  occurs  in  connective  tissue  and  espe- 
cially in  the  ligamcntum  nuchie. 

Among  the  cleavage  products  of  proteid  which  have  been  obtained  from 
elastin,  are  the  guanidin  rest,  leucin,  diamino  acids,  tyrosin  and  indol,  but 
neither  glutamic  acid  nor  carbohydrates. 

E.  Collagen,  a  sulphur-containing  substance;  insoluble  in  water,  salt  solu- 
tions, and  very  weak  acids  and  bases,  but  swelling  up  in  less  dilute  acids;  it  is 
the  chief  constituent  of  fibrillar  connective  tissue  and  occurs  in  bone  (ossein) 
and  other  tissues. 

When  collagen  is  boiled  for  a  long  time  with  water,  it  passes  over  into 
gelatin  (glutin). 

F.  Gelatin,  a  colorless,  amorphous,  nondiffusible  substance  of  about  the 
same  chemical  constitution  as  collagen.  It  swells  up  in  cold  water  and  is  dis- 
solved in  warm  water.     On  cooling  the  solution  sets  into  a  jellylike  mass. 

Neither  carbohydrates,  cystin,  serin,  tyrosin,  nor  indol  occurs  in  the  mole- 
cule of  gelatin.  Sixteen  and  six-tenths  per  cent  of  the  total  nitrogen  is  present 
as  arginin,  and  not  less  than  8.4  per  cent  in  the  form  of  g'lycocoU. 

Gelatin  solutions  are  not  coagulated  on  boiling,  and  are  not  precipitated  by 
mineral  acids,  acetic  acid,  alum,  lead  acetate  or  metallic  salts.  They  are  pre- 
cipitated by  tannic  acid  in  the  presence  of  salt,  by  acetic  acid  and  iSTaCl  in 
substance,  by  mercuric  chloride  in  the  presence  of  HCl  and  XaCl. 

By  prolonged  cooking  gelatin  is  transformed  into  a  nongelatinizing  modi- 
fication. It  is  acted  upon  by  the  digestive  enzymes  yielding  gelatin  albumoses 
and  peptones. 

G.  Reticulin,  a  constituent  of  the  connective  tissue  framework,  of  the  lymph 
glands,  of  the  spleen,  of  the  intestinal  mucosa,  the  liver,  kidneys  and  alveoli  of 
the  lungs. 

D.  OTHER  NITROGENOUS  SUBSTANCES 

Among  the  remaining  nitrogenous  substances  which  may  be  isolated  from 
animal  tissues,  lecithin  should  be  especially  mentioned.  It  is  found  in  almost 
all  animal  and  plant  cells,  especially  in  the  brain,  the  nerves,  the  blood  cor- 
puscles and  in  egg  yolk ;  it  occurs  also  in  almost  all  animal  fluids. 

Lecithin    represents    an    esterlike    compound    of    a    base,    cholin,    oxyethyl- 

GTT  Oil 
trimethyl-ammonium-hydroxide,      nu  y/^njx  ^    qH     ^^*^     glycerin-phosphoric 

acid  which  is  united  with  two  fatty  acid  radicles  into  a  glyceride.  There 
are  different  lecithins  therefore  according  to  the  kind  of  the  fatty  acid 
radicles.      The   stearic-palmitic   acid    lecithin    to    be   obtained    from    egg   yolk, 

0.000,333 

C3H5O.  COCi-.II,,.  (0113)3         -^  ^TT  takes  the  form  of  a  crystalline,  waxlike  mass 

O.PO(OH).O.OH,OH/^-^^' 
readily  soluble  in  alcohol  and  ether.    With  water  it  swells  up  forming  an  opales- 
cent solution,  from  which  it  is  precipitated  again  hy  means  of  different  salts. 
Lecithin   is   found   in   several  cases   in  loose  combination   with   proteid   or 


THE  NONNITROGENOUS  SUBSTANCES  79 

other  substances.  In  protagon  which  occurs  in  the  wliite  substance  of  the  cen- 
tral nervous  system,  and  probably  represents  a  mixture  of  substances,  lecithin 
is  bound  up  with  the  cerebrosides,  ]^-containing*,  phosphorus-free  substances, 
which  on  boiling  with  dilute  mineral  acids  yield  a  reducing  sugar.  Ovo- 
vitillin  is  a  combination  of  proteid  and  lecithin,  and  similar  compounds  are  said 
to  be  obtained  as  insoluble  residues  from  peptic  digestion  of  the  gastric  mu- 
cosa, liver,  kidneys,  etc.  These  lecithin  albumins  represent  therefore  a  new 
group  of  proteids  (cf.  under  B).  Jecorin,  which  has  been  demonstrated  in  the 
liver  and  in  the  blood,  is  a  combination  of  lecithin  and  glucose. 

§  2.    THE   NONNITROGENOUS    SUBSTANCES 

A.    FATS 

The  fats  are  esters  of  the  triatomic  alcohols,  the  gh^cerins,  with  mono- 
basic fatty  acids,  chief  of  which  in  the  animal  fats  are :  stearic  acid,  CigHoeOo, 
palmitic  acid,  C^JI^oO^,  and  oleic  arid,  CigHj^O,.  The  triglycerides  of  the 
first  two — stearin,  Cs'ii..{C\sR.,fi2).,.,  and  palmitin,  C^R,^.(C^,^Ro.^O.)^ — melt 
only  at  a  temperature  far  above  that  of  the  body.  The  glyceride  of  oleic  acid, 
olein,  03X15.(018113302)3,  is  on  the  other  hand  fluid  at  ordinary  temperatures 
and  solidifies  in  the  form  of  crystalline  needles  only  at  —  5°  0.  The  melting 
point  of  a  mixture  of  the  three  glycerides  must  therefore  depend  upon  the  rela- 
tive content  of  olein — the  greater  the  relative  quantity  of  this  fat,  the  lower  is 
the  melting  point  of  the  mixture.  Moreover  the  melting  point  of  fat  shows 
considerable  variation  not  only  in  different  species  of  animals,  but  also  in 
different  parts  of  the  same  individual,  which  means  that  the  relative  quantity 
of  olein  present  varies  considerably.  Traces  of  fatty  acids  are  also  found  in 
animal  fat. 

The  following  reactions,  among  others,  serve  to  distinguish  the  different 
fats:  (1)  the  arid  equivalent,  which  is  the  measure  of  the  content  of  free  acid  in  a 
fat,  and  is  obtained  by  titration  of  the  fat  dissolved  in  alcohol  ether  with  n/10 
alcoholic  caustic  potash;  (2)  The  saponification  equivalent — i.e.,  the  number  of 
mg.  of  KOH  combined  with  fatty  acid  in  saponification  of  1  g.  of  the  fat  with 
alcoholic  caustic  potash;  (3)  The  Reichert-Meissl  equivalent,  which  gives  the 
amount  of  volatile  fatty  acid  obtained,  when,  after  saponification,  the  fat  is 
distilled  off  in  the  presence  of  a  mineral  acid;  (4)  The  iodine  equivalent — i.e., 
the  quantity  of  iodine  taken  up  by  a  fat,  and  serving  as  the  measure  of  the 
content  of  olein. 

In  the  body  fat  is  to  be  found  for  the  most  part  inclosed  in  the  cells  of 
the  fatty  tissues.  These  represent  in  fact  a  kind  of  storehouse  for  fats  (cf. 
Chapter  lY).  It  occurs  also  in  very  small  quantities  in  the  blood  and  in 
other  fluids  of  the  body. 

Fats  are  insoluble  in  water,  are  dissolved  by  boiling-hot  alcohol,  but  are 
precipitated  again  on  cooling.  They  are  readily  soluble  in  ether,  benzol  and 
chloroform.  On  boiling  with  caustic  alkalies  they  are  decomposed  and  are 
split  into  glycerin  and  fatty  acids,  the  latter  of  which  unite  with  the  alkali 
to  form  soap.  The  fatty  acids  are  set  free  from  the  soap  by  strong  acids. 
Like  the  neutral  fats  they  are  soluble  in  ether,  but  this  is  not  the  case  with 
soaps. 


80  THE  CHEMICAL  CONSTITUENTS  OF  THE  BODY 


B.    CHOLESTERIN 

Cholesterin  is  a  monatomic  alcohol,  C^jH^^OH,  which  occurs  especially  in 
certain  biliary  concretions,  also  in  the  brain,  in  nerves  and  in  animal  cells  gen- 
erally. From  an  alcoholic  solution  it  crystallizes  in  the  form  of  leaflets  which 
have  the  appearance  of  mother-of-pearl.  With  the  higher  fatty  acids  cholesterin 
forms  esters,  which,  unlike  the  fats,  are  very  resistant  toward  decomposing 
reagents  and  are  therefore  specially  suitable  for  protection  to  the  skin,  being 
found  on  both  hair  and  feathers.  Lanolin,  a  compound  of  this  kind  prepared 
from  wool  fat,  has  found  wide  practical  use. 


C.    CARBOHYDRATES 

The  name  carbohydrates  i?  applied  to  substances  composed  of  C,  H,  and 
0,  in  which  tlie  H  and  0  are  present  in  the  proportions  to  form  water.  This 
definition  however  is  not  sufficient,  for  there  are  substances  with  the  same 
relative  quantities  of  H  and  0  which  are  not  carbohydrates;  and  for  other 
reasons  it  cannot  be  regarded  as  satisfactory  from  a  scientific  point  of  view. 
A  perfectly  satisfactory  definition  of  carbohydrates  has  not  yet  been  given; 
they  are  characterized  only  as  aldehyde  or  ketone  derivatives  of  polyhydric 
alcohols. 

The  carbohydrates  are  divided  into  three  chief  groups,  namely,  monosac- 
charides, disaccharides  and  polysaccharides,  in  each  of  which  are  found  sev- 
eral familiar  substances. 

A.  The  monosaccharides  are  the  direct,  isomeric  or  stereo-isomeric  alde- 
hydes or  ketones  of  the  corresponding  alcohols.  They  occur  ready  formed  in 
nature,  and  have  also  been  prepared  s3Tithetically. 

The  monosaccharides  most  interesting  to  us  in  tkis  connection  are  the 
hexoses,  CgHj^Or, :  dextrose,  mannose,  galactose,  and  levulose,  which  are  the  first 
oxidation  products  of  the  stereo-isomeric  hexatomic  alcohols :  sorbite,  raannite, 
and  dulcite.  The  latter  have  the  following  constitution:  CH„.OH.(CH.OH),. 
CH,.OH.  Dextrose,  mannose,  and  galactose  are  the  respective  aldehydes  of  these 
alcohols,  CH.,.OH.(CH.OH),.CHO;  levulose  is  the  ketone  of  mannite,  CH.. 
0H.(CH.0H)3.C0.CH,0H. 

The  following  reactions  are  common  for  all  these  substances :  They  are 
directly  fermentable,  and  under  the  influence  of  the  yeast  plant  are  decom- 
posed into  CO,  and  alcohol:  C„H,A  =  2C,H,.0H  +  2C0,.  They  are  easily 
oxidized  and  hence  reduce  the  metallic  oxides  on  heating  in  alkaline  fluids. 
This  property  is  made  use  of  in  quantitative  determinations  of  the  monosaccha- 
rides. They  are  for  the  most  part  cr\-stalline  substances  of  a  sweetish  taste; 
readilj^  soluble  in  water,  diificultly  soluble  in  alcohol.  The  hexoses  occurring  in 
nature,  in  solutions  rotate  the  plane  of  polarized  light  either  to  the  right  or  to 
the  left.     This  property  also  is  valuable  for  their  quantitative  determination, 

1.  Dextrose  (synonyms:  grape  sugar,  glucose)  occurs  in  sweet  fruits  (e.g., 
grapes)  and  in  honey.  Under  normal  circumstances  dextrose  is  found  in  small 
quantities  in  the  blood  and  lymph.  In  diabetes  its  quantity  in  these  fluids  is 
greater,  and  it  is  found  in  large  quantities  in  the  urine.  Dextrose  rotates  the 
plane  of  polarized  light  to  the  right. 

2.  Levulose  (synon:vTns:  fruit  sugar,  fructose)  occurs  together  with  dextrose 
in  sweet  fruits  and  in  honey.    It  rotates  the  plane  of  polarized  light  to  the  left. 


THE  NONNITROGENOUS  SUBSTANCES  81 

Of  the  other  monosaccharides  the  pentoses,  CsHjoOj,  have  been  demonstrated 
in  animal  fluids  (urine)  and  among  the  cleavage  products  of  animal  substances. 
Arabinose,  found  in  the  urine,  and  xylose  in  the  pancreas  are  the  most  important 
pentoses.  They  do  not  ferment  under  the  influence  of  the  yeast  plant;  but 
with  a  certain  other  fungus,  not  definitely  determined,  Salkowsky  obtained  a 
large  quantity  of  alcohol  from  1-arabinose. 

B.  The  disaccharides  are  anhydric  compounds  of  two  molecules  of  mono- 
saccharides— e.  g.,  2C6Hi20g  =  Cj^HjoOii  -|-  H2O.  On  boiling  with  dilute 
mineral  acids  they  break  up  with  the  absorption  of  water  into  monosac- 
charides. The  most  important  members  of  this  group  are  saccharose  (cane 
sugar),  lactose  (milk  sugar)  and  maltose  (malt  sugar),  all  having  the 
formula  C^oH^oOn. 

The  disaccharides  are  crystalline  bodies  of  a  sweetish  taste,  readily  soluble 
in  water.  Lactose  and  maltose  reduce  an  alkaline  copper  solution,  saccharose 
does  not.  By  boiling  with  dilute  mineral  acids  and  by  the  ag'ency  of  certain 
enzymes  the  disaccharides  take  up  one  molecule  of  water  and  split  into  two 
molecules  of  monosaccharides  thus :  saccharose  into  dextrose  and  levulose ;  lactose 
into  dextrose  and  galactose;  maltose  into  two  molecules  of  dextrose. 

Saccharose  is  dextro-rotatory;  on  its  cleavage  into  dextrose  and  levulose  it 
becomes,  on  account  of  the  stronger  rotating  power  of  levulose,  laevo-rotatory. 
For  this  reason  the  cleavage  of  saccharose  is  called  inversion. 

C.  The  polysaccharides,  n(C,.}I^f^O-),  like  the  disaccharides  are  regarded 
as  anhydrides  of  the  monosaccharides,  but  they  have  their  origin  in  the  union 
of  many  molecules  of  the  latter  and  have  a  high  molecular  weight,  which 
varies  widely. 

The  polysaccharides  have  no  sweetish  taste  and  for  the  most  part  are  amor- 
phous. Some  are  soluble  in  water,  others  swell  up  in  water,  while  still  other 
members  of  this  series  are  not  visibly  changed  by  water.  By  various  means  all 
of  them  can  be  transformed  by  absorption  of  water  into  monosaccharides. 

The  polysaccharides  are  divided  into  three  chief  groups :  starches,  gums, 
and  cellulose. 

1.  The  starches  are  not  directly  fermentable  and  do  not  reduce  alkaline  copper 
solutions.     To  these  belong : 

(a)  Vegetable  starches  (amylum).  These  are  found  in  many  plant  cells  laid 
down  in  the  form  of  microscopic,  round  or  oblong  granules  which  have  an  organic 
structure  and  are  insoluble  in  cold  water.  On  heating  with  water  they  swell  up 
at  50°,  burst  and  partially  dissolve,  forming  a  slimy  solution,  known  as  starch 
paste,  which  can  be  filtered.  The  soluble  part  is  called  starch  granulose,  the  in- 
soluble part  starch  cellulose.  On  boiling  with  dilute  acids  starch  is  changed  first 
into  dextrin  (see  below)  and  later  into  dextrose.  By  digestion  with  saliva  or 
pancreatic  juice,  or  through  the  influence  of  malt-diastase  it  is  split  into  dextrin 
and  maltose  (cf.  Chapter  YII). 

(6)  Glycogen  is  an  animal  starch  which  has  a  very  wide  distribution  in  the 
animal  body.  It  is  found  in  almost  all  the  tissues  of  the  body,  but  in  largest 
quantities  in  the  liver  and  in  the  muscles;  it  is  a  constituent  of  embryonic  tissues 
especially  and  all  others  in  which  an  active  cell  formation  is  taking  place.  Gly- 
cogen is  an  amorphous,  tasteless  and  odorless  white  powder;  with  water  it  forms 
an  opalescent,  dextro-rotatory  solution.  It  is  changed  by  diastatic  enzymes  into 
maltose  or  dextrose  according  to  the  nature  of  the  enzyme. 


82 


THE  CHEMICAL  CONSTITUENTS  OF  THE  BODY 


2.  Gums  are  amorphous,  transparent,  tasteless  and  odorless  substances  which 
with  cold  water  fonn  viscous  fluids.  They  are  very  widely  distributed  in  the 
plant  kingdom. 

(a)  Among'  the  gums  the  dextrins  claim  our  chief  interest  here,  for  thej'  are 
formed  as  intermediate  products  in  the  transformation  of  starch  in  the  alimen- 
tary canal.  They  are  obtained  also  by  heating  starch  up  to  200°-210°  C.  In 
these  transformations  of  starch  a  series  of  dextrins  is  formed  which  have  smaller 
and  smaller  molecular  weights.  The  dextrins  are  white  or  yellowish  white,  amor- 
phous, gumlike  masses  whose  aqueous  solutions  are  dextro-rotatory.  They  are 
not  directly  fermentable. 

(h)  An  animal  gum  is  said  to  be  split  off  from  mucin  through  the  influence  of 
superheated  steam  and  of  alkalies.  This  is  not  true,  however,  for  all  mucins,  for 
several  kinds  yield  gumlike  substances  which  represent  nitrogenous  bodies  de- 
rived from  the  carbohydrates. 

3.  Cellulose  forms  the  chief  constituent  of  the  cell  walls  of  all  plants  and 
exhibits  an  organic  structure.  To  obtain  pure  cellulose  plant  fibers  are  digested 
successively  with  different  reagents,  such  as  dilute  acids  and  alkalies,  potassium 
chlorate  and  nitric  acid,  alcohol  and  ether.  The  cellulose  remains  as  the  insolu- 
ble residue. 


Table  showing  the  ji^rcentage  composition  of  the  most  important  substances  discussed  in 

this  chapter : 


C 

H 

N 

s 

o 

P 

1.  Proteids  in  general. 

50.6-55 

6.5-7.7 

15.0-18.5 

0  3-2  2 

20.5-23.5 

2.  Casein 

52.7-54.0 

7.0 

15.6-15.7 

0.7-0.8 

22.8 

0.8 

3.  Xiiclein 

40.8-42.1 

5.4-6.1 

14.7-16.0 

0.4-0.6 

31.1-31.3 

5.2-6.2 

4.  Nucleic  acid 

34.1-37.3 

4.2-5.2 

15.3-18.2 

32.5-35.6 

7.7-9.9 

5.  Xucleohi<ton 

48.5 

7.0 

16.9 

0.7 

24.0 

3.0 

6.  Mucin     

48.3-50.3 
47.3 

6.4-8.2 
6.4 

11.8-13.7 
12.6 

0.8-1.8 
2  4 

27.4-32.7 
31.3 

7.  Chondroniucoid  . .  . 

8.  Keratin .         

49.8-58.5 
54.0-54.3 

6.4-8.2 
7.0-7.3 

11.5-17.5 
16.7-16.8 

2.5-5.0 
0.4 

19.6-22.9 
21.8-21.9 

9.  Elastin 

10.  Collagen 

50.8 

6.5 

17.9 

0.6 

24.3 

11.  Gelatin 

49.3-51.5 

6.5-7.1 

17.5-18.6 

0.3 

25.2-25.4 

12.  Reticulin    

52.9 
65.4 
76.5 

7.0 
11.2 
12  2 

15.6 

1.7 

1.9 

20.0 
17.8 
11.5 

0  3 

13.  Lecithin 

3.8 

14.  Fats  (mean) 

15.  Cholesterin  

83.9 

11.9 

4.1 

16.  Monosaccharides... 

40.0 

6.7 

53.3 

17.  Disaccharides 

42.1 

6.4 

51.5 

18.  Polysaccharides. . . . 

44.4 

6.1 

49.4 

Referexces. — The  text-books  of  physiological  chemistry:  of  Bunge,  second 
English  edition  by  E.  H.  Starling,  Philadelphia,  1902;  of  Hallihurton,  latest 
edition,  London  and  New  York,  1904;  of  Hammarsten,  fourth  English  edition 
by  John  A.  Mandel,  'New  York,  1904;  of  Neumeister,  second  edition,  Jena,  1897. 
0.  Cohnheim,,  "  Chemie  der  Eiweisskorper."  Braunschweig,  1900.  F.  Hofmeister 
in  "Ergebnisse  der  Physiologic,"  I,  1.  Wiesbaden,  1902.  A.  Kossel,  "  Ber.  d. 
Beutschen  Ges.,"  34,  3,  1902. 


CHAPTER    IV 

METABOLISM    AXD    NUTRITIOX 

The  physiology  of  metabolism  and  nutrition  ^  seeks  to  discover  what  sub- 
stances are  necessary  for  the  maintenance  and  growth  of  the  body,  to  deter- 
mine the  character  and  extent  of  the  combustion  taking  place  in  its  tissues 
and  fluids  under  different  circumstances,  and  to  understand  the  significance 
of  the  different  substances  for  these  processes. 

The  substances  in  question  admit  of  division  into  three  groups,  namely: 
(1)  organic  foodstuffs,  substances  which  supply  potential  energy  and  serve 
therefore  to  maintain  the  combustion  in  the  body;  (2)  water  and  inorganic 
foodstuffs,  which  must  be  taken  to  make  good  the  constant  loss  from  the  body 
of  these  constituents,  without  which  profound  and  eventually  fatal  disturb- 
ances in  health  may  ensue;  (3)  oxygen  necessary  for  the  maintenance  of 
combustion. 

FIRST    SECTION 

METABOLISM 

§  1.    ON   THE    METHOD    OF   METABOLISM   EXPERIMENTS 

A.    THE   INGESTA 

Organic  as  well  as  inorganic  foodstuffs,  mixed  together  in  varying  pro- 
portions and  mixed  witli  other  substances  not  needed  in  the  body,  occur  in 
our  common  articles  of  food  and  in  our  meals  prepared  from  them.  Chemical 
analysis  of  the  foods  has  shown  that  the  organic  foodstuffs  are  chiefly  of  three 
kinds,  namely:  (1)  proteids  and  allied  substances;  (3)  fats;  (3)  carbohy- 
drates. To  the  inorganic  foodstuffs,  which  are  designated  also  as  ash  con- 
stituents, belong  numerous  salts  which  we  shall  discuss  more  in  detail  later. 
By  chemical  analysis  of  the  food  we  learn  its  composition,  both  qualitatively 
and  quantitatively,  and  determine  in  this  way  precisely  the  intake  of  the 
body. 

In  analysis  of  the  foods  and  the  faeces,  (1)  the  nitrogen  is  determined  and 
the  proteid  is  calculated  by  multiplying  this  result  by  6.25.     Since,  however, 

>  It  may  serve  to  differentiate  the  two  divisions  of  the  subject  somewhat,  if  we  define 
metabolism  as  coverins;  all  those  chemical  transformations  of  the  foodstuffs  by  which 
energy  is  supplied  to  the  cells,  and  nutrition  as  coverinji  all  the  processes  by  which  the 
materials  which  the  cells  require  are  supplied.  Obviously  the  two  are  inseparable  and 
represent  merely  different  aspects  ef  the  same  subject.  A\'e  spenk  of  the  substances  as 
undergoing  metabolism  and  of  the  organism  as  nourishing  itself. — Ed. 

83 


84  METABOLISM  AND  NUTRITION 

nitrogen-containing  substances  other  than  proteid  occur  in  both  animal  and 
vegetable  foods,  the  quantity  as  calculated  by  this  method  is  too  high.  Espe- 
cially with  a  low  percentage  of  proteid  a  considerable  error  might  thus  arise. 
Moreover,  the  kind  of  proteid  eaten  is  not  a  matter  of  indifference,  since  one 
may  well  imagine  that  different  proteid  bodies  behave  differently  in  metabolism. 
The  little  we  know  on  this  subject  will  be  summarized  later.  (2)  As  fat,  is 
reckoned  the  total  extract  with  ether,  although  this  contains  also  other  sub- 
stances soluble  in  ether.  (3)  The  dry  substance  and  (4)  the  ash  constituents 
are  determined  by  desiccation  at  100°  C.  and  by  incineration  respectively. 
(5)  The  carbohydrates  are  determined  usually  by  subtracting  from  the  total 
dry  substance  the  proteid  +  the  fat  +  the  ash. 

Finally,  under  the  ingesta  is  to  be  reckoned  the  oxj'gen,  methods  for  the 
determination  of  which  will  be  given  under  B. 


B.    DETERMINATION   OF  THE  EXCRETA 

The  products  of  metabolism  are  eliminated  by  the  lungs,  skin,  intestine 
and  kidneys. 

The  excreta  resulting  from  the  combustion  of  organic  foods,  to  which  we 
shall  confine  ourselves  for  the  present,  contain  the  following  elements :  IST,  S, 
P,  C,  H,  and  0.  Xitrogen,  sulphur  and  phosphorus  are  derived  from  pro- 
teids;  carbon,  hydrogen  and  oxygen  are  contained  in  all  the  organic  foods. 
In  estimating  the  excreta  we  have  therefore  to  determine  quantitatively  the 
amount  of  X.  S.  P,  C,  and  H  eliminated  within  a  certain  time. 

The  determinations  can  he  simplified  considerably,  however.  Ordinarily, 
in  order  to  find  out  how  much  proteid  has  been  metabolized  in  the  body,  it 
is  sufficient  to  determine  the  amount  of  nitrogen  eliminated.  One  need  not 
consider  the  sulphur  and  phosphorus  unless  the  investigation  is  especially 
concerned  with  the  behavior  of  the  phosphorus-containing  proteids.  The  anal- 
ysis for  a  complete  metabolism  experiment  therefore  can  be  restricted  to 
X,  C,  and  H.     Commonly  the  excretion  of  hydrogen  also  is  neglected. 

The  amount  of  proteid  destroyed  in  the  body  is  obtained  by  multiplying 
the  amount  of  nitrogen  eliminated  as  a  product  of  metabolism  by  6.25. 

Analysis  for  the  elernents  found  in  the  excreta  is  by  no  means  always  suffi- 
cient; in  many  cases  it  is  necessary  either  for  the  purpose  of  gaining  a  deeper 
insight  into  the  mode  of  the  metabolic  processes,  or  in  order  to  estimate  the 
percentage  of  combustible  materials  in  the  faeces,  to  determine  the  separate 
compounds  quantitatively.  In  the  latter  case  the  analysis  is  carried  out  in 
precisely  the  same  way  as  in  making  similar  determinations  for  the  food  to 
be  ingested. 

If  the  metabolism  experiment  is  to  be  of  any  use  whatever,  it  is  necessary 
to  collect  every  trace  of  the  excreta  for  exactly  the  period  covered  by  the 
experiment.  The  urine  and  the  fseces  offer  no  particular  difficulties  in  this 
respect,  although  some  remarks  with  regard  to  the  latter  seem  called  for. 

It  is  apparent  at  once  that  analysis  of  the  faeces  can  only  be  of  importance 
for  the  study  of  metabolism,  if  they  can  be  identified  as  belonging  to  a  definite 


ON  THE  METHOD  OF  METABOLISM  EXPERIMENTS  85 

diet.  But  in  all  animals,  as  in  man,  the  intestine  is  always  more  or  less  filled 
and  one  cannot  tell  without  special  means  whether  a  given  mass  of  fseces  comes 
from  the  diet  which  is  being  studied.  To  do  so  it  is  necessary  to  separate  the 
faeces  corresponding  to  the  diet  in  question  from  preceding  and  subsequent 
faeces.  The  subject  is  allowed  to  fast  for  some  twenty  hours,  then  the  particular 
diet  is  begun,  and  with  the  first  meal  some  substance  is  given  which,  like  finely 
powdered  charcoal,  will  impart  a  characteristic  color  to  the  faeces.  After  the 
last  meal  the  subject  is  permitted  to  fast  again  for  twenty  hours,  and  with  the 
first  food  eaten  after  this  period  charcoal  is  once  more  given.  With  herbivorous 
animals  it  is  impossible  to  get  a  satisfactory  separation;  but  this  difiiculty  may 


;  jff 


Fig.  39. — Face  mask  for  respiration  experiments,  after  Loven.  Longitudinal  section.  A,  the 
mouthpiece.  B  and  C  are  thin  membranes  which  act  as  valves  and  serve  to  separate  in- 
spired from  expired  air.     Inspiration  takes  place  through  B,  expiration  through  C. 

be  overcome  by  giving  the  particular  diet  under  investigation  for  several  days 
before  beginning  the  experiment. 

In  order  to  collect  the  solid  constituents  contained  in  the  sweat,  the  sub- 
ject is  required  to  wear  thoroughly  washed  woolen  clothes  which  will  absorb  and 
retain  all  such  solids. 

Rather  complicated  method.?  must  be  employed  to  collect  and  analyze  the 
gaseous  products  of  metabolism  (carbon  dioxide  and  water  vapor),  and  to 
determine  the  amount  of  oxygen  absorbed.  ]\Iethods  for  all  these  purposes 
were  u.sed  by  Lavoisier  (1780),  but  they  have  been  developed  and  improved 
in  many  ways  since  his  day. 

The  simplest,  if  not  the  most  satisfactory  method,  is  to  collect  the  respira- 
tory products  by  the  use  of  a  face  mask.  The  mask  is  connected  by  means  of 
tubes  with  apparatus  for  the  measurement  and  collection  of  the  inspired  and 
expired  air,  the  two  currents  of  air  being  separated  by  means  of  automatic  valves 
(Fig.  39).  Instead  of  the  face  mask  a  gutta-percha  plate,  so  arranged  as  to  fit 
between  the  lips  and  teeth  and  provided  with  a  tube  through  which  the  air 
passes,  may  also  be  used.  A  much  more  nearly  air-tight  closure  of  the  mouth 
is  possible  with  this  apparatus. 

By  this  method  which  has  recently  been  improved,  especially  by  Zuntz,  the 
cutaneous  respiration  is  of  course  not  determined,  but  it  is  of  no  particular 
importance  (cf.  Chapter  XIII).  A  more  serious  objection  is,  that  with  this 
method  it  is  very  difficult,  if  not  impossible,  to  continue  the  experiment  for 
more  than  a  quarter  of  an  hour  to  an  hour.     Where  it  is  necessary  to  determine 


86 


METABOLISM  AND  NUTRITION 


the  C0„  and  water  excreted  and  the  oxygen  absorbed  for  a  whole  day  or  longer, 
other  methods  must  be  used. 

For  these  purposes  several  different  forms  of  respiration  apparatus  have  been 
constructed,  among  which  we  shall  very  briefly  describe  the  following: 

1.  [The  Apparatus  of  Atwater  and  Benedict.— In  its  general  features  this 
apparatus,  constructed  for  experiments  on  human  subjects,  embodies  the  princi- 
ples of  one  originally  constructed  by  Eegnault  and  Rieset  (1849)  for  experiments 
on  smaller  animals.  The  subject  is  placed  in  a  respiration  chamber  of  suitable 
size  (5.03  cubic  meters  capacity)  and  is  supplied  with  pure  air,  as  indicated  in 
the  diagram  below  (Fig.  40).  The  air  containing  the  respiratory  products  is 
drawn  out  of  the  chamber  by  the  pump  and  is  made  to  pass  in  turn  over  H.SOi 
and  soda  lime.     The  gain  in  weight  of  the  former  gives  the  amount  of  water 


RESPIRATION     CHAMBER 
o    used 


CO, 


°  j  produced 


ooz         o  deficient 


H2O 


I I  COi  I 1      I 1    ^ipj      I ^ 

absorbed   by       absorbed   by  g  deficient  —        >    pump    S 

Fig.  40. — Schema  of  the  Atwater-Benedict  respiration  calorimeter. 


eliminated  by  the  respiration  and  evaporation ;  the  gain  in  weight  of  the  latter, 
the  amount  of  carbon  dioxide  eliminated.  Pure  oxygen  is  next  admitted  to  make 
up  what  has  been  taken  out  by  the  subject.  To  determine  exactly  how  much 
oxygen  has  been  thus  absorbed  it  is  necessary  to  know  how  much  was  contained 
in  the  air  at  the  beginning  and  how  much  at  the  end  of  the  experiment.  Sub- 
tracting the  amount  present  at  the  end  from  the  total  amount  supplied — i.  e.,  the 
amount  present  at  the  beginning  plus  the  amount  admitted — gives  directly  the 
amount  absorbed. 

The  respiration  chamber  in  this  apparatus  is  provided  also  with  means  of 
measuring  the  heat  lost  from  the  subject's  body  by  radiation  and  conduction,  so 
that  the  entire  apparatus  is  described  as  a  respiration  calorimeter. — Ed.] 

2.  Tlie  Apparatus  of  PettenTcoffer. — This  consists  of  a  respiration  chamber 
with  a  capacity  of  12.Y  cubic  meters  into  which  and  from  which  air  is  pumped 
in  a  continuous  stream.  The  air  is  analyzed  both  as  it  goes  in  and  as  it  comes 
out  of  the  chamber,  a  uniform  fractional  i)art  of  the  total  volume  flowing  out 


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88 


METABOLISM  AND  NUTRITION 


being  led  off  to  suitable  apparatus  for  the   absorption  of  carbon  dioxide   and 
water. 

[A  smaller  apparatus  embodying  the  same  principles  has  been  constructed 
by  Voit  for  experiments  on  smaller  animals  (Fig.  41).  The  cage  (A)  is  ven- 
tilated by  a  current  of  air  kept  moving  by  rotation  of  the  gas  meter  (D). 
Throughout  the  experiment  a  sample  of  this  air  is  continually  led  off  by  a  side 
tube  (E)  and  is  passed  over  pumice  stone  soaked  in  sulphuric  acid  and  then 
through  Ba(OH):.  The  quantity  of  H,0  in  this  air  is  obtained  directly  by  the 
difference  in  the  weight  of  the  H,SO,  flasks/  the  amount  of  CO,  by  titration 
of  the  Ba(OPI),.  The  large  gas  meter  (D)  measures  the  total  volume  of  air 
passing  through  its  works,  and  the  small  gas  meter  (H)  measures  the  volume 
of   the   sample.     A   duplicate   analysis  is   made  by  means   of  a   second   set   of 

m 


55555^^^ 


Fig.  42. — The  respiration  apparatus  of  Sonden  and  Tigerstedt.  A,  container  for  sample  of  the 
room  air;  B,  apparatus  for  determination  of  CO2;  C,  electric  motor;  D,  rheostat;  E,  hydraulic 
pump. 

vessels,  and  this  sample  is  measured  by  a  similar  gas  meter.  Duplicate  analyses 
of  the  air  which  enters  the  cage  are  made  in  the  same  manner  and  the  respiratory 
products  calculated  by  difference. 

If  the  determination  of  water  vapor  is  satisfactory,  the  amoiuit  of  oxygen  ab- 
sorbed by  the  animal  can  be  obtained  by  subtracting  the  combined  weight  of  the 
animal  at  the  beginning  of  the  experiment  and  the  total  ingesta  for  the  period 


'  Voit  and  Pettenkoflfer  made  very  thorough  tests  of  this  method,  and  found  that  the 
water  is  obtained  to  within  1  or  2  per  cent,  the  slight  error  being  due  to  condensation  on 
the  walls  of  the  tubes.  Rubner,  employing  the  same  principles  of  ventilation  for  his  calo- 
rimeter, obtained  still  more  exact  results.  By  shortening  the  distance  which  the  air  must 
travel  on  its  way  from  the  cage  to  the  H^  SO4  fla.sks,  he  was  able  to  prevent  entirely  the 
condensation  of  water  on  the  walls  of  the  tubes.  For  short  experiments  he  relied  upon  hair 
hydrometers  placed  inside  the  cage. — Ed. 


ox  THE  iMETHOD   OF   METABOLISM  EXPERIMENTS  89 

from  the  combined  weight  of  the  animal  at  the  end  and  the  total  excreta  for  the 
period. — Ed.] 

3.  The  Apparatus  of  Sonden  and  Tigerstedt  (Fig.  42). — The  subject  is 
housed  in  an  ordinary  room  with  a  capacity  of  100.6  cu.m.  The  walls,  ceiling, 
and  floors  are  covered  with  sheet  zinc  and  are  made  air-tight  by  soldering  all  the 
joints.  By  means  of  a  hydraulic  pump  (E)  air  is  drawn  from  this  respiration 
chamber  to  a  gas  meter,  where  it  is  measured.  Fresh  air  from  outdoors  replaces 
the  foul  air  drawn  out,  A  uniform  diffusion  of  the  air  in  the  room  is  insured 
by  a  ventilating  fan. 

To  obtain  air  for  analysis,  a  narrow  tube  branches  off  from  the  main  inlet 
pipe  (red),  and  by  means  of  another  hydraulic  pump  a  constant  stream  is  main- 
tained through  it,  so  that  the  air  in  the  branch  always  has  the  same  composi- 
tion as  that  in  the  main  inlet.  At  stated  intervals  samples  for  analysis  are  then 
taken  (in  the  vessel  A)  from  this  branch  and  the  carbon  dioxide  is  estimated 
by  the  method  of  Pettersson  (B)  for  the  analysis  of  gases.  The  quantity  of 
carbon  dioxide  is  calculated  by  the  ventilation  formula  of  Lenz. 

But  the  body  suffers  other  losses  in  organic  substance  than  those  resulting 
from  combustion.  Here  belong  the  losses  by  sloughing  off  of  the  epidermis, 
cutting  the  hair  and  nails,  ejection  of  sperm  and  menstrual  blood,  secretion 
of  milk.  etc.  Such  losses,  however,  are  either  so  slight  that  they  do  not  affect 
the  results  of  the  investigation,  or  they  come  in  only  occasionally  and  can 
generally  be  neglected,  unless  the  investigation  is  being  directed  especially 
to  them. 

C.    APPORTIONMENT  OF  THE   INDIVIDUAL  ELEMENTS  TO  THE 
DIFFERENT  EXCRETA 

(1)  Expired  Air. — It  has  been  known  since  the  beginning  of  scientific 
investigation  of  metabolism  and  can  be  demonstrated  without  the  least  diffi- 
culty that  carbon  and  hydrogen  leave  the  body  as  COo  and  H,0  in  the  expired 
air.  Xot  so  with  the  nitrogen  and  nitrogenous  compounds.  A  priori  one 
cannot  deny  that  such  substances  also  might  be  given  off  from  the  body  as 
products  of  metabolism  in  the  expired  air.  But  from  the  many  researches 
w^hich  have  been  carried  out  with  reference  to  this  question,  it  appears  certain 
that  this  is  not  the  case.  So  far  as  metabolism  is  concerned  we  need,  there- 
fore, to  consider  among  the  respiratory  products  only  carbon  dioxide  and 
water  vapor. 

(2)  Sweat. — Water  is  the  principal  substance  given  off  through  the  skin. 
However,  the  sweat  contains  also  some  solid  substances,  the  most  important 
of  which  is  urea.  With  copious  sweating,  as  under  severe  labor  or  in  a  vapor 
bath,  the  quantity  of  these  constituents  may  rise  so  much  that  to  neglect  them 
would  involve  considerable  error.  Thus,  under  such  circumstances,  0.76  g.  X 
have  been  found  in  the  sweat ;  at  the  same  time  the  nitrogen  excretion  in  the 
urine  was  ]5.9  g.  for  twenty-four  hours.  In  this  case,  therefore,  the  sweat 
contained  4.8  per  cent  of  the  X  eliminated  through  the  kidneys  (Argutinsky). 

(3)  Urine. — Of  the  chemical  elements  derived  from  the  organic  food- 
stuffs and  found  in  the  urine,  nitrogen  and  carbon  are  to  be  specially  con- 
sidered. Both  of  these  occur  mainly  in  the  form  of  urea  and  uric  acid.  The 
daily  quantity  of  nitrogen  eliminated  in  the  urine  of  an  adult  man  amounts 


90  METABOLISM  AND  NUTRITION 

to  about  15-16  g.,  but  exliibits  wide  variations,  depending  primarily  upon  the 

quantity  of  nitrogen  ingested  in  the  food. 

The  quantity  of  carbon  in  the  urine  as  compared  with  that  in  the  expired 
air  is  verj-  small.  Only  when  very  great  exactness  is  desired  does  it  need  to  be 
determined  directly,  for  it  can  generally  be  calculated  without  any  considerable 
error  from  the  nitrogen  of  the  urine.  The  ratio  N :  C  in  the  urine  exhibits  but 
very  slight  variations;  according  to  Atwater,  it  has  for  a  mixed  diet  a  mean 
value  of  about  1:0.72  (0.64-0.79). 

(4)  Fceces. — The  fseces  are  composed  partly  of  unabsorbed  residues  of  the 
food,  partly  of  residues  of  the  digestive  fluids,  and  partly  of  worn-out  epithelial 
cells  and  excretory  products  from  the  alimentary  tract.  In  a  fasting  man 
these  residues  make  up  a  faecal  mass,  which  contains  from  0.11  to  0.32  g.  of 
nitrogen  per  twenty-four  hours.  When  a  nonnitrogenous  diet,  or  one  very 
poor  in  nitrogen,  is  given,  from  0.5  to  0.4  g.  of  X  appear  in  the  faeces  per  day 
(Rubner,  Eieder).  This  quantity  of  IST  must  evidently  have  its  origin  in  the 
intestine  itself.  We  can  say,  therefore,  that  the  intestine  has  a  very  large  share 
in  the  formation  of  the  fsces,  and  that  in  round  numbers  one  gram  of  the  N 
eliminated  as  a  product  of  metabolism  is  to  be  found  in  the  intestinal  evacu- 
ations. The  nitrogen  contained  in  the  bacteria  of  the  fseces  is  also  included 
in  this  figure. 

Since  experiments  from  Pawlow's  laboratory  (Chapter  VII)  show  that  the  se- 
cretion of  the  digestive  juices  and  their  X-content  present  considerable  variations 
with  different  diets,  one  might  be  tempted  to  look  upon  the  total  quantity  of 
nitrogen  in  the  faeces  as  a  pure  product  of  metabolism.  But  this  is  not  true,  for 
many  observations  have  shown  that  with  certain  articles  of  diet  a  considerable 
part  of  this  fsecal  nitrogen  actually  represents  a  residue  of  the  food. 

In  any  given  case  therefore  it  is  quite  impossible  to  decide  how  much  of 
the  fsecal  nitrogen  comes  from  the  one  source  and  how  much  from  the  other. 
For  this  reason  it  has  become  customary  to  regard  the  total  nitrogen  in  the 
fseces  as  a  residue  of  the  food.  Although  it  must  be  admitted  that  such  an 
assumption  is  quite  incorrect  from  a  purely  theoretical  point  of  view,  it  makes 
no  difference  in  the  calculation  of  results  of  metabolism  experiments.  For  if 
we  suppose  that  the  faeces  are  exclusively  a  product  of  metabolism,  the  implica- 
tion is  that  all  the  food  was  absorbed  without  loss;  and  vice  versa,  if  we  regard 
the  faeces  as  only  a  residue  of  the  food,  then  the  quantity  utilized  must  be 
diminished  by  the  mass  of  the  faeces.  In  both  cases  we  reach  exactly  the  same 
result  with  regard  to  the  amount  of  metabolism  actually  taking  place.  In  this 
presentation  of  the  subject  of  metabolism,  therefore,  we  shall  reckon  the  faeces 
as  a  residue  of  the  food. 

Eespecting  the  nonnitrogenous  substances  given  off  in  the  faeces,  we  may 
merely  mention  here  the  fact  that  fat  occurs  in  appreciable  quantity  both  on 
a  fat-free  diet  and  in  fasting.  In  the  latter  case  O.G-1.4  g.  per  day  have  been 
found  in  the  faeces,  and  on  a  fat-free  diet,  3-7  g.  per  day.  If,  therefore,  on  a 
fat  diet  the  faeces  do  not  contain  more  than  7  g.  of  fat  per  day,  we  can  say 
that  the  fat  in  the  food  has  been  almost  entirely  absorbed  in  the  intestine. 

In  the  faeces  the  ratio  of  XiC  for  a  mixed  diet  is  about  1:9.2  (6.8-13.8). 
Inasmuch  as  the  quantity  of  nitrogen  in  the  fasces  ordinarily  does  not  amount 
to  more  than  2  g.  per  day,  in  most  cases  it  is  sufficient  to  calculate  the  carbon 
from  the  nitrogen. 


ON   THE   METHOD   OF  METABOLISM   EXPERIMENTS 


91 


We  have  already  seen  that  under  normal  circumstances  no  nitrogen  is 
eliminated  in  the  expired  air  as  a  product  of  metabolism,  and  that  in  the 
sweat  only  in  exceptional  cases  is  the  quantity  of  any  importance.  Hence 
the  channels  by  which  nitrogen  is  excreted  are  the  kidneys  and  the  intestine 
as  will  appear  plainly  from  a  case  of  nitrogenous  equilibrium. 

If  an  animal  be  given  a  diet,  which  from  day  to  day  contains  exactly  the 
same  quantity  of  nitrogen  and  does  not  vary  with  regard  to  the  nonnitrogenous 
foodstuffs,  after  a  few  days  one  finds  in  the  urine  and  faeces  exactly  as  much 
nitrogen  (and  sulphur)  as  had  been  ingested  in  the  food.  This  condition  is 
called  nitrogenous  equilihrium.  As  an  example  the  following  experiment  from 
G ruber  may  be  given  : 


Days  of  Experiment. 

N-intake  g. 

N-output  g. 

Per  cent  dif. 

Sintake  g. 

S-output  g. 

I.   1-5 

90.00 
131.60 

35.80 
144.50 

154.81 
213.72 

89.81 
132.75 

36.16 
143.13 

153.02 
213.20 

-0.21 

+  0.88 

+  1.00 
-  0.86 

-0.51 
-0.21 

"i'i.'77 

6-12    

II.  1-3    

3-11 

HI.  1-7 

8-17 

12.79 

D.    EXAMPLE   OF   A   METABOLISM   EXPERIMENT 

The  following  table  after  Atwater  contains  a  summary  of  the  ingesta  and 
excreta  in  an  experiment  with  mixed  food.  The  experiment  lasted  four  days, 
the  subject  being  a  man  thirty-two  years  of  age  and  of  about  64  kg.  body 
weight,  who  remained  as  quiet  as  possible  throughout  the  experiment. 


Ingesta.  mean  iceigl 

it  in  g. 

jjer  day 

Articles  of  Diet. 

Total 
weight. 

Vv'ater. 

Proteid. 

Fat. 

Carbo- 
hydi-ate. 

N. 

C. 

H.  in 

organic 

sub 
stance. 

Meat 

160 
70 

450 

50 

64 

30 

1,500 

310 

105.6 
7.4 

405.9 
2.9 

'i'.4 

1.500.0 
129.3 

44.5 
0.8 

17.1 
5.5 

'k'.b 

24  ".5 

6.7 

59.9 

0.5 

4.2 

2:5 

8^7 

22 ;  5 
36.5 
64.0 
23.3 

143  .'5 

7.1 
0.1 
2.8 
0.9 

b'.s 

3.9 

28.4 
43.8 
19  6 
22.4 
26.9 
13.2 

84^  7 

4.2 

Butter 

7.1 

Skiniiiied  milk 

Maize,  breakfast  food 
Sugar  

2.8 
3.2 

4.2 

Pepper  cake 

Water 

Bread 

2.0 
12^7 

Total  

2,634 

2,152.5 

94.4 

82.5 

289.8 

15.1 

239.0 

36.2 

Excreta,  mean  iceigJit  in  g.  per  day 


Faeces 

Urine      

54.7 
1.449.5 

40.6 

1.403.1 

963.8 

5.4 

3.7 

3.2 

0.9 
16.2 

7.4 

12.2 

207.3 

1.0 
3.5 

Respiration  and  skin . 

Total 

2,406.5 

17.1 

226.9 

4.5 

Balance 

-254.0 

-2.0 

+  12.1 

+  31.7 

92 


METABOLISM   AND   NUTRITION 


If  wo  consider  the  f:vces  as  pure  loss  (cf.  page  90),  the  body  has  dis- 
posed of  (94.4:  g.  ingested  —  5.4  g.  excreted  =)  89.0  g.  proteid  containing 
(Ui.2  -  2.0  =)  14.2  g.  N,  besides  (82.5  -  3.7  =)  78.8  g.  fat,  and  (289.8  - 
3.2=)  28G.6  g.  carbohydrates.  In  the  urine  16.2  g.  N  were  given  off;  but 
2.0  g.  of  the  X  have  come  from  tlie  body  itself— i.  e.,  (6.25  X  2  =)  12.5  g. 
of  the  body's  proteid  has  been  lost.  The  total  proteid  metabolism,  therefore, 
has  been  (89  g.  +  12.5  =)  101.5  g.  (or  16.2  X  6.25). 

The  ratio  of  N  to  C  contained  in  proteid  is  1 :  3.28.  In  the  proteid  de- 
stroyed by  this  man  therefore  there  were  3.28  X  16.2  =  53.1  g.  C.  The  total 
quantity  of  C  eliminated  in  the  respiration  and  in  the  urine  was  219.5  g. ; 
there  remain  166.4  g.  which  must  have  been  derived  from  nonnitrogenous  food. 

Of  carbohydrates  286.6  g.  (289.8  ingested  -  3.2  excreted)  were  absorbed 
from  the  intestine,  and  this  by  calculation  was  found  to  have  contained  124.7 
g.  C.  Xow  we  shall  see  later  that  carbohydrates  burn  in  the  body  more  easily 
than  fat.  We  therefore  deduct  first  the  C  belonging  to  carl)ohydrate.  This 
leaves  41.7  g.  C  (166.4  -  124.7)  which  must  have  come  from  fat — i.e.,  since 
the  fat  used  contained  about  seventy-six  per  cent  C,  54.6  g.  fat  were  burned 
in  the  body. 

We  conclude  that  the  l)ody  has  decomposed  a  mean  quantity  of  101.5  g. 
proteid,  54.6  g.  fat  and  286.6  g.  carbohydrate  per  day.  Comparison  with  the 
ingesta,  having  regard  to  the  C  resulting  from  proteid  destroyed,  shows  that 
the  body  has  lost  12.5  g.  of  its  proteid  but  has  stored  up  24.2  g.  fat,  containing 
12.2  -f  6.5  g.  C. 

§  2.    POTENTIAL   ENERGY   OF   THE   FOODSTUFFS 

The  energy  stored  in  a  combustible  substance  is  measured  by  the  quantity 
of  heat  generated  in  its  combustion,  and  is  constant  for  every  individual 
substance.  The  heat  values  of  the  substances  most  important  for  our  present 
purpose,  as  determined  by  the  calorimeter,  are  given  in  the  following  table. 
All  data  are  for  1  g.  of  the  substance  and  the  heat  values  here,  as  elsewhere 
in  this  discussion,  are  expressed  in  large  Calories  (Cal.). 


Substance. 

One  g.  of  dry  sub- 
stance yields— 

One  g.  of  ash-free 
substance  yields— 

Author. 

Proteid  ' 

5.754  Cal. 
5.345    " 

5.778  Cal. 
5.656    " 
9.464-9.492  Cal. 
9.231  Cal. 
3.743    " 
3.737    " 
3.955    " 
4.183    " 
7.080    " 

Rubner 

Muscle  (free  of  fat) 

Animal  fat.  .      .        

Stohmann 

Butter  fat 

Grape  sugar      

^i 

^lilk  suijar 

a 

Cane  sugar 

a 

Rice  starch 

Alcohol 

Berthelot 

When  fat  or  carbohydrates  are  burned  in  the  body,  they  are  completely 
oxidized  into  carbon  dioxide  and  water.     If,  therefore,  the  principle  of  con- 

'  Meat  extracted  with  water,  alcohol,  and  ether. 


POTENTIAL   ENERGY   OF  THE  FOODSTUFFS  93 

servation  of  energy  is  true  for  the  body,  the  heat  value  of  these  substances 
as  determined  by  the  calorimeter  must  be  their  heat  value  in  the  body. 

Quite  otherwise  is  it  with  proteid.  The  end  products  of  its  metabolism 
are  not  all  completely  oxidized,  and  hence  contain  not  a  little  potential  energy. 
To  obtain  the  heat  value  of  proteid  for  the  body  we  must  therefore  deduct 
from  its  calorimetric  heat  value  the  heat  value  of  the  waste  products  resulting 
from  its  metabolism.    This  Rubner  has  done  in  the  following  way. 

He  fed  a  small  dog  with  a  proteid  material  whose  calorific"  energy  had 
been  previously  determined  by  combustion,  and  then  determined  the  calorific 
energy  of  the  corresponding  urine  and  fgeces.  The  former  for  1  gram  of 
proteid  decomposed  was  1.0945  Cal. ;  the  latter,  also  for  1  g.  of  proteid,  was 
0.1854  Cal.  Finally,  he  deducted  0.05  Cal.  for  the  hydrolytic  absorption  on 
the  part  of  the  proteid  while  in  the  body  and  for  the  solution  of  urea.  For 
1  g.  of  dry  proteid  we  would  have  therefore  a  physiological  heat  value  of 
5.754-(1.0945  + 0.1854 +  0.05)=  4.424  Cal. 

In  an  analogous  way  the  net  physiological  heat  value  of  muscle  deprived  of 
its  fat  only  was  found  to  be  4.001  Cal.,  and  that  of  the  proteid  of  the  body 
destroyed  in  fasting  3.842  Cal.  For  every  gram  of  N  found  in  the  excreta  after 
feeding  the  fonner  we  should  estimate,  therefore,  25.98  (6.25  X  4.001)  Cal.  and 
in  fasting  24.94  (6.25  X  3.84)  Cal. 

Human  urine  yields  on  the  average  8.0  Cal.  for  every  gram  of  nitrogen  con- 
tained. Human  faeces,  per  1  g.  of  X,  yield  all  the  way  from  66  to  159  Cal.,  but 
per  gram  of  organic  substance  the  fairly  constant  value  of  5.2-7.7  (mean  6.5) 
Cal.  (Rubner,  Atwater,  Loewy). 

In  most  metabolism  experiments  one  has  to  deal  not  with  pure  lean  meat, 
pure  starch,  or  a  definite  kind  of  fat,  but  with  a  mixture  of  various  fats, 
carbohydrates,  etc.  One  must  be  content  with  the  determination  by  direct 
analysis  of  the  quantity  of  total  proteid,  total  fat  and  total  carbohydrate ; 
for  absolutely  exact  analysis  of  separate  kinds  of  proteid,  etc.,  would  make  all 
metabolism  experiments  impracticable.  From  such  determinations  as  those 
above  mentioned,  Ruljner  calculated  the  mean  dynamic  value  of  the  chief 
groups  of  the  organic  foodstuffs  to  be  as  follows : 

1  g.  proteid 4.1  Cal. 

Ig.fat 9.3    " 

1  g.  carbohydrate 4.1    " 

From  the  standpoint  of  the  conservation  of  energy,  it  is  to  be  assumed 
beforehand  that  these  theoretical  calorific  values  must  be  correct  also  for  these 
substances  when  burned  in  the  living  body.  In  fact  wc  have  direct  experi- 
mental proofs  of  this ;  and  precisely  because  these  proofs  verify  the  assumption, 
they  are  of  the  greatest  importance  for  the  whole  subject  of  physiology. 

As  long  ago  as  1883,  Rubner  showed  by  a  long  series  of  experiments,  the 
details  of  which  we  cannot  enter  into  here,  that  the  different  organic  foodstuffs 
can  replace  one  another  in  isodynamic  quantities — i.  e.,  in  quantities  which 
yield  equal  amounts  of  calorific  energy.  The  foregoing  assumption  was  suf- 
ficiently substantiated  by  these  results  alone.  But  Rubner  carried  his  investi- 
8 


94 


METABOLISM   AXD   NUTRITION 


gations  still  further  (1894).  By  the  use  of  the  calorimeter  he  determined 
on  dogs  (direct  calorimetry)  the  amount  of  heat  lost,  and  at  the  same  time 
estimated  from  the  excreta  the  total  metabolism  (see  page  93)  ;  then,  from 
the  calorific  values  of  the  foodstuffs,  he  calculated  the  amount  of  heat  pro- 
duction (indirect  calorimetry)  in  the  body  represented  by  this  metabolism. 
The  result  was  that  in  eight  series  of  experiments  covering  altogether  forty- 
six  days  the  mean  difference  between  the  heat  production  as  calculated  from 
the  metabolism  and  the  heat  loss  determined  by  the  calorimeter  was  only 
0.3  per  cent. 

In  some  very  careful  experiments  with  men  on  a  mixed  diet  Atwater 
has  obtained  similar  results.  In  these  experiments  not  only  were  the  food  and 
the  total  excreta  analyzed,  but  the  calorific  values  of  the  food,  the  urine  and 
the  fa?ces  were  determined  directly;  and  at  the  same  time  the  heat  given  off 
by  the  subject  was  measured  by  the  calorimeter  in  which  he  was  confined. 

In  the  following  table  are  summarized  experiments  taken  at  random  from 
Atwater's  papers,  and  in  parallel  columns  are  placed  figures  representing 
(1)  the  amoimt  of  heat  production  as  calculated  by  him.  and  (2)  the  amount 
of  heat  loss  determined  directly.  Besides,  in  order  to  test  by  these  observations 
the  heat  values  of  the  organic  foodstuffs  as  given  by  Eubner,  which  are 
generally  accepted  as  standard,  we  have  calculated  from  Atwater's  data  the 


Mean  per  Day 


Number  or 
Experiment. 

Dura- 
tion in 
days. 

A 

Heat  pro- 
duction 
calculated 
by  Atwater. 

B 

Heat  loss 

determined 

directly. 

C 

Difference 
between 
A  and  B. 

D 

Mean  of 
A  and  B. 

E 

Heat  pro- 
duction 

calculated 
by  the 
author. 

F 

Difference 
between 
D  and  £. 

Best. 
5 

4 
4 
4 
4 
4 
3 
4 
3 
3 
3 
3 
3 
3 

Cal. 
2.482 
2.434 
2,361 
2,277 
2,268 
2,112 
2,131 
2,216 
2,238 
2,304 
2,242 
2,043 
2,067 

Cal. 
2.379 
2,394 
2,287 
2.309 
2,283 
2,151 
2.193 
2.176 
2,272 
2,279 
2,244 
2,085 
2,079 

Per  cent. 
-4.1 
-1.6 
-3.2 
+  1.4 
+  0.7 
+  1.8 
+  2.9 
-1.8 
+  1.5 
-1.1 
+  0.1 
+  2.0 
+  0.6 

Cal. 
2,430 
2,414 
2,324 
2,293 
2,272 
2.131 
2,162 
2,196 
2,255 
2,291 
2.243 
2,064 
2,073 

Cal. 
2,501 
2,480 
2,359 
2.292 
2,277 
2,125 
2,127 
2,154 
2,197 
2,300 
2.270 
2,038 
2,071 

Per  cent. 
+  2.9 

7 

+  2.7 

8 

+  1.5 

9      

-0.04 

10 

+  0.2 

13        

-0.3 

14    

-1.6 

23          

—  1.9 

24        

—  2.6 

21              

+  04 

25      

+  12 

26 

—  1.3 

28      

—  0  1 

Mean 

45 

4 
4 
3 
3 
3 
3 

2,244 

3,829 
3,901 
3,515 
3,439 
3,573 
3,629 

2,241 

3,726 
3,932 
3,589 
3,420 
3,565 
3,587 

-0.1 

-2.7 
+  0.8 
+  2.1 
-0.6 
-0.2 
-1.2 

2,243 

3,777 
3,916 
3,552 
3,430 
3.569 
3,608 

2,245 

3,819 
3,936 
3,549 
3,434 
3,553 
3,605 

+  0.1 

Work. 
6 

+  11 

11 

+  05 

29 

—  0  1 

31                 

+  01 

32 

—  0  5 

34 

—  0  1 

Mean 

20 

3,647 

3,637 

-0.3 

3,642 

3,649 

+  02 

Mean  of  all       \ 
experiments  / 

65 

2,688 

2,687 

-0.2 

2,685 

2,689 

+  0.2 

METABOLISM  IN   FASTING  95 

amount  of  heat  produced  in  each  experiment  by  the  destruction  of  proteid, 
fats  and  carbohydrates.     These  results  are  given  in  other  columns.^ 

The  greatest  difference  between  A  and  B  is  4.1  per  cent,  the  least  difference 
is  0.1  per  cent.  In  the  rest  series  the  mean  difference  is  0.1  per  cent,  in  the 
work  series  0.3  per  cent. 

It  is,  therefore,  conclusively  demonstrated  by  Rubner's  and  by  Atwater's 
experiments  that  the  foodstuffs  generate  the  same  quantity  of  heat  when 
burned  within  the  body  as  when  burned  outside  the  body.  From  a  com- 
parison of  column  E  with  D,  in  the  foregoing  table,  it  follows  also  that  the 
calorific  estimation  of  metabolism  by  means  of  the  standard  heat  values  of  the 
organic  foodstuffs  yields  very  satisfactory  results  in  the  light  of  the  heat 
production  as  actually  measured. 

§  3.    METABOLISM   IN   FASTING 

Quantitatively  considered,  metabolism  takes  the  simplest  form  in  the  fast- 
ing condition,  when  the  body  is  living  exclusively  at  the  expense  of  its  own 
combustible  materials.  Hence  it  will  be  best  to  begin  the  discussion  of  the 
processes  of  metabolism  with  a  presentation  of  that  which  takes  place  in 
fasting. 

A.    THE  GENERAL  CONDITION  IN  FASTING 

It  is  commonly  supposed  that  fasting  is  a  very  painful  state.  But  this 
is  not  the  case.  Observations  on  starving  animals  as  well  as  fasting  experi- 
ments recently  carried  out  on  men  show  that  no  real  pain  is  felt. 

During  the  first  day  of  fasting,  especially  at  the  usual  meal  times,  there  is 
a  feeling  of  hunger,  but  it  soon  disappears ;  and  it  may  even  happen  that  when 
the  individual  is  again  permitted  to  eat,  he  has  no  real  desire  for  food.  Neither 
animals  nor  men  have  any  great  need  for  water  during  the  fasting  condition. 
Fasting  dogs  often  do  not  drink  when  water  is  offered  them,  and  fasting  men 
give  out  much  more  water  than  they  take  in. 

What  is  especially  characteristic  of  the  fasting  condition  is  the  progressive 
loss  of  strength.  But  even  this  is  not  always  pronounced,  as  will  be  seen  from 
the  case  of  Succi  observed  by  Luciani.  Succi  fasted  for  thirty  days,  and  on  the 
twelfth  day  he  took  a  horseback  ride  lasting  one  hour  and  forty  minutes;  the 
same  evening  he  walked  around  the  room  a  great  deal,  ran  an  endurance  race 
with  three  young  students  which  lasted  for  eight  minutes,  and  then  went  through 
a  fencing  exercise.  On  this  day  he  took  19,900  steps.  On  the  twenty-third  day 
of  his  fast,  he  visited  the  theater  in  the  evening,  and  there  engaged  in  two  bouts 
with  swords,  in  which  he  showed  endurance,  strength  and  agility.  On  this  day 
he  took  7,000  steps. 

The  pulse  frequency  decreases  during  rest  in  the  fasting  state;  but  with 
very  slight  exercise  it  rises  much  higher  than  normal.  The  body-temperature 
(rectum)  remains  normal  or  falls  only  0.1°-0.3°  C,  until  within  the  last  few 
days    (third   to  ninth)    before   death  by   starvation,   when    it  falls   rapidly  and 


'  Since  the  Calorie  as  used  by  Atwater  is  based  upon  water  at  a  temperature  of  20"  C, 
and  is  therefore  about  1  per  cent  lower  than  that  usually  employed  (0°  C),  we  have  used 
the  following  figures  in  this  calculation:  1  g.  proteid  =  4.2  Cal..  1  g.  fat  =  9.4,  1  g.  carbo- 
hydrate =  4.15. 


96 


METABOLISM  AND   NUTRITION 


suddenly.  The  body  weight  very  gradually  declines.  The  average  daily  loss  in 
the  first  five  to  ten  days  of  long  fasting  periods  endured  by  men,  has  been  found 
to  be  1.0-1.5  per  cent  of  the  original  weight. 

During  fasting  a  mass  consisting  of  worn-out  epithelial  cells  and  residues 
of  the  digestive  fluids  accumulates  in  the  intestine,  which  either  during  the  fast 
or  after  it  is  broken  is  evacuated  as  fasces  (cf.  Chapter  VII).  From  observations 
on  fasting  men,  the  daily  quantity  of  fresh  faeces  is  estimated  at  9.5-22.0  g.,  of 
dry  ffeces  at  2-3.8  g.  They  contain  0.113-0.316  g.  of  nitrogen,  0.44-1.35  g. 
of  ether  extract  and  0.25-0.48  g.  of  ash.  Microscopic  examination  of  fasces 
reveals  numerous  fine,  needle-shaped  crystals  of  the  fatty  acids  embedded  within 
a  finely  granular,  amorphous  ground  substance,  but  no  true  formed  constituents. 

B.    CHARACTER   OF  THE   METABOLISM   IN   FASTING 

In  fasting  the  total  metabolism  falls  gradually  from  the  first  day  onward. 
Estimated  per  kg.  of  body  weight,  however,  the  daily  decline  is  only  rela- 
tively small  and  remains  for  a  long  time  at  about  the  minimum  reached  at 
the  beginning  of  the  fasting  period.  As  proof  of  this  statement,  we  give  here 
the  results  of  a  five-day  fasting  experiment  on  a  man. 


Last  food  day . . . 

First  fast  day.  . . 
Second  fast  day. 
Third  fast  day .  . 
Fourth  fast  day. 
Fifth  fast  day  . . 
First  food  day  . . 
Second  food  dav, 


Decomposed ;  g.  of— 

Total 

Body 
weight ;  kg. 

N. 

Fat. 

Carbo- 
hydrate. 

Alcohol. 

olism, 
Cal. 

67.8 

23.41 

87 

267 

28 

2,705 

67.0 

12.17 

206 

2,220 

65.7 

12.85 

192 

2,102 

64.9 

13.61 

181 

2,024 

64.0 

13.69 

178 

1,992 

63.1 

11.47 

181 

1,970 

64.0 

25.44 

64 

250 

23 

2,437 

65.6 

18.07 

72 

248 

37 

2,410 

Cal. 
Per  kg. 
of  body 
weight 


39.9 
33.2 
32.0 
31.2 
31.1 
31.2 
38.1 
36.8 


As  is  customary  in  fasting  experiments,  we  have  assumed  that  the  total 
quantity  of  carbon  from  nonnitrogenous  substances  comes  from  fat.  But  the 
body  contains  at  the  beginning  of  the  fast  a  certain  quantity  of  glycogen, 
whose  heat  value  calculated  per  g.  of  carbon  is  less  than  that  of  fat.  This 
glycogen  disappears  for  the  most  part  during  the  first  day  of  starvation  and 
a  part  of  the  carbon  reckoned  as  fat  doubtless  has  its  origin  in  this  glycogen. 
Our  figures  for  the  total  metabolism,  during  the  first  two  fasting  days  at 
least,  are,  for  this  reason,  too  large;  and  hence  it  is  possible  that  the  body 
reaches  its  minimum  metabolism  on  the  first  or  second  day  of  fasting. 

To  enter  further  into  the  processes  of  metabolism  in  fasting  it  will  be 
necessary  for  us  to  discuss  the  decomposition  of  proteid  and  fat  more  fully. 
Nothing  further  can  be  said  at  present  concerning  the  share  of  carbohydrates 
stored  in  the  body  in  these  decompositions,  and  in  any  case  it  must  be  regarded 
as  imimportant  in  comparison  with  that  of  fat. 

Experiments  show  that  with  well-nourished  animals,  having  a  plentiful 
deposit  of  fat  in  their  bodies,  the  destruction  of  proteid  gradually  declines 
day  by  day  until  death;  whereas  with  poorly  nourished,  lean  animals  after  a 


METABOLISM  IN  FASTING  97 

preliminary  fall  there  occurs  a  rise  in  the  proteid  metabolism,  sometimes  of 
considerable  size. 

This  great  diminution  in  the  proteid  metabolism  in  fasting,  although  occur- 
ring with  various  iluctuations,  has  been  verified  also  for  men.  In  the  thirty- 
day  fasting  experiment  on  Succi  the  N-output  on  the  tenth  day  was  forty-nine 
per  cent  of  the  output  at  the  beginning;  on  the  twentieth  day  it  was  thirty-two 
per  cent,  and  on  the  twenty-ninth  day  it  was  thirty  per  cent.  In  men  also  we 
meet  with  this  peculiar  relationship :  the  N-output  in  the  urine  increases  from 
the  third  or  fourth  day,  then  falls  off  again  (cf.  table,  page  90).  The  chief 
reason  for  this  behavior  probably  is  that  on  the  first  day  the  glycogen  deposited 
in  the  body  spares  a  part  of  the  proteid  from  being  destroyed ;  but  since  most  of 
the  glycogen  is  used  up  on  this  day,  so  that  on  the  second  day  its  protecting 
influence  has  ceased  to  exist,  more  proteid  is  then  attacked.  In  this  way  the 
body  must  become  impoverished  in  available  proteid,  consequently  its  destruc- 
tion falls  again  and  from  now  on  the  combustion  in  the  body  is  maintained  to 
a  large  extent  by  the  fat,  provided  the  body  be  not  too  poor  in  fat  (Prausnitz). 

From  facts  concerning  metabolism  after  feeding,  which  will  be  summa- 
rized under  §  4,  we  know  that  of  all  the  foodstuffs  ingested  proteid  is  the  most 
easily  decomposed.  Xevertheless  in  fasting  the  share  of  proteid  in  the  total 
metabolism  (calculated  in  calories)  of  animals  previously  well  nourished  is 
only  seven  to  seventeen  per  cent.  Inasmuch  as  this  proteid  comes  from  the 
tissues  themselves,  it  follows  that  they  are  not  by  any  means  so  easily  decom- 
posed as  is  the  food  proteid,  or  more  correctly  stated,  they  give  up  proteid 
from  their  own  substance  only  in  relatively  small  quantities. 

The  increase  in  the  destruction  of  proteid  which  takes  place  in  the  later 
stages  of  fasting  and  which  continues  thence  until  shortly  before  death,  is  a 
very  interesting  phenomenon.  Voit,  who  first  observed  the  phenomenon,  ex- 
plained it  by  supposing  that  the  fat  had  all  been  used  up,  hence  the  proteid 
metabolism  was  increased  in  order  to  keep  up  the  energy  requirements  of  the 
body.  This  conclusion  was  fully  confirmed  by  the  following  experiment  by 
Rubner.  The  N-output  per  day  he  found  to  be:  first  to  third  day,  1.67  g. ; 
fourth  to  fifth  day,  1.46  g. ;  sixth  to  eighth  day,  3.21  g.  The  amount  of  fat 
burned  proved  to  be:  on  the  second  day,  10.3  g. ;  fourth  day,  10.3  g. ;  eighth 
day,  2.4  g. 

When  at  the  conclusion  of  the  fast  food  is  again  supplied,  the  body  shows 
a  pronounced  ability  to  make  good  its  losses,  and  now  lays  on  both  proteid 
and  fat  in  large  quantities.  In  the  five-day  fasting  experiment  cited  above 
the  subject  lost  during  the  five  days  399  g.  proteid,  938  g.  fat,  37  g.  ash  and 
3,829  g.  water.  On  the  succeeding  diet,  which  was  a  rich  one,  and  of  which 
4,141  Cal.  were  absorl)ed  daily,  he  destroyed  a  mean  quantity  for  two  days 
of  only  2,424  Cal.  daily,  and  thus  recovered  in  these  two  days  twenty  per  cent 
of  the  lost  proteid,  thirty-six  per  cent  of  the  lost  fat,  seventy-one  per  cent  of 
the  lost  water,  and  sixty-nine  per  cent  of  the  lost  ash. 

C.    LOSS   OF  SUBSTANCE  FROM  THE  DIFFERENT  ORGANS 

In  fasting  the  body  Urcs  at  the  expense  of  its  own  substance.  On  purely 
antecedent  grounds  it  would  be  most  natural  to  suppose  that  the  organs  in 


98  METABOLISM  AND  NUTRITION 

which  the  greatest  amount  of  work  is  done  would  be  destroyed  to  the  greatest 
extent.  But  this  is  not  true;  on  the  contrary,  these  very  organs  seem  to 
suffer  the  least  loss  of  substance,  while  the  loss  is  greatest  from  those  organs 
upon  which  little  or  no  demand  is  made  in  fasting. 

If  this  conception  be  correct — and  it  must  be  admitted  that  direct  ob.serva- 
tions  are  still  very  inadequate — it  would  follow  that  in  fasting  the  organs 
do  not  do  their  work  at  the  expense  of  their  own  substance.  It  seems  that 
all  the  organs  contribute  to  the  support  of  the  body ;  but  those  organs  which 
are  of  primary  importance  for  the  maintenance  of  life,  utilize  the  materials 
thus  contributed  by  all,  in  the  performance  of  their  particular  functions ;  that 
is  to  say,  they  work  at  the  expense  of  the  less  vital  organs:  their  oAvn  state  of 
nutrition  suffers  less,  and  hence  they  decrease  in  weight  relatively  little. 

This  view  receives  support  from  certain  experimental  facts.  The  bones,  for 
example,  bear  a  part  in  the  general  \evj  made  upon  the  organs.  E.  Voit  fed 
pigeons  with  food  which  was  sufficient  in  every  other  respect,  but  was  very  poor 
in  calcium.  The  birds  fared  very  well  and  were  killed  after  some  time.  On 
section  it  became  evident  that  those  bones  which  were  used  in  the  movements 
of  the  animal  were  normal,  while  others  such  as  the  sternum  and  the  skull  were 
brittle  and  in  places  were  even  perforated.  Since  calcium  was  being  lost  from 
the  body  all  the  time,  and  none  was  being  supplied  in  the  food  to  replace  it, 
the  "  resting  "  bones  gave  up  their  calcium  to  the  "  active  "  bones. 

Probably  a  still  more  interesting  example  is  furnished  by  Miescher's  investi- 
gations on  the  Ehine  salmon.  This  fish  leaves  the  sea  in  the  best  condition  of 
nourishment,  but  it  remains  in  fresh  water  for  six  to  nine  months  without  eat- 
ing anything.  During  this  time  it  naturally  becomes  exceedingly  thin  and 
gaunt,  and  its  muscles  greatly  diminished  in  size ;  but  the  reproductive  organs 
become  the  more  strongly  developed.  The  substance  of  muscle  has  gone  to  make 
ova  and  sperm  cells. 

Sooner  or  later,  however,  there  comes  a  time  when  the  activity  of  the  vital 
organs  and  of  those  most  necessary  for  the  generation  of  heat  in  the  body, 
falls  to  the  minimum.  If  animals  be  wrapped  up  in  bedding  they  can  be 
kept  alive  for  a  brief  time  longer.  But  respiration  and  the  heart  beat  soon 
cease  and  the  animal  dies  in  a  state  of  the  most  profound  exhaustion. 

§  4.    INFLUENCE   OF   FOOD    ON  THE   METABOLISM 

The  most  noteworthy  thing  about  metabolism  with  food  is  the  peculiar 
position  which  proteid  occupies  with  reference  to  the  other  organic  foodstuffs. 
If  a  dog  be  given  a  sufficient  quantity  of  proteid  with  no  fat  or  carbohydrate, 
under  proper  circumstances  the  body  will  remain  in  an  equilibrium  of  sub- 
stance, the  ingesta  and  the  excreta  completely  balancing  each  other.  If,  how- 
ever, the  dog  receive  carbohydrate  and  fat  in  plentiful  quantities  but  no  pro- 
teid, equilibrium  never  occurs.  The  body  continually  excretes  nitrogenous 
waste  products — which  means  that  proteid  is  continually  being  destroyed — 
and  after  a  time,  which  is  somewhat  longer  than  when  no  food  at  all  is  given, 
the  animal  finally  dies  of  "  proteid  starvation." 

Since  we  have  no  reason  to  suppose  that  there  is  any  essential  difference 
between  the  chemical  processes  involved  in  the  final  decomposition  of  the  food- 
stuffs in  the  dog  and  in  man,  it  is  theoretically  conceivable  that  a  man   also 


INFLUENCE  OF   FOOD  ON   THE  METABOLISM 


99 


could  be  nourished  exclusively  with  proteids.  But  the  capabilities  of  the  digest- 
ive organs  must  be  considered.  In  man  they  are  not  able  to  digest  and  absorb 
proteid  enough  to  maintain  the  body;  hence  man  is  always  compelled  to  eat 

nonnitrogenous  foodstuffs  in  addition  to  proteid. 


A.    INFLUENCE  OF  THE  QUANTITY  OF  PROTEID   IN   THE  FOOD   ON 
PROTEID  METABOLISM 

This  exceptional  position  of  proteid  prompts  us  to  discuss  the  conditions 
of  its  metabolism  first.  Let  us  begin  by  inquiring  how  the  quantity  of  proteid 
supplied  to  the  body  affects  the  proteid  destruction  therein.  The  following 
summary  of  a  series  of  experiments  by  Bischoff  and  Voit  may  serve  to  give 
us  our  bearings.  The  animal  received  nothing  but  meat,  which  was  carefully 
freed  of  fat,  bones,  cartilage,  etc.  The  percentage  of  nitrogen  in  the  meat 
is  estimated  at  3.4  per  cent  (corresponding  to  about  twenty-one  per  cent 
of  proteid). 


• 

Experiments. 

N  ingested,  g.  per  day. 

N  excreted,  g.  per  day. 

N-balance,  g.  per  day. 

N 

o,  1 .                      

61.2 
51.0 
40.8 
30.6 
20.4 
10.2 
6.0 
0.0 
61.2 
85.0 

57.5 
51.4 
41.9 
37.1 
23.1 
15.4 
12.5 
7.7 
58.4 
81.4 

+  3.7 

'    2 

-0.4 

♦    3 

-1.1 

'4.             

-6.5 

'5.                    

-2.7 

'    6 

-5.2 

'7 

-6.5 

'    8 

-7.7 

'    9 

+  2.8 

'  10 

+  3.6 

From  this  and  other  similar  series  of  experiments  it  follows  without  ques- 
tion:  (1)  that  increasing  the  supply  of  proteid  increases  its  destruction  in 
the  l)ody ;  ( 2 )  that  the  entire  supply  of  proteid.  or,  when  it  is  large,  almost  the 
entire  supply,  is  destroyed;  and  (3)  that  proteid  is  retained  in  the  body  (cf. 
numbers  1,  9,  10)  only  when  fed  in  very  large  quantities. 


Experiments. 

Food  per  day. 

N  excreted, 
g.  per  day. 

N-balance, 

g.  N. 

g.  Fat. 

g.  per  day. 

No.   1 

5.1 
8.5 
15.3 
17.0 
25.5 
34.0 
42.5 
51.0 

23.8 

20.4 

14.6 

8.8 

5.1 

0.0 

250 
250 
250 
250 
250 
250 
250 
250 

Starch. 
150 
150 
200 
250-350 
350-430 
450 

7.9 
9.2 

11.7 
15.1 
22.4 
29.8 
39.2 
47.0 

26.3 
23.1 
18.8 
13.4 
10.7 
5.7 

-2.8 

"     2 

-0.7. 

"    3 

+  3.6 

"    4 

+  1.9 

"    5  

+  3.1 

"     6 

+  4.2 

"     7 

+  3.3 

"    8  

+  4.0 

No.  1  

-2.5 

"    2 

-2.7 

"    3 

-4.2 

"    4 

-5.6 

"     5 

-5.6 

"    6 

-5.7 

100 


METABOLISM   AND   NUTRITION 


The  proteid  metabolism  behaves  in  essentially  the  same  way  when  the  diet 
contains  a  constant  quantity  of  nonnitrog'enous  organic  foodstuffs  in  addition 
to  proteid.     This  may  be  seen  from  the  preceding  table. 

Just  as  the  body  can  destroy  very  different  quantities  of  proteid,  it  can 
also  be  placed  in  nitrogenous  equilibrium  with  very  different  quantities  of 
this  foodstuff  (cf.  first  table  on  page  91). 

The  following  experiments  from  Voit  will  give  some  idea  of  the  time 
required  to  reach  nitrogenous  equilibrium : 


Day. 

N-lntake,  g.  per  day. 

X-output,    g.  per  day. 

N-balance,  g.  per  day. 

No.  1 

17.0 
51.0 
51.0 
51.0 
51.0 
51.0 
51.0 
51.0 

18.6 
41.6 
44.5 
47.3 
47.9 
49.0 
49.3 
51.0 

-1.6 

•    2 

+  9.4 

'    3 

+  6.5 

'    4 

.     +  3.7 

'    5 

+  31 

'     6 

+  2.0 

+  1.7 

•     8 

0.0 

II 


No.  1. 
"  2. 
"  3. 
"  4. 
"  5. 
"    6. 


51.0 
34.0 
34.0 
34.0 
34.0 
34.0 


51.0 
39.2 
36.9 
37.0 
36.7 
34.9 


0.0 
-5.2 
-2.9 
-3.0 
-2.7 
-0.9 


The  two  experiments  were  carried  out  on  the  same  animal.  Previous  to  the 
first  the  dog  had  received  17  g.  of  N  (500  g.  meat)  daily.  Equilibrium  had  not 
been  established  with  this  quantity,  for  on  the  last  day  of  this  period  he  lost 
1.6  g.  of  N  from  the  body.  The  supply  of  N  (in  meat)  was  then  increased  to 
51  g. ;  immediately  the  X-metabolism  rose,  but  perfect  equilibrium  was  not 
reached  until  the  seventh  day,  and  during  this  time  26.4  g.  N  were  retained 
in  the  body. 

What  became  of  this  nitrogen  ?  It  might  have  been  retained  as  dead  pro- 
teid, as  living  protoplasm,  or  in  the  form  of  decomposition  products.  The  last 
possibility  has  been  rendered  very  improbable  by  various  experiments  of  Voit. 
We  shall  return  later  to  the  question  of  whether  the  nitrogen  is  stored  as  proteid 
or  as  protoplasm. 

The  second  experiment  is  just  the  reverse  of  the  first.  Here  the  animal  had 
previously  received  51  g.  N  (1,500  g.  meat)  and  had  been  in  nitrogenous  equi- 
librium. The  X-supply  was  then  cut  down  to  34  g.  The  result  was  that  on  the 
verj'  first  day  the  iS[-excretion  was  less  than  before,  and  during  the  following 
days  it  sank  lower  and  lower  until  on  the  fifth  day  it  reached  approximately  the 
level  of  the  amount  supplied.  During  these  five  days  the  animal  lost  14.8  g. 
N  from  his  body. 

Xitrogen  excretion  runs  a  similar  course  during  the  first  few  days  of  starva- 
tion. If  the  same  animal  be  made  to  fast,  in  the  one  case  after  feeding  a  plenti- 
ful supply  of  meat,  and  in  the  other  after  feeding  a  scant  supply,  the  excretion 
of  N  in  the  urine  during  the  first  few  days  behaves  very  differently:  the  greater 


INFLUENCE  OF  FOOD  ON  THE   METABOLISM 


101 


the  supply  of  proteid  previous  to  starvation,  the  greater  is  the  excretion  of  N 
during  the  first  few  days  of  starvation.  It  falls  rapidly,  however,  and  after  about 
five  days  the  amount  of  N  eliminated  is  about  the  same  whatever  the  compo- 
sition of  the  food  may  have  been  previous  to  the  experiment  (Fig.  43). 

Various  circumstances  favor  the  idea  that  this  excess  of  nitrogen  excreted 
from  the  body  does  not  come  from  nitrogenous  decomposition  products  left  over 
from  previous  days,  but  that,  in  the  transition  from  a  N-rich  to  a  X-poor  diet  or 
to  fasting,  a  certain  quantity  of  the  proteid  stored  in  the  body  undergoes  decom- 
position until  the  organism  has  adapted  itself  to  the  diminished  supply  of  proteid. 


60 

\ 

SO 

\ 

\ 

*o 

^ 

30 

20 

■^ 

■^^ 

X, 

■'--. 

\ 

"~^^ 

■^ 

^ 

_- 

„.^. 

■~--  — 

--, 

- , 

to 
gm. 

^^^^=^== 

— ,=__ 

Urea 

-    -J 

Day 


a 


Fig.   43. — Three  experiment.s  on  the  elimination  of  urea  by  fasting  dogs,  after  Voit.    The  food 

previous  to  the  fasting  period  in  tlie  experiment  ——  consisted  of  2,500  g.  meat;  in -- 

1,500  g.  meat;  and  in only  a  little  proteid. 


The  body  places  itself  in  nitrogenous  equilibrium  when  the  food  contains 
both  nitrogenous  and  nonnitrogenous  substances,  in  exactly  the  same  way  as  it 
does  on  an  exclusively  proteid  diet. 

The  fact  that  proteid  decomposition  depends  primarily  upon  the  amount  of 
proteid  supi)liod  is  confirmed  in  a  very  interesting  way  by  observations  on  the 
nitrogen  excretion  during  the  different  hours  of  the  twenty-four.  The  hourly 
excretion  proves  to  be  dependent  to  a  very  great  extent  upon  the  nitrogen  absorp- 
tion from  the  intestine.  The  curves  in  Fig.  44  will  serve  as  an  illustration. 
They  represent  the  N-elimination  in  the  urine  in  two-hour  periods,  from  8  a.  m. 
until  12  P.  M.  The  dotted  line  shows  the  elimination  in  fasting,  the  continuous 
line,  on  ordinary  diet. 


102 


METABOLISM   AND  NUTRITION 


B.    THE  TOTAL  METABOLISM  AFTER  INGESTION   OF  PROTEID 

So  far  we  have  confined  ourselves  to  the  decomposition  of  proteid  without 
inquiring  how  the  nonnitrogcnous  organic  foodstuffs  behave  at  the  same  time. 
But  in  order  to  interpret  correctly  the  phenomena  just  discussed  we  must 
consider  also  the  metabolism  of  the  latter — i.  e.,  we  must  know  the  total 


1.2 

1 

1.0 

0.8 



0.6 

1 

-i 



0.4 
g.N. 

1 

OS 

a 
a 

(5 

o. 

3 

1 

12                 4  A.M.                8                      12                     4  P.M.               8  12  4  a.m.  8 

Fig.  44. — The  elimination  of  N  in  the  urine  of  man,  determined  every  two  hours,  after  Teng- 
wall.     on  ordinary  diet; fasting. 

metabolism.  As  a  basis  for  this  discussion  we  may  start  with  the  famous 
experiments  of  Pettenkoffer  and  Voit  on  equilibrium,  which  are  given  in 
the  following  tables: 

In  tlie  first  series  of  experiments  meat  only  was  fed.  The  nonnitrogenous 
metabolism  is  calculated  from  the  carbon  excreted  (cf.  page  90)  and  is 
estimated  in  terms  of  fat. 


Experiments. 

N  in  food, 

N  excreted, 
g- 

N-balance,  g. 
per  day. 

Fat-balance, 
g.  per  day. 

Total  metabo- 
lism, Cal. 

No,  1 

i7!6 

34.0 
51.0 
61.0 
68.0 
85.0 

5.6 
20.4 
36.7 
51.0 
59.7 
69.5 
85.4 

-5.6 
-3.4 

-2.7 

+  i;3 

-1.5 
-0.4 

-98.0 
-61.0 
-43.0 
-24.0 
-36.0 
+    8.0 
+    4.0 

1,067 

"     2 

1,106 

"     3 

1,360 

••     4 

1,552 

•'     5 

1,893 

"     6 

1,741 

"     7 

2,181 

In  this  and  the  following  tables  from  Pettenkoffer  and  Voit,  the  carbon  of  proteid  is 
calculated  by  the  ratio,  N  :  C  r=  1  :  3.28.  [This  ratio  was  first  determined  by  Rubner  in 
Voit's  laboratory,  but  is  generally  attributed  to  Pfliiger. — Ed.] 


INFLUENCE   OF   FOOD  ON   THE  METABOLISM  103 

We  see  that  as  the  amount  of  proteid  fed  increases  the  amount  of  fat 
burned  decreases,  so  that,  when  from  68  to  85  g.  of  X  are  supplied  (in  meat), 
a  small  amount  of  fat  is  stored  in  the  body. 

Estimation  of  the  total  metabolism  in  Cal.  shows  that  as  the  amount  of 
proteid  in  the  food  is  increased,  not  only  is  the  proteid  decomposition  in- 
creased but  also  the  total  decomposition,  although  the  latter  to  a  much  less 
extent  than  the  former.  With  85  g.  X  (2,500  g.  meat)  in  the  food  the  total 
metabolism  is  about  twice  as  great  as  in  fasting  or  with  17  g.  N  (500  g.  meat), 
whereas  the  proteid  decomposition  is  fifteen  times  as  great  as  in  fasting  and 
about  four  times  what  it  is  with  17  g.  N"  in  the  food. 

In  his  experiments  on  the  metabolism  of  proteid  in  the  body  Voit  thought 
he  had  found  that  the  smallest  quantity  of  proteid  with  which  the  body  can  place 
itself  in  N-equilibrium,  even  when  carbohydrates  or  fats  are  administered  freely, 
was  higher  than  the  quantity  destroyed  in  starvation  after  the  first  few  days  of 
abstinence.  Further  investigations  have  shown,  however,  that  in  case  the  body 
receives  enough  nonnitrogenous  foodstuffs  to  enable  it  to  maintain  a  general 
equilibrium  of  substance,  the  quantity  of  proteid  can  be  smaller  than  this. 

From  experiments  by  Hirschfeld,  Kumagawa  and  Klemperer  it  appeared 
that  N-equilibrium  with  small  quantities  of  X  in  the  food  is  only  obtained  when 
the  total  amount  of  food  supplied  is  much  in  excess  of  the  usual  diet.  Thus, 
while  an  adult  man  at  rest  maintains  himself  in  X-equilibrium  on  about  100  g. 
proteid  a  day  with  a  total  energy  supply  of  32-35  Cal.  per  kg.,  in  their  experi- 
ments when  the  supply  of  proteid  was  cut  down  to  43.5  g.,  X-equilibrium  only 
occurred  when  the  total  supply  of  energy  was  as  much  as  47.5  Cal.  per  kg.;  and 
with  33  g.  proteid  only  when  the  total  supply  reached  78.5  Cal.  per  kg. 

Siven  has  shown  however  that  when  the  X-supply  is  not  cut  off  suddenly, 
but  is  reduced  gradiially,  no  such  excess  of  the  total  supply  of  energy  is  neces- 
sary. Under  such  circumstances  X-equilibrium  was  obtained,  in  the  case  of  a 
man  doing  a  moderate  amount  of  work,  with  41.4  Cal.  per  kg.  per  day,  although 
the  diet  contained  only  28.3  g.  nitrogenous  substance.  The  quantity  of  actual 
proteid  here  was  only  12.4  g.  In  other  words,  this  man  received  only  0.08  g. 
total  X  per  kg.,  of  which  only  0.03  g.  was  proteid  X,  and  yet  he  maintained  his 
X-equilibrium. 

In  the  fasting  experiment  on  Succi  (cf.  page  95)  from  the  twenty-first  to 
the  twenty-fifth  day,  0.09  g.  X  per  kg.  were  excreted  in  the  urine.  In  view  of  the 
long  abstinence  here,  it  is  likely  that  this  nitrogen  came  exclusively  from  pro- 
teid. This  being  true,  it  follows  that  the  body  can  be  brought  into  X-equi- 
librium with  a  supply  of  proteid  which  is  considerably  less  than  the  amount 
destroyed  in  the  later  stages  of  starvation. 

In  experiments  on  dogs  with  food  deficient  in  proteid  but  otherwise  suffi- 
cient, I.  Munk  and  Rosenheim  observed  from  the  sixth  to  the  eighth  week 
onward  various  severe  disorders  in  the  health,  which  finally  led  to  the  death  of 
the  animals  some  weeks  later.  According  to  this,  a  diet  poor  in  nitrogen  when 
taken  continuously  would  be  dangerous  even  if  X-equilibrium  were  established. 
The  experiments  of  Jagerroos  stand  sqviarely  opposed  to  this  view.  They  show 
that  a  dog  can  live  much  longer  than  eight  weeks  on  such  a  food  without  exhibit- 
ing any  disturbance  to  the  health,  provided  he  receive  bis  proteid  in  the  form 
of  fresh  raw  meat.  It  appears,  therefore,  that  in  the  earlier  experiments  it  was 
not  the  deficiency  of  nitrogen  itself,  but  the  unsuitable  character  of  the  food 
which  was  the  cause  of  sickness  and  death. 


104 


METABOLISM   AND   NUTRITION 


C.    METABOLISM   AFTER   INGESTION   OF   FAT 

If  an  animal  be  given  as  much  fat  as  he  uses  from  his  own  body  in  fasting, 
the  latter  is  entirely  replaced  by  the  fat  in  the  food.  This  will  appear  from  the 
following  observations  on  the  dog  (Voit)  : 


Experiments. 

Food  in  g. 

N  excreted, 
g.  per  day. 

Fat  destro.ved, 
g.  per  daj'. 

Mean  fat, 
g.  per  day. 

No.  1  

ioo  fat. 
100  fat. 

6.0 
5.3 

5.4 
4.5 

Ill) 
85  ( 
93  1 

100  f 

98 
07 

"    2 

"    3  

"     4 

When  the  supply  of  fat  is  considerably  greater  than  the  amount  of  fat 
destroyed  in  starvation,  its  metabolism  is  increased. 


Experiments. 

Food  in  g. 

N  excreted, 
g.  per  day. 

Fat  destroyed, 
g   per  day. 

Mean  fat, 
g.  per  day. 

No.    1            

350  fat. 

11.6 
5.7 

4.7 
7.7 

96 
108 
103 
167 

) 

"     2       

[         103 

"     3 

J 

«     4 

At  the  same  time  the  total  metabolism  becomes  greater;  in  Xo.  1,  table  B, 
it  amounts  to  1,209  Cal.,  in  No.  4,  to  1.780  Cal.  The  increase  is  forty  per 
cent.  Quite  similar  results  have  been  obtained  in  similar  experiments  by 
Rubner. 

The  following  table  contains  a  summary  of  experiments  ])y  Pettenkoffer 
and  Voit  on  the  total  metabolism  after  feeding  meat  and  fat : 


Experiments. 

Food. 

N  excreted, 

Fat  destroyed, 
g- 

Total  nietab- 

N.  g. 

Fat,  g. 

Cal. 

No.  1 

17.0 
17.0 
17.0 
51.0 
51.0 
51.0 
51.0 
51.0 
51.0 

ioo 

200 

'30 
60 

100 
100 
150 

20.4 
16.7 
17.6 
51.0 
49.5 
51.0 
47.7 
49.3 
49.5 

61 
75 
116 
24 
27 
51 
35 
18 
40 

1.106 

"    2   

1,144 

"    3 

1,555 

"    4 

1,552 

"     5 

1,542 

"    6 

1,807 

"     7 

1,569 

"     8      

1.451 

"     9 

1,663 

We  have  here  two  series  of  experiments  on  the  same  animal,  tlie  one  with 
17,  the  other  with  51  g.  X,  and  with  varying  quantities  of  fat  in  each  case. 


INFLUENCE  OF   FOOD  ON   MET.\BOLISM  105 

In  the  first  the  destruction  of  fat  increases  slightly  with  the  amount  of  fat 
fed.  In  the  second  we  see  that  the  addition  of  30-150  g.  fat  to  1,500  g.  meat 
(51  g.  X)  increases  neither  the  fat  destruction  nor  the  total  metabolism. 
Metabolism,  therefore,  is  not  influenced  by  feeding  fat  to  anything  like  the 
same  extent  that  it  is  by  feeding  proteid. 

D.    METABOLISM   AFTER  INGESTION  OF  CARBOHYDRATES 

In  order  to  decide  to  what  extent  carbohydrates  fed  have  participated  in 
the  total  metabolism  it  is  not  sufficient  to  determine  merely  the  X  and  C  in 
the  excreta;  for  we  have  in  these  data  alone  no  means  of  telling  how  much 
C  belonging  to  the  nonnitrogenous  substances  came  from  carbohydrates  and 
how  much  from  fat.  But  if  the  0.  absorbed  in  the  same  period  be  determined 
also,  it  is  possible  to  decide  whether  the  nonnitrogenous  metabolism  has  been 
mainly  from  carbohydrates  or  mainly  from  fat. 

When  carbohydrates  alone  are  burned  the  ratio  between  the  volumes  of 
carbon  dioxide  excreted  and  oxygen  absorbed — i.  e.,  the  respiratory  quotient 
/OUa\_-g  j^g^  equal  to  1;  when  fat  alone  is  burned,  it  is  only  0.71.     The 

amount  of  CO^-elimination  and  Oo-absorption  corresponding  to  the  proteid 
destroyed  can  be  calculated  without  any  difficulty  from  the  X-excretion.  But 
a  certain  quantity  of  carbon  dioxide  eliminated  and  of  oxygen  absorbed  re- 
mains to  be  accounted  for  by  the  oxidation  of  fat  or  carbohydrate  or  both. 
Now  if  the  respiratory  quotient  is  high  (near  1)  we  know  that  carbohydrates 
have  participated  to  a  great  extent,  but  if  it  is  low  (near  0.75)  we  know  that 
fat  has  entered  largely  into  the  metabolism. 

So  far  only  brief  experiments  performed  by  the  use  of  the  face  mask  have 
been  made  along  this  line.  From  these  it  may  be  gathered :  that  on  a  carbo- 
hydrate diet  the  respiratory  quotient  increases  over  that  found  in  fasting; 
that  the  carbohydrates,  therefore,  are  attacked  immediately  after  their  ab- 
sorption from  the  intestine;  and  that  in  part  at  least  they  take  the  place  of 
body  fat  in  the  general  metabolism. 

From  these  experimental  facts  it  has  been  concluded  further,  that  the 
carbohydrates  fed  are  all  destroyed  before  the  body  fat,  and  also  before  the 
fat  in  the  food:  and  the  results  of  all  experiments  in  which  carbohydrates 
are  ingested  by  the  body  are  calculated  on  this  basis.  This  conclusion,  how- 
ever, is  not  fully  warranted  by  the  facts,  and  in  opposition  thereto  it  might 
be  urged,  among  other  things,  that  even  in  fasting  the  body  protects  its 
glycogen ;  and  hence  this  carbohydrate  at  least  is  not  all  destroyed  before 
the  body  fat. 

The  matter  can  only  be  settled  positively  by  experiments  covering  a  long 
period  of  time,  in  which  either  the  amount  of  oxygen  consumed  or  the  amount 
of  heat  lost  from  the  body  shall  be  determined  directly.  Although  unfor- 
tunately we  have  no  experiments  of  this  kind,  still  in  the  calorimetric  studies 
of  Atwater  there  are  some  very  valuable  results  which  permit  us  to  take 
perfectly  definite  ground  with  regard  to  this  question  (cf.  page  94).  As 
mentioned  before,  the  total  transformation  of  energy  in  these  experiments  was 
both  calculated  indirect! v  from  the  heat  of  combustion  of  the  food  and  ex- 


106 


METABOLISM   AND   NUTRITION 


creta,  and  determined  directly  from  calori metric  measurement  of  the  heat 
given  off  by  the  subject  of  the  experiment.  In  all  the  experiments  carbo- 
hydrates were  given  in  fairly  large  quantities  and  in  the  calculation  of  the 
heat  values  it  was  presumed,  in  conformity  with  the  current  view,  that  they 
were  burned  first.  Xow  the  experiments  actually  show  a  very  close  agree- 
ment between  the  calculated  and  the  observed  heat  production.  From  which 
it  follows  that  the  theoretical  presumption  is  a  correct  one,  and  that  the  total 
quantity  of  carbohydrates  absorbed  is  burned  before  the  body  fat. 

Especially  instructive  are  two  series  of  experiments  in  which  both  the  total 
calories  supplied  (2,490  and  2,489  respectively)  and  the  quantity  of  proteid 
were  the  same,  but  where  the  proportion  of  fat  to  carbohydrates  was  consider- 
ably ditferent  in  the  two.  In  the  one  experiment  94.8  g.  fat  -|-  247.2  g.  carbo- 
hydrates were  administered,  in  the  other  40.3  g.  fat  -)-  375.2  g.  carbohydrates. 
Direct  calorimetric  determination  of  the  heat  production  yielded  in  the  first 
2,085  Cal.,  in  the  second  2,079  Cal.,  showing  that  the  ratio  of  carbohydrates  to 
"fats  within  these  limits  at  least  is  a  matter  of  indifference  to  the  organism. 

Let  us  see  now  in  which  direction  the  addition  of  carbohydrates  will 
influence  the  total  metabolism. 

Experiments  of  Pettenkoffer  and  Voit  along  this  line  gave  the  following 
results : 


Experiments. 

N. 

Food  in  g. 

G.  of  N 
excreted. 

Destroyed  g.  of 

Total  metab- 

Fat. 

Carb. 

Fat.i 

Carb. 

Cal. 

No.  1 

17.0 
17.0 
17.0 
51.0 
51.0 
61.3 
61.2 

i6;2 

4.6 
10.3 

17.' 5 

2Q.h 

379 

167 

182 
167 

172 

379 

7.3 
7.2 
20.4 
19.3 
18.3 
18.0 
51.0 
50.2 
59.7 
50.0 

103.0 
-56.3            379 

61.0    ; 
-19.9           167 

1,164 

"     2 

1,208 

"     3 

1,106 

"     4 

998 

"     5 

-10.9 
-14.0 

182 
167 

1,117 

"     6  

1,020 

"     7 

24.0     \       ... 
-38.1     1       172 
36.0 
-  112.9           379 

1,552 

"    8 

1,649 

"    9 

1,893 

"  10 

1,782 

From  Experiments  1  and  2  it  appears  that  the  total  metabolism  after 
ingestion  of  carbohydrates  (and  a  little  fat)  is  not  greater  than  it  is  in 
starvation,  that  carbohydrates  therefore  can  completely  replace  the  fat  de- 
stroyed in  starvation.  From  the  series  with  500  g.  meat  (17  g.  N)  no  influ- 
ence of  the  carbohydrates  on  the  total  metabolism  is  indicated.  With  1,500 
g.  of  meat  addition  of  172  g.  carbohydrates  produces  only  a  slight  increase 
(less  than  ten  per  cent),  with  1,800  g.  meat,  379  g.  carbohydrates  produce 
no  increase  at  all. 


'  A  —  sign  means  that  fat  has  been  stored  in  the  body. 

*  1  g.  N  =  26.0  (25.98)  Cal.,  1  g.  fat  =  9.46  Cal.,  1  g.  carbohydrate  =  4.1  Cal. 


INFLUENCE  OF  FOOD  ON  METABOLISM 


107 


E.    SUMMARY   AND   DISCUSSION 

It  appears  from  the  experimental  facts  brought  together  under  divisions 
Be  to  De,  that  the  ingestion  of  proteid  always  raises  metabolism  to  a  con- 
siderable extent,  whereas  ingestion  of  fat  and  carbohydrates  either  produces 
no  increase,  or  at  most  only  a  slight  one. 

The  experiments  of  Pettenkoffer  and  Volt,  from  which  these  conclusions 
are  drawn,  were  not  carried  out  in  a  continuous  series,  and  it  is  possible  that 
the  result  was  due  in  part  to  the  changed  condition  of  the  animal.  The  follow- 
ing series  by  Rubner  is,  therefore,  more  decisive,  because  the  experiments  came 
one  immediately  after  the  other: 


Day. 

N,  g. 

Ingesta. 

Metabolism,  Cal. 

Fat,  g. 

Carb.,  g. 

Cal. 

Total. 

Per  kg. 

2 

969 

40.2 

3 

4 

56.8 

1,513 

1,072 
947 

44.8 
39.9 

5 

6 

167 

1,536 

963 
922 

40.9 
39.6 

7 

8 

411 

1,446 

982 
977 

42.3 
42.1 

In  fasting  (days  2,  4,  6  and  8)  the  average  metabolism  was  40.4  Cal.  per  kg. 
of  body-weight;  on  feeding  56.8  g.  N  it  was  44.8  Cal.  per  kg.;  with  167  g.  fat, 
40.9  Cal.;  and  with  411  g.  carbohydrate,  42.3  Cal.  The  percentage  increase  over 
the  fasting  metabolism  was  therefore  11.9  for  proteid,  1.2  for  fat,  and  4.2  for 
carbohydrate — although,  as  is  evident  from  the  table,  the  heat  value  of  the  food 
in  all  cases  was  almost  exactly  the  same. 

In  another  series  on  feeding  1,500  g.  meat  Rubner  found  an  increase  of 
24.3  per  cent  over  the  fasting  metabolism,  and  on  feeding  153  g.  lard  or  456  g. 
carbohydrates,  an  increase  of  5.1  per  cent. 

The  results  of  Pettenkoffer  and  Voit  are  abundantly  confirmed  by  these 
more  recent  experiments. 

In  explanation  of  the  fact  that  increasing  the  supply  of  food  produces, 
under  certain  circumstances,  an  increase  in  the  metal^olism,  we  might  suppose 
either  that  the  greater  store  of  combustible  material  itself  induces  a  more 
extensive  combustion,  or  that  the  increa.se  of  total  metabolism  is  due  to  the 
work  of  digestion  or  to  muscular  movements,  etc.  The  matter  can  be  definitely 
settled  only  by  experiments  on  men  where  the  voluntary  movements  can  be 
controlled. 

Both  Magnus-Levy  and  Koraen  have  made  such  experiments  and  have 
shown  that  a  clearly  marked  increase  in  the  metabolism  of  the  resting  body 
makes  its  appearance  only  after  ingestion  of  proteid.  This  increase,  however, 
is  scarcely  to  be  ascribed  to  the  work  of  digestion,  but  is  rather  the  expression 
of  a  specwl  property  [what  Rubner  calls  "specific  dynamic  action  "—Ed.] 
of  proteid  to  intensify  the  metal)olism  independently  of  muscular  movements. 

Nevertheless,  it  should  not  be  asserted  that  the  work  of  digestion  causes 


108  METABOLISM  AND  NUTRITION 

no  increase  of  combustion,  for  it  is  evident  that  the  contractions  of  the  gastric 
and  intestinal  walls  as  well  as  the  secretion  of  the  glands  represent  dissim- 
ilative  processes,  taking  place  with  the  liberation  of  kinetic  energy. 

The  negative  effect  of  fat  or  of  carbohydrates  on  the  total  metabolism  may 
be  explained  in  one  of  two  ways:  either  the  work  of  digesting  them  is  too 
small  to  produce  a  distinct  rise,  or  the  combustion  in  other  parts  of  the  body 
than  the  digestive  organs  is  correspondingly  reduced. 

But  this  would  apply  only  in  case  the  bodily  movements  were  suppressed 
as  much  as  possible.  We  know  from  the  subjective  feeling  of  improved  capac- 
ity for  muscular  work  after  eating  and  from  an  increased  tonus  of  the  muscles 
resulting  from  the  mere  ingestion  of  food,  that  the  amount  of  metabolism 
may  well  be  increased  by  the  foods  named,  if  voluntary  movements  continue. 
It  is  evident,  however,  that  such  an  increase  would  be  wholly  independent  of 
the  kind  of  food,  and  would  be  only  indirectly  connected  with  the  act  of 
ingestion. 

If  the  food  be  of  such  a  quality  or  quantity  as  to  make  unusual  demands 
upon  the  organs,  the  work  of  digestion  may  cause  a  considerable  increase  in  the 
metabolism.  Thus  in  one  of  Rubner's  experiments  in  which  20-30  g.  bones 
were  fed,  the  metabolism  rose  ten  per  cent ;  and  in  an  experiment  of  Magnus- 
Levy  where  900-1,000  g.  of  bones  were  fed  the  absorption  of  oxygen  increased 
twenty-four  to  thirty-three  per  cent  during  the  first  six  hours.  Likewise  after 
administration  of  saline  purgatives,  Mering  and  Zuntz  observed  a  distinct  rise 
in  the  metabolism  due  to  increased  muscular  activity  of  the  intestine. 

F.    METABOLISM   AFTER  INGESTION  OF  ALBUM  OSES,  FATTY   ACIDS, 
GELATIN,   ALCOHOL,   ETC. 

Now  that  we  have  become  acquainted  with  the  metabolism  after  ingestion 
of  each  of  the  three  principal  kinds  of  organic  foodstuffs,  we  shall  consider 
briefly  the  food  value  of  some  substances  closely  related  to  them,  which  either 
are  formed  in  the  course  of  digestion,  or  occur  more  or  less  commonly  in  our 
ordinary  articles  of  diet. 

1.  The  digestion  of  proteid  passes  through  a  number  of  different  stages 
(Chapter  VII).  It  will  be  of  interest  here  to  inquire  whether  the  substances 
representing  these  different  stages  are  themselves  all  of  equal  value  for  the 
nourishment  of  the  body. 

If,  with  a  constant  quantity  of  fat  and  carbohydrate,  an  animal  be  given 
meat  on  one  day,  and  on  another  the  so-called  protoalbumose  formed  in  proteid 
digestion  so  that  in  both  cases  he  receives  the  same  quantity  of  nitrogen,  the 
N-excretion  and  the  N-retention  exhibit  no  differences  whatever  in  the  two. 
This  albumose,  therefore,  possesses  the  same  food  value  as  proteid  (Blum). 
Heteroalbumose  and  peptone  behave  quite  differently.  They  have  the  power  to 
replace  proteid  to  a  certain  extent,  but  it  appears  that  they  cannot  maintain 
the  body  in  N-equilibrium.  The  reason  for  this  doubtless  is  that  certain  carbon 
nuclei  of  the  proteid  molecule  which  occur  in  protoalbumose  are  wanting  in 
heteroalbumose  and  peptone.  Investigations  on  the  constitution  of  the  different 
products  of  proteid  digestion  have  shown  in  fact  that  the  groups  which  yield 
tyrosin  and  indol  do  not  occur  in  heteroalbumose.  Since,  apparently,  the  aro- 
matic groups  are  not  built  up  in  the  body,  we  can  readily  understand  why  hetero- 
albumose alone  does  not  have  the  full  food  value  of  proteid.  However,  we  are 
not  justified  in  concluding  from  this  that  a  part  of  the  proteid  ingested  becomes 


METABOLISM   AFTER   INGESTION   OF   FOOD  109 

of  less  value  in  the  process  of  digestion,  for  it  may  well  be  supposed  that  all  the 
digestive  products  taken  together  are  of  more  service  in  metabolism  than  are 
single  ones  eaten  alone. 

2.  On  few  physiological  questions  have  opinions  changed  so  much  as  on  the 
food  value  of  gelatin.  It  was  once  supposed  that  gelatin  is  the  most  important 
food  constituent  of  meat,  because  it  alone  could  be  dissolved.  Then  the  pendu- 
lum swung  to  the  opposite  extreme,  and  it  was  claimed  that  gelatin  is  of  no 
food  value  whatever.  Continued  investigation  has  shown  that  both  views  were 
equally  overdrawn. 

Since  gelatin,  like  proteid,  is  not  completely  oxidized  in  the  body,  its  physio- 
logical heat  value  is  less  than  that  determined  directly  by  the  calorimeter.  One 
gram  of  ash-free  gelatin  yields  to  the  body  3.884  Cal. — i.  e.,  21.2  Cal.  per  1  g.  of  N. 

Voit,  Oerum,  and  others  have  found  that  in  its  combustion  in  the  body 
gelatin  spares  proteid  to  a  considerable  extent,  acting  in  this  way  much  more 
powerfully  than  equal  quantities  of  fat  or  of  carbohydrates  (see  page  120). 
Gelatin  cannot  completely  replace  proteid,  partly  at  least  because  it  lacks  the 
tyrosin  and  indol  groups.  But  by  feeding  gelatin  the  supply  of  proteid  can 
be  reduced  considerably  without  disturbing  X-equilibrium.  Thus  by  feeding  a 
quantity  of  proteid-free  gelatin  sufficient  to  cover  one  hundred  and  one  per  cent 
of  the  daily  requirements  of  energy  Krummacher  found  that  the  proteid  destruc- 
tion was  reduced  by  about  thirty-seven  per  cent  of  the  amount  destroyed  in 
starvation. 

[Murlin  has  recently  shown  that  when  the  full  calorific  requirements  of  the 
body  are  made  up  with  nonnitrogenous  foods  (of  which  a  large  percentage  is 
carbohydrates),  nitrogen  equilibrium  can  be  maintained  in  dogs  and  man,  if 
two-thirds  of  the  starvation  requirements  for  nitrogen  are  supplied  in  the  form 
of  gelatin  and  the  other  one-third  in  the  form  of  meat. 

Kauffmann  also  has  made  a  most  beautiful  experiment  on  himself.  He  es- 
tablished nitrogen  equilibrium  on  a  diet  containing  42  Cal.  per  kilogram  with 
casein  as  the  source  of  proteid  nitrogen.  He  then  replaced  the  casein  with  a 
mixture  of  gelatin  and  certain  amino  acids,  tyrosin,  cystin,  and  tryptophan, 
which  are  lacking  in  the  gelatin.  The  mixture  contained  exactly  the  same 
quantity  of  nitrogen  as  the  casein  and  was  distributed  as  follows :  Gelatin,  ninety- 
three  per  cent;  tyrosin,  four  per  cent;  cystin,  two  per  cent;  and  tryptophan,  one 
per  cent.     Perfect  equilibrium  was  maintained  for  a  period  of  five  days. — Ed.] 

Gelatin  spares  fat  and  carbohydrate  as  well.  Thus  a  dog  fed  on  200  g.  of 
gelatin  lost  only  15  g.  proteid  and  38  g.  fat  from  his  body  per  day,  while  on  the 
eighth  day  of  starvation  the  same  dog  lost  29  g.  proteid  and  102  g.  of  fat. 

Gelatin  and  glutin-forming  substances  (which  behave  just  like  gelatin, 
Etzinger  and  Voit),  play  but  a  subordinate  part,  however,  in  the  normal  nutri- 
tion. They  occur  in  the  ordinary  articles  of  diet  in  relatively  small  quantities, 
and  to  this  extent  have  exactly  the  same  importance  as  an  equal  quantity  of 
proteid.  When  gelatin  is  fed  in  larger  quantities  to  an  animal,  he  soon  refuses 
to  eat.  It  must  then  be  given  forcibly  by  hand  and  soon  causes  indigestion. 
[Kauffmann  complains  of  great  languor  and  general  indisposition  for  work  dur- 
ing his  gelatin  experiment — effects  which  he  ascribes  to  the  lack  of  the  extractive 
substances  necessary  to  give  the  diet  the  proper  flavor  and  to  stimulate  the 
nervous  system. — Ed.] 

3.  Fat  is  split  up  in  digestion  into  fatty  acids  and  glycerin  (cf.  Chapter 
VII).  The  former  when  fed  alone  have  exactly  the  same  effect  on  metabolism 
as  a  corresponding  quantity  of  fat.  I.  Munk  placed  a  dog  in  N-equilibrium 
with  800  g.  meat  and  70  g.  fat.  Then  instead  of  the  fat  he  gave  the  fatty  acids 
derived  from  70  g.  of  fat :  the  animal  continued  in  N-equilibrium. 
9 


110  METABOLISM   AND   NUTRITION 

It  has  been  shown  that  glycerin,  which  constitutes  about  nine  per  cent  of 
fat  and  has  a  heat  value  per  gram  equal  to  about  half  that  of  fat,  can  be  burned 
in  the  body  and  can  spare  both  fat  and  proteid. 

4.  Cellulose,  which  forms  so  large  a  part  of  the  vegetable  foods,  is  acted 
upon  by  the  digcstiA-e  fluids  of  the  lower  animals  (snail,  Biedermann;  carp, 
Knauthe)  ;  but  in  herbivorous  mammals  it  is  broken  up  only  by  the  fermenta- 
tive action  of  Bacteria,  the  end  products  being  carbon  dioxide,  marsh  gas,  butyric 
acid,  and  acetic  acid  (Tappeiner). 

It  may  be  regarded  as  established  that  cellulose  is  dissolved  to  some  extent 
also  in  the  intestine  of  man.  From  twenty-five  to  sixty-three  per  cent  of  the 
cellulose  of  carrots,  celery,  cabbage  and  lettuce  is  decomposed  in  the  intestine. 
Cooking  appears  to  favor  its  solution.  The  cellulose  in  "  whole-wheat  "  bread 
also  is  dissolved  in  considerable  quantity  (Hultgren  and  Landergren). 

Nitrogen  occurs  in  plants  in  a  number  of  nonproteid  compounds,  which  with 
the  exception  of  asparagin  (amino-succinic  acid)  appear  to  have  no  real  food 
value.  The  case  of  asparagin  is  not  without  its  practical  interest,  for  this  sub- 
stance is  a  rather  abundant  constituent  of  leguminose  seeds,  oatmeal  and  potatoes. 

5.  It  is  perfectly  certain  that  alcohol  is  burned  in  the  body.  Of  the  total 
amount  absorbed  from  the  stomach  only  about  two  per  cent  is  eliminated  from 
the  body  unchanged;  the  rest  is  oxidized  to  carbon  dioxide  and  water  (Atwater 
and  Benedict). 

If  alcohol  were  destroyed  in  the  body  without  protecting  other  substances 
from  destruction,  the  CO„-excretion  ought  of  course  to  be  correspondingly  in- 
creased. But  this  is  not  the  case.  Experiments  by  Zuntz  and  Berdez  and  by 
Geppert  show  that  a  dose  of  alcohol,  so  long  as  it  is  not  large  enough  to  intoxi- 
cate, produces  no  appreciable  increase  in  the  consumption  of  oxygen,  and  only 
an  insignificant  increase,  if  any  at  all,  in  the  excretion  of  carbon  dioxide. — By 
means  of  experiments  in  which  the  total  metabolism  as  well  as  the  heat  loss 
were  determined  directly,  Atwater  and  Benedict  were  able  to  demonstrate  also 
that  alcohol  can  replace  the  nonnitrogenous  foodstuffs  to  the  full  extent  of  its 
heat  value. — Replacing  a  certain  quantity  of  fat  by  an  isodynamic  quantity  of 
alcohol  produces  at  first  a  distinct  increase  in  the  destruction  of  proteid.  If 
the  experiments  were  interrupted  at  this  time,  the  result  naturally  would  indi- 
cate that  alcohol  does  not  save  proteid,  but  rather  intensifies  its  decomposition. 
If,  however,  the  experiments  be  continued,  the  destruction  of  proteid  falls  again 
and  comes  back  to  the  original  level.  The  body  therefore  must  become  accus- 
tom.ed  to  alcohol,  before  the  latter  can  exercise  its  proteid-sparing  power  (Xeu- 
mann,  Clopatt). 

But  alcohol  cannot  play  any  considerable  part  in  the  normal  nutrition  of 
man.  The  quantity  which  one  unaccustomed  to  its  use  can  drink  without  symp- 
toms of  intoxication  is  very  small — only  16-25  g.  With  a  heat  value  of  7  Cal. 
per  g.,  this  would  amount  to  112-175  Cal. — that  is,  estimating  the  requirements 
of  metabolism  at  2,500  Cal.,  4.5-7  per  cent  of  the  total  energy  might  be  supplied 
in  the  form  of  alcohol.  Only  in  very  exceptional  cases  can  alcohol  be  of  any 
practical  importance  as  a  foodstuff.  In  diseases  accompanied  by  reduced  powers 
of  digestion,  it  appears  to  be  of  great  service  as  a  direct  food,  quite  independently 
of  its  effect  upon  the  nervous  system. 

§  5.    INFLUENCE   OF   MUSCULAR   WORK   ON   METABOLISM 

It  was  apparent  from  Lavoisier's  original  experiments  on  the  respiratory 
exchange  that  combustion  is  increased  by  muscular  work,  and  investigations 
carried  out  since  that  time  have  established  the  fact  bevond  all  doubt. 


INFLUENCE  OF   MUSCULAR   WORK   ON   METABOLISM 


111 


When  Liebig,  with  much  greater  clearness  than  had  been  attained  up  to 
his  time,  had  made  out  the  chemical  composition  of  foods  and  of  the  tissues 
of  the  dead  body,  he  set  himself  the  task  of  determining  what  foodstuffs  are 
consumed  in  the  work  of  the  body  and  what  significance  in  general  the 
different  groups  of  organic  foodstuffs  have  for  metabolism. 

Since  organisms  are  distinguished  chemically  by  the  fact  that  they  con- 
tain proteid,  he  assumed  that  the  activity  of  the  body  and  especially  of  the 
muscles  takes  place  at  the  expense  of  the  living  protoplasm,  and  that  this 
in  turn  is  built  up  from  the  proteid  in  the  food.  The  nonnitrogenous  sub- 
stances, he  said,  are  used  in  the  formation  of  heat  in  the  body  by  direct 
oxidation,  and  thus  by  taking  possession  of  the  oxygen  they  protect  proteid 
from  its  harmful  effects.  On  this  basis  the  organic  foodstuffs  were  classified 
as  tissue  forming  or  plastic,  and  heat  forming  or  respiratory. 

The  second  proposition  of  this  hypothesis  can  be  disposed  of  immediately. 
Experiment  has  shown  definitely  that  decomposition  of  nonnitrogenous  food- 
stuffs is  not  inaugurated  by  oxygen  but  by  the  activity  of  the  tissues.  The 
dependence  of  heat  production  upon  the  nei-vous  system  is  evidence  of  this  fact 
(cf.  Chapter  XIV). 

If  this  view  that  bodily  work  takes  place  at  the  expense  of  the  living 
substance  of  the  muscles,  were  correct,  one  would  expect  that  work  would 
be  accompanied  by  an  increased  output  of  nitrogen.  But  in  the  great  majority 
of  the  experiments  made  to  test  this  point  either  no  increase  or  only  a  very 
slight  one  is  found  on  working  days. 

The  following  experiments  by  Voit  on  the  dog  will  serve  as  an  illustration : 


1.  Dog. 


2.  Dog. 


N  excreted,  g.  per  day. 


5.6 

resting 

5.7 

running 

5.1 

resting 

51.8 
55.3 

resting 
running 

51.8 
53.8 
52.3 

resting 

running 

resting 

The  same  result  was  obtained  by  Pettenkoffer  and  Voit  in  their  experiments 
on  man.  The  subject  was  required  to  turn  a  wheel  with  a  crank — a  kind  of  work 
to  which  he  was  accustomed — the  wheel  being  so  loaded  as  to  demand  aliout  the 
same  expenditure  of  energy  as  his  customary  work  demanded.  He  worked  nine 
hours  of  the  twenty-four.  Fasting  and  resting,  he  gave  off  12.3-12.5  g.  N; 
fasting  and  working,  11.7  g.  On  a  moderate  diet  at  rest,  he  eliminated  16.5- 
17.4  g.  N  and  at  work  17.0-17.4  g.  IST.  Here  likewise  there  is  no  increase  in  the 
daily  excretion  of  nitrogen  due  to  work. 

Fick  and  Wislicenus  made  a  very  important  experiment  on  themselves. 
They  ascended  the  Faulhorn  in  Switzerland,  a  mountain  which  has  an  altitude 
of  1,956  meters  above  the  lake  at  its  base.  Seventeen  hours  before  the  ascent 
they  ate  their  last  nitrogenous  meal;  the  ascent  itself  lasted  six  hours,  and  seven 


112  METABOLISM   AND   NUTRITION 

hours  later  they  ate  the  first  nitrogenous  food  after  the  experiment.  The  urine 
was  collected  from  the  beginning  of  the  ascent  until  seven  hours  after  its  con- 
clusion, and  was  analyzed  for  nitrogen.  Pick's  urine  contained  5.74  g.  N  and 
that  of  Wislicenus  5.55  g.,  representing  a  work  equivalent,  calculated  from  the 
heat  value  of  the  proteid  burned,  of  63,378  and  62,280  kilogram-meters  respec- 
tively. Pick's  weight  was  66  kg.  and  Wislicenus's  was  76  kg.;  hence  the  amount 
of  external  work  actually  done  in  lifting  their  bodies  1,956  meters  was  129,096 
and  148,656  kg.  m.  respectively.  The  work  done  at  the  expense  of  proteid  there- 
fore could  not  have  been  more  than  one-half  that  expended  merely  in  lifting  their 
bodies,  not  taking  into  account  the  work  of  the  heart,  of  the  respiratory  muscles 
and  of  the  other  muscles  constantly  in  use  in  maintaining  equilibrium. 

But  it  might  1)6  argued  that  the  increased  excretion  of  nitrogen  corre- 
sponding to  the  work  of  a  given  day  would  be  eliminated  from  the  body  the 
following  day.  This  idea,  first  expressed  by  Liebig.  was  tested  by  Argutinsky 
and  Krummacher  on  themselves,  and  was  reported  by  them  to  be  correct. 
The  force  of  their  experiments  is  considerably  diminished,  however,  by  the 
fact  that  neither  of  the  authors  was  in  nitrogenous  equilibrium  during  the 
resting  days,  and  that  their  food  was  much  too  poor  in  absolute  quantity  of 
nutrient  substances. 

Moreover,  Krummacher  himself  has  shown  elsewhere  that  when  plenty  of 
energy  is  supplied,  the  increased  output  of  nitrogen  on  the  day  following  work 
is  quite  insignificant.  Thus  a  man  engaged  in  hard  labor  received  daily  89.3  g. 
proteid  (^14.3  g.  nitrogen),  175  g.  fat,  and  903  g.  carbohydrate  (=5,701  Cal.). 
During  rest  while  on  this  diet,  he  excreted  on  the  average  13.46  g.  isT  in  the  urine 
and  faeces.  Then  followed  a  workday  on  which  he  did  402,000  kg.  m.  of  external 
work,  and  excreted  14.05  g.  X.  The  output  on  the  two  following  rest  days  was 
13.70  and  13.47  g.  X  respectively.  Only  on  the  first  of  the  two  was  there  any 
increase  over  the  elimination  previous  to  the  workday,  and  then  it  was  only  0.24 
g.  X.  This  experiment  also  shows  in  a  particularly  beautiful  way  that  muscular 
work  is  not  done  at  the  expense  of  proteid  when  a  sufiicient  supply  of  nonnitro- 
genous  food  is  given.  The  external  work  of  the  one  day  was  equivalent  to  945 
Cal.,  whereas  the  total  metabolism  of  proteid  on  the  workday  plus  the  excess 
on  the  day  following  (14.05  g.  X  +  0.24  g.  X  ^  90  g.  proteid)  was  equivalent 
to  only  364  Cal. 

But  we  are  not  to  suppose  that  proteid  cannot  serve  as  the  source  of 
muscular  energ}'.  For  in  extreme  cases  when  there  is  no  fat  and  no  carbo- 
hydrate at  the  disposal  of  the  body,  if  muscular  work  is  done,  it  can  only 
be  at  the  expense  of  proteid. 

PflUger  fed  a  large  dog  for  a  long  time  on  nothing  but  meat  which  contained 
as  little  fat  and  carbohydrate  as  possible.  The  dog  was  already  very  lean  before 
the  beginning  of  the  experiment,  so  that  there  was  no  stored  fat  and  glycogen 
to  draw  upon.  From  time  to  time  he  was  compelled  to  do  severe  work  varj'ing 
in  amount  from  73,072  kg.  m.  to  109,608  kg.  m.,  and  since  the  fat  and  carbo- 
hydrate in  the  food  were  far  from  sufficient  to  produce  this  amount  of  energy, 
the  work  must  have  been  done  largely  at  the  expense  of  the  proteid. 

• 

It  is  perfectly  easy  to  show  that  the  nonnitrogmous  foodstuffs  furnish 
energy  for  muscular  work.     The  excretion  of  carbon  dioxide   rises  almost 


INFLUENCE  OF   MUSCULAR   WORK  ON   METABOLISM  113 

immediately  as  soon  as  work  begins  and  has  been  known  to  increase  from 
27  to  131  g.  per  hour.  There  is  no  corresponding  increase  in  the  excretion 
of  N,  as  we  have  seen,  hence  this  excess  of  CO,  must  represent  an  increased 
oxidation  of  nonnitrogenous  food. 

In  the  experiments  of  Pettenkoffer  and  Yoit  on  men,  the  daily  amovmt  of 
fat  destroyed  in  fasting  rose  171  g.  as  the  result  of  work,  and  upon  an 
ordinary  diet  it  rose  101  g.  The  experiments  of  Atwater  have  yielded  similar 
results.  In  one  of  his  subjects  the  total  metabolism  during  rest  amounted 
to  2,357  Cal.,  of  which  429  came  from  proteid.  and  1,928  came  from  non- 
nitrogenous  food.  With  severe  muscular  work  the  metabolism  rose  to  the 
mean  value  of  5,119  Cal.,  of  which  462  came  from  proteid,  and  4,657  from 
nonnitrogenous  food. 

By  parallel  experiments,  in  which  on  the  one  hand  chiefly  fat,  and  on  the 
other  chiefly  carbohydrates  were  fed,  Zuntz  has  shown  very  definitely  that  the 
muscles  can  use  one  kind  of  nonnitrogenous  food  as  well  as  the  other.  The  same 
appears  also  from  Atwater's  experiments. 

We  can  say,  therefore,  that  the  muscles  are  able  to  perform  their  work  at 
the  expense  of  all  three  classes  of  organic  foodstuffs,  that  they  prefer  the 
nonnitrogenous  substances,  and,  as  it  appears,  they  draw  upon  the  carl)ohy- 
drates  first.  Thus  the  one  group  or  the  other  is  utilized  according  to  the 
kind  of  food  eaten.  The  specifically  carnivorous  animals  perform  their  mus- 
cular work  at  the  expense  of  proteid  and  fat;  the  herbivorous  animals,  espe- 
cially our  domesticated  farm  animals,  at  the  expense  of  carbohydrates,  and 
in  view  of  the  large  quantity  of  carbohydrates  eaten  by  man  the  latter  is 
probably  true  of  the  hui^ian  l)ody  also. 

It  is  of  special  importance  for  the  physiology  of  general  metabolism  as 
well  as  for  the  physiology-  of  the  muscle  itself,  to  determine  how  large  a  part 
of  the  increased  transformation  of  energy  accompanying  muscular  activity 
takes  the  form  of  external  work. 

For  this  purpose  the  respiratory  exchange  has  been  determined  both  during 
rest  and  while  an  accurately  measured  quantity  of  work  was  being  performed. 
Subtraction  of  the  carbon  dioxide  excretion  and  the  oxygen  absorption  during 
rest,  from  the  corresponding  factors  during  work,  shows  an  absolute  increase 
which  represents  the  known  quantity  of  external  work.  In  this  way  one  can 
readily  obtain  the  amount  of  metabolism  which  1  kg.  m.  of  work  represents  and 
these  figures  can  be  reduced  to  heat  equivalents. 

Such  determinations  have  been  made  in  Zuntz's  laboratory  in  Berlin,  and 
it  has  been  found  that  the  dog  uses  0.007-0.0077  Cal.  to  do  1  kg.  m.  of 
external  work  and  the  horse  0.00G9  Cal.  at  the  same  kind  of  work  (walking 
uphill).  And  since  theoretically  1  kg.  m.  =  0.00235  Cal.,  or  425  kg.  m.  =  1 
Cal..  we  conclude  that  in  these  animals  aliout  one-third  of  the  actual  energy 
developed  in  muscular  work  appears  as  effective  external  work.  In  man  the 
heat  equivalent  of  1  kg.  m.  of  work  with  the  lower  extremities  (mountain 
climbing)  is  about  the  same,  namely  0.0072  Cal. ;  so  that  one-third  of  the 
total  energy  developed  in  our  own  muscles  also  is  utilized  as  external  work. 

Even  the  slightest  muscular   movements   influence   the  metabolism  per- 


114 


METABOLISM   AND  NUTRITION 


ceptibly,  and  if  one  wishes  wholly  to  exclude  this  effect  it  is  necessary  vol- 
untarily to  suppress  all  muscular  movements  and  tensions.  Under  such 
circumstances,  that  is,  lying  as  quietly  as  possible,  Johansson  found  the 
CO^-excretion  in  himself  to  be  about  20  g.  per  hour.  Ordinarily  while  av/ake 
we  never  observe  muscular  rest  so  complete  as  this,  and  hence  when  Johansson 
merely  lay  resting  in  bed  without  special  effort  to  suppress  muscular  move- 
ments, his  COo-excretion  rose  to  25  g.  per  hour.  In  general  we  may  say  that 
the  respiratory  exchange  in  a  man  not  doing  any  real  physical  labor,  and  yet 
not  in  absolute  rest,  is  about  forty  per  cent  greater  than  in  sleep. 


§  6.    INFLUENCE   OF   THE   SURROUNDING   TEMPERATURE   ON 

METABOLISM 

The  cold-blooded  and  warm-blooded  animals  react  very  differently  toward 
changes  in  temperature.  WHiereas  in  the  latter  the  respiratory  exchange,  which 
may  be  taken  as  a  relative  expression  of  the  total  metabolism,  rises  when  the 
temperature  falls,  and  falls  when  the  temperature  rises,  in  the  former  the 
respiratory  exchange  varies  directly  with  the  external  temperature.  The  fol- 
lowing experimental  results,  after  H.  Schultz,  may  be  given  as  an  example 
of  the  reaction  of  cold-blooded  animals: 


Temperature  of  the  animal  (frog).    °C. 

COa-output  per  kg.  per  hour. 

1.0-1.6 

6.4 

14.5-15.4 

25.0-25.3 

32.5-33.5 

34.0 

0.008-0.015 

0.067 
0.069-0.085        ^"^ 
0.150-0.171 
0.550-0.670 

0.639 

It  was  first  established  l)y  experiments  from  Pfliiger's  lal)oratory  that  when 
the  external  temperature  declines  the  metabolism  of  warm-blooded  animals 
increases  over  that  characteristic  of  a  medium  temperature.  By  increasing 
the  heat  production  the  body  protects  itself  against  the  heat  loss  occasioned 
by  the  cooling.  Conversely,  however,  it  is  to  be  ol)served  that  a  rise  of  the 
body  temperature  also  produces  an  increase  in  metabolism;  which  shows  that 
the  energy  of  the  oxidation  processes  in  the  warm-blooded  also  as  well  as  in  the 
cold-blooded  animals  increases  with  the  temperature  of  the  organs.  There  is 
here  a  fundamental  agreement  in  the  basal  properties  of  living  tissues  in  all 
animals.  The  increa.se  of  metabolism  accompanying  a  decline  in  the  external 
temperature  is  to  be  considered  as  a  later  acquirement  on  the  part  of  warm- 
blooded animals — as  something  in  fact  which  has  been  gradually  evolved  in 
the  special  interest  of  a  constant  temperature  (Pfliiger). 

How  exact  this  adjustment  of  metabolism  to  external  temperature  may  be 
has  been  most  beautifully  shown  by  Rubner,  as  for  example,  in  the  following 
experiment  on  the  dog: 


INFLUENCE   OF  SURROUNDING  TEMPERATURE   ON   METABOLISM     115 


Dog  I. 

Dog  II. 

External 

temperature. 

"C. 

Cal.  per  kg. 
per  hour. 

External 
temperature. 

Cal.  per  kg. 
per  hour. 

External 
1     temperature. 

Cal.  per  kg. 
per  hour. 

13.8 
14.9 
17.3 
18.0 

78.7 
74.7 
69.8 
67.1 

11.8 
12.9 
15.9 
17.5 

40.6 
39.1 
36.0 
35.2 

'.          13.4 
19.5 
27.4 

39.7 
35.1 
30.8 

The  following  experiment  on  a  grown  guinea  pig  fasting,  is  given  as  an 
example  of  the  rise  in  metabolism  appearing  with  a  higher  body  temperature : 


External 

temperature. 

°C. 

Temperature 

of  animal. 

°C. 

CO,,  g.  per  kg. 
per  hour. 

External 
temperature. 

Temperature 
of  animal. 

CO2,  g.  per  kg. 
per  hour. 

0. 

11.1 

20.8 
25.7 

37.0 
37.2 
37.4 
37.0 

2.9 
2.2 

1.8 
1.5 

30.3 
34.9 
40.0 

37.7 
38.2 
39.5 

1.3 
1.3 

1.5 

The  influence  of  food  on  the  metabolism  at  different  external  temperatures 
is  a  matter  of  great  interest.  The  following  experiment  of  feeding  a  small 
dog  with  different  quantities  of  meat  is  one  of  the  many  published  by  Eubner 
on  this  subject. 


External 

Calories  per  kg.  and  twenty-four  hours. 

temperature. 
"C. 

Fasting. 

100  g.  Meat 
=  24  Cal.  per  kg. 

200  g.  Meat 
-  48  Cal.  per  kg. 

320  g.  Meat 
=  81  Cal.  per  kg. 

7.0 
15.0 
20.0 
25.0 
30.0 

86.4 
63.0 
55.5 
54.2 
56.2 

55!9 
55.5 
55.6 

77.7 

57^9 
64.9 
63.4 

87.9 
86.6 
76.3 

83!6 

From  this  and  other  experiments  of  the  same  purport  we  learn  that  with 
a  sufficiently  large  supply  of  meat  the  metabolism  l)ecomes  almost  independent 
of  the  external  temperature  (experiment  with  320  g.  meat),  while  with  a 
supply  which  is  too  low  to  furnish  the  calorific  energy  necessary  even  at  a 
high  temperature,  the  effect  of  the  external  temperature  is  felt  to  the  full 
extent.  This,  in  the  judgment  of  the  writer,  shows  that  the  ingestion  of  pro- 
teid  beyond  a  certain  limit  increases  the  metabolism  both  at  a  liigh  and  at  a 
low  temperature.  If  the  heat  production  obtained  in  this  way  alone  is  suffi- 
cient to  cover  the  requirements  of  the  body  even  at  a  low  temperature,  a 
fall  in  the  temperature  will  have  no  power  of  itself  to  produce  a  further  rise 
of  metabolism.  But  if  the  rise  due  to  proteid  is  not  sufficient,  a  fall  in  the 
temperature  will  force  the  metabolism  up,  though  to  a  less  degree  than  when 
no  proteid  had  l)cen  fed. 


116 


METABOLISM  AND   NUTRITION 


The  alterations  of  metahoUsni  in  the  service  of  heat  regulation  do  not 
make  their  appearance,  if  the  influence  of  the  central  nervous  system  on  the 
muscles  be  terminated  either  by  curare  poisoning  or  l)y  section  of  the  spinal 
cord  at  a  high  level.  This  is  shown  by  the  following  experiment  of  Velton 
on  a  curarized  rabbit. 


Temperature  of  the  animal. 
"C. 

Oxygen  absorbed,  cc.  per  kg.  per 
hour. 

COj  excreted,  cc.  per  kg.  per 
hour. 

38.3 
37.4 
31.4 
26.2 
23.1 

581 
557 
386 
219 
181 

571 
541 
383 
202 

178 

These  facts  naturally  suggest  that  under  normal  circumstances  the  rise 
in  metabolism  here  being  considered  is  due  to  muscular  activity  called  out 
by  the  central  nervous  system,  and  this  is  very  generally  assumed  to  be  the 
case.  But  a  question  arises  as  to  whether  gross,  plainly  visible  muscular 
movements  necessarily  occur. 

In  small  animals,  such  as  mice,  the  bodily  movements  become  very  active 
when  the  external  temperature  is  greatly  lowered.  In  dogs,  on  the  other  hand, 
Rubner  never  observed  any  movements  which  were  directly  occasioned  by  the 
heat  or  cold,  although  he  emphasizes  the  statement  that  at  the  upper  and  lower 
extremes  of  temperature  marked  unrest  was  at  times  to  be  observed. 

In  the  present  writer's  opinion,  it  is  very  diificult  or  probably  impossible  to 
solve  the  question  of  the  part  taken  by  the  muscles  in  the  heat  regulation  by 
experiments  on  animals,  for  there  must  always  be  a  certain  amount  of  muscular 
tension  and  the  like  which  can  scarcely  be  estimated  with  any  accuracy,  although 
the  metabolism  may  be  verv  considerably  increased  by  them.  Thus  in  experi- 
ments by  Johansson,  the  COj-elimination  in  an  ordinary  resting  condition,  lying 
in  bed,  was  twenty  to  thirty-one  per  cent  more  than  when  great  care  was  taken 
to  observe  absolute  muscular  rest.  Hence  in  order  to  exclude  muscular  move- 
ments altogether,  it  is  obviously  necessary  to  carry  out  the  experiments  on  per- 
sons who  are  willing  and  able  to  enforce  the  desired  state  of  relaxation  of  their 
own  bodies. 

From  the  experiments  of  Loewy  it  appears  that  within  a  period  of  one  and 
one-quarter  to  one  and  one-half  hours  the  respiratory  exchange  does  not  al- 
ways increase,  even  though  the  temperature  fall  considerably.  But  whenever 
an  increase  did  occur,  if  the  experiment  was  being  performed  on  an  intelligent 
individual  intrusted  with  the  regulation  of  his  o-wn  respiration,  shivering  or 
increased  tone  of  the  muscles  was  distinctly  evident.  By  maintaining  com- 
plete rest  for  one  and  one-half  hours  Johansson  w^as  unable  to  secure  any 
evident  influence  of  external  temperature  upon  the  excretion  of  carbon  diox- 
ide, although  the  body  was  naked  and  the  temperature  varied  from  14°  to 
22°  C.  Under  Rubner's  direction,  experiments  continued  from  four  to  six 
hours  gave,  on  the  whole,  similar  results. 

One  is  likely  to  conclude  from  these  experimental  facts  that  when  mus- 
cular movements  are  voluntarily  suppressed,  the  production  of  heat  in  man 


METABOLISM   IX  ANI^L\LS   OF   DIFFERENT   SIZE 


117 


i.^i  for  a  time  independent  of  the  external  temperature.  But  since,  as  Voit 
showed  most  clearly,  the  human  body  does  undoubtedly  react  against  the 
influence  of  a  falling  temperature  by  a  more  active  production  of  heat,  the 
conclusion  we  are  to  draw  from  the  experiments  just  mentioned  is  rather 
that  visible  muscular  movements  constitute  the  real  cause  of  increased 
metabolism. 

§  7.    METABOLISM   IN   ANIMALS    OF   DIFFERENT    SIZE 

It  is  evident  that,  other  things  being  equal,  the  total  metabolism  must 
vary  with  the  mass  of  the  body.  But  if,  in  animals  of  difEerent  size  the 
metabolism  be  calculated  according  to  the  unit  of  weight,  it  proves  to  be 
relatively  greater  in  S7nall  animals  than  in  large  ones. 

This  proposition  may  best  be  tested  on  fasting  animals  because  the  metab- 
olism in  them  is  constant,  not  being  influenced  by  the  kind  and  quantity  of 
food.  The  following  table,  with  the  exception  of  experiment  number  one,  is 
compiled  from  Eubner: 


Species. 

Fast  days. 

Weight,  kg. 

Average  of  fast  days      ,                 Calories, 
per  kg.  of  weight. 

N-excr.          Fat  metab.         ^^.^j^jj^;          of  surface. 

No.  1.  Man 

"    2.  Dog 

"3.     "     

"4.     "     

"5.     "     

"6.     "     

"7.     "     

"8.     "     

"    9.  Rabbit 

"10.        "      

"  11.  Guinea  pig.. 

3-5 

6,10 

1-3 

4,8,9 

1,  3 

2,3 

1,2,5 

1,  3,  5 

4,5 

3-8 

64.0 

30.4 

23.7 

19.2 

17.7 

11.0 

6.5 

3.1 

2.6 

2.1 

0.55 

0.20 
0.17 
0.26 
0.17 
0.31 
0.14 
0.35 
0.59 
0.58 
0.51 
0.64 

2.81              31.2 
3.28              35.3 
3.51       '       39.7 
4.24       '       44.4 
3.94               45.0 
5.74               58.8 
5.51              60.9 
7.46       ;       85.3 
4.00       '       52.2 
4.78              57.9 
13.68            145.3 

995 

997 
1,069 
1,135 
1,040 
1.109 
1.054 
1.091 
615 » 
740 
1,341 

It  is  fairly  evident  that  some  variations  between  the  different  species  of  ani- 
mals occur,  probably  because  the  covering  of  the  body  and  some  other  bodily 
characters  are  not  the  same  in  all  species.  With  this  exception,  however,  the 
table  shows  a  very  uniform  relationship,  the  cause  of  which  will  be  apparent  from 
the  followino:  considerations. 

The  smaller  an  animal  is,  the  greater  is  its  superficial  area  in  proportion  to 
its  volume  and  weight.  Suppose  we  have  two  balls,  the  one,  A,  2  cm.,  the  other,  B, 
4  em.  in  diameter,  the  surface  of  A  is  then  12.56  sq.  cm.,  that  of  B  50.24  sq.  cm.; 
their  volumes  are  4.18  and  33.49  cc.  respectively.  In  the  smaller  ball  the  ratio 
of  volume  to  surface  is  as  1 : 3,  in  the  larger  as  1:1 .5.  Xow  the  animal  body 
loses  its  heat  very  largely  (about  four-fifths)  through  the  skin.^  and  the  quan- 
tity of  heat  thus  given  off  is  evidently  proportional  to  the  skin  surface.  In 
order  that  the  temperature  may  remain  constant,  the  production  of  heat — i.  e., 
the  metabolism — must  also  be  proportional  to  the  skin  surface.     If,  therefore, 


1  [It  has  been  shown  that  when  the  rabbit's  ears  are  exchided  this  animal  forms  no 
exception. — Ed.  ] 


118 


METABOLISM  AND   NUTRITION 


a  large  and  a  small,  warm-blooded  animal  with  fur  of  the  same  thickness  are  to 
have  the  same  bodily  temperature  in  the  same  atmospheric  temperature,  the 
small  animal  must  produce  more  heat  in  proportion  to  its  weight  than  the  large 
one — i.  e.,  the  metabolism  per  kilogram  of  weight  must  be  greater  in  the  former 
than  in  the  latter  (C.  B^rgmann). 

In  the  experimental  proof  of  this  relationship  which  Rubner  furnished  later 
(above  table  numbers  2-8),  he  measured  the  superficial  area  of  the  body  and 
calculated  the  metabolism  per  square  meter  of  the  surface.  It  proved  to  be 
the  same  for  all  the  dogs  regardless  of  size  (last  column  of  the  table).  The  same 
relationship  is  demonstrable  also  for  animals  on  food. 

That  the  growing  organism  has  a  greater  metabolism  per  kilogram  of 
weigljt  than  has  the  adult,  is  evident  from  the  mere  difference  in  size.  But 
experiment  shows  further  that  when  calculated  per  square  meter  of  surface/ 
the  metabolism  in  younger  individuals  is  higher  than  in  older  ones ;  in  other 
words,  the  metabolism  is  influenced  hi/  something  peculiar  to  the  young  hodij, 
which  serves  to  keep  it  at  a  higher  pitch. 

The  following  table  contains  a  number  of  observations  by  Magnus-Levy 
and  Falk  in  support  of  this  statement.  They  were  made  on  individuals  who 
had  not  eaten  for  some  time  and  who  were  resting  quietly,  lying  down. 


BLales. 

Females. 

Age. 
Years. 

Weight 
kg. 

g.    COj-exc. 
per  sq.  M. 

surface 
per  hour. 

Age. 
Years. 

Weight 
kg. 

g.    COj-exc. 
per  sq.  M. 

surface 
per  hour. 

2h 

11.5 
14.5 
18.4 
19.2 
20.8 
21.8 
26.5 
30.6 
36.1 
36.8 
39.3 
40.0 
43.0 
44.3 
57.5 
57.5 
43.2-88.0 

17.7 
17.4 
15.5 
17.5 
17.4 
15.3 
14.4 
15.7 
13.8 
13.5 
13.3 
14.1 
14.0 
15.3 
12.4 
12.9 
11.2 

15.3 
18.2 
24.0 
25.2 
31.0 
35.0 
35.5 
40.2 
42.7 
31.0-68.2 

6" 

7 

15.7 

6 

6i 

15.2 

7 

12 

14.3 

7 

12 

12.4 

9 

13 

14.9 

11 

11 

14.0 

10 

14 

13.7 

14 

12 

12.6 

14 

11 

13.5 

16 

17-40 

11.8 

17 

14 

17 

16 

16 

23-56  ........ 

The  few  direct  observations  which  Ave  have  on  the  total  metaholism  of 
growing  children  give  the  same  result,  as  will  be  seen  from  the  following 
summary : 


^  The  following  formula  devised  by  Meeh  is  used  in  calculating  the  superficial  area  of 
the  body  from  its  weight:  A  =  c-^W',  where  W  is  the  weight  in  grams  and  c  is  a  constant 
empirically  determined  for  each  animal  species.  This  constant  varies  somewhat  with  age, 
and  for  man  it  has  a  mean  value  of  12.3,  for  the  dog,  11.2,  for  the  rabbit,  12.9,  for  the  rat, 
9.1,  and  for  the  guinea  pig,  8.9. 


METABOLISM   IN  ANIMALS  OF   DIFFERENT  SIZE 


119 


Age. 
Years. 

Weight 
kg. 

Total 

metabolism 

per  kg. 

Calories 
per  sq.  M. 

surface 
in  24  hours. 

Author. 

9i 

23.2 
24.0 
26.0 
32.1 
38.0 
38.3 
41.0 
70.0 

63.0 

5216 
56.0 

48;6 
44.0 
32.0 

1,499             Hellstrum, 

9i 

1,377             Riibner. 

11 

1,290 
1,391 
1,300 
1,254 
1,321 
1,071 

Rubner  (not  in  N-equilibrium). 

11 

Sonden  and  Tigerstedt. 

12 

Rubner. 

12 

Sonden  and  Tigerstedt. 

11 

Rubner, 

Adult 

The  results  of  Camerer  and  others  on  the  amount  of  food  taken  by  chil- 
dren of  different  ages  give  exactly  the  same  result.  We  give  here  only  the 
figures  obtained  bv  Camerer. 


Males. 

Females. 

Age. 
Years. 

Weight 
,        kg. 

Calories 
per  kg. 

Calories 
per  sq.  M. 
of  surface. 

1          Age. 
Years. 

Weight 
kg. 

Calories 
per  kg. 

Calories 
per  sq.  M. 
of  surface. 

5-6 

18.0 

77.0 

1.680 

2-4 

!      13.0 

75.0 

1,470 

7-10 

24.0 

62.0 

1,440 

5-  7  ..... 

I      17.0 

69.0 

1.460 

11-14  

34.0 

47.0 

1,250 

8-10 

22.0 

59.0 

1,390 

15-16  

53.0 

40.0 

1,220 

11-14  

32.0 

52.0 

1,330 

17-18  

59.0 

38.0 

1,200 

15-18  

41.0 

33.0 

930 

Adult 

70.0 

32.0 

1,071 

21-14  

45.0 

40.0 

1,150 

1 

Adult 

1 

56.0 

32.0 

999 

In  infancy,  as  was  to  be  expected,  the  metabolism  per  kilogram  of  weight 
proves  to  be  much  higher  than  in  adult  life ;  but  calculated  per  unit  of 
surface  of  the  body  it  is  decidedly  less  than  in  children  somewhat  older 
(cf.  the  following  table).  This  is  probably  connected  with  the  fact  that 
the  new-born  child  sleeps  most  of  the  time  and  the  tonus  of  its  muscles  is  but 
slightly  developed. 


Age. 

Weight 
kg. 

Metabolism. 

Calories 
per  sq.  M. 
surface. 

Remarks. 

Al-THOR. 

Weeks. 

Total. 

Per  kg. 

9 

30 

80 

30 

2 

4 

7 

10 

14 

17 

20 

5.1 
7.6 
7.6 
7.7 

3.2 
3.7 
4.4 
5.0 
5.6 
6.1 
6.6 

352 
528 
569 
632 

258 
330 
440 
420 
440 
460 
470 

69.0 
69.0 
75.0 
82.0 

81.0 
89.0 
100.0 
84.0 
79.0 
75.0 
71.0 

1,006 
1,143  ) 
1,233  ]■ 
1,378  ) 

1,0001 

1.150 

1.370 

1,200  y 

1.170 
1.150 
1.120J 

Breast-fed. 
The  same  child 

fed   on    cow's 

milk. 

The  same  child 
fed    on    cow's 
milk. 

Rubner  and  Heubner. 
Camerer. 

120  METABOLISM  AND  NUTRITION 

In  ohi  age  the  metabolism  estimated  bv  the  square  meter  of  surface  is 
appreciably  less  than  in  middle  life.  While  the  COa-excretion  in  men  be- 
tween the  ages  of  twenty-two  and  fifty-six  was  found  to  be  11.16  g.  per  square 
meter  per  hour,  between  the  ages  of  seventy  and  seventy-seven  years  it  was 
only  9.18  g. ;  for  women  between  the  ages  of  seventeen  and  forty  it  was  found 
to  be  11.75  g.,  between  the  ages  of  seventy-one  and  eighty-six,  9.79  g.  (Magnus- 
Levy  and  Falk).  The  results  of  Ekholm  on  metabolism  in  the  aged  agree 
perfectly  with  these.  This  author  found  the  mean  of  ten  experiments  on  in- 
dividuals between  sixty-eight  and  eighty-one  years  of  age  to  be  902  Cal.  per 
square  meter  of  body  surface  per  day,  while  in  resting  men  of  middle  age 
it  amounts  to  1,071  Cal. 

We  can  say,  therefore,  that  the  age  of  tlie  ijuUridiial  is  one  of  the  factors 
determining  the  intensity  of  metabolism,  it  being  greater  per  square  meter  of 
body  surface  during  the  period  of  growth  (with  the  exception  of  infancy) 
than  in  middle  life,  and  greater  in  middle  life  than  in  old  age. 


§8.    RETENTION   OF   PROTEID   IN   THE   BODY 

In  our  study  of  the  decomposition  of  proteid  in  the  body,  supplied  with 
meat  alone,  w^e  found  that  but  a  few  days  elapse  before  the  body  places  itself 
in  N-equilibrium.  The  retention  of  proteid  with  such  a  diet  continues  there- 
fore for  only  a  short  time  and  cannot  reach  any  considerable  amount.  The 
greatest  quantity  of  "  flesh  "  which  A^oit  was  able  to  lay-on  in  dogs  kept  on  a 
pure  meat  diet  was  1,365  g.  (=  46.5  g.  IST).  On  the  average  he  was  unable 
to  bring  about  a  deposit  of  more  than  500  g.  (=  17  g.  N).  With  meat  alone 
one  may  keep  an  animal  in  a  uniform  condition  of  proteid  nutrition  which 
has  been  attained  previously  in  some  other  way,  but  once  it  is  lost  he  cannot 
restore  this  condition  with  an  exclusively  proteid  diet,  nor  bring  about  a 
"  deposit  of  flesh." 

From  his  experiments  on  an  exclusive  meat  diet  Voit  drew  the  further 
conclusion  that  under  circumstances  otherwise  the  same,  proteid  is  stored  to 
a  greater  extent  and  for  a  longer  time  before  N-equilibrium  sets  in,  if  the 
animal  be  already  fat  than  if  he  be  lean.  In  other  words,  the  fat  already 
deposited  in  the  body  saves  the  proteid  fed  from  l^eing  destroyed  and  thereby 
permits  a  greater  retention. 

We  have  already  seen  that  the  X-output  equals  the  X-intake  even  with  a 
mixed  diet  composed  of  proteid  and  nonnitrogenous  substances.  But  the 
destruction  of  proteid  is  reduced  to  a  certain  extent  l)y  the  presence  of  these 
N-free  substances;  hence  we  might  expect  that  a  more  extensive  storage  of 
proteid  continuing  for  a  longer  time  could  be  brought  about  by  feeding  non- 
nitrogenous  substances  with  proteid. 

Voit's  many  experiments  with  such  combinations  show  this  to  be  true.  It 
is  evident  from  these  same  experiments,  however,  that  the  saving  of  "  flesh  "  is 
not  much  greater  with  a  rich  supply  of  meat  than  with  a  small  supply.  With 
2,000  g.  of  meat  and  250  g.  of  fat  the  daily  sparing  was  186  g.;  with  1,000  g. 
meat  and  300  g.  fat  it  was  167  g.,  while  with  1,800  g.  meat  and  250  g.  fat  it 
was  140  g.,  and  with  1,500  g.  meat  and  150  g.  fat,  only  70  g.    It  is  impossible  to 


RETENTION   OF   PROTEID  IN  THE  BODY  121 

formulate  any  definite  law  from  these  experiments,  but  they  appear  to  indicate 
that  a  large  daily  sparing  of  proteid  depends  not  only  upon  the  absolute  quan- 
tity of  meat,  but  is  best  attained  when  the  supply  of  fat  in  proportion  to  the 
supply  of  meat  is  relatively  large. 

But  we  are  concerned  not  so  much  with  the  conditions  for  a  large  daily 
deposit  of  proteid.  as  with  those  which  insure  a  large  aggregate  deposit.  It 
may  well  be  that  with  a  certain  combination  of  meat  and  fat  the  daily 
deposit  of  proteid  would  be  high,  but  would  continue  for  only  a  few  days; 
while  with  another  combination  the  deposit  per  day  would  be  less  but  would 
hold  out  longer,  so  that  the  total  deposit  would  be  greater  in  this  case  than 
in  the  first  before  X-equilibrium  sets  in. 

It  appears  in  fact  from  Voit's  observations  that  it  is  not  the  greatest  supply 
of  proteid  which  brings  about  the  greatest  total  deposit.  \\''ith  1,800  g.  of  meat 
and  250  g.  of  fat  N-equilibrium  appeared  in  one  case  after  seven  days,  and  in 
this  time  there  was  a  total  retention  of  854  g.  of  "  flesh  " ;  with  the  same  animal 
on  500  g.  meat  and  250  g.  fat,  N-equilibrium  did  not  appear  within  thirty-two 
days,  but  during  this  time  not  less  than  1,794  g.  "  flesh  "  was  laid  on.  ^Yith 
this  combination  the  storage  of  proteid  was  very  evenly  distributed  over  the 
entire  period :  in  the  first  twelve  days  the  mean  daily  deposit  was  71  g.,  in  the 
following  ten  days  42  g.,  and  in  the  last  ten  days  52  g. 

In  order  to  obtain  the  greatest  total  deposit  of  proteid  in  the  body,  just 
as  for  the  largest  daily  deposit,  it  appears  to  be  best,  therefore,  to  give  a  rela- 
tively large  quantity  of  fat  in  proportion  to  the  quantity  of  meat.  It  is 
evident,  of  course,  that  the  supply  of  proteid  must  not  fall  below  a  certain 
limit. 

The  carbohydrates  bear  the  same  relation  to  the  retention  of  proteid  as 
does  fat,  with  the  exception  only  that  their  proteid-sparing  power  is  much 
greater  than  isodynamic  quantities  of  fat. 

This  superiority  of  carbohydrates  is  shown  in  a  very  suggestive  way  by  the 
experiments  of  Landergren.  He  gave  an  adult  man  an  almost  N-f  ree  diet,  con- 
sisting (after  deduction  of  the  loss  by  fa?ces)  of  1.6  g.  proteid,  738  g.  carbo- 
hydrate, and  17  g.  alcohol,  yielding  altogether  45.2  Cal.  per  kilogram  of  body 
weight.  On  this  diet  the  nitrogen  excretion  in  the  urine  fell  from  12.8  g.  on 
the  day  before  the  experiment  to  3.8  g.  on  the  fourth  day  of  the  experiment. 
From  the  fifth  day  on  the  carbohydrates  were  almost  entirely  excluded,  and 
instead  an  isodynamic  quantity  of  fat  was  given  (a  net  supply  of  304  g.  fat, 
2.1  g.  carbohydrate,  and  30.4  g.  alcohol,  yielding  altogether  43.7  Cal.  per  kilo- 
gram). On  this  diet  the  nitrogen  excretion  in  the  urine  from  the  fifth  to  the 
seventh  day  rose  as  follows :  4.3,  8.9,  9.6  g. 

In  explanation  of  these  facts  it  has  been  supposed  that  carbohydrates  are 
in  a  less  stable  state  of  equilibrium,  owing  to  their  aldehyde  or  ketone  groups, 
than  fat  is,  and  for  this  reason  they  are  more  readily  decomposed  and  thus 
protect  proteid  to  a  greater  extent.  But  this  can  scarcely  be  true,  for  as 
Landergren  has  shown,  the  carbohydrates  exhibit  their  characteristic  proteid- 
sparing  effect  even  when  they  are  fed  with  a  considerable  quantity  of  fat. 
Thus  in  an  experiment  with  a  net  supply  (i.  e.,  deducting  the  loss  by  the 
faeces)  of  6.5  g.  proteid,  143  g.  fat.  and  308  g.  carbohydrate,  yielding  alto- 


122 


METABOLISM   AND  NUTRITION 


gether  -15  Cal.  per  kilogram,  the  X-excretion  in  the  urine  on  the  fourth  day 
was  reduced  to  3  g.  The  same  thing  appears  from  an  experiment  by  Tall- 
qvist,  in  which  X-equilibrium  was  recovered  just  as  easily  with  forty-four 
per  cent  of  the  nonnitrogenous  energy  supplied  by  carbohydrates  as  with 
eighty-three  per  cent.  Therefore,  in  the  presence  of  a  certain  minimum  of 
carbohydrate,  fat  exercises  just  as  great  a  X-protection  as  an  isodynamic 
quantity  of  carbohydrate,  whether  X  is  being  supplied  in  the  food  or  not. 
The  cause  of  this  we  shall  discuss  later. 

We  have  no  detailed  experiments  to  show  what  conditions  favor  the  greatest 
total  deposit  of  proteid  under  the  protecting  influence  of  carbohydrates.  But 
considering  that  the  metabolism  of  proteid  runs  the  same  with  carbohydrate 
feeding  as  with  fat  feeding,  it  is  probable  that  there  is  an  agreement  in  other 
respects  also  and  that  the  storage  of  proteid  is  greatest  when  the  proportion  of 
carbohydrates  to  proteids  in  the  food  is  high. 

These  results  are  of  great  practical  importance,  for  they  show  that  it  is  not 
best  to  feed  a  convalescent  or  a  man  in  a  poorly  nourished  general  condition 
with  proteid  to  the  exclusion  of  other  foods.  Proteid  cannot  be  deposited,  and 
this  means  that  the  organs  cannot  be  built  up,  on  a  diet  composed  only  of  pro- 
teid.   Plenty  of  fats  and  carbohydrates  are  necessary  as  well  as  proteid. 

It  is  generally  supposed  to  be  rather  difficult  for  the  adult  body  to  Jaij  on 
proteid,  and  this  is  borne  out  by  the  fact  that  X-equilibrium  is  very  quickly 
established  even  with  a  very  rich  supply  of  proteid  in  the  food.  This  behavior 
is  really  what  one  would  expect.  An  excess  of  proteid  would  of  necessity 
either  raise  its  percentage  in  the  fluids  of  the  body  (blood  or  lymph),  or 
would  be  organized  into  the  living  protoplasm.  The  upper  limit  for  the 
quantity  of  proteid  in  the  former  state  is  of  course  soon  reached,  and  if  still 
more  proteid  is  to  be  retained,  it  can  only  be  deposited  as  protoplasm.  But, 
as  V.  Hoesslin  has  pointed  out,  the  body  seeks  to  maintain  its  normal  mass 
of  living  substance  within  the  narrowest  limits  possible ;  because  a  dispropor- 
tionately large  consumption  is  associated  with  the  growth  of  cells,  and  with 
this  large  consumption  there  goes  an  increased  functional  capacity,  just  as 
a  diminished  capacity  accompanies  a  falling  off  of  living  substance.  The 
body  maintains  an  average,  even  level  of  efficiency  by  keeping  the  mass  of  its 
functional  parts  approximately  constant.  The  opposite  of  this,  namely,  an 
intimate  dependence  of  the  organism  and  of  its  functional  state  on  the  amount 
of  protoplasm,  or  a  rapid  fluctuation  in  the  mass  of  the  body  proteid  would 
not  be  to  the  purpose — i.  e.,  would  be  less  advantageous  than  the  existing 
arrangement.  For  this  reason  the  body  destroys  most  of  the  excess  of  proteid 
which  it  gets  from  the  food. 


Dura- 
tion OP 
Experi- 
ment IN 

Days. 

^v^rvT     i    N-supply, 

^irdir,pe-3^.. 

N  stored, 

mean 

per  day, 

g- 

N  stored 
in  per  cent           Subject  of 
of  N-               Experiment. 
supply. 

Author. 

15 '             72.0            '15.5 

27 32.5-38.0    20.2-24.6 

18 70.0-90.0    17.2-24.2 

11 67.0-96.0    15.0-17.3 

3.3 

2.8 
3.8 
5.7 

21        Self. 
10-16 

~1.  (•  \  Female  patient. 

Krug. 
Dapper. 

Kauf  mann  and  Mohr. 

RETENTION   OF   PROTEID   IN   THE   BODY 


123 


But,  as  appears  in  the  table  on  the  preceding  page,  with  a  sufficient  excess 
of  calorific  energy  a  considerable  storage  of  proteid  can  be  accomplished  even 
by  the  adult  human  body. 

From  this  we  see  that  while  an  excess  of  nourishment  is  of  first  importance 
for  the  retention  of  proteid,  still  other  conditions  are  necessary.  In  adults, 
especially,  muscular  activity  exerts  a  very  great  influence  which  cannot  be 
explained  solely  by  the  greater  supply  of  food  which  the  working  body  de- 
mands.    This  is  evident  from  the  following  experiment  by  Caspari. 

A  dog  received  a  constant  ration,  containing  2,088-2,099  Cal.  and  25.1  g.  X 
per  day.  During  rest  the  N-balance  for  three  days  was  —  0.5,  -|- 1.3,  and 
+  1-2  g. ;  then  followed  a  working  period  of  four  days  with  a  daily  X-balance  of 
—  1.4,  0.0,  +0.1,  -f- 1.5  g.  A  period  of  rest  inserted  showed  a  X-balance  of 
+  1.3  g. ;  whereupon  the  following  five  days  at  work  gave  +2.5,  +3.7,  +2.9, 
+  3.5,  +  3.5  g.  At  the  same  time  the  animal  fell  off  in  weight  during  the  first 
working'  period  from  33.0  to  32.6  kg.,  and  in  the  second  from  32.9  to  32.1  kg.  In 
this  case  there  was  no  excess  of  nourishment,  and  yet  a  considerable  quantity 
of  nitrogen  was  retained. 

To  study  more  closely  the  conditions  for  the  storage  of  proteid  in  the 
growing  body,  and  at  the  same  time  to  exclude  the  influence  of  mere  size,  it 
is  necessary  to  compare  the  metabolism  of  two  individuals  of  the  same  size, 
one  of  which  is  grown  and  the  other  still  growing.  ■  For  this  purpose  Soxhlet 
has  brought  together  the  results  obtained  by  him  on  a  suckling  calf  50  kg. 
in  weight  with  those  obtained  by  Henneberg  on  a  grown  sheep  weighing 
45.5  ksr. 


In  food  per  kg. 

Grams 

N  excreted 

per  kg. 

Grains 
N  retained  iu 

N,  g. 

C,  g. 

body 
per  kg. 

Suckling  calf 

0.784 
0.212 

9.8 
5.6 

0.204 
0.167 

0.580 

Sheep 

0.045 

From  facts  considered  further  back,  we  know  that  in  the  adult  body  the 
rule  is  for  the  quantity  of  nitrogen  excreted  to  agree  very  closely  with  the 
quantity  in  the  food.  But,  as  the  table  shows,  this  is  not  true  in  the  suckling 
calf.  Hence,  it  follows  that  the  conditions  for  the  combustion  of  proteid  in 
the  growing  body  are  much  less  favorable  than  in  the  adult  body.  And  since 
this  difference  cannot  all  be  due  to  the  greater  absolute  quantity  of  food 
for  the  calf,  we  cannot  choose  but  suppose  that  the  cells  of  the  growing  organ- 
ism possess  a  special  ability  to  appropriate  proteid  from  the  fluids  of  the 
body,  and  to  convert  it  into  protoplasm.  More  than  this  we  do  not  know  at 
present. 

From  facts  obtained  on  the  dog,  concerning  N-metabolism  with  a  low 
supply  of  N"  in  the  food,  the  view  has  often  been  expressed  that  in  order  to 
protect  a  store  of  proteid  once  obtained,  as  much  proteid  must  be  ingested  as 
was  necessary  to  acquire  it,  or  at  least  that  the  supply  of  calories  must  be  as 
great.     But  the  experiments  by  Caspari  mentioned  above  are  opposed  to  this 


12-4 


METABOLISM   AND  NUTRITION 


conclusion,  and  other  observations  tend  in  the  same  direction.  It  is  evident 
from  fasting  experiments  that  the  body  offers  great  resistance  to  the  disso- 
lution of  proteid  once  it  has  been  organized  into  living  protoplasm  (cf.  page 
97)  ;  and  the  following  experiment  bv  Siven  shows  that  the  body  can  main- 
tain its  status  of  proteid  on  a  very  small  amount  of  proteid  in  the  daily  ration. 

The  subject  was  a  man,  thirty  years  of  age,  whose  ordinary  diet  contained 
about  16  g.  N  daily  (=100  g.  proteid).  By  giving  a  cori-espondingly  larger 
quantity  of  nonnitrogenous  food,  his  proteid  was  gradually  reduced  to  6.3  g.  X 
per  day.     The  results  are  summarized  briefly  in  the  following  table: 


Series. 

N'umber  of  days 
in  experiment. 

N-supply, 
g.  per  day. 

Time  before 
N-equil. 

Total  N-loss 
before  N-equil. 

Total  N  stored 
during  series. 

I 

8 
6 
6 

12.69 

10.40 

8.71 

6.26 

1  dav. 
1      •'■ 
At  once. 
3  days. 

0.53 
0.31 

2.09 

9.73 

II 

6.04 

Ill 

4.39 

IV 

-0.58 

During  this  experiment  the  body  not  only  did  not  lose  proteid,  but  during 
the  first  three  series  it  actually  gained  20.16  g.  X,  and  even  in  the  fourth 
series  lost  but  0.58  g.  That  is  to  say,  by  proper  adjustment  of  the  diet  the 
supply  of  proteid  can  be  reduced  to  a  very  low  level, ^  without  entailing  any 
loss  of  the  bod}'"s  own  proteid. 

Recently  several  authors,  notably  Loewi,  have  published  observations  accord- 
ing to  which  the  final  end  products  of  proteolytic  digestion  not  only  can  replace 
proteid "  in  the  metabolism,  but  are  able  to  bring  about  a  X-retention  in  the  body. 
If  these  observations  should  be  confirmed  in  their  entirety,  the  fact  would  be  of 
the  greatest  significance  for  our  conception  of  the  metabolic  processes.  For  the 
present  we  would  not  venture  to  express  any  definite  opinion  on  the  subject. 

§  9.    STORAGE    OF   CARBOHYDRATES   IN   THE   BODY 

In  1848  CI.  Bernard  and  Barreswill  rejjorted  that  the  liver  differs  from 
all  the  other  organs  in  that  it  contains  a  large  amount  of  sugar,  whatever  the 
character  of  the  food.  Some  years  later  Bernard  demonstrated  that  this  sugar 
is  produced  by  the  liver  from  a  substance  difficultly  soluble  in  water,  and  in 
1857  he  isolate<^  this  mother-substance  as  glycogen. 

Glycogen  is  very  tvidehj  distributed  in  organic  nature  and  probably  occurs 
in  all  animals.  In  the  vertebrates  it  has  been  found  in  almost  all  organs 
where  it  has  been  sought,  which  must  mean  that  gl3^cogen  is  of  great  physio- 
logical importance  in  the  body. 

The  amount  of  gh^cogen  in  the  different  organs  varies  considerably.  It 
occurs  most  abundantly  in  the  liver  and  the  muscles,  but  in  the  latter  it  is 
to  be  observed  that  different  muscles  in  the  same  animal  may  have  a  very 
different  percentage  of  glycogen.     Likewise,  corresponding  muscles  on  the  two 


^  For  discussion  of  the  optimum  amount  of  proteid  in  the  diet  see  page  142. 
'  Cf.  also  page  109. 


STORAGE   OF  CARBOHYDRATES   IX   THE   BODY 


125 


sides  of  the  body  do  not  have  exactly  the  same  percentages;  hence  it  is  not 
sufficient  to  analyze  single  muscles  in  order  to  obtain  the  amount  of  glycogen 
in  the  animal  body. 

In  the  following  table  are  brought  together  some  data  on  the  percentage  of 
glycogen  in  the  new-born  child,  in  a  dog  after  a  twenty-eight  days'  fast,  and 
in  the  frog: 


Okgan. 


Liver. . . 
Muscle . 
Skin  . . . 
Blood . . 
Lungs.. 
Brain  . . 
Ovaries 


New-born  child. 
(Cramer.) 


Fasting  dog. 

(Calculated  as  sugar 

(Pfliiger.) 


Frog.    (Athanasiu.) 


Per  cent. 

Per  cent. 

Per  cent. 

1.00-2.15 

4.79 

8.73 

O.ST-l.So 

0.16 

1.00 

0.05-0. or 

0.03 
0.01 

6.i6-i).i9 

0.01-0.0-2 

0.07 
1.10 

The  total  quantity  of  glycogen  calculated  as  sugar  in  Pfliiger's  fasting  dog  was 
52.5  g. — i.  e.,  1.5  g.  per  kilogram  of  body  weight. 

The  amount  of  glycogen  in  the  body  is  raised  considerably  hy  rich  feeding. 
In  a  fattened  goose,  as  much  as  23.3  g.  per  kilogram  of  body  weight  has 
been  observed. 


From  many  analyses  of  the  organs  of  hens  and  rabbits,  Otto  has  found  that 
the  absolute  quantity  of  glycogen  in  the  liver  is  about  half  the  total  quantity 
in  the  body.  The  same  appears  from  Pfliiger's  experiment  on  the  fasting  dog. 
When  therefore  Pavy  found  in  the  dog's  liver  alone  a  quantity  of  glycogen 
amounting  to  7.82  g.  per  kilogram,  it  is  to  .be  supposed  that  the  total  quantity 
in  the  animal's  body  was  about  15  g.  per  kilogram.  Pfliiger  takes  11  g.  as  the 
average  amount  of  glycogen  per  kilogram  in  the  dog. 

In  man  the  glycogen  in  the  liver  is  estimated  at  150  g..  and  the  total  amount 
in  the  body  at  300  g.,  which  is  only  about  4  g.  per  kilogram.  Possibly  this  esti- 
mate is  too  low. 

Glycogen  is  laid  down  in  the  cells  of  the  liver  in  large  flakes  (Fig.  45). 
It  is  deposited  in  the  muscles  partly  between  the  fibrillge  and  partly  in  them. 

It  is  evident  that  glycogen  must  be  formed  in  the  liver  because  not  only 
does  it  occur  there  in  largest  C[uantities,  liut  when  animals  previously  deprived 
of  most  of  their  glycogen  by  a  fasting  period  are  fed  with  carbohydrates,  the 
liver  is  the  first  of  all  the  organs  to  show  a  storage  of  glycogen.  An  inde- 
pendent formation  of  glycogen  in  other  organs,  and  especially  in  muscles,  is 
not  thereby  excluded,  however,  and  in  fact  there  are  certain  indications  that 
glycogen  is  thus  formed.  For  example :  glycogen  has  been  demonstrated  in 
chick  embryos  before  the  rudiment  of  the  liver  appears,  whereas  the  egg,  be- 
fore development,  is  said  to  contain  no  gh'cogen ;  the  glycogen  of  the  muscles 
of  fowls  presents  certain  differences  from  the  liver  glycogen :  again  paralyzed 
muscles  are  loaded  with  glycogen,  etc.  But  this  question  probably  ought  not 
to  be  regarded  as  definitely  settled. 


126 


METABOLISM   AND   NUTRITION 


In  view  of  the  great  variations  in  the  percentage  of  glycogen  in  the  body, 
if  one  is  to  determine  directly  the  influence  of  different  foodstuffs  on  its  storage, 
it  is  necessary  first  to  deprive  the  animal,  as  far  as  possible,  of  all  its  glycogen. 
As  appears  from  Pfliiger's  experiment  on  the  dog  cited  above,  a  considerable 
quantity  of  glycogen  may  remain  in  the  body  even  after  prolonged  fasting. 
Glycogen  is  far  more  completely  removed  from  the  body  by  severe  muscular  work ; 
in  fact  under  such  circnmstances  it  sometimes  disappears  almost  completely, 
both  from  the  liver  and  from  muscles,  in  the  course  of  a  few  hours.  Naturally, 
the  effect  of  muscular  work  is  assisted  by  a  previous  fasting  period. 

There  are  a  great  number  of  different  substances  which  have  been  claimed 
to  bring  about  an  increase  in  the  percentage  of  glycogen  in  the  liver.     Among 


1        i*f*i 


b 


Fig.  45. — Preparations  from  the  liver  of  a  man,  after  Frerichs.  A,  section  through  the  normal 
liver  containing  glycogen;  B,  section  through  the  liver  of  a  diabetic,  almost  free  of  glycogen. 
Both  preparations  treated  with  iodine. 

them  are  several  which,  at  most,  act  only  indirectly,  either  by  stimulating  the 
liver  cells  to  produce  glycogen  or  by  diminishing  its  consumption.  We  shall 
pass  over  these  substances  and  consider  here  only  the  true  glycogen  formers. 

There  is  no  longer  any  doubt  that  certain  carbohydrates  constitute  an 
important  source  of  glycogen ;  proofs  of  this  are  present  on  every  hand.  For 
example,  after  feeding  with  cane-sugar,  grape-sugar  or  starch,  14.7  per  cent 
of  glycogen  has  been  found  in  the  liver  of  hens,  10.5  per  cent  in  that  of  the 
goose,  and  16.9  per  cent  in  the  rabbit's  liver. 

It  might  be  supposed  that  the  carbohydrates  had  not  contributed  directly 
to  this  storage  of  glycogen,  but  that  they  only  protect  glycogen  split  off  from 
proteid  from  being  further  oxidized.  Otto  has  shown,  however,  that  even  if  we 
assume  that  the  greatest  possible  amount  of  glycogen  has  been  formed  from  pro- 
teid, there  always  remains  a  considerable  excess  which  could  only  have  come 
from  carbohydrates.     Similarly  Popielski  found  that  in  dogs  in  which  an  Eck 


STORAGE   OF  CARBOHYDRATES   IN  THE   BODY  127 

fistula  had  been  made  between  the  portal  vein  and  inferior  vena  cava,  but  which 
were  otherwise  healthy,  from  twelve  to  twenty-four  per  cent  of  the  sugar  eaten 
was  excreted  in  the  urine.  At  least  this  quantity  therefore  is  retained  by  the 
liver  of  normal  animals  (and  is  converted  into  glycogen). 

The  following  carbohydrates  at  least  can  serve  as  a  source  of  glycogen: 
dextrose,  levulose,  galactose,  milk-sugar,  cane-sugar,  maltose,  the  last  three  after 
being  inverted.  In  this  connection  it  is  noteworthy  that  the  glycogen  coming 
from  levulose  is  also  dextrorotatory.  Levulose,  therefore,  is  either  changed  first 
into  dextrose,  or  it  passes  directly  into  a  dextrorotatory  glycogen;  in  either  case 
the  ketone  group  of  levulose  is  transformed  into  an  aldehyde  group. 

Many  authors  have  found  a  second  source  of  glycogen  in  proteids.  In  fact 
it  has  been  observed  that  the  quantity  of  glycogen  in  the  liver  increases  after 
feeding  meat  extracted  with  boiling  water,  fibrin  or  chemically  pure  proteid 
substances.  Pfliiger  on  the  other  hand  comes  forward  with  the  claim  that  the 
quantity  of  glycogen  demonstrated  in  such  experiments  is  not  greater  than 
the  maximum  which  has  been  observed  in  fasting  animals  of  the  same  species. 
Schondorff  found  no  increase  of  the  glycogen  in  frogs  after  feeding  them 
with  casein. 

The  problem  has  been  attacked  also  from  another  side.  Under  normal 
circumstances  sugar  appears  in  the  urine  only  in  mere  traces ;  the  total  quan- 
tity of  carbohydrate  absorbed  from  the  intestine  is  therefore  either  burned 
in  the  body,  or  is  stored  up  after  having  been  transformed  into  glycogen  or 
into  fat.  It  is  only  when  the  percentage  of  sugar  in  the  blood,  due  to  a  rich 
supply  of  sugar  in  the  food,  exceeds  a  certain  low  limit  (0.2-0.3  per  cent), 
that  a  part  of  the  sugar  is  eliminated  through  the  kidneys  {alimentary  glyco- 
suria). In  this  respect  starch  forms  an  exception  to  the  rule  for  the  carbo- 
hydrates, which  is  probably  due  to  its  relatively  slow  rate  of  digestion,  a 
sudden  flooding  of  the  blood  with  sugar  being  thereby  prevented.  But  in 
diabetes  mellitus  as  well  as  after  complete  extirpation  of  the  pancreas,  or  after 
poisoning  loith  pliloridzin,  the  body  loses  to  a  greater  or  less  extent  either  its 
power  to  burn  carbohydrates  or  its  power  to  store  them,  and  the  urine  under 
these  circumstances  always  contains  more  or  less  sugar. 

These  facts  have  been  made  use  of  in  attempting  to  determine  whether  or 
not  sugar  is  formed  from  proteid.  Thus,  sugar  appears  in  the  urine  in  these 
diseased  conditions  after  feeding  proteid,  and  if  it  can  be  shown  that  this 
sugar  actually  comes  from  proteid,  we  should  have  proof  that  under  some 
circumstances  at  least  glycogen  can  be  formed  from  proteid.  For  the  sugar 
formed  from  proteid,  as  well  as  any  other  sugar,  could,  from  what  we  have 
seen,  be  changed  into  glycogen. 

It  is  a  matter  of  great  moment  in  these  experiments  to  decide  whether 
more  sugar  appears  in  the  urine  than  can  be  accounted  for  by  the  glycogen 
already  deposited  in  the  body  at  the  beginning  of  the  experiment.  Pfliiger, 
who  recently  has  subjected  the  observations  on  this  subject  to  a  searching 
criticism,  takes  the  view  that  no  proof  has  thus  far  been  given  for  the  forma- 
tion of  sugar  from  proteids.  It  appears,  however,  that  this  is  going  somewhat 
too  far;  for  in  many  of  the  experiments,  to  explain  the  quantity  of  sugar 
appearing  in  the  urine  as  derived  from  the  body  glycogen,  it  would  be  neces- 
sary to  suppose  that  the  animal  at  the  beginning  of  the  experiment  had  had 
10 


128  METABOLISM   A\D   NUTRITION 

its  maximum  percentage  of  glycogen ;  but  this  can  scarcely  have  been  the  case 
in  all  the  experiments. 

[For  example,  Lusk  and  his  co-workers  have  shown  that  producing  phloridzin 
diabetes  in  fasting  dogs  may  cause  the  proteid  metabolism  to  rise  333  to  560 
per  cent.  They  have  also  shown  that  in  these  diabetic  dogs,  whether  fasting, 
or  fed  on  meat  alone  or  on  fat  alone,  no  more  fat  is  burned  than  in  the  same 
dog  when  he  is  normal  and  fasting.  Thus,  in  one  experiment  a  dog  weighing 
11  kg.  burned  on  the  second  fasting  day  20.19  g.  proteid  and  55.87  g.  fat  with 
a  total  of  606.81  Cal.  Made  diabetic,  he  lost  on  the  fifth  day  39.4  g.  of  dextrose 
in  the  urine.  He  burned  on  this  day  67.38  g.  proteid  and  51.15  g.  fat,  a  total 
of  605.77  Cal.  The  calories  lost  in  the  urinary  sugar,  therefore,  are  very  exactly 
compensated  for  in  the  increased  proteid  metabolism.  Since  this  dog  had  re- 
ceived only  115  g.  of  fat  as  food  in  the  seven  days,  it  is  of  course  impossible  that 
the  great  amount  of  sugar  in  the  urine  should  have  come  from  glycogen  stored 
in  the  body  (cf.  also  page  125).     It  must  have  come  largely  from  proteid. — Ed.] 

Eecently  the  question  of  a  final  conversion  of  fat  into  glycogen  has  been 
actively  discussed.  As  proof  of  this  cases  of  diabetes  occurring  naturally  or 
produced  artificially  have  been  cited,  in  which  on  a  carbohydrate-free  diet  the 
quantity  of  sugar  in  the  urine  was  too  large  to  be  accounted  for  by  the  proteid 
destro3ed. 

The  first  question  to  be  asked  in  this  connection  is,  how  much  sugar  can 
proteid  yield?  In  a  number  of  experiments  on  dogs  with  pancreatic  diabetes, 
Minkowski  found  the  ratio  of  N  to  dextrose  in  the  urine  to  be  1 :  2.8 ;  in  phlo- 
ridzin diabetes,  as  v.  Mering  has  shown,  the  ratio  may  be  1 :  5.^  Remembering 
that  for  every  1  g.  N  in  the  human  urine,  on  the  average  0.72  g.  C  are  elimi- 
nated by  the  same  channel,  and  that  proteid  contains  3.28  g.  C  for  every  gram 
of  N,  the  carbon  remaining  in  the  body  which  might  go  to  form  sugar  would 
amount  to  2.56  g.  (3.28  —  0.72)  for  each  gram  of  X  ingested.  Since  dextrose  is 
forty  per  cent  carbon,  2.56  g.  C  would  correspond  to  6.49  g.  dextrose  and  hence 
the  utmost  yield  from  proteid  alone  would  be  6.4  g.  dextrose  for  each  gram  of  N. 

In  order  to  prove  a  formation  of  glycogen  from  fat  it  is  necessary  there- 
fore that  the  proportion  of  dextrose  to  X  in  the  urine  should  be  greater  than 
6.4  to  1.  [Xow  Lusk  has  shown  that  in  phloridzin  diabetes  in  dogs  and  in 
the  most  acute  form  of  diabetes  mellitus  the  ratio  is  fairly  constant  at  3.65 
to  1 ;  and  nobody  has  ever  positively  observed  a  ratio  so  high  as  6.4  to  1. — Ed.] 
For  the  present  then  we  must  say  that  fat  {,9  not  to  he  recl-oned  among  the 
sources  of  glycogen  or  sugar  in  the  body.  On  the  other  hand  it  is  fairly  certain 
that  glycerin  is  a  mother-substance  of  glycogen. 

Proceeding  on  the  assumption  that  fat  is  not  a  producer  of  glycogen,  Lander- 
gren  has  endeavored  to  explain  the  ability  of  carbohydrates,  mentioned  at  page 
121,  to  spare  proteid  to  a  greater  extent  than  does  fat.  In  his  opinion  the  body 
has  a  specific  need  for  carbohydrates.    If  they  are  not  supplied  in  the  food,  they 

*  [In  the  experiments  of  Lusk  and  others  a  ratio  as  high  as  this  is  only  obtained  imme- 
diately after  the  injection  of  phloridzin,  when  there  is  a  preliminary  sweeping  out  of 
sugar. — Ed.] 


STORAGE  OF   FAT   IN  THE   BODY  129 

must  be  formed  from  proteid ;  hence  the  increase  of  proteid  destruction  when 
carbohydrates  are  excluded  from  the  diet.  Since  in  such  experiments  on  man 
the  N-excretion  rose  some  5  g.  per  day,  the  daily  requirement  of  carbohydrates 
would  amount  to  about  32  g.  (5X6.25  =  31.25;  proteid  Cal.  =  carbohydrate 
Cal.). 

§  10.    STORAGE    OF   FAT   IN   THE   BODY 

Voit  laid  special  stress  upon  proteid  as  the  most  important  source  of  the 
fat  which  is  stored  in  the  body.  Using  the  ratio  of  N :  C  in  proteid  as  found 
by  Voit  and  Pettenkoffer,  their  experiments  on  the  state  of  equilibrium  actually 
show  that  a  considerable  portion  of  the  C  ingested  in  the  form  of  proteid  was 
retained.  Since  the  formation  of  glycogen  was  never  very  large,  Voit  and  Pet- 
tenkoffer were  fully  justified  in  concluding  that  some  of  the  C  was  retained  as  fat. 

But  the  percentage  of  C  in  proteid  is  not  so  high  as  Voit  and  PettenkoflEer 
supposed.  Calculating  their  results  on  the  basis  of  1:3.28,  the  ratio  of  N:C 
now  generally  accepted,  a  very  different  conclusion  is  reached.  Pfliiger  has 
shown  that  instead  of  57.8-58.5  g.  of  fat,  which  Voit  and  Pettenkoffer  estimated 
as  the  amount  stored  in  the  dog  as  the  result  of  feeding  2,000  g.  of  meat  per 
day,  the  newer  ratio  allows  only  11.8-13.6  g.,  and  that  with  1,500  g.  of  meat 
practically  no  fat  could  have  been  stored.  We  are  compelled,  therefore,  to  con- 
clude that  these  experiments  contain  no  proof  of  a  transformation  of  proteid 
into  fat. 

Later,  however,  Cremer  obtained  in  the  cat  a  retention  of  C  from  excessive 
meat  feeding  which  he  regarded  as  a  safe  indication  of  the  production  of  fat 
from  proteid.  The  cat  excreted  11.2  g.  of  N  per  day  and  31.2  g.  C  per  day.  But 
calculating  the  C  from  the  X  pn  the  basis  of  the  ratio  of  1:3.2  would  give 
85.7  g.  C  as  the  amount  ingested.  Since  only  31.2  g.  of  this  was  eliminated  in 
the  excreta,  4.5  g.  of  C  per  day  must  have  been  retained,  and  in  seven  days  this 
would  amount  to  31.5  g.  According  to  Cremer's  subsequent  analysis  the  ani- 
mal's body  contained  not  more  than  40  g.  of  glycogen  with  18  g.  C.  The  remain- 
der of  the  31.5  g.  of  C,  namely  13.5  g.,  must  therefore  have  been  laid  on  as  fat. 
Unfortunately  this  experiment  is  quite  too  short,  and  stands  too  much  alone 
to  be  accepted  as  a  positive  demonstration  of  the  point.  (Gruber  accomplished 
a  retention  of  81.9  g.  C  in  a  similar  experiment  on  a  dog,  but  the  amount  of 
glycogen  was  not  determined.) 

The  other  ground  on  which  Voit  based  his  idea  that  proteid  is  an  important 
source  of  fat,  was  the  degeneration  of  proteid  under  some  circumstances  into 
fat,  and  the  great  production  of  fat  in  the  larvse  of  blowflies  living  exclusively 
on  meat.  As  regards  the  former,  we  now  know  that,  at  least  in  the  case  of  the 
phosphorus  poisoning  of  the  frog  (Athanasiu),  the  supposed  fatty  degeneration 
is  in  fact  an  infiltration  of  fat  transported  from  the  fatty  deposits  of  the  body 
and  deposited  in  the  cells,  instead  of  a  formation  in  situ  by  the  destruction  of 
proteid.  Whether  all  forms  of  fatty  degeneration  are  to  be  explained  in  the 
same  way,  has  not  yet  been  settled.  Lindemann  has  found  that  the  fat  of  the 
degenerated  cardiac  tissue  is  different  in  some  essential  respects  from  the  fat 
deposited  elsewhere  in  the  body,  as  about  the  kidneys  and  under  the  skin.  This 
fact,  however,  does  not  constitute  strict  proof  against  an  eventual  transportation 
of  fat,  for  it  is  easily  conceivable  that  the  fat  might  undergo  some  change  in 
the  process  of  its  liberation  from  the  depository  whence  it  came. 

Pfliiger  explains  the  occurrence  of  fat  in  the  larvfe  of  blowflies  which  lived 
on  blood,  as  observed  by  Hofmann,  by  supposing  that  the  fat  was  formed  from 
the  blood  under  the  influence  of  Bacteria,  and  was  merely  absorbed  as  such  by 


130  METABOLISM  AND  NUTRITION 

the  larvae.  Moreover,  as  0.  Franck  has  shown,  the  method  of  determining  the 
fat,  which  was  employed  by  Hofmann,  does  not  permit  of  any  positive  conclu- 
sion from  his  experiment. 

When  we  examine  these  observations  critically,  we  must  conclude  with 
Pfliiger  that  no  single  experiment  has  yet  been  given  which  proves  beyond 
question  that  fat  is  formed  from  proteid.  Since,  however,  most  of  the  proteids 
contain  a  carbohydrate  group  and  the  body  in  all  probability  can  form  glyco- 
gen at  the  expense  of  proteid,  and  since  carbohydrates  are  unquestionably  a 
source  of  fat,  the  possibility  of  a  final  production  of  fat  from  proteid  cannot 
be  excluded  entirely ;  although  to  judge  from  results  thus  far  obtained,  such  a 
roundabout  production  is  not  large  and  never  takes  place  except  with  a  very 
rich  supply  of  proteid.  In  man  a  transformation  of  proteid  into  fat  is  scarcely 
to  be  admitted  at  all,  for  he  has  the  power  to  digest  and  absorb  only  a  rela- 
tively small  quantity  of  proteid. 

On  the  other  hand,  we  have  any  number  of  experiments  which  show  that 
fat  can  be  formed  in  the  body  from  nonnitrogenous  substances. 

That  fat  given  in  the  food  can  be  directly  stored  in  the  body,  follows  from 
the  experiments  of  Pettenkoffer  and  Voit  cited  on  page  104,  and  is  shown 
vrith  particular  clearness  by  the  following  experiment  of  I.  Munk. 

Munk  let  a  dog  starve  for  thirty-three  days,  during  which  time  most  of  the 
fat  was  of  course  lost  from  his  body.  He  then  gave  the  dog  300  g.  meat  and 
160  g.  rape-seed  oil  daily  for  seventeen  days,  and  killed  him  at  the  end  of  that 
time.  On  dissection  a  very  large  deposit  of  fat  was  found,  which  could  not  pos- 
sibly have  been  derived  from  the  meat  fed.  This  in  itself  showed  that  the  fat 
of  the  oil  had  been  stored;  but  in  addition  to  this  erucic  acid,  which  is  a  con- 
stituent of  rape-seed  oil  but  does  not  occur  in  dog  fat,  could  be  demonstrated  in 
the  fat  laid  down  from  the  food. 

Moreover,  soaps  and  free  fatty  acids  of  the  food  can,  after  synthesis  into 
neutral  fat.  be  directly  stored  in  the  body.  This  Radziejewski  and  Munk  have 
shown  in  the  same  way  as  in  the  experiment  just  mentioned,  by  feeding  a  soap 
of  rape-seed  oil  and  the  fatty  acids  set  free  from  mutton  fat,  respectively. 

Whether  or  not  fat  can  he  formed  from  carbohydrates  in  the  body,  is  a 
question  which  has  been  discussed  for  a  long  time.  Since  the  latter  spare  fat 
from  being  metabolized,  great  importance  has  always  attached  to  them  in 
the  laying  on  of  fat,  and  weighty  reasons  w^ere  found  for  such  a  transformation 
in  the  case  of  herbivorous  animals  and  especially  of  swine  and  cattle,  which 
are  fattened  for  the  market  very  largely  on  carbohydrates.  Thereupon,  the 
discussion  turned  to  carnivorous  animals  and  man ;  and  it  has  now  been 
completely  demonstrated  by  I.  Munk  and  Rubner  in  experiments  which  we 
cannot  go  into  here,  that  the  transformation  takes  place  in  these  also. 

We  see,  therefore,  that  fattening  always  occurs  if  the  supply  of  nonnitroge- 
nous substances  is  greater  than  the  needs  of  the  body.  Under  such  circum- 
stances the  body  can  store  almost  any  quantity  of  fat.  Underneath  the  skin, 
around  the  internal  organs,  in  short  everywhere  in  the  body,  fat  can  be  accu- 
mulated. 


THE   INORGANIC  FOODSTUFFS  131 


§  11.    THE   INORGANIC   FOODSTUFFS 

A.    GENERAL 

If  an  animal  be  fed  proteid,  fat  and  carbohydrates  sufficient  in  quantity, 
but  deprived  as  far  as  possible  of  mineral  constituents,  very  evident  disorders 
in  the  health  of  the  animal  soon  make  their  appearance.  Such  food,  poor  in 
salts,  will  not  be  eaten  voluntarily,  and  even  though  the  animal  may  receive 
plenty  of  organic  foodstuffs,  and  though  he  may  absorb  them  for  a  long  time 
in  perfectly  normal  fashion,  he  becomes  continually  weaker  and  gaunter. 
Within  two  weeks  symptoms  of  general  weakness  come  on,  the  gait  is  sluggish 
and  staggering,  the  muscles  tremble,  and  the  animal  becomes  exceedingly 
irritable  in  disposition.  If  the  experiment  be  carried  still  further,  convul- 
sions ensue  and  finally  death. 

If,  late  in  the  course  of  events,  the  animal's  ordinary  diet  be  restored,  at 
first  he  shows  no  desire  to  eat.  The  appetite  however  increases  gradually, 
and  finally  becomes  ravenous.  The  symptoms  of  weakness,  trembling  of  the 
muscles,  etc.,  pass  away  but  slowly,  and  traces  of  them  are  to  be  observed 
for  a  month  or  more  after  the  salts  are  restored  to  the  diet. 

It  is  perfectly  certain  therefore  that  the  mineral  constituents  of  the  food 
are  just  as  important  as  are  the  organic  foodstuffs.  In  fact,  it  appears  from 
researches  by  Forster,  that  the  body  can  endure  absolute  abstinence  better 
than  it  can  endure  deprivation  of  salts. 

In  order  to  understand  the  reason  for  this  great  importance  of  the  mineral 
substances,  it  is  necessary  to  know  the  effect  of  deprivation  on  the  secretions 
and  excretions  of  the  body.  We  saw  above  that  digestion  goes  on  normally 
for  a  relatively  long  time;  later,  however  (after  three  and  one-half  to  four 
and  one-half  weeks),  digestive  disorders  are  exhibited.  The  animal  vomits 
his  food;  or  it  may  remain  in  the  stomach  for  hours  without  being  digested. 
In  any  case  the  vomited  contents  always  contain  a  fairly  large  quantity  of 
chlorine. 

Forster  has  shown  that  the  excretion  of  PjOj  never  ceases  entirely,  it  only 
becomes  less  than  with  the  usual  food;  and,  moreover,  it  decreases  in  proportion 
to  the  quantity  of  ash-free  food  ingested.  The  same  is  true  of  NaCl:  during 
the  first  days  of  deprivation  a  relativelj'  large  quantity  is  excreted;  later  it  falls 
off  considerably  so  that  finally  in  200  cc.  of  urine  only  indeterminably  small 
traces  could  be  demonstrated.  During  the  last  days,  when  the  animal  was  draw- 
ing heavily  upon  his  own  body  for  organic  substances,  larger  quantities  of  XaCl 
were  given  off  in  the  urine. 

Forster  considers  himself  justified  by  these  experimental  results  in  gen- 
eralizing as  follows:  although  the  mineral  constituents  of  the  body  are  elim- 
inated in  smaller  quantities  when  salts  are  no  longer  supplied,  their  excretion 
never  ceases  entirely.  The  quantity  eliminated  is  least  when  organic  food- 
stuffs are  fed  in  abundance. 

This  is  because  mineral  constituents  for  the  most  part  form  loose  com- 
pounds with  the  combustible  substances  of  the  body,  especially  the  proteids. 
When  organic  foodstuffs  are  not  supplied  in  sufficient  quantity  so  that  the 


132  METABOLISM  AND  NUTRITION 

body  must  draw  on  its  own  store  of  those,  the  mineral  constituents  are  set 
free,  find  their  way  into  the  iiuids  of  the  body,  and  are  eliminated  through 
the  kidneys. 

If  an  animal  receive  more  salts  in  his  food  than  he  needs  the  excess  is  like- 
wise eliminated  in  the  excretions. 

The  importance  of  the  individual  elements  has  already  been  discussed  on 
general  lines  at  page  25.  It  remains  for  us  to  mention  briefly  the  behavior 
of  some  of  them  in  metabolism.  It  will  be  necessary  to  limit  the  discussion 
to  phosphorus,  calcium  and  magnesium.    With  regard  to  iron  cf.  Chapter  X. 

B.    PHOSPHORUS 

Phosphorus,  like  several  other  inorganic  foodstuffs,  is  eliminated  mainly  in 
the  faeces.  In  following  the  metabolism  of  proteids  containing  phosphorus  we 
have  therefore  to  consider  both  the  urine  and  the  fteces,  whereas  the  metabolic 
products  of  proteids  containing  no  phosphorus  are  almost  all  given  off  in  the 
urine. 

For  a  long  time  it  was  assumed  that  only  the  inorganic  phosphorus  com- 
pounds are  absorbed  from  the  intestine.  This  was  based  partly  on  residts  indi- 
cating that  the  excretion  of  phosphorus  in  the  urine  plainly  rose  after  the  addi- 
tion of  phosphates,  and  partly  on  the  supposition  that  the  phosphorus  component 
of  different  proteids  was  indigestible.  It  has  been  shown,  however:  that  pan- 
creatic juice,  acting  for  one  to  two  hours,  dissolves  from  one-half  to  one-third 
of  the  phosphorus  in  the  nuclein  of  thymus  (Popoff)  ;  that  in  the  digestion  of 
casein  by  gastric  juice  the  greater  part  of  the  phosphorus  passes  into  the  soluble 
digestive  products  (Salkowski)  ;  and  that  under  the  action  of  pancreatic  juice 
almost  all  of  the  phosphorus  of  casein  is  brought  into  solution  (Sebelien). 

It  is  not  a  difficult  matter  to  show  that  the  phosphorus  from  these  substances 
is  actually  absorbed  from  the  intestine.  In  some  experiments  on  dogs  Marcuse 
found  that  at  least  eighty-one  to  eighty-four  per  cent  of  the  phosphorus  of  casein 
was  absorbed ;  and  in  experiments  on  man  Loewi  observed  an  absorption  of  about 
seventy-nine  per  cent  of  phosphorus  derived  from  nuclein. 

But  we  cannot  decide  positively  from  these  experiments  whether  the  phos- 
phorus is  actually  absorbed  in  organic  combination  or  not.  We  know,  indeed, 
that  phosphorus  is  very  easily  split  off  from  such  substances  by  all  sorts  of 
agencies.  In  any  case  if  it  could  be  shown  that  phosphorus  is  stored  in  the  body 
only  after  feeding  with  a  proteid  containing  phosphorus  in  its  molecule,  we 
should  then  know  that  the  body  must  depend  upon  such  compounds  as  a  source 
for  this  element.  The  experiments  of  Zadig  seem  in  fact  to  prove  that  this  is 
the  case;  but  in  a  more  recent  series  of  expei-iments  Leipziger  was  able  to  demon- 
strate a  storage  of  phosphorus  after  feeding  a  P-free  edestin  and  a  phosphate. 
Hence  there  is  as  yet  no  proof  that  phosphorus  may  not  be  supplied  as  well  in 
inorganic  as  in  organic  form.  Experiments  by  Loewi  have  shown  however  that 
the  ratio  of  N  retained  to  P  retained  after  excessive  feeding  with  the  nucleins 
agrees  fairly  well  with  the  ratio  of  their  percentages  in  the  food,  and  indicates 
therefore  that  nucleins  may  be  absorbed  from  the  intestine,  partly  at  least,  in 
unchanged  form. 

In  order  to  determine  the  absolute  requirement  of  the  human  body  in  phos- 
phorus it  is  necessary  to  measure  directly  the  income  and  the  output. 

In  human  fteces  the  quantity  of  P  varies,  according  to  the  character  of  the 
food  and  the  P  contained  in  it,  from  0.25  g.  to  3  g.  and  more  per  day.  In 
the  urine  the  limits  for  an  adult  are  0.4  g,  and  2.8  g.     When  the  phosphorus  is 


FLAVORS  133 

drawn  from  the  body  itself,  the  quantity  in  the  urine  is  less — only  0.4—0.7  g. 
per  day.  If  after  a  period  of  deprivation  plenty  of  phosphorus  is  supplied,  the 
elimination  in  the  urine  is  only  about  0.9  g.  The  absolute  need  of  the  adult 
human  body,  therefore,  would  be  0.9  g.  plus  the  amount  in  the  faeces.  But  under 
ordinary  circumstances  in  P-equilibrium,  the  quantity  eliminated  in  the  urine 
appears  to  be  somewhat  larger,  and  may  be  estimated  at  1.5  g.  Adding  to  this 
the  average  daily  quantity  in  the  f^ces  (0.75-1  g.),  the  total  requirement  of  the 
adult  body  for  P-equilibrium  would  be  something  more  than  2  g. 

C.    CALCIUM   AND  MAGNESIUM 

Both  these  elements  are  absorbed  from  the  intestine  in  inorganic  compounds. 
This  we  know  from  their  appearance  in  the  urine  after  the  administration  of 
calcium  and  magnesium  salts. 

An  unlimited  absorption  of  Ca  and  Mg  is  impossible  because  of  the  alkaline 
reaction  of  the  blood,  although  it  appears  to  be  easier  for  Mg  than  for  Ca.  It 
is  also  very  probable  that  Ca  occurs  in  the  blood  only  in  the  form  of  a  proteid 
compound  which  is  not  precipitable  by  an  alkaline  reaction  merely  (Kiihne).  If, 
therefore,  these  elements  occur  in  the  diet  in  large  quantities,  the  greater  part 
is  passed  out  unabsorbed  in  the  faeces.  Besides,  Ca  and  Mg,  like  P,  are  excreted 
through  the  intestinal  mucosa,  proof  of  which  is  afforded  by  their  occurrence 
even  in  starvation  faeces.  (In  the  case  of  Cetti  0.07  g.  Ca  and  0.006  g.  Mg  per 
day;  in  the  case  of  Breithaupt  0.03  and  0.01  g.  respectively  per  day.)  With  a 
diet  extremely  poor  in  mineral  constituents  generally,  Eenwall  observed  in  the 
faeces  an  average  of  0.16  g.  Ca  and  0.06  g.  Mg  per  day. 

When  we  compare  the  herbivora  with  the  carnivorous  animals  we  find  con- 
siderable difference  in  the  proportion  of  the  calcium  and  magnesium  excreted 
in  the  urine  and  the  iseces.  In  the  former,  only  about  four  to  five  per  cent  of 
the  Ca  and  twenty-four  to  thirty-two  per  cent  of  the  Mg  appear  in  the  urine, 
while  in  the  latter,  the  urine  contains  as  much  as  twenty-seven  per  cent  of  the 
total  Ca  excretion  and  sixty-five  per  cent  of  the  total  Mg  excretion. 

From  the  few  obseiwations  thus  far  reported,  we  may  judge  that  the  excre- 
tion of  Ca  in  the  human  faeces  would  amount  to  thirty-six  to  fifty-eight  per 
cent  of  the  total  Ca  excretion,  and  that  of  Mg  sixty  to  seventy  per  cent  of  its 
total,  the  exact  amount  in  each  case  depending  on  the  power  of  the  urine  to 
dissolve  the  metal. 

Very  few  attempts  have  been  made  to  place  the  human  body  in  an  equi- 
librium of  Ca  and  Mg,  and  for  this  reason  it  is  scarcely  possible  to  give  definite 
figures  as  to  the  actual  need  for  them.  From  the  few  facts  at  hand  we  may 
conjecture  that  an  adult  man  would  reach  an  equilibrium  on  a  daily  supply  of 
0.3-0.7  g.  Ca,  and  of  something  more  than  0.4  g.  Mg. 

§  12.    FLAVORS 

A  diet  consisting  of  pure  proteid,  pure  fat,  pure  carbohydrates,  ash  and 
water,  each  in  sufficient  quantity,  would  not  be  agreeable  and  would  not  be 
eaten  except  in  case  of  extreme  necessity.  And  yet  we  have  in  such  a  diet 
everything  that  one  needs  with  a  single  exception — namely,  something  to  give 
the  food  an  agreeable  taste  and  odor;  in  short,  a  favor  to  make  it  palatable. 
We  must  not  suppose  that  this  aversion  to  the  pure  foodstuffs  is  due  to  the 
love  of  pleasurable  sensations  which  characterizes  man  in  the  civilized  state, 
for  an  animal  will  not  voluntarily  eat  a  perfectly  tasteless  food,  even  if  it 
contains  everything  that  he  needs. 


134  METABOLISM  AND  NUTRITION 

We  may  reckon  among  flavors  not  only  the  substances  commonly  under- 
stood by  the  word  in  its  strictest  sense,  such  as  that  which  gives  the  character- 
istic taste  to  roast  beef,  or  that  developed  in  the  baking  of  bread,  the  spices, 
extracts,  etc.,  but  also  coffee,  tea,  alcoholic  drinks,  tobacco,  etc. — in  short,  any- 
thing which  adds  to  a  meal  an  element  of  pleasure.  In  this  sense  we  might 
include  also  the  various  extraneous  means  of  making  a  meal  enjoyable,  like 
neat  service,  lively  conversation,  etc. 

Some  of  the  foodstuffs  themselves  serve  at  the  same  time  as  flavors — e.  g., 
sugar  and  salt.  The  body  requires  XaCl;  but  in  the  quantities  in  which  we 
ordinarily  eat  salt,  it  is  really  a  flavor. 

The  physiological  importance  of  favors  consists  in  the  stimulus  they  afford 
for  the  secretion  of  the  digestive  fluids.  Sight  or  smell  or  even  the  thought 
of  an  appetizing  dish  makes  the  mouth  water — i.  e.,  makes  the  salivary  glands 
secrete  profusely.  As  we  shall  see  later  under  digestion,  the  same  can  be 
demonstrated  for  the  gastric  glands.  If  a  meal  or  its  accompaniments  are 
not  pleasant,  these  reflex  effects  are  not  forthcoming  (cf.  Chapter  VII). 

If  one  eats  too  much  or  too  frequently  of  a  dish  once  palatable,  it  becomes 
distasteful  or  even  "  turns  against "  him ;  and  the  more  pronounced  the  taste 
of  the  dish,  the  more  quickly  will  it  become  distasteful.  On  this  account  there 
are  only  a  few  articles  of  diet,  such  as  bread,  which  we  can  eat  every  day  or  in 
large  quantities.  Herein  lies  the  importance  of  variation  in  diet,  even  different 
modes  of  preparing  the  same  articles  being  advantageous.  For  example,  the 
people  who  live  mainly  on  flour  or  meal  of  cereals  do  not  eat  these  substances 
exclusively  in  the  form  of  bread,  but  use  them  also  in  the  preparation  of 
dumplings,  noodles,  pancakes,  etc. 


§  13.    ON  THE   THEORY   OF  METABOLISM 

In  order  to  comprehend  fully  the  processes  of  metabolism  it  is  needful 
that  we  inquire  to  what  extent,  if  any,  the  organized  substance  of  the  body  is 
broken  down  in  combustion. 

When  we  consider  how  very  much  the  destruction  of  proteid  depends  upon 
the  amount  ingested  (page  99),  how  the  X-excretion  after  meals  is  very 
closely  connected  with  the  absorption  of  proteid  into  the  blood  (page  101), 
and  when  we  remember  that  the  nonnitrogenous  foodstuffs  do  not  essentially 
alter  the  destruction  of  proteid  (page  105),  and  that  physical  work  with 
plenty  of  IST-free  foodstuffs  supplied  does  not  increase  the  proteid  combustion 
(page  111),  we  are  almost  compelled  to  suppose  with  Voit  that  it  is  the 
proteid  of  the  food  and  not  the  living  protoplasm  which  first  breaks  down  in 
metabolism. 

Since  the  living  protoplasm  is  derived  from  proteid,  and  upon  its  degrada- 
tion after  death  again  forms  proteid,  it  is  quite  common  in  the  physiology  of 
nutrition  to  apply  to  it  the  name  of  tissue  proteid,  and  to  the  dead  proteid 
coming  from  food  and  found  in  the  fluids  of  the  body,  the  name  "  circulating 
proteid."  In  order  to  avoid  misunderstanding  we  shall  use  here  the  terms: 
living  substance,  in  whatever  tissues  it  may  occur,  and  food  proteid — i.  e.,  the 
proteid  absorbed  from  food  but  not  transformed  into  living  substance. 


ON  THE  THEORY   OF  METABOLISM  135 

The  food  proteid  is  distinguished  in  the  first  place  by  the  ease  with  Avhich 
it  is  destroyed  by  the  organs  of  the  body.  Xo  other  organic  foodstuff  can 
compare  with  it  in  this  respect.  It  is  true  that  fat  and  carbohydrates,  if 
supplied  in  sufficient  quantity,  can  reduce  the  destruction  of  proteid  to  a 
certain  extent,  but  in  a  general  way  this  destruction  bears  about  the  same 
relation  to  the  proteid  ingestion  whether  the  X-free  foodstuffs  be  eaten  or  not. 

The  digested  proteid  passes  into  the  blood  as  food  proteid.  If  the  quan- 
tity absorbed  is  not  too  small,  and  if  at  the  same  time  plenty  of  N-free  food- 
stuffs are  present,  a  part  of  it  may  remain  in  the  body  undestroyed,  but,  as 
a  rule,  the  greater  part  of  it  is  destroyed  within  twenty-four  hours. 

In  sharp  contrast  with  this  is  the  fact  that  the  mass  of  living  substance 
has  but  a  very  slight  influence  on  the  amount  of  proteid  destroyed.  We  have 
seen  (page  117)  that  there  is  no  ,direct  proportion  between  the  weight  of 
the  body  and  the  amount  of  proteid  metabolism,  and  (page  134)  that  beyond 
a  certain  lower  limit  the  body  can  maintain  its  proteid  status  on  widely  dif- 
ferent quantities  of  proteid,  provided  only  that  the  nonnitrogenous  foodstuffs 
be  present  in  sufficient  quantity. 

It  follows,  therefore,  that  the  living  substance  is  not  destroyed  either  in 
the  metabolism  of  proteid  or  in  that  of  the  nonnitrogenous  foodstuffs,  but  on 
the  whole  is  relatively  stable. 

The  doctrine  of  Voit,  given  preference  here,  that  the  food  proteid  is  de- 
stroyed first  and  the  living  substance  only  when  the  food  proteid  is  not  sufiicient 
for  the  needs  of  the  body,  is  still  disputed  by  many  authors  of  high  rank,  who 
advocate  the  view,  first  put  fonvard  by  Liebig,  but  modified  later  by  Pfliiger  and 
others.  According  to  this  view  the  living  molecules  of  which  the  cells  are  com- 
posed are  continually  being  destroyed  and  built  up  again  in  the  life  process; 
the  cells  as  such  do  not  break  down,  but  their  molecules  are  incessantly  chang- 
ing; the  living  molecule  disintegrates  much  more  easily  than  that  of  dead  pro- 
teid, and  the  latter  is  destroyed  only  after  it  has  been  transformed  into  living 
molecules ;  of  itself  it  is  much  more  stable  than  the  living  substance. 

It  is  indeed  a  matter  of  everyday  experience  that  when  an  organ  is  taken 
out  of  the  living  body,  it  dies  within  a  relatively  short  time,  and  on  the  other 
hand,  that  dead  proteid  in  a  dry  condition  can  be  preserved  for  any  length  of 
time  unchanged.  But  we  are  not  to  conclude  from  such  observations  that  in 
the  living  body,  dead  proteid  is  less  destructible  than  living  protoplasm.  For 
an  extirpated  organ,  by  the  very  act  of  its  removal  from  the  body,  is  placed  in 
altogether  abnormal  circumstances.  In  the  living  body  the  medium  in  which 
the  cells  and  the  tissues  carry  on  their  activities  is  the  lymph.  Wherever  this 
fluid  is  wanting,  or  has  not  the  proper  temperature  and  the  normal  constitution, 
is  not  renewed  often  enough  or  is  not  provided  with  sutflcient  oxygen,  protoplasm 
there  represents  a  very  destructible  substance.  But  we  are  not  justified  by  this 
alone  in  maintaining  that  the  living  substance  behaves  in  the  same  way,  when 
the  lymph  is  perfectly  normal.  What  we  know  is,  that  when  the  lymph  is  nor- 
mal, the  living  substance  carries  on  its  functions ;  and  there  is  no  ground  for  the 
assumption  that  it  is  then  less  stable  than  the  dead  substances  found  in  the  fluid 
by  which  it  is  bathed. 

If  the  living  substance  were  always  breaking  down  when  it  is  active,  what 
a  tremendous  work  of  synthesis  would  be  required  in  order  to  keep  it  restored 
from  the  dead  food  proteid !  And  if  this  were  true,  how  should  we  explain  the 
extraordinary  difficulty  with  which  the  adult  body  lays  on  proteid?    If  the  food 


136  METABOLISM   AND   NUTRITION 

proteid  had  first  to  be  organized  in  order  to  be  used  by  the  cells,  the  same  would 
of  necessity  be  true  of  the  nonnitrogenous  foodstuffs,  of  alcohol,  etc.;  before 
they  could  be  destroyed  they  would  have  to  become  integral  constituents  of  the 
living  substance.  We  cannot  get  away  from  this  consequence;  but  what  direct 
proof  have  we  for  it? 

How  much  simpler  is  the  other  view  that  the  organized  tissues  do  not  them- 
selves break  down — their  molecules  not  being  destroyed — during  activity,  but 
are  relatively  stable  substances  which  perform  their  duties  at  the  expense  of  the 
combustible  stuffs  present  in  the  lymph;  that  the  tissues  draw  upon  the  lymph 
for  whatever  they  require;  that  in  all  probability  they  take  up  these  stuffs  (pro- 
teid, fat,  carbohydrate,  etc.),  into  their  own  mass,  not,  however,  organizing  them 
into  their  own  substance,  but  destroying  them  sooner  or  later,  according  to  the 
intensity  of  their  vital  activities,  as  so  much  fuel. 

In  so  regarding  the  living  substance  as  relatively  stable,  we  do  not  mean 
to  say  that,  longer  periods  of  time  considered,  it  may  not  be  destroyed 
and  be  restored  again.  Indeed,  it  will  be  found  expressly  stated  under  the 
appropriate  sections,  that  certain  organized  structures,  like  the  blood  corpus- 
cles, epidermal  cells  of  the  skin  and  its  appendages,  epithelia  of  the  intestine, 
etc.,  are  all  the  time  breaking  down  and  being  lost,  and  it  is  more  than 
probable  that  the  other  tissues  exhibit  the  same  phenomena. 

There  is  another  question,  the  satisfactory  solution  of  which  is  of  the 
greatest  importance  for  tliis  conception  of  metabolism,  namely.  Why  is  it  that 
with  sufficient  nonnitrogenous  foodstuffs  to  cover  the  calorific  requirements 
of  the  body,  it  cannot  entirely  dispense  with  proteid  in  the  food  ? 

Of  course  this  is  partly  due  to  the  fact  that  the  living  substance  is  being 
destroyed  to  a  certain  extent,  and  needs  proteid  for  its  restitution.  More 
than  this,  proteid  is  used  up  in  the  formation  of  the  digestive  fluids,  in  the 
secretion  of  milk,  etc.  Just  how  great  is  the  quantity  necessary  to  cover  these 
absolute  requirements  of  the  body,  cannot  be  stated  at  this  time;  but  it  is 
considerably  less  than  the  quantity  which  appears  to  be  necessary  to  maintain 
the  body  in  a  satisfactory  state  of  nutrition. 

Yoit  answered  the  question  before  us  by  simply  saying  that  the  tissues  have 
need  of  a  certain  amount  of  proteid  for  their  own  maintenance.  But  this  answer 
is  only  another  way  of  stating  the  facts  to  be  explained.  The  following  appears 
to  throw  some  light  on  the  question. 

The  lymph  is  the  medium  in  which  the  cells  and  the  tissues  live.  It  con- 
tains proteid  as  one  of  its  necessary  constituents.  But  when  proteid  is  present, 
it  is  destroyed  by  the  tissues  with  the  greatest  avidity.  In  starvation  the  pro- 
teid of  the  lymph,  therefore,  is  gradually  used  up,  so  that  the  latter  would  become 
unsuitable  as  a  medium  for  the  tissues,  if  they  did  not  themselves  give  up  some 
of  their  proteid  to  the  lymph.  This  proteid  is  in  its  turn  destroyed,  and  a  new 
moiety  from  the  tissues  takes  its  place.  Thus  it  goes  on  continually;  and  our 
question,  why  proteid  is  destroyed  in  the  body  not  only  in  starvation  but  even 
when  the  supply  of  nonnitrogenous  food  is  as  great  as  possible,  is  to  be  answered 
through  this  continual  need  of  a  lymph  with  the  same  peculiar  constituents  all 
the  time,  and  through  the  peculiar  preference  of  the  cells  for  proteid  before  all 
the  other  organic  foodstuffs.  Such  an  explanation  does  not  require  us  to  sup- 
pose that  the  tissues  or  the  organized  molecules  themselves  must  break  down 
with  ever\'  manifestation  of  life.  From  the  same  point  of  view  we  can  explain 
also  the  phenomena  attending  deprivation  of  salt   (cf.  page  131). 


NUTRITION   OF   MAN  137 

[On  the  basis  of  some  very  thorough  studies  of  the  composition  of  normal 
human  urines  following  different  diets,  Folin  has  worked  out  a  theory  of  proteid 
metabolism  which  has  received  such  extensive  notice  as  to  deserve  mention  in 
this  connection.  Folin  finds  that  in  order  to  explain  the  changes  in  the  com- 
position of  the  urine  w^ith  reference  to  nitrogen  and  sulphur,  it  is  necessary  to 
assume  that  the  proteid  metabolism  is  of  two  kinds.  "  One  kind  is  extremely 
variable  in  quantity,  the  other  tends  to  remain  constant.  The  one  yields  chiefly 
urea  and  inorganic  sulphates,  no  creatinin  and  probably  no  neutral  sulphur.  The 
other,  the  constant  metabolism,  is  largely  represented  by  creatinin  and  neutral 
sulphur  and  to  a  less  extent  by  uric  acid  and  ethereal  sulphates." 

The  variable  metabolism  is  conceived  as  consisting  of  a  series  of  hydrolj-tic 
splittings  of  food  proteid  (cf.  Chap.  VII),  begun  in  the  intestinal  wall  and  com- 
pleted in  the  liver,  which  result  in  the  elimination  of  the  proteid  nitrogen  as 
urea.  This  is  called  exogenous  metaholism.  The  constant  metabolism  repre- 
sented by  creatinin  (and  uric  acid)  is  regarded  as  a  true  index  of  that  destruc- 
tion of  living  suhstance  necessary  to  the  continuation  of  life,  and  is  therefore 
called  endogenous  metaholism.  In  Folin's  view,  only  that  amount  of  proteid 
necessarj'  for  the  endogenous  metabolism  is  really  needed  by  the  body.  The 
greater  part  of  the  proteid  in  ordinary  diets,  i.  e.,  that  amount  representing  the 
exogenous  metabolism,  is  not  needed,  or  at  least  its  nitrogen  is  not  needed. 

This  theory  agrees  with  Voit's  theory  as  stated  above  in  regarding  the  liv- 
ing substance  as  relatively  stable,  but  differs  from  it  in  regarding  the  more  ready 
dissolution  of  ingested  food-proteid  not  as  a  matter  of  preference  on  the  part 
of  the  cells,  but  as  a  specially  developed  means  for  removing  the  unnecessary 
nitrogen  of  the  proteid  ingested.  The  carbonaceous  part  of  the  proteid  mole- 
cule, which  alone  is  conceived  as  undergoing  true  oxidations  similar  to  those 
which  fats  and  carbohydrates  undergo,  is  thereby  rendered  available. 

The  theory  seems  to  explain  the  facts  of  proteid  metabolism  as  stated  by 
the  author  in  this  chapter  quite  as  well  as  Voit's  theory,  and  in  addition  seems 
to  place  a  new  physiological  significance  on  the  portal  circulation. — Ed.] 


SECOXD    SECTION 

NUTRITION   OF   MAN 

If  the  diet  contains  in  sufficient  quantities  and  in  the  proper  proportion 
all  those  substances  which  the  body  needs,  it  constitutes  what  Voit  calls  a 
"  food."  As  applied  to  a  healthy  adult  man,  this  ration  is  that  quantity  of 
foodstuffs  which  is  necessary  to  keep  the  body  in  an  equilibrium  of  substance. 
For  growing  children  as  well  as  for  adults  in  a  poor  state  of  nutrition,  the 
ration  must  be  more  plentiful  so  that  a  part  of  it  can  be  retained  in  the  body. 

In  this  section  we  have  to  stud}'  the  nutritive  requirements  of  man  and 
some  of  the  circumstances  affecting  them.  Naturally  we  cannot  go  into  de- 
tails here;  important  as  they  are.  they  belong  to  hygiene  and  dietetics,  rather 
than  to  the  physiology  of  nutrition. 

The  nutritive  requirements  of  a  man  are  represented  by  those  quantities 
of  the  different  foodstuffs  which  must  be  added  to  the  body  from  the  intestine 
every  day.  But  inasmuch  as  we  do  not  commonly  eat  pure  foodstuffs,  but 
meals  prepared   from  various  articles  of  food,   the  question  may  be  raised, 


138  METABOLISM  AND   NUTRITION 

whether  the  foodstuflfs  contained  in  the  different  articles  of  food  are  utilized 
in  the  intestine  to  an  equal  extent.  Experiment  has  shown  that  as  a  matter 
of  fact  the  utilization  of  the  foodstuffs  in  different  articles  of  food  and 
"  dishes  "  is  very  different  (Rubner).  For  the  method  of  these  investigations 
and  the  share  which  the  intestine  has  in  the  formation  of  the  faeces,  see 
pages  85  and  96,  also  Chapter  VII. 

§  1.    UTILIZATION   OF   THE   FOODSTUFFS 

A.   PROTEID 

We  have  already  seen  that  the  quantity  of  N  in  the  faeces  which  comes 
from  the  body  itself,  and  therefore  represents  a  product  of  metabolism, 
amounts  to  0.5-1.4  g.  per  day.  If  then  we  find  only  this  quantity  of  nitro- 
gen in  the  faeces  after  a  certain  diet,  we  may  say  that  the  ingested  nitrogen 
has  all  been  utilized. 

This  is  generally  the  case  with  animal  foods.  In  experiments  with  meat, 
fish,  eggs,  milk  and  cheese,  the  daily  elimination  of  IST  in  the  faeces  varies 
from  O.l-I  to  1.9  g. ;  only  in  one  case — with  4,100  g.  of  milk — do  we  find  in 
the  literature  of  this  subject  a  greater  quantity  (3.1  g.)  of  N  in  the  faeces. 
If  the  total  N  in  the  faeces  be  calculated  as  lost  from  the  N  ingested,  it 
amounts  to  only  3.0-7.7  per  cent. 

Kermauner  has  taken  the  pains  to  estimate  quantitatively  the  residue  of 
meat  recognizable  as  such  in  the  faeces  of  three  individuals,  and  has  found  that 
after  an  ingestion  of  266  g.  meat  per  day  the  highest  amount  in  the  ffeoes  was 
4.7  g.  and  the  lowest  0.3  g.  (=0.16  and  0.01  g.  N  respectively). 

With  vegetable  foods  the  quantity  of  N  in  the  faeces  is  considerably  greater, 
and  in  certain  experiments  has  been  known  to  reach  the  high  value  of  9.09  g. 
per  day;  the  loss  in  this  case  amounts  to  as  much  as  forty-eight  per  cent  and 
as  a  rule  is  more  than  fifteen  per  cent. 

This  is  due  primarily  to  the  fact  that  vegetable  foods  contain  nitrogenous 
compounds  in  their  husks,  coats,  etc.,  which  are  not  proteid  and  are  not  digested 
in  the  intestine.  The  more  husk,  etc.,  a  vegetable  food  contains,  the  less  favor- 
ably does  the  utilization  of  its  nitrogen  prove  to  be.  For  this  reason  we  find 
in  the  faeces  from  rye  bread  made  from  whole  meal  2-4  g.  nitrog'en,  represent- 
ing a  loss  of  thirty  to  forty  per  cent.  If,  on  the  other  hand,  most  of  the  bran 
be  removed,  the  utilization  appears  more  favorable  with  a  loss,  namely,  of  only 
2  g.  N  or  ten  to  twenty  per  cent.  Other  factors  tending  to  make  the  utilization 
of  coarse  vegetable  foods  less  favorable  are  their  relative  bulkiness,  the  acid 
fermentation  of  the  carbohydrates,  and  the  percentage  of  indigestible  substances. 
All  these  conditions  tend  to  stimulate  the  musculature  of  the  intestine  and  thus 
to  produce  a  more  rapid  evacuation  of  the  intestinal  contents. 

B.    UTILIZATION   OF  FAT  AND   CARBOHYDRATES 

The  daily  faeces  from  a  diet  which  contains  no  fat  will  lose  3-7  g.  by 
extraction  with  ether.  If,  therefore,  the  faeces  after  ingestion  of  a  certain 
fat  contain  no  more  fat  than  this,  we  can  say  that  that  particular  fat  has 


UTILIZATION   OF   THE   FOODSTUFFS  139 

all  been  absorbed  from  the  intestine.  This  is  true  of  eggs,  milk,  butter, 
margarine,  lard — in  fact,  of  fats  generally  which  are  fluid  at  the  temperature 
of  the  body  and  are  not  surrounded  by  membranes.  However,  even  with  other 
fats,  like  bacon  fat.  which  is  inclosed  in  membranes,  the  utilization  is  com- 
monly very  complete.  Thus,  with  350  g.  per  day,  most  of  which  was  bacon 
fat  (un rendered  lard),  only  45  g.  appeared  in  the  fseces. 

Carbohydrates  also  are  well  absorbed  in  the  intestine,  inasmuch  as  the 
loss  by  the  faeces  from  the  ordinary  articles  of  diet  rises  only  to  about  ten 
or  eleven  per  cent  at  the  highest,  being  as  a  rule  smaller  than  this.  It  is 
true  of  carbohydrates  also  that  with  finely  prepared  foods  the  utilization  is 
much  better  (0.8-3.2  per  cent  loss)  than  with  coarse  foods  (6.9-11  per  cent 
loss).     The  digestibility  of  cellulose  has  already  been  discussed  at  page  110. 

By  microscopic  examination  of  the  fa?ces  J.  Moeller  has  shown  that  healthy 
men  digest  the  starch  of  cereals  and  potatoes  almost  completely,  even  if  the 
starchy  food  is  but  imperfectly  ground  up.  If,  however,  the  starch  is  present 
in  the  form  of  leguminous  seeds  or  is  eaten  in  green  vegetables,  it  is  passed  out 
undigested.  The  hard-walled  cells  of  the  ripe  leguminous  seeds  appear  not  to 
be  digested  at  all,  so  that  only  that  part  of  the  starch  which  is  liberated  from 
the  cells  by  mechanical  destruction  of  their  walls  is  of  any  benefit  in  nutrition. 
The  starch  of  green  leguminous  plants,  on  the  other  hand,  is  just  as  completely 
digested  as  that  of  cereals.  The  gluten  layer  of  the  latter  behaves  like  the 
leguminous  seeds :  their  membranes,  consisting  of  pure  cellulose,  are  not  digested, 
and  their  contents,  consisting  of  proteid  and  fat,  are  digested  only  so  far  as 
they  are  set  free  by  rupture  of  the  cell  membranes. 

The  absorption  of  mineral  constituents  of  the  diet,  calculated  in  percent- 
ages of  the  amount  supplied,  is  generally  rather  poor.  But  we  must  remember 
that  the  ash  of  the  faeces  comes  mainly  from  the  body  itself,  seeing  that  many 
mineral  substances  are  excreted  through  the  intestinal  wall. 

C.    UTILIZATION   OF  A  MIXED   DIET 

The  experiments  which  we  have  discussed  so  far  relate  chiefly  to  the 
absorption  of  individual  articles  of  food.  We  might  suppose,  however,  that 
a  mixed  diet,  such  as  is  ordinarily  eaten  by  man,  w^ould  be  utilized  more 
advantageously  than  these  experiments  indicate ;  and  in  fact  it  has  been  shown 
that  certain  mixtures  are  absorbed  better  than  their  separate  components. 
But  all  the  experiments  on  the  utilization  of  a  mixed  diet  which  we  have 
as  yet,  go  to  show  that  animal  nitrogen  is  absorbed  better  than  vegetable 
nitrogen. 

A  few  words  remain  to  be  added  on  the  utilization  of  the  total  potential 
energy  of  the  diet.  We  assume  here  as  before,  that  the  total  faeces  represent 
a  residue  of  the  ingested  food.  For  a  mixed  diet  Eubner,  on  the  basis  of 
one  experiment  on  the  heat  value  of  the  faeces,  estimates  the  loss  at  8.11 
per  cent  of  the  gross  calorific  value  of  the  food.  In  those  experiments  with 
a  mixed  diet  in  which  the  utilization  of  all  the  foodstuffs  has  been  investigated, 
the  results  show  a  loss  in  potential  energy  of  4.8  to  L3.9  per  cent.  By  direct 
determinations  of  the  heat  value  of  the  food,  and  of  the  faeces,  Atwater  has 
found  in  117  experiments  with  a  mixed  diet  of  easily  digestible  substances, 


140  METABOLISM  AND  NUTRITION 

that  the  loss  of  potential  energy  was  from  2.6  per  cent  to  11. T  per  cent.  In 
this  important  series  the  loss  in  proteid  was  3.8  to  11.7  per  cent,  in  fat  1.7 
to  12.7  per  cent,  in  carbohydrates  0.9  to  5.2  per  cent. 

An  average  figure  to  express  the  utilization  of  energy  in  the  food  ought  not 
be  placed  too  low.  Suppose  we  assume  that  ten  per  cent  of  the  potential  energy 
is  lost,  then  to  supply  a  man  with  3,000  Cal.  his  diet  should  have  an  indicated 
value  of  3,333  Cal.  Because  of  the  many  analyses  necessary,  a  complete  experi- 
ment on  the  utilization  of  foods  in  the  intestine  is  attended  by  considerable 
difficulties.  But  for  all  practical  purposes  it  is  sufficient  to  determine  the  dry 
residue  of  the  diet  and  of  the  corresponding  ffeces;  for  the  percentage  loss  in 
dry  substance,  so  far  as  our  experience  yet  goes,  varies  but  slightly  from  the 
percentage  loss  in  energy. 

§  2.  THE  ENERGY  REQUIREMENTS  OF  AN  ADULT 

It  is  already  clear  that  the  requirements  of  an  adult  must  be  determined 
essentially  by  the  physical  Avork  to  be  done,  for  work  is  inseparable  from  a 
consumption  of  substance.  Hence  we  have  first  to  investigate  how  great  the 
total  supply  must  be  for  different  amounts  of  work.  The  problem  is  simpli- 
fied materially  by  excluding  the  inorganic  foodstuffs,  for  it  has  been  shown 
that  if  the  diet  is  sufficient  and  has  the  proper  constitution  in  other  respects, 
it  will  contain  also  plenty  of  inorganic  substances. 

To  determine  the  minimal  requirement,  observations  must  be  made  on  the 
metabolism  in  complete  muscular  rest.  Such  observations  have  given  the 
following  results: 

A  woman,  twenty-five  years  of  age,  weighing  49.5  kilograms,  who  was  in  an 
hysterical  sleep  and  ate  nothing,  excreted  in  twenty-four  hours  6.21  g.  N"  and 
107  g.  C  =  38.8  g.  proteid  and  113.2  g.  fat,  corresponding  to  1,228  Cal.,  or  1.03 
Cal.  per  kilo  per  hour. 

In  his  calorimetric  experiments  Atwater  obtained  as  a  mean  of  sixteen  deter- 
minations of  the  heat  loss  in  sleep  (from  1  a.  m.  to  7  A.  M.),  the  value  of  1.03  Cal. 
per  kilo  per  hour. 

The  minimal  requirement  of  the  adult  man  may  be  placed,  therefore,  at 
1  Cal.  per  kilo  per  hour — i.  e.,  for  a  man  of  70  kg.  1,680  Cal. 

But  for  patients  in  a  weak  bodily  condition  muscular  rest  so  complete 
as  this  never  occurs.  The  skeletal  muscles  are  always  moved  to  a  greater 
or  less  extent ;  hence  metabolism  must  be  somewhat  greater  than  in  sleep. 

The  experiments  of  Pettenkoffer  and  Voit  on  individuals  at  rest  give  an 
average  (for  twenty-four  hours)  of  2,303  Cal.  in  fasting  and  2,675  Cal.  on  a 
moderate  diet — i.  e.,  32.9  and  38.2  Cal.  respectively  per  kilo  per  day.  In  experi- 
ments by  Sonden  and  the  author  on  eight  resting  men  between  the  ages  of  nine- 
teen and  forty-four  years,  the  metabolism  varied  from  1,853  to  2,292  Cal.,  or 
from  26.3  Cal.  to  36.0  Cal.  per  kilo  per  day.  Eckholm's  results  on  ten  students 
and  thirteen  soldiers  between  nineteen  and  twenty-five  years  gave  a  mean  result 
of  35.6  and  37.0  Cal.  respectively.  From  Atwater's  calorimetric  experiments 
carried  out  on  three  different  subjects  and  covering  forty-five  days,  we  get  a  total 
metabolism  for  the  resting  man  of  2,241  Cal. — i.  e.,  32.9,  33.3,  and  33.4  Cal.  per 
kilogram. 


THE  ENERGY  REQUIREMENTS  OF  AN  ADULT 


141 


The  metabolism  of  a  grown  man,  who  neither  rests  absolutely,  nor  does 
any  real  physical  work  (providing  he  receive  not  too  limited  a  supply  of 
food),  may  be  estimated,  therefore,  at  30-36  Cal.  per  kilogram  per  twenty- 
four  hours — i.  e.,  for  a  body  weight  of  70  kg.,  2,100  to  2,520  Cal.  Con.se- 
quently  a  ration  which  does  not  supply  at  least  2,000  Cal.  net  (i.  e.,  allowing 
ten  per  cent  waste;  cf.  page  140)  must  be  declared  insufficient  for  a  physical 
laborer. 

Laborers'  rations  may  be  divided,  according  to  the  amount  of  energy 
required,  into  several  different  groups.  The  following  is  arranged  especially 
for  men : 


Group. 

Calories  (net). 

Sufficient  for  a 

Climate. 

I 

2,001-2,400 
2,401-2,700 
2,701-3,200 
3,201-4,100 
4,101-5,0(X) 
Over  5,000 

Shoemaker. 

Weaver. 

Soldier. 

Farm  laborer. 

Excavator. 

Lumberman. 

England. 

II 

Saxony. 

Ill 

IV 

V 

VI 

Germany. 
Scotland. 
France. 
Bavaria. 

The  following  may  be  given  as  examples  of  rations  which  would  yield  an 
average  supply  of  energy  sufficient  for  each  of  these  classes: 


Group. 

Proteid, 

gross 

g- 

Fat. 

Carbo- 
hydrate, 

Calories, 
gross. 

Calories        Calories  per  kg. 
calories,           ^^^^.  ^.gi^ijt 

^^^-            (mean  =  70  kg.). 

I 

84 

88 

130 

141 

167 

56 
39 
64 
71 
89 
139 

399 
512 
520 
677 
774 
1,062 

2,483 
2,825 
3,257 
4,020 
4,685 
6,269 

2,235 
2,538 
2,932 
3,618 
4,218 
5,642 

32 

II 

36 

Ill 

42 

IV 

52 

V      

60 

VI 

152 

81 

Within  the  last  few  years  a  large  number  of  observations  on  the  nutrition 
of  men  who  had  free  choice  of  their  own  food,  have  been  made  under  At- 
water's  direction  in  the  United  States.  The  results  are  recorded  in  the 
followins:  table: 


Group. 

Cal.,  net. 

Number 
of  obser- 
vations. 

Proteid, 
gross;  g. 

Fat,  g. 

Carbo- 
hyd.,  g. 

£*'•      i  Cal.,  net. 
gross.     1         ' 

Cal. 
per  kg., 
b.  w.  (70). 

I 

II 

Ill 

IV 

V 

2,001-2,400 
2.401-2.700 
2.701-3,200 
3,201-4,100 
4,100-5,000 

23 

15 
37 
35 
14 

87 

89 

103 

124 

145 

90 
112 
125 
147 
215 

303 
362 
409 
510 
612 

2,434          2,191 
2,891     •     2,602 
3,262         2,936 
3,966         3,569 
5,102         4,592 

30 
37 
41 
51 
66 

Volt  based  his  practical  conclusions  for  the  nutrition  of  an  adult  man  on 
the  requirements  of  a  moderate  worker.    He  describes  as  a  "  moderate  worker," 


142  METABOLISM   AND   NUTRITION 

a  man  strong  enough  to  do  nine  to  ten  hours"  work  every  day  heavier  than 
that  of  a  tailor  and  lighter  than  that  of  a  blacksmith — the  work  for  example 
of  a  mason,  a  carpenter,  or  a  joiner.  Moderate  work  so  defined  corresponds 
fairly  well  to  the  amount  done  by  most  manual  laborers,  and  comes  nearest 
to  Group  III  in  our  classification. 

Voit's  ration  for  the  moderate  worker  is:  118  g.  proteid,  56  g.  fat,  and 
500  g.  carbohydrate  :=  3,055  Cal.  gross  or  2,749  Cal.  net. 

While  it  has  been  generally  admitted  that  the  absolute  supply  of  energy  in 
this  ration  corresponds  well  with  the  actual  requirements  and  is  estimated  rather 
too  low  than  too  high,  it  has  been  remarked  by  many  that  the  amount  of  pro- 
teid is  too  high  and  that  a  moderate  Avorker  can  get  along  perfectly  with  less 
proteid.  Munk  for  example  proposes  110  g.  proteid  instead  of  118  g.  Now  it 
is  not  a  matter  of  great  moment  whether  the  diet  contain  110  or  118  g.  proteid. 
The  rations  which  we  have  brought  together  for  our  Group  III  contain  on  the 
average  130  g.  with  113  and  151  g.  as  the  extremes.  From  Atwater's  results  we 
have  for  the  same  group  103  g.  with  52  and  152  g.  as  the  extremes.  This  is  not 
the  place  to  discuss  the  grounds  which  have  been  taken  for  a  reduction  of  pro- 
teid in  the  ration.  In  the  opinion  of  the  author  these  grounds  are  by  no  means 
sufficient  for  the  purpose  intended,  hence  the  best  thing  to  do  is  to  choose  for  a 
normal  ration  on  containing  not  less  than  118  g.  proteid,  even  is  many  observa- 
tions do  show  that  a  "  moderate  worker  "  can  get  along  with  less. 

[Chittenden's  recent  experiments  on  several  groups  of  men  of  different  de- 
grees of  muscular  and  mental  activity  (university  professors,  college  athletes, 
and  United  States  soldiers)  indicate  strongly  that  Volt's  proteid  ration  is  ex- 
cessive. He  found  that  without  exception  these  persons  (numbering  twenty-six 
in  all)  were  able  to  maintain  their  physical  and  mental  vigor  for  periods  of 
from  five  to  nine  months  on  an  average  of  56  grams  of  proteid  per  day.  These 
results  accord  with  Folin's  theory  of  metabolism  (cf.  page  137),  which  looks 
upon  a  large  part  of  the  proteid  ingested  in  the  average  diet  as  so  much  waste 
material  to  be  removed  at  once  from  the  circulation  by  the  liver. — Ed.] 

Voit's  motive  in  dividing  the  nonnitrogenous  foodstuffs  for  a  moderate 
worker  between  fat  and  carbohydrates  as  he  did,  was  to  make  the  diet  as 
inexpensive  as  possible.  He  takes,  therefore,  as  much  carl)ohydrate  as  in  his 
opinion  the  intestine  can  digest  easily — i.  e.,  500  g.  The  remainder  of  the 
energy  required  he  takes  from  fat. 

Of  course  it  would  not  be  correct  to  regard  500  g.  as  a  real  maximum  of 
carbohydrates — and  Voit  does  not.  The  intestine  can  manage  greater  quanti- 
ties; but  this  alone  is  no  reason  for  increasing  the  carbohydrate  at  the  expense 
of  fat.  Experience  has  shown  with  perfect  clearness  that  the  human  body  has 
a  very  pronounced,  if  not  always  a  perfectly  intelligible,  need  for  fat ;  so  that 
the  quantity  in  Voit's  ration  (56  g.)  ought  probably  to  be  regarded  as  the 
minimum  for  the  diet  of  a  moderate  worker  (cf.  tables  on  page  141). 

When  the  amount  of  work  to  be  done  is  greater  than  that  of  a  moderate 
worker,  experience  teaches  us  that  both  proteid  and  X-free  substances  are 
eaten  in  greater  quantities,  but  the  supply  of  proteid  is  not  increased  as  much 
as  that  of  the  X-free  substances.    According  to  Voit,  soldiers  in  field  maneu- 


NUTRITION  OF   THE   YOUNG 


143 


vers  (hard  labor)  require  135  g.  proteid,  80  g.  fat,  and  500  g.  carbohydrates 
=  3,348  Cal.  gross  and  3,013  Cal.  net,  and  in  war  (severe  labor)  145  g. 
proteid,  100  g.  fat  and  500  g.  carbohydrate  =z  3,575  Cal.  gross  and  3,218 
Cal.  net. 

Our  Group  IV  contains  on  the  average  3,618  Cal.  net  which  can  be  supplied 
in  141  g.  proteid,  71  g.  fat,  and  677  g.  carbohydrates.  We  see  that  this  ration 
agrees  on  the  whole  very  well  with  that  demanded  by  Voit.  For  a  similar  class 
(3,569  Cal.)  Atwater  (IV)  finds  124  g.  proteid,  147  g.  fat,  and  510  g.  carbo- 
hydrates to  be  the  requirement. 

The  following  data  by  Atwater  may  be  given  as  further  examples  of  diets 
suited  to  severe  labor:  Participants  in  a  rowing  contest  (American  students): 
155  g.  proteid.  177  g.  fat,  440  g.  carbohydrates  =  4,085  Cal.  gross.  Football 
players:  (1)  181  g.  proteid,  292  g.  fat,  557  g.  carbohydrates  =  5,740  Cal.  (gross); 
(2)  270  g.  proteid,  416  g.  fat,  and  710  g.  carbohydrates  =  7,885  Cal.  (gross). 

Direct  information  on  the  diet  of  women  is  still  extremely  meager.  Hav- 
ing a  smaller  body  than  man,  and  doing  as  a  rule  less  physical  work,  a  woman 
naturally  requires  a  smaller  supply  of  energy  than  a  man.  Assuming  that 
the  weight  of  the  woman's  body  is  four-fifths  that  of  the  man's  and  that  her 
metabolism  bears  the  same  relation  to  his,  we  obtain  Voit's  ration  for  female 
workers:  94  g.  proteid,  45  g.  fat  and  400  g.  carbohydrates  =:  2.444  Cal. (gross) 
and  2,200  Cal.  (net). 

§  3.    NUTRITION   OF   THE    YOUNG 

Tt  is  evident  that  the  growing  l)ody  needs  relatively  more  food  than  the 
adult,  both  l)ecause  it  is  smaller  and  because  its  organs  must  increase  in  size. 
Moreover,  experiment  has  shown  that  the  j^oung  body  has  a  more  active 
metabolism  per  unit  of  hodi/  surface  regardless  of  its  smaller  size  (page  118). 

In  order  to  make  possil)le  a  fuller  presentation  of  the  metabolism  in  the 
growing  body,  we  have  brought  together  in  the  following  table  a  number  of 
observations  on  the  mean  COo-output  taken  a  short  time  after  a  meal  while 
the  individuals  were  sitting  quiet.     Still  other  data  will  be  found  on  page  119  : 


Males. 

Females. 

.              Mean 
Age,  years.   Bodyweight,  kg. 

CO,,  g.  per  hour. 

A  ™«»         Mean 
^^®-      Bodyweight,  kg. 

COj.  g.  per  hour. 

93^ 

28 
SO 
32 
34 
45 
45 
51 
56 
60 
65 
68 
68 
77 
85 

33 
33 

34 
34 
45 
44 
42 
45 
43 
38 
38 
35 
37 
34 

8 

22 
27 
31 

25 

10^ 

lU 

10 

11 

23 
26 

12i 

14 

12 30 

13 40 

14 44 

27 

28 

14i  

29 

15i 

17 

15 

49 

27 

16 

50 
54 
54 
67 
67 

32 

\H 

17*  

27 

23; 

25 

35 

30 

45 

653 

29 
37 
26 

45 

58..... 

11 


144  METABOLISM  AND   NUTRITION 

With  males  we  see  that  the  excretion  of  carbon  dioxide  is  greater  between 
the  ages  of  fourteen  and  nineteen  than  in  older  or  younger  individuals  of  the 
same  sex.  This  agrees  very  well  with  Key's  observation  on  the  growth  of  boys, 
namely  that  beginning  with  the  fourteenth  year  the  increase  of  the  body  in 
length  and  weight  takes  place  much  more  rapidly  than  during  the  years  imme- 
diately preceding  (nine  to  thirteen).  This  period  of  rapid  growth  continues 
for  four  years  (cf.  Chapter  XXVI,  second  section). 

To  judge  by  the  elimination  of  CO,,  a  boy  from  nine  to  thirteen,  therefore, 
would  need  almost  as  much  food  as  a  man  resting,  and  boys  between  fourteen 
and  nineteen  still  more.  We  must  not  overlook  the  fact,  however,  that  the 
calorific  value  of  the  CO,  is  very  different  according  as  it  has  its  origin  in  the 
metabolism  of  fat,  carbohydrates  or  proteid.  Since  in  the  above  table  the  in- 
dividuals on  whom  the  experiments  were  made  belonged  to  the  same  class 
of  society,  and  so  far  as  the  diet,  etc.,  were  concerned  lived  on  the  whole  on 
the  same  plane,  it  may  be  assumed  with  great  probability  that  the  average 
composition  of  their  diet,  and  consequently  the  share  of  the  different  foodstuffs 
in  the  formation  of  CO,,  was  about  the  same. 

With  females  the  COo-elimination  does  not  show  the  significant  rise  which 
appears  in  boys  between  fourteen  and  nineteen.  From  the  eleventh  year  on 
but  slight  differences  due  to  age  make  their  appearance :  in  an  eleven-year-old 
girl  the  COo-excretion  was  26  g.,  in  a  woman  of  thirty,  29  g.  We  might  say, 
therefore,  that  the  requirements  of  a  girl  of  eleven  are  just  as  great  as  those 
of  an  adult  woman  at  rest. 

Comparison  of  the  CO^-output  of  males  and  females  of  the  same  weight  and 
age  shows  that  during  the  years  of  grovpth  it  is  considerably  greater  with  the 
former  than  with  the  latter,  and  that  the  ratio  of  female  metabolism  to  male 
metabolism  estimated  per  kilogram  of  body  weight  is  about  100:140.  In  men 
and  women  who  have  already  passed  the  period  of  growth  this  difference  gradu- 
ally diminishes,  and  as  old  age  comes  on  disappears  altogether. 

The  figures  of  this  table  differ  considerably  from  those  given  by  Magnus- 
Levy  and  Falk  in  the  table  on  page  118.  The  reason  is  that  the  subjects  of  their 
experiments  had  not  eaten  recently  and  were  in  absolute  muscular  rest,  while 
the  results  brought  together  in  the  table  now  under  consideration  were  obtained 
upon  individuals  in  a  sitting  posture  shortly  after  a  meal.  On  this  account 
Magnus-Levy  and  Falk  found  no  difference  in  the  CO,-excretion  by  males  and 
females.  The  difference  which  we  have  noted  above  is,  in  all  probability,  traceable 
to  a  greater  tonus  in  boys'  muscles  than  in  girls'. 

By  way  of  comparison  with  the  direct  data  on  the  metabolism  of  the  grow- 
ing body  we  may  add  also  the  standard  figures  which  Atwater  uses  in  appor- 
tioning the  diet  of  a  family  to  its  different  members.  Taking  the  food  require- 
ments of  the  father  as  1,  the  requirements  of  the  others  would  be : 

Of  the  mother 0.8  ; 

"       sons,  14-1 7  years 0.8; 

"       daughters,  14-17  years 0.7  ; 

"       children,  10-13  years 0.6; 

6-9  years 0.5; 

"  "  2-5  years 0.4; 

"*  "         under  2  years 0.3. 


CONSTRUCTION   OF   DIET   FROM   DIFFERENT  ARTICLES   OF   FOOD     145 

§  4.    CONSTRUCTION   OF   THE    DIET   FROM   THE    DIFFERENT 
ARTICLES   OF   FOOD 

In  satisfying  the  requirements  of  his  body,  man  has  a  great  variety  of 
foods,  both  animal  and  vegetable  in  origin,  from  which  to  choose.  Recently 
the  question  has  been  much  discussed  in  certain  quarters  whether  the  natural 
food  of  man  should  be  mixed  or  should  be  purely  vegetable. 

That  a  purely  animal  diet  is  not  suited  to  the  requirements  of  the  human 
body  after  the  period  of  infancy  is  passed  need  not  be  proved  at  length.  On 
the  one  hand,  if  we  except  milk  and  liver,  the  carbohydrates  are  practically 
absent  entirely  from  such  a  diet ;  and  on  the  other  hand,  the  relatively  long 
human  intestine  is  not  sufficiently  stimulated  by  an  exclusively  animal  diet 
to  prevent  the  residues  of  the  food  and  the  digestive  fluids  from  remaining 
overlong  in  the  intestine. 

All  the  requirements  of  the  body  can  be  met,  however,  by  foods  of  vegetable 
origin  alone ;  for  they  contain  fats  and  carbohydrates  as  well  as  proteid. 

Vegetarians  assume  that  a  purely  plant  diet  is  the  only  natural  food  of 
man.  But  a  number  of  objections  can  be  raised  against  this  conception.  For 
example,  fat  occurs  in  plants  in  large  quantities  only  in  the  form  of  vegetable 
oils,  and  the  only  place  the  latter  figure  to  any  extent  in  the  preparation  of 
victuals  is  in  southern  coitntries.  Hence,  in  many  regions  it  is  not  easy  on 
a  purely  vegetable  diet  to  supply  the  body  with  a  sufficient  quantity  of  fat. 
To  obtain  fat  the  body  must  appropriate  animal  foods.  Again,  most  vegetable 
foods  in  proportion  to  their  percentage  of  proteid  are  much  more  bulky  than 
animal  foods,  and  their  volume  is  still  more  increased  by  the  absorption  of 
water  in  their  preparation,  whereas  animal  foods  lose  water  in  preparation  and 
hence  become  less  bulky.  Besides,  the  nitrogenous  constituents  of  most  vege- 
table foods  are  but  poorly  absorbed  in  the  intestine.  In  order  to  supply  the 
body  with  plenty  of  proteid  from  purely  vegetable  sources  one  is  compelled, 
therefore,  to  eat  a  rather  voluminous  diet.  In  so  doing  he  runs  the  risk  of 
exacting  too  much  work  of  the  digestive  organs,  whence  various  untoward 
effects  might  result.  To  prevent  these,  it  is  needful  that  a  part  of  the  daily 
ration  be  drawn  from  animal  sources. 

This  is  admitted  by  the  vegetarian  who  eats  no  meat,  but  allows  himself  the 
pleasure  of  milk,  eggs  and  dairy  products.  In  his  ease  the  diet  is  no  longer 
purely  vegetable,  for  it  contains  both  fat  and  proteid  derived  from  animal 
sources.  Cheese  is  an  article  vei-y  rich  in  proteid,  and  in  butter  and  milk  the 
body  can  get  all  the  fat  it  requires.  So  far  as  the  question  is  debatable  at  all, 
it  narrows  itself  to  whether  or  not  meats  shall  be  included  in  the  diet. 

From  a  purely  physiological  point  of  view,  we  can  find  no  reason  why  a 
healthy  man  should  forego  the  use  of  so  excellent  an  article  of  food,  considered 
with  respect  to  its  content  of  proteid  and  fat  or  its  eminent  adaptability,  as  we 
know  meat  to  be.  But  in  so  stating,  I  do  not  wish  to  be  understood  as  saying 
that  one  should  eat  any  quantity  of  meat  he  pleases,  or  should  cover  too  much 
of  his  requirements  with  meat.  In  too  large  quantities  the  extractive  substances 
found  in  meat  may  possibly  produce  disorders  of  one  kind  or  another  in  the 
body  (cf.  Chapter  XII,  §  1).  The  metabolism  might  also  take  an  abnormal  or 
unfavorable  form,   if  the  fluids  of  the  body  were  flooded  with  too  much  pro- 


14(5  METABOLISM   AND    Xl'TRITIOX 

teid.     Finally,  it  is  possible  that  in  certain  diseased  conditions,  meat  would  be 
harmful,  and  that  some  persons  have  a  positive  aversion  to  it. 

If,  therefore,  the  individual  get  a  sufficient  supply  of  protcid  and  fat  in 
other  articles  of  diet,  like  cheese  and  butter,  so  that  great  bulkiness  can  be 
avoided,  meats  are  not  absolutely  necessary.  But  from  the  standpoint  of  the 
physiology  of  nutrition,  there  is  no  reason  for  avoiding  them. 

Against  the  claim  that  the  vegetable  foods  constitute  the  natural — 1.  e..  the 
original  diet  of  man — this  additional  objection  can  be  raised :  the  most  im- 
portant of  the  vegetable  foods,  namely  the  cereals,  are  subject  to  the  action 
of  the  digestive  fluids  only  after  thorough  preparation;  whereas  man  had 
lived  a  long  time  on  the  earth  before  he  had  progressed  so  far  as  to  under- 
stand how  to  cultivate  the  soil,  cook  his  food,  grind  his  grain  and  bake  bread. 
Meat,  however,  requires  no  further  preparation  for  eating  than  to  be  divided 
into  small  pieces.  We  have  reason,  therefore,  for  claiming  rather  that  man 
was  originally  carnivorous. 

There  are  those  who  would  have  us  believe  that  the  really  natural  diet  of 
man  consists  of  fruits.  But  it  is  not  a  very  easy  matter  at  best  to  get  proteid 
and  fat  enough  from  fruits,  and  besides,  in  many  inhabited  lands  it  is  quite 
impossible  to  raise  any  fruits  or  any  kind  of  vegetable  foods  in  large  enough 
quantities  to  provision  the  population. 

Our  conclusion  is  that  the  diet  most  generally  suitable  for  man  is  a  mixed 
diet,  composed  of  both  animal  and  vegetable  foods.  It  is  only  by  reason 
of  his  ability  to  utilize  all  sorts  of  foods  that  it  has  been  possible  for  man 
to  people  the  entire  earth  from  the  equator  to  the  poles. 

References. — Armshy,  "Principles  of  Animal  Xutrition,"  Xew  York,  1903. 
— Atwater  and  others,  U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Station,  Bul- 
letins Xos.  44,  63,  69,  109,  136.— Atwater  and  Benedict,  "A  Respiration  Calo- 
rimeter, with  Appliances  for  the  Direct  Determination  of  Oxygen,"  Publications 
of  the  Carnegie  Institution  of  Washington,  Xo.  42,  1905. — R.  H.  Chittenden^ 
"Physiological  Economy  in  Xutrition,"  Xew  York,  1905. — Otto  Folin,  "A 
Theory  of  Protein  Metabolism,"  in  American  Journal  of  Physiology,  XIII,  1905. 
— Robert  Hutchinson,  "  Food  and  Dietetics,"  2d  edition,  Xew  York  and  London, 
1906. — Ludolf  Krehl,  "  Pathologische  Physiologic,"  Leipzic,  1904. — Graham  Lush, 
"Elements  of  the  Science  of  Xutrition,"  Philadelphia,  1906. — 7.  Munk  and 
C.  A.  Ewald,  "  Die  Ernahrung  des  gesunden  und  kranken  Mensehen,"  3d  edi- 
tion, Wien  and  Leipzic,  1896. — Pfliiger,  "  Glycogen,"  2d  edition,  Bonn,  1905. — 
Ruhner,  "  Energieverbrauch,"  Leipzic  and  Wien,  1902. — C.  Voit,  "Physiologic 
des  allgemeinen  Stoffwechsels  und  der  Ernahrung"  (Hermann's  Handhuch  d. 
Physiologic,  VI,  1),  Leipzic,  1881. 


CHAPTER    V 


THE     BLOOD 


The  hlood  is  the  common  nutritive  fluid  of  the  body.  Driven  by  the  heart 
through  the  vascular  system  in  an  uninterrupted  stream,  it  supplies  all  parts 
of  the  body  with  all  the  substances  necessary  for  their  growth  and  mainte- 
nance, as  well  as  for  the  combustion  going  on  in  them.  Besides,  the  blood 
removes  from  ail  parts  of  the  body  the  greater  part  of  the  decomposition 
products  formed  in  the  life  processes,  and  is  in  its  turn  relieved  of  these 
products  during  its  passage  through  the  excretory  organs. 

The  blood  is  a  red,  opaque  fluid,  somewhat  heavier  than  water  (sp.  gr. 
in  man  1.057-1.066,  in  woman  1.053-1.061).  It  has  a  salty  taste,  a  neutral 
reaction,  and  a  peculiar,  stale  odor.  Its  specific  heat  amounts  to  0.8693  (at 
about  38°  C). 

The  blood  holds  its  neutral  reaction  with  the  greatest  tenacity.  In  order 
to  obtain  a  red  coloration  with  phenolphthalein  by  addition  of  caustic  soda  to 
the  serum  of  ox  blood,  one  must  add  seventy  times  as  much  of  the  alkali 
as  would  be  necessary  if  it  were  being  added  to  pure  water  in  order  to  obtain 
the  same  reaction.  The  same  serum  mixed  with  methyl-orange  requires  three 
hundred  and  twenty-seven  times  as  much  n/10  HCl  as  does  pure  water  in  order 
to  bring  out  the  red  coloration.  The  explanation  of  this  behavior  lies  in  the 
variable  acid  and  basic  character  of  the  semm  proteids  (Friedenthal). 

On  microscopic  examination  the  l)lood  is  found  to  consist  of  a  fluid,  the 
plasma,  in  which  float  great  numbers  of  formed  elements.  These  latter  con- 
stituents which  cause  the  opacity  of  tlie  l)lood  are:  (1)  the  red  hlood  corpus- 
cles to  which  the  blood  owes  its  red  color;  (2)  the  ichite  corpuscles;  (3)  the 
platelets. 

A  few  minutes  (in  man  three  to  twelve)  after  the  blood  is  drawn  from 
an  open  blood  vessel  it  sets  into  a  jellylike  mass,  which,  as  will  be  more  fully 
discussed  later,  is  due  to  the  fact  that  a  proteid  l)ody  present  in  the  plasma 
is  separated  out  (coagulated)  in  the  form  of  a  solid,  tlie  so-called  fibrin. 

The  coagulated  fibrin  is  a  fibrous  structure,  which,  although  it  amounts 
to  only  0.2-1.0  per  cent  of  the  l)lood,  permeates  and  incloses  in  its  meshes  the 
entire  mass  of  the  clot.  Gradually  the  fibrin  shrinks,  in  consequence  of  which 
a  pale  yellowish  fluid  is  pressed  out.  The  quantity  of  this  fluid,  the  serum. 
increases  progressively  and  finally  there  remains  of  the  coagulum  a  smaller 
residual  mass,  which  consists  of  the  fil)rin.  the  blood  corpuscles  inclosed  in  it, 
and  the  serum  still  present  in  its  interstices.  The  blood  plasma  therefore 
consists  of  fibrin  and  serum, 

11*  147 


148  THE  BLOOD 

Fibrin  may  be  separated  out  also  by  whipping  shed  blood  with  a  stick. 
After  this  operation  the  blood  remains  fluid,  the  fibrin  having  been  collected 
in  the  form  of  a  white,  stringy  mass  on  the  stick. 


§  1.    THE  AMOUNT   OF  BLOOD   IN   THE   BODY 

The  method  of  determining  the  amount  of  blood  in  the  l^ody  is  in  brief 
as  follows:  a  normal  sample  of  blood  (h)  is  first  drawn;  then  the  animal  is 
bled  and  the  vascular  system  is  washed  out  with  water  until  the  wato^r  flows 
out  perfectly  clear.  The  water  and  blood  are  added  together  and  the  total 
quantity  designated  w.  The  normal  sample  of  blood  is  now  brought  by  addi- 
tion of  water  v  to  the  same  color  as  a  sample  of  uk  Then  if  we  designate 
l)y  ij  the  amount  of  blood  washed  out,  it  is  evident  that  h:h-{-v::y:  iv.    From 

which  ;/  =  - — \ The  total  quantity  in  the  bodv  is  therefore  &  -]-  7/  =  &  -f 

-  (Welcker).     This  method  is  not.  however,  quite  exact,  for  after  the 

washing  there  still  remains  in  the  organs  from  eight  to  sixteen  per  cent  of 
the  total  haemoglobin. 

The  amount  of  blood  determined  in  this  way  amounts  to  seven  to  nine 
per  cent  of  the  body  weight  in  the  dog,  five  to  nine  per  cent  in  the  rabbit  (in 
the  latter  after  removal  of  the  intestinal  contents).  BischofP  found  in  the 
dead  bodies  of  two  executed  criminals  the  quantities  7.1  and  7.7  per  cent  of 
the  body  weight. 


§  2.    THE   FORMED   CONSTITUENTS   OF   THE   BLOOD 

A.    THE  RED   BLOOD  CORPUSCLES 

In  most  mammals  the  red  blood  corpuscles  are  thin,  flat,  slightly  bicon- 
cave, circular  disks,  composed  of  a  soft,  extensible  and  very  elastic  substance. 
By  transmitted  light  the  color  in  thin  layers  is  yellowish  green;  in  thick 
layers,  red.  In  birds,  reptiles,  amphibia  and  most  fishes,  as  well  as  in  the 
camel  family,  they  are  oval  instead  of  circular.  In  the  cold-l)looded  animals 
and  in  birds  they  have  a  nucleus :  in  the  mammals  no  nucleus  is  present  in 
the  mature  form  of  the  corpuscle  (cf.  page  17). 

The  diameter  of  the  red  blood  corpuscle  in  man  is  0.007-0.008  mm.,  its 
thickness  about  0.0016  mm.  The  volume  of  a  single  corpuscle,  according  to 
Welcker,  amounts  to  0.000000072  cu.  mm.,  and  its  surface  to  0.000128  sq. 
mm.  One  cu.  mm.  of  human  blood  contains  about  5,000,000  red  corpuscles 
for  man  and  about  4,500,000  for  woman.  The  total  surface  of  the  red  cor- 
puscles in  1  cu.  mm.  of  blood  therefore  amounts  to  640  sq.  mm.  in  man  and 
576  sq.  mm.  in  woman.  Since  the  total  mass  of  the  blood  in  man  is  about 
seven  per  cent  of  the  body  weight,  i.  e.,  in  a  body  weighing  70  kg.,  about 
5  kg.  in  round  numbers,  the  total  number  of  red  blood  corpuscles  in  a  man 
is  35,000,000,000,000,  and  their  total  surface  3,200  sq.  m.  (=  0.8  acre  nearly). 


THE  FORMED  CONSTITUENTS  OF  THE  BLOOD  149 

(The  body  surface  of  a  grown  man  is  only  about  2  sq.  m.)  This  enormous 
extent  of  surface  of  the  red  blood  corpuscles  is  of  great  significance  in  con- 
nection with  their  function  in  respiration   (Chapter  IX). 

Moreover  the  number  of  red  blood  coii^uscles  in  1  cu.  mm.  of  blood  varies 
not  a  little  under  perfectly  normal  circumstances.  Some  authors  have  observed 
an  increase,  others  a  decrease  in  the  number  after  meals.  There  is  substantial 
agreement,  however,  that  complete  or  partial  abstinence  from  food  does  not 
reduce  the  number.  Rarefaction  of  the  air,  as  on  mountain  tops,  increases  the 
number  of  red  corpuscles  per  cubic  millimeter  of  blood  very  considerably,  and 
the  effect  is  not  due  to  an  excessive  elimination  of  water  from  the  body,  for 
the  same  thing  has  been  noted  on  animals  where  an  increased  transpiration  of 
water  was  impossible.  The  increase  has  been  regarded  as  an  attempt  on  the 
part  of  the  organism  to  offset  incomplete  saturation  of  the  blood  with  oxygen, 
resulting  from  lower  air  pressure.  But  this  explanation  does  not  suffice,  for 
the  increase  takes  place  just  the  same  before  the  reduction  of  pressure  is  suffi- 
cient to  affect  the  absorjition  of  oxygen. 

It  should  be  remarked  in  connection  with  these  and  other  normal  variations 
in  the  number  of  red  blood  corpuscles,  that  blood-counts  give  us  only  the  rela- 
tive number,  and  do  not  throw  any  light  on  the  total  number  of  corpuscles. 
For  it  must  not  be  forgotten  that  under  some  circumstances  the  relative  num- 
ber of  corpuscles  in  different  parts  of  the  body  varies  greatly  (Zuntz),  nor  that 
an  exudation  of  plasma  from  the  vessels  may  produce  an  apparent  increase 
(Bunge) — in  short,  it  is  not  an  easy  matter  properly  and  exactly  to  estimate 
the  total  nimiber  of  blood  coi*puscles. 

The  specific  gravity  of  the  red  corpuscles  (1.008-1.105)  is  greater  than 
that  of  the  plasma  or  of  the  serum  (the  sp.  gr.  of  the  latter  in  man  amounts 
to  about  1.017).  Hence  they  sink  to  the  bottom  of  a  vessel  in  which  the  blood 
is  caught,  provided  we  are  dealing  with  whipped  blood,  or  blood  whose  coagu- 
lation is  artificially  stopped  or  retarded.  Since  the  separation  of  the  blood 
corpuscles  from  the  plasma  or  serum  can  be  accomplished  much  more  rapidly 
with  the  centrifuge  than  by  mere  settling,  this  instrument  is  often  used  in 
blood  work. 

On  the  addition  of  very  small  quantities  of  most  acids  or  acid  salts  of 
Fe,  Al,  Zn,  Cu,  Hg,  Sn,  Ag.  Au,  Ur.  Mb,  the  red  blood  corpuscles  become 
agglutinated,  and  thereby  precipitated.  The  same  takes  place  even  with  hamio- 
globin-free  stromata  as  well  as  with  the  leucocytes,  and  is  probably  caused 
by  an  effect  on  the  contained  globulin  (Peskind). 

The  weight  of  the  red  blood  corpuscles  in  100  parts  of  blood  is  estimated, 
according  to  Alex.  Schmidt,  in  the  following  manner:  (1)  The  percentage  of 
dry  residue  (T)  in  the  whole  blood  is  determined;  (2)  the  percentage  of  dry 
residue  (/)  in  the  serum  belonging  to  this  quantity  of  blood;  (3)  the  dry  resi- 
due (r)  of  the  red  blood  corpuscles  obtained  from  TOO  g.  of  blood.  The  dry 
residue  of  the  serum  o])tained  from  100  g.  of  blood  is  then  T—r,  and  the 

100  X  (T r) 

corresponding  quantity  of  serum  is — '■ — -,  so  that  the  weight  of  the 

red  blood  corpuscles  in  100  parts  of  blood  is  TOO  — — ^^ —L. 


150 


THE   BLOOD 


Bv  this  method  it  has  been  found  that  tlie  weight  of  the  corpuscles  in 
100  g.  of  de fib ri noted  blood  i^  JfS  g.  (mean  of  nine  observations)  for  the  man 
and  35  g.  (mean  of  eleven  observations)  for  the  woman. 

The  red  blood  corpuscles  are  continually  going  to  pieces  in  the  body  in 
great  numbers,  especially,  as  it  appears,  in  the  liver.  Xaturally  there  is, 
under  normal  conditions,  a  corresponding  production  of  new  ones.  In  em- 
bryonic life  the  liver  and  spleen  play  a  prominent  part  in  their  formation. 
In  the  adult,  according  to  most  authors,  red  l:)lood  corpuscles  are  formed  only 
in  the  red  marrow  of  the  bones.  ( For  the  importance  of  Fe  in  the  formation 
of  hfemoglobin,  see  Chapter  YIII.) 

The  blood  corpuscles  owe  their  red  color  to  the  pigment  substance  haemo- 
globin, whose  chemical  properties  were  lirst  closely  investigated  by  Hoppe- 

Seyler.  It  unites  with  oxygen  into  a 
compound  called  oxyhcemoglobin,  the 
amount  of  which  depends  (to  some  ex- 
tint)  upon  the  partial  pressure  of  the 
available  oxygen.  The  haemoglobin  in 
the  arterial  blood  occurs  chiefly  in  this 
form ;  in  venous  blood  htemoglobin  as 
well  as  ox3'ha?moglobin  is  found :  but  in 
asphyxiated  blood  only  hcemoglobin. 

By  thinning  with  water,  by  repeated 
freezing  and  thawing,  by  addition  of 
ether,  chloroform  or  bile,  or  of  acids  or 
bases,  the  coloring  matter  may  be  washed 
out  of  the  corpuscles  and  Ijrought  into 
solution.  The  blood  is  then  said  to  be 
of  a  lal-y  color,  or  is  lal-ed.  In  many 
cases  the  passage  of  the  ha?moglobin  out 
of  the  corpuscle  does  not  run  parallel  to 
the  outward  diffusion  of  the  electrolytes. 
Under  certain  circumstances  the  haemoglobin  passes  out  while  the  electrolytes 
remain  behind.  Under  others  the  opposite  takes  place:  the  electrolytes  leave 
the  corpuscle  and  the  hsemoglobin  remains.  This  shows  that  the  mode  of 
combination  of  the  hsemoglobin  and  of  the  electrolytes  is  somewhat  different 
(Stewart). 

According  to  Hoppe-Seyler  neither  the  hasmoglobin  nor  the  oxyhemoglobin 
is  present  as  such  in  the  red  corpuscle,  but  as  a  tolerably  firm  combination 
with  another  substance,  probably  lecithin.  The  combination  which  contains 
oxyha?moglobin  is  called  arterin,  while  that  of  which  hemoglobin  is  a  con- 
stituent is  known  as  phlcbin. 

After  the  coloring  matter  is  dissolved  out  of  the  red  blood  corpuscles  there 
remains  a  colorless  mass  called  the  stroma.  This  consists  of  lecithin,  choles- 
terin,  proteids,  urea,  and  mineral  substances,  chiefly  potassium,  phosphoric 
acid  and  chlorine,  and  in  the  red  blood  corpuscles  of  man,  sodium. 

By  far  the  greatest  part  (eighty-seven  to  ninety- five  per  cent)  of  the  dry 
substance  of  the  red  blood  corpuscle  consists  of  haemoglobin:  the  stroma  of 
the  blood  corpuscles  amounts  therefore  to  only  five  to  thirteen  per  cent.     In 


Fig.  46. — Blood  crystals,  after  Funke. 
a,  from  the  human  blood ;  b,  from  the 
blood  of  the  guinea  pig;  c,  from  the 
blood  of  a  squirrel. 


THE  FORMED  CONSTITUENTS  OF  THE  BLOOD 


151 


the  blood  of  a  man  there  is  found  13.8  per  cent  hemoglobin,  and  in  that  of  a 

woman  12.6  per  cent. 

The  quantity  of  ha?moglobin  in  the  V)lood  shows  great  variations  under 

different  circumstances,  and  as  a  rule,  though  not  always,  it  varies  directly 

as  the  number  of  corpuscles.     The  quantity  of 

haemoglobin  in  proportion  to  the  body  weight  is 

greatest  in  the  newborn  and  sinks  rapidly  during 

the  first  few  days  after  birth — e.  g.,  in  the  rabbit 

in  twenty-two  days,  it  sinks  from  about  13  g.  to 

4  g.  per  kg.  of  body  weight.     During  this  time 

the  absolute  quantity   of   haemoglobin   increases 

and  the  iron  stored  up  in  the  body  in   other 

forms  decreases  (Abderhalden). 

Oxyhaemoglobin  crystallizes  out   of  its   solu- 
tion more  or  less  readily.    The  cr3'stals  (Fig.  46) 

are  blood  red,  are  transparent,  and  belong,  what- 
ever their  form,  to  the  rhombic  system  (Lang). 

From  fresh  human  blood  one  may  obtain  three 

forms  of  crystals,  namely:    (1)    large,   scalari- 

f orm  plates,  ( 2 )  sharply  defined,  dark  red,  doubly 

refractive,  four-angled  prisms,  and   (3)   sharply 

defined  rods  much  split  up  at  the  ends   (Frie- 

boes).     Only  the  ox3'haemoglobin  of  the  squirrel 
(Fig.  46  c)  crystallizes  in  six-sided  tablets  of  the 

hexagonal  system. 

Hemoglobin  is  distinguished  from  oxyhemo- 
globin chiefly  by  being  more  easily  soluble,  and 

more  difficult  of  crystallization,  although  the  two 

are  as  a  rule  isomorphic.     The  crystals  and  the 

water  solution  of  hemogloljin  are  darker,  more 

violet,  or  purple  colored  than  the  crystals  and 
the  solution  of  oxyhemoglobin.  In  thin  layers 
hemoglobin  is  greenish,  in  thicker  layers  red. 
Oxyhemoglobin  solutions  are  always  red  what- 
ever the  thickness.  Finally,  the  two  show  note- 
worthy differences  in  their  absorption  spectra. 
as  will  be  evident  from  Figs.  47  and  48.  If 
the  solution  is  not  too  concentrated  the  absorp- 
tion spectrum  of  oxyhemoglobin  shows  two 
bands  a  and  /3  between  the  D  and  E  lines. 
With  weaker  solutions  the  /3  band  disappears 
first.  The  more  concentrated  the  solution  is, 
however,  the  broader  the  ])ands  become  imtil 
finally  they  fuse  together,  whereby  the  blue  and 
the  violet  parts  of  the  spectrum  are  at  the  same  time  more  and  more  obscured. 
The  absorption  spectrum  of  hemoglobin  on  the  contrary  shows  a  single  broad 
band  between  the  D  and  E  lines.  l)ut  nearer  the  D. 

In  mcth(Emoglohin  oxygen  occurs  in  the  same  quantity  as  in  oxyhemo- 


152  THE   BLOOD 

globin.  but  is  more  firmly  united.  There  is  also  a  compound  of  haMuoglobin 
which  contains  less  oxygen  than  the  oxyhiemoglobin.  but  is  not  completely 
reduced  like  the  hemoglobin.  It  is  called  pseudohcemoglohin  and  has  the 
same  absorption  spectrum  as  hjemoglobin  (Siegfried). 

Haemoglobin  unites  with  still  other  substances,  as  carbon  monoxide  {car- 
hon-monoxide  hcrmoglobin)  a  compound  corresponding  to  oxyhfemoglobin  but 
more  stable,  with  carbon  dioxide  {carbon-dioxide  hcemoglohin,  cf.  Chapter 
IX)  and  nitric  oxide  (nitric-oxide  hcemoglohin) . 

From  anahiiical  data  Hiifner  has  calculated  the  following  formula  for  the 
hsmoglobin  of  the  dogs  blood:  CgseHioosXie^FeSaOisi  (molecular  weight  = 
14,129). 

In  different  animals  haemoglobin  has  a  somewhat  different  constitution :  for 
the  haemoglobin  of  the  dog",  horse,  swine,  guinea  pig,  and  squirrel  various  authors 
have  found  the  following  constitution:  C  51.2-54.9  per  cent,  H  6.8-7.4  per  cent, 
N  16.1-17.9  per  cent,  S  0.39-0.86  per  cent,  Fe  0.34-0.59  per  cent.  O  19.5-23.4 
per  cent. 

For  every  molecule  of  haemoglobin  contained  in  oxyhsemoglobin  there  is 
one  molecule  of  oxygen — i.  e.,  for  1  atom  of  iron,  2  atoms  of  oxygen.  From 
this  it  can  be  shown  that  1  g.  of  haemoglobin  can  absorb  1.34  c.c.  of  oxygen. 
The  dependence  of  the  oxygen  absorption  by  haemoglobin  upon  partial  pres- 
sure will  be  discussed  more  fully  in  Chapter  IX. 

Ha?moglol:)in  is  a  conjugated  proteid  (cf.  page  75)  in  which  a  simple  pro- 
teid  is  coupled  with  an  iron-containing  pigment,  hcemochromogen  (Hoppe- 
Seyler).  In  100  parts  of  hemoglobin  there  are  94  parts  proteid  and  4  parts 
coloring  matter.  The  former  consists  for  the  most  part  of  a  histon-like  basic 
body,  glol)in  (Schulz).  which  like  other  simple  proteids  is  levorotatory.  while 
henioglo1:)in  itself  is  dextrorotatory  (Gamgee  and  Croft-Hill). 

On  cleavage  of  hemoglobin,  ha?mochromogen  is  formed,  and  by  ab- 
sorption of  oxygen  it  passes  over  into  hcematin:  Cg^Hg^OjX^Fe  (Kiister), 
C34H3505X5Fe"^(Ze\Tiek).  By  treatment  of  the  blood  pigment  with  HCl. 
hcemin  is  obtained  "(Fig.  49):  Cg^Hj.OsX.FeCl   (X^encki). 

Acids  change  hematin  by  loss  of  iron  into  the  pigments  meso porphyrin, 
CieHi^OoXg  (Xencki)  and  hcematoporphyrin,  CieHigOgX,  (Xencki).  Ener- 
getic reduction  of  the  latter  yields  an  oily,  oxygen-free  substance,  hcemopyrrol, 
CgHjgX  (Xencki),  which  according  to  Xencki  and  Zaleski  is  either  an  iso- 
butyl  pyrrol  or  a  methyl-propyl  pyrrol. 

Hsematoporphyrin  is  only  slightly  different  from  a  chlorophyll  derivative, 
phyUoporphyrin  C„;Hi80X„,  prepared  by  Schunk  and  Marehlewski.  This  fact 
which  indicates  a  close  agreement  between  the  structure  of  the  most  important 
coloring  matter  of  plants,  and  that  of  the  most  important  coloring  matter  of 
animals  sugg-ested  to  Nencki  and  Marehlewski  the  possibility  of  obtaining  iden- 
tical products  from  the  two.  They  succeeded  in  producing  htemopyrrol  from 
chlorophyll.  In  view  of  the  importance  of  pyrrol  in  the  molecule  of  both  haemo- 
globin and  chlorophyll,  we  may  conclude  that  the  two  are  in  fact  very  closely 
related. 


THE  FORMED  CONSTITUENTS  OF  THE  BLOOD 


153 


B.    THE  WHITE  CORPUSCLES 

These  are  colorless,  nucleated  cells.  Some  varieties  of  them,  at  least,  have, 
like  the  free-living  amceboe,  the  power  to  move  independently  from  one  place 
to  another  by  the  protrusion  of  pseudopodia.  On  account  of  this  ver}'  remark- 
able property  they  probably  play  a  very  important  role  in  many  processes 
of  the  body,  although  this  role  is  not  yet 
sufficiently  well  kno^^Ti.  Their  activity  is 
entirely  independent  of  the  nervous  system 
and  is  controlled,  in  great  part  at  least, 
by  chemotactic  influences  (cf.  page  54). 
Their  general  function,  so  far  as  investi- 
gation has  yet  been  able  to  determine.  Is 
to  provide  for  the  transportation  of  vari- 
ous substances  inside  the  body  and  to 
destroy  or  to  remove  foreign  substances 
from  the  body. 

The  number  of  white  corpuscles  shows 
considerable  variation  under  normal  cir- 
cumstances, a  fact  dependent  in  part  at 
least  on  their  entrance  into  or  withdrawal 
from  the  blood  stream  in  greater  or  less 
numbers.     (Concerning  the  multiplication 

of  white  blood  corpuscles  appearing  in  digestion  cf.  Chapter  YIII.)  In  the 
adult  the  average  number  is  8.000  to  9.000  per  cu.  mm. — i.  e.,  one  white  to 
every  500  to  600  red  corpuscles.  In  the  newborn  the  leucoc}i:es  are  much 
more  numerous  and  reach  on  the  average  18.000  per  cu.  mm. 

The  white  corpuscles  are  formed  in  extrauterine  life  chiefly  in  the  spleen 
and  lymphatic  glands:  from  these  issue  mononuclear  cells  (lymphocytes)  which, 
according  to  some  authors,  are  transformed  into  polynuclear  cells  in  the  blood 
stream.  Moreover  they  exhibit  a  variety  of  forms  and  are  divided  according  to 
their  appearance  and  staining  reactions  into  several  groups  (see  text-books  of 
histology). 


Fig.    49. 


-Hfemin    crystals,    after 
Prever. 


C.    THE  BLOOD  PLATELETS 

Discovered  by  Hayem  (1877)  and  demonstrated  in  the  circulating  blood 
by  Bizzozero  and  Laker,  the  blood  platelets  are  spherical  or  ellipsoidal  bodies 
which  send  out  in  all  directions  processes  of  variable  number  and  length, 
composed  of  the  same  shiny  material  as  the  body.  According  to  the  investi- 
gations of  Deetjen.  Dekhuyzen  and  others,  they  have  the  full  value  of  cells, 
consist  of  nucleus  and  protoplasm,  and  are  capable  of  amwboid  movement. 
Their  size  varies  between  0.005  and  0.0055  mm.  Their  number,  according 
to  Brodie  and  Russel,  amounts  to  about  635,000  in  1  cu.  mm.  of  blood.  With 
respect  to  their  chemical  constitution  it  is  especially  emphasized  that  they 
contain  a  nuclein  body  coupled  with  proteid ;  and  with  respect  to  their  physio- 
logical purpose  it  is  assumed  by  several  authors  that  they  play  an  essential 
part  in  the  coagulation  of  the  blood.     Their  origin  is  as  yet  conjectural. 


154  THE   BLOOD 


§  3.    THE    PLASMA 

As  already  mentioned  on  page  HT,  the  blood  coagulates  a  few  minutes 
after  it  has  left  the  body,  and  before  a  separation  of  the  plasma  from  the 
blood  corpuscles  can  take  place.  Coagulation  may  be  postponed  ])y  chilling 
the  blood  to  0°  C.  Then  on  account  of  their  greater  weight  the  corpuscles 
sink  to  the  bottom  and  (especially  with  horse's  blood)  a  plasma  entirely  free 
of  corpuscles  may  be  obtained  for  study.  Most  investigations  on  the  fluids 
of  the  l)lood  relate  however  to  the  serum,  which  is  distinguished  from  the 
plasma  chiefly  by  the  fact  that  it  contains  no  fibrinogen  and  less  ash,  because 
the  fibrin  when  it  separates  out  carries  down  with  it  either  mechanically  or 
in  chemical  combination,  some  of  the  ash  constituents. 

A.    CHEMICAL  CONSTITUTION   OF  THE   PLASMA 

Both  plasma  and  serum  are  clear,  faintly  yellow  fluids  with  a  specific 
gravity  of  about  1.028.  The  specific  heat  of  serum  is  0.9401,  greater  there- 
fore than  that  of  the  whole  blood. 

Besides  water,  plasma  contains  chiefly  proteid  substances  of  different  kinds, 
and  mineral  constituents.  The  osmotic  tension  of  plasma  is  about  equal  to 
that  of  a  0.9  per  cent  XaCl  solution  and  is  dependent  mainly  on  its  mineral 
constituents.  The  proteid  bodies  also  appear  to  influence  this  property,  though 
only  to  a  relatively  slight  extent. 

The  mineral  constituents  in  the  serum  are  dissociated  into  their  ions  to 
the  extent  of  about  seventy-five  per  cent  (Bugarsky  and  Tangl)  ;  while  in  the 
Avhole  blood,  electrolytic  dissociation  amounts  to  onlv  about  fortv  per  cent 
(Oker-Bloom). 

The  electrical  conductivity  of  the  whole  blood  is  less  than  that  of  the 
serum,  because  this  property  is  diminished  by  the  presence  of  the  corpuscles, 
as  in  general  the  conductivity  of  a  solution  is  diminished  by  nonconducting 
particles  in  suspension  (Bugarsky  and  Tangl.  Oker-Blom,  et  al.). 

The  mineral  substances  in  the  serum  differ  essentially  from  those  in  the 
corpuscles,  in  that  sodium  salts  predominate  in  the  former,  potassium  salts 
in  the  latter.  Among  the  sodium  compounds,  common  salt  occurs  in  greatest 
quantity  (about  0.6  per  cent).  Besides  this,  various  other  inorganic  sul^stances 
have  been  found  in  the  serum.  On  the  whole  the  mineral  substances  in  the 
serum  of  human  Ijlood  amount  to  about  0.85  per  cent. 

The  organic  substances  in  the  serum  amount  to  about  ten  time>  as  much, 
namely,  7.7-9.0  per  cent.  Among  these  the  proteids  are  the  most  important 
and  make  up  by  far  the  greatest  part  of  the  organic  matter  (about  nine- 
tenths).  The  chief  proteids  of  the  blood  plasma  are  fibrinogen,  serum  glol)U- 
lin  and  serum  albumin.  The  latter  two  however  are  not  to  be  regarded  as 
indivisible  substances ;  for  numerous  investigations  in  recent  years  have  shown, 
if  one  may  judge  by  their  behavior  in  salting  out.  that  at  least  two.  probably 
several,  globulins  (euglobulin.  pseudoglolralin)  are  present  in  the  blood  (cf. 
page  74)  ;  and,  according  to  results  of  fractional  heat  coagulation,  that  serum 
albumin  also  is  a  mixture  of  different  proteid  substances. 


THE   PLASMA  155 

Besides  the  proteids  we  find  in  the  blood:  fats  (and  the  cholesterin  ester 
of  fatty  acids,  but  as  a  rule  no  free  cholesterin,  Hiirthle)  ;  glycerin  and  carbo- 
hydrates (sugar,  probably  for  the  most  part  in  combination'  with  lecithin  as 
jecorin :  Jacobsen,  Henriques,  Bing)  ;  also  substances  which  are  formed  in  the 
activity  of  the  tissues  and  either  represent  decomposition  products  to  be  given 
off  from  the  body  (like  urea,  uric  acid,  ereatin,  carbamic  acid,  paralactic  acid, 
hippuric  acid,  etc.)  or  are  formed  for  the  purpose  of  influencing  the  functions 
of  different  organs  (internal  secretions,  cf.  Chapter  XI) — in  short,  everything 
which  the  tissues  have  need  of  for  their  activity,  and  most  of  the  products 
arising  from  this  activity. 

With  the  exception  always  of  the  proteids,  these  substances  occur  in  very- 
small  quantities  in  the  blood.  In  the  intervals  of  digestion  one  finds  from  one 
to  seven  per  cent  of  fat  in  the  serum,  while  during  digestion  it  mounts  much 
higher.  Even  in  starvation  (one  hundred  and  twenty  hours  after  food  has  been 
taken)  the  fat  content  of  the  blood  is  higher  than  in  the  inanitiate  condition 
(twelve  hours  after  the  last  meal) — a  fact  connected  with  the  movement  of  the 
body's  fat  for  the  purpose  of  covering  the  food  requirements  (Sehulz).  In  the 
healthy  condition  the  sugar  content  of  the  serum  amounts  to  about  1-1.5  per 
cent,  but  after  verj-  abundant  feeding  of  carbohydrates  may  increase  to  three 
per  cent'  and  higher.  The  maximum  urea  content  is  about  one  per  cent,  etc. 
These  quantities  appear  at  first  sight  to  be  astonishingly  small,  but  they  become 
intelligible  when  we  reflect  that  the  blood  is  in  continual  motion  and  its  con- 
tributions of  fat  and  carbohydrates  to  all  the  tissues  are  continually  being 
replaced  from  the  great  storehouses  of  the  body.  In  the  same  way  it  takes  up 
the  decomposition  products  from  the  tissues,  and  continually  eliminates  them 
by  way  of  the  excretors'  organ  so  that  under  normal  conditions  it  contains  at 
any  given  time  a  very  small  quantity  of  these  substances  also. 

Various  enzymes  have  been  demonstrated  in  the  blood.  Thus  according 
to  Michaelis  and  Cohnstein,  there  is  an  enzyme  which  in  the  presence  of 
red  blood  corpuscles  and  oxygen  destroys  fat  (lipolytic  enzyme).  Arthus  has 
found  an  enzyme  which  splits  monobutyrin  into  glycerin  and  butyric  acid ; 
but  an  enzyme  Avhich  would  split  neutral  fat  has  not  been  certainly  demon- 
strated. Further,  a  diastatic  enzyme  which  changes  starch  into  maltose,  one 
changing  the  latter  into  dextrose,  and  an  enzyme  by  which  sugar  is  destroyed 
(glycolytic  enzyme),  are  said  to  be  present.  Hedin  mentions  a  feeble  enzyme 
which  digests  proteid  in  an  alkaline  medium. 

Likewise  there  are  found  in  the  blood  substances  which  act  against  the 
enzymes  peculiar  to  the  body,  represent  therefore  antienzymes,  and  develop 
antipeptic.  antitryptic,  and  antichymotic  effects. 

Serum  contains  moreover  certain  substances  wliich  have  the  power  to  l-ill 
Bacteria  and  foreign  cells  generally.  The  serum  of  one  animal  species  destroys 
the  blood  corpuscles  of  another  species,  if  the  species  are  not  very  closely 
related — a  fact  which  explains,  in  part  at  least,  the  harmful  effects  of  a 
transfusion  of  foreign  blood.  This  globulicidal  action,  as  it  is  called,  as  well 
as  bactericidal  action  of  the  blood  is  very  different  in  different  genera  of 
animals.  Thus  the  serum  of  horse's  blood  is  only  slightly  poisonous  to  man 
and  is  tolerated  in  pretty  large  doses.  The  serum  of  human  blood  exercises 
a  powerful  effect  on  the  typhoid  and  cholera  bacteria,  while  on  the  pus- 


156  THE   BLOOD 

forming  staphylococci  a  weaker  effect,  and  on  the  streptococci,  the  diphtheria 
and  anthrax  bacilli,  no  effect  at  all.  On  the  other  hand  the  serum  of  the 
rabbit  kills  the  bacteria  of  anthrax  and  of  typhoid  fever,  but  is  harmless 
for  the  pus-forming  staphylococci,  etc. 

It  has  long  been  known  that  many  diseases  confer  on  the  inJiviJual  who 
survives  them,  as  an  after  effect,  an  immunity  or  unsusceptibility  toward  those 
particular  diseases.  Xow  it  has  been  shown  (Behring  and  Kitasato,  1890) 
that  the  blood  or  the  serum  of  an  individual  who  has  l)ecome  immune  in  this 
way  against  an  infectious  disease,  has  the  property,  when  it  is  injected  in 
stifhcient  quantity,  of  conveying  the  immunity  to  another  individual  previously 
susceptible  to  the  disease.  A  blood  or  serum  of  an  individual  who  has  success- 
fully withstood  the  disease  receives  therefore  as  an  after  effect  properties  which 
it  did  not  possess  before. 

These  discoveries  represent  the  point  of  departure  of  numerous  investiga- 
tions on  the  various  changes  which  appear  in  the  Wood  after  injection  of  dif- 
ferent substances.  In  general,  one  may  say  that  if  a  foreign  substance  of  a 
certain  kind  (such  as  the  toxins  formed  by  the  Bacteria,  foreign  blood,  various 
proteid  substances,  finely  minced  organs,  etc.)  is  brought  into  the  animal  by 
subcutaneous,  intraperitoneal  or  intravenous  injection,  the  blood  of  the  animal 
acquires  the  ability  to  change  the  foreign  substance  in  some  way,  and  thus  to 
neutralize  its  elBFect  on  the  organism.  Since  in  such  eases  there  are  found  in 
the  blood  specific  antibodies,  we  infer  that  the  changes  appearing  in  the  blood 
are  of  different  kinds  according  to  the  nature  of  the  substance  injected. 

If  a  bacterial  toxin  is  injected  into  the  blood,  there  arises  in  the  latter  an 
antitoxin  specific  for  just  this  toxin,  which  has  the  power  to  abolish  the  effect 
of  the  former,  probably  by  a  kind  of  neutralization.  Different  toxins  possess 
an  elective  power  for  different  cells  of  the  body;  and  precisely  those  cells  which 
are  attacked  by  a  definite  toxin  appear  to  be  most  active  in  the  formation  of 
the  antitoxin.  By  a  kind  of  internal  secretion  the  antitoxin  is  given  off  to 
the  blood  and  in  such  abundance  that  it  may  be  used  (for  example,  diphtheria 
serum)  as  a  remedy  in  other  animals. 

The  power  of  the  blood  to  destroy  blood  corpuscles.  Bacteria  and  foreign 
cells  generally,  like  its  antitoxic  properties,  can  be  increased  by  the  addition  of 
appropriate  substances.  Here  also  we  have  to  suppose  that  under  the  influence 
of  the  foreign  cells,  the  cells  of  the  body  (certain  leucocytes  especially)  are  the 
seat  of  production  of  the  antibodies.  As  with  the  antitoxin  serum,  the  cytolytic 
serum  can  also  exercise  its  specific  effects  outside  of  the  body — from  which  it 
follows  that  these  are  not  bound  up  in  the  formed  constituents  of  the  blood,  and 
in  general  not  in  the  living  substance. 

If  the  serum  of  an  animal  immunized  against — say  typhoid  fever — is  mixed 
with  a  fluid  culture  of  Bacillus  typhosus,  the  latter  become  stuck  together,  agglu- 
tinated. There  has  been  formed  in  the  blood  of  the  animal  therefore  a  substance 
which  produces  this  effect.  The  same  influence  may  be  observed  also  on  the 
blood  coipuscles.  When  an  animal  has  been  treated  with  a  foreign  blood,  its 
own  serum  added  to  the  blood  in  question  brings  about  an  entirely  similar  agglu- 
tination of  the  corpuscles  of  the  foreign  blood. 

After  intraperitoneal  injection  of  cow's  milk  the  serum  of  the  animal  em- 
ployed acquires  the  ability  to  throw  down  a  precipitate  in  the  cow's  milk — i.  e., 
a  precipitin  has  been  formed  in  the  blood.  By  injection  of  different  kinds  of 
blood  or  proteid  solutions,  one  may  obtain  different  precipitins  which  on  the 
whole  are  specific  since  they  produce  precipitates  especially  well  in  solutions  of 


THE  PLASMA  157 

the  substances  injected.  This  specific  character  is  not  however  by  any  means 
absolute. 

If  we  add  to  what  has  been  said  above,  that  after  the  injection  of  an 
agglutinating  serum  into  an  animal  an  antiagglutinating  effect  may  be  obtained, 
after  injection  of  a  precipitating  seriun  an  antiprecipitating  effect,  after  a 
cytolytic  serum  an  antilytic  effect,  it  ought  to  be  apparent  without  further  dis- 
cussion that  under  the  influence  of  various  chemical  agents,  extraordinarily 
important  and  complex  changes  can  be  induced  in  the  blood. 

These  changes  are  produced  in  part  by  a  special  activity  of  different  cells 
of  the  body,  developed  by  the  attack,  in  part  by  certain  leucocytes. 

There  can  be  no  doubt  that  all  these  changes  are  protective  adaptations  of 
the  body  against  harmful  influences.  Especially  is  this  true  of  the  antitoxins, 
the  bacterialysins,  and  agglutinins. 

The  matter  is  not  so  clear  with  regard  to  the  other  lysins  and  the  pre- 
cipitins; but  it  is  to  be  presumed  that  they  also  have  some  definite  purpose. 
It  appears  that  they  are  specialized  substances,  which,  like  the  antienzymes, 
come  down  in  the  globulin  precipitates ;  but  whether  they  are  true  proteid  bodies 
or  are  only  attached  to  such,  cannot  be  said  definitely  as  yet. 

We  must  forego  a  presentation  of  the  theoretical  views  which  are  held  in 
explanation  of  these  phenomena,  since  a  discussion  of  them  would  require  too 
much  space.  We  would  not,  however,  omit  to  mention  the  side-chain  theory  of 
Ehrlich,  since  tliis  has  had  a  very  stimulating  effect  on  research  in  this  field, 
and  has  very  successfully  gathered  together  under  one  general  p(jint  of  view  the 
complicated  phenomena  which  confront  us  in  this  province. 

Since  the  chemical  processes  in  different  organs  are  in  many  respects  very 
different,  the  blood  returning  by  the  vein  must  have  a  more  or  less  variable 
constitution  according  to  the  organ  from  ivhich  it  flows.  Analysis  of  these 
different  kinds  of  blood  would  be  well  calculated  to  give  at  some  future  time 
very  valuable  conclusions  as  to  the  chemical  transformations  taking  place  in 
the  corresponding  organs.  At  present  however  our  information  is  quite  too 
inadequate  for  any  discussion  of  the  subject. 

The  blood  flowing  from  the  different  parts  of  the  body  is  collected  finally 
in  the  two  venae  cavfe  and  is  emptied  by  them  into  the  right  heart,  where  the 
different  kinds  of  blood,  not  yet  thoroughly  mixed  in  the  veins,  are  mixed 
together;  so  that  blood  driven  from  the  left  ventricle  to  all  oarts  of  the 
body  is  entirehj  homogeneous. 

B.    COAGULATION  OF  BLOOD 

If  blood  be  drawn  directly  from  an  open  artery  into  a  saturated  solution 
of  magnesium  sulphate,  it  can  be  kept  for  days  without  coagulating.  The 
blood  corpuscles  can  be  removed  from  such  blood  by  filtering,  by  centrifugal- 
izing,  or  simply  by  letting  it  stand,  and  in  this  way  a  fluid  is  obtained  known 
as  the  salt  plasma  (Alex.  Schmidt).  By  precipitation  with  an  equal  volume 
of  saturated  XaCl  solution,  there  is  thrown  down  a  proteid  body,  the  fibrino- 
gen, which  can  be  further  purified  by  various  means.  Fibrinogen  is  soluble  in 
weak  NaCl  solution  and  its  solution  will  keep  at  room  temperature  until 
putrefaction  sets  in  without  showing  a  trace  of  coagulation.  If  however  some 
blood  or  blood  serum  be  added  to  such  a  solution,  fibrin  formation  takes  place 


158  THE  BLOOD 

at  once.  The  same  effect  is  produced  also  by  blood  clot  washed  free  of  all 
color  with  water.  Such  a  clot  contains  fibrin  and  the  remains  of  white  cor- 
puscles, so  that  one  is  inclined  for  many  reasons  to  assume  that  the  substance 
which  must  be  added  to  a  solution  of  fibrinogen  to  make  it  clot,  and  which 
has  been  designated  the  fibj'in  ferment  or  thromhin  (A.  Schmidt)  comes 
directly  from  the  white  blood  corpuscles.  It  appears  from  several  observations 
that  the  white  corpuscles  themselves  do  not  of  necessity  break  down  under 
such  circumstances,  and  Arthus  has  expressed  the  view  that  they  give  off 
the  fibrin  ferment  by  a  process  of  secretion. 

Coagulation  cannot  take  place,  as  Arthus  was  the  first  to  demonstrate, 
without  the  presence  of  a  soluble  calcium  salt.  This  is  probably  due  to  the 
fact  that  fibrin  ferment  does  not  exist  in  the  blood  as  such  but  in  the  form 
of  a  mother  substance,  or  zymogen,  and  is  activated  only  in  the  presence  of  Ca 
salts  (Hammarsten.  Pekelharing) .  The  calcium  does  not  appear  to  be  neces- 
sary for  the  formation  of  fibrin,  however,  for  a  solution  of  fibrinogen  coagu- 
lates in  the  presence  of  thrombin  even  when  the  calcium  salts  are  removed 
by  an  oxalate. 

Coagulation  is  considerably  accelerated  hy  addition  of  extracts  of  all  pos- 
sible kinds  of  organs,  and  even  by  mere  contact  of  the  l)lood  with  the  wound. 
On  this  account  it  has  been  assumed  that  the  contained  nucleo-proteids  might 
represent  precursors  of  the  thrombin.  On  the  contrary  Arthus,  Morawitz 
and  others  believe  that  they  only  hasten  the  formation  of  the  enzyme  and 
that  the  mother  su])stance  of  the  latter  occurs  exclusively  in  the  blood. 

According  to  Mora^dtz  the  organ  extracts  effect  the  formation  of  the 
proenzyme  from  a  zymogen  stage,  thrombogen.  whereupon  thromljin  arises 
from  the  proenzyme  under  the  influence  of  the  calcium  ions. 

The  formation  of  thrombin  is  stopped  immediately  by  sodium  fluoride 
and  by  addition  of  this  salt  in  small  quantities  it  is  possible  therefore  to  follow 
the  course  of  thrombin  formation  more  closely.  In  this  way  it  has  been 
shown  that  at  the  moment  it  flows  from  the  vessel  the  l)lood  contains  no 
thrombin  at  all,  that  the  quantity  of  the  enzyme  increases  quite  slowly  at 
first,  and  that  shortly  before  coagulation  it  undergoes  a  rapid  increase. 
Thrombin  is  formed  for  a  time  also  after  coagulation  has  taken  place 
(Arthus). 

When  blood  serum  stands  exposed  to  the  air  its  enzyme  gradually  decreases 
in  quantity  and  disappears  entirely  after  about  six  days.  No  more  enzyme  is 
obtained  after  this  time  by  addition  of  calcium  salts.  But  by  means  of  acids, 
alkalies,  alcohol,  etc.,  one  can  demonstrate  an  effective  fibrin  ferment;  there  is 
present  therefore  in  the  serum  a  body  from  which  active  fibrin  ferment  may  be 
formed.  This  body  is  absent  from  nomial  plasma  and  seems  to  make  its  appear- 
ance for  the  first  during  coagulation.  According  to  Fuld  and  Morawitz,  it  is 
probable  that  this  substance  is  thrombin  itself,  which  had  merely  passed  over 
to  an  inactive  state. 

The  transformations  brought  about  by  enzymes  in  general  appear  to  pro- 
ceed in  such  a  way  that  the  substance  acted  on  al)sorbs  water  and  is  subse- 
quently split  into  two  new  substances.  This  is  prol)ably  the  case  in  fibrin 
formation;  the  fibrinogen  is  split  into  insoluble  fibrin  which  constitutes  the 


THE  PLAS>L\  159 

chief  bulk,  and  fib rino- globulin  which  remains  in  solution  and  is  formed  only 
in  small  quantity  (Hammarsten). 

The  difficulties  with  which  the  subject  of  coagulation  's  beset,  and  which 
we  have  been  able  to  discuss  here  only  in  a  cursory  manner,  are  still  more 
multiplied  when  we  ask  why  the  blood  does  not  clot  in  the  vessels.  That  the 
constant  movement  of  the  blood  is  not  the  reason  is  proved  by  the  fact  that 
blood  coagulates  outside  the  body  more  rapidly  when  it  is  stirred.  Cooling 
of  the  blood  cannot  account  for  coagulation,  for  it  is  possible  to  postpone 
the  process  for  a  long  time  by  this  very  means.  Xeither  can  contact  with  the 
air  be  considered,  for  coagulation  goes  on  in  the  usual  manner  if  blood  is 
collected  (over  mercury)  by  exclusion  of  air. 

Coagulation  does  not  occur  if  the  blood  is  drawn  by  means  of  an  oiled 
cannula,  or  if  it  is  caught  in  an  oiled  vessel :  in  fact  it  can  now  be  stirred 
with  an  oiled  rod  without  producing  coagulation.  But  if  it  is  stirred  with 
an  ordinary  rod.  or  if  small  solid  particles  be  introduced,  coagulation  takes 
place  immediately  (Freund).  The  reason  why  coagulation  does  not  take 
place  under  the  above-mentioned  circumstances  doubtless  lies  in  the  fact  that 
the  blood  is  prevented  by  the  oil  from  coming  in  contact  with  the  wall  of 
the  vessel.  Attempts  have  been  made  to  explain  the  absence  of  coagulation 
in  the  blood  vessels  in  a  similar  manner,  by  assuming  that  in  health  the 
necessary  adhesion  of  the  blood  to  the  walls  is  wanting.  When  the  endothelial 
lining  of  the  vessels  becomes  abnormally  changed  in  any  way  so  that  internal 
adhesion  occurs,  intravascular  clotting  ensues.  Against  this  conception  how- 
ever it  may  be  objected  that  the  blood  always  thoroughly  wets  the  internal 
wall  of  the  blood  vessels  (B.  Lewy). 

Beautiful  exam^ples  of  the  inhibiting:  property  of  the  vascular  walls  are 
found  in  the  facts  that  blood  remains  fluid  for  a  long  time  in  a  section  of  a 
vein  ligated  olf  at  both  ends  (Hewson)  :  and  that  a  turtle's  heart  filled  with 
blood  beats  for  days  without  any  clotting  if  the  temperature  of  the  contained 
blood  be  low  (Briicke). 

Opinions  differ  considerably  as  to  the  real  nature  of  the  changes  produced 
by  adhesion  of  the  blood  to  rough  surfaces,  so  that  at  this  time  we  are  unable 
to  form  any  definite  conception  of  the  matter.  But  since  stibstances  have 
been  found  in  the  blood  which  exercise  an  inhibiting  influence  on  coagulation. 
it  is  at  least  conceivable  that  during  life  and  with  uninjured  vascular  walls, 
the  inducing  and  inhibiting  bodies  neutralize  each  other,  while  in  shed  blood 
the  former  preponderate  and  thus  bring  about  coagtilation. 

In  the  living  body  the  coagulability  of  the  blood  can  be  abolished  by  intra- 
vascular injection  of  aibumoses  (Schmidt-MUhlheim.  Fano)  or  of  leech  ex- 
tracts (Ha3-craft).  If  the  blood  is  diverted  from  the  liver  and  the  intestine 
so  that  it  circulates  only  through  the  extremities,  the  head  and  the  lungs,  it 
likewise  loses  its  ability  to  coagulate. 

Coagulation  of  the  blood  is  of  extremely  great  importance  as  a  means  of 
protection  for  the  body,  since  bleeding  from  injured  vessels,  unless  they  be  too 
large,  is  thereby  stopped.  If  the  blood  did  not  coagulate  every  slight  injury 
would  involve  great  loss  of  blood.  ^Yhen  the  larger  vessels  are  ruptured  coagu- 
lation does  not  suffice:  for  the  blood  flows  out  in  such  quantity  and  with  such 
12 


160  THE  BLOOD 

speed  that  the  first  blood  does  not  have  time  to  coagulate  before  new  blood 
replaces  it.  And  if  coagulation  should  take  place  in  the  wound,  the  clot 
would  not  be  sufficiently  firm  to  withstand  the  great  force  of  the  escaping 
blood. 

Referen'ces. — L.  Aschoff,  "  Ehrlich's  Seitenketteutheorie  und  ihre  Anwend- 
ung-  auf  kiinstlichen  Inununisierungsprozesse."  Jena,  1002. — Hermann  Sahli, 
"Diagnostic  Methods/'  Chapter  on  "Examination  of  the  Blood";  English  edi- 
tion edited  by  Kinnicutt  and  Potter,  Philadelphia,  1905. — Alex.  Schmidt,  "  Zur 
Blutlehre,"  Leipzic,  1892. — "  Weitere  Beitrage  zur  Blutlehre,"  Wiesbaden,  1895. 
— The  Textbooks  of  Physiological  Chemistry  mentioned  on  page  82. 


CHAPTER    VI 

CIRCULATION    OF    THE    BLOOD 

If  the  blood  were  to  stand  still  in  any  particular  vascular  region,  it  would 
become  impoverished  in  nutrient  substances,  especially  oxygen,  would  become 
overladen  with  products  of  tissue  activity,  and  so  would  be  rendered  unfit 
to  fulfill  its  physiological  purposes.  But  by  the  fact  that  tJie  blood  is  con- 
tinuaUy  in  motion,  this  is  prevented,  for  as  it  moves  it  both  replenishes  its 
store  of  nutrient  substances  taken  from  different  parts  of  the  body  and  gets 
rid  of  the  products  which  are  useless  or  harmful  to  the  body. 

This  continual  movement  is  maintained  by  the  activity  of  the  heart.  The 
heart  represents  the  motive  power  which  drives  the  blood  through  the  vessels. 
The  latter  however  are  not  mere  passive  tubes,  but  in  various  ways  they 
actively  participate  in  the  distribution  of  the  blood  throughout  the  body. 


FIRST    SECTIOX 

GENERAL   SURVEY   OF  THE   BLOOD'S  MOVEMENTS 

The  heart  of  warm-blooded  animals  is  divided  by  means  of  a  septum 
running  from  above  downward,  into  two  completely  separated  halves,  a  rigid 
and  a  left  (Vesalius,  1542).  Each  half  consists  of  two  communicating  cham- 
bers, an  upper,  the  auricle,  and  a  lower,  the  ventricle.  The  opening  between 
auricle  and  ventricle  can  be  closed  in  both  halves  of  the  heart  by  means  of 
valves. 

Blood  vessels  connect  with  both  auricles  and  ventricles.  In  those  leading 
from  the  ventricles  blood  fiows  from  the  heart,  and  they  are  called  arteries. 
In  the  vessels  communicating  with  the  auricles  blood  is  conveyed  to  the  heart, 
and  they  are  called  veins. 

The  arteries  communicate  with  the  veins  by  means  of  the  capillaries,  so 
that  the  heart  and  the  vessels  form  a  connected  system  of  tubes  entirely  shut 
off  from  the  outside. 

In  this  S3'stem,  as  was  first  established  by  Harvey  (1628),  the  blood  moves 
in  the  following  manner  (Fig.  50).  It  is  poured  by  the  two  venae  cavae  into 
the  right  anride,  and  is  driven  by  the  latter  into  the  right  ventricle.  By  the 
contraction  of  the  ventricle  it  is  pressed  out  into  the  pulmonary  arteries  pro- 
ceeding therefrom,  and  flows  through  the  vessels  of  the  lungs  and  the  pul- 
monary veins  into  the  left  auricle.  This  part  of  the  circulation  is  called. the 
lesser  circulation,  and  was  first  described  by  Servet  (1553)  and  Colombo 
(1559).     From  the  left  auricle  the  blood  is  driven  into  the  left  ventricle  and 

161 


162 


CIRCULATION    OF   THE   BLOOD 


from  there  again  into  the  aorta.  Thence  it  flows  through  all  branches  of 
the  aorta  to  the  capillaries,  from  there  to  the  systemic  veins  and  through  the 
vencB  cavce  back  to  the  right  auricle.     That  portion  of  the  circulation  from 

the  left  ventricle  to  the  right  auricle  is  called 
I  the  greater  circulation. 

In  warm-blooded  animals  the  entire  quantity 
of  the  blood  must  flow  through  the  lungs  in  order 
to  pass  from  the  right  half  of  the  heart  to  the 
left.  During  a  complete  circuit  therefore  the 
blood  flows  through  two  systems  of  capillaries : 
namely.  ( 1 )  that  of  the  greater  circulation,  and 
(2)  the  pulmonary  system.  For  the  blood  which 
passes  through  the  capillaries  of  the  stomach, 
intestine,  pancreas  and  spleen  still  another  capil- 
lary system  is  interpolated.  This  blood  flows  to 
the  liver  in  the  portal  vein  which  there  breaks 
up  into  a  new  S3'stem  of  capillaries,  whence  arise 
the  hepatic  veins,  conducting  the  blood  away  to 
the  heart.  The  same  is  true  of  the  kidney  blood, 
for  in  the  kidneys  themselves  the  blood  flows  first 
through  the  capillaries  which  form  the  glomeruli 
of  the  ilalpighian  corpuscles,  and  secondly 
through  the  capillary  plexus  by  which  the  kidney 
tubules  are  surrounded. 

The  contraction  of  the  heart  is  designated  the 
systole  and  its  relaxation,  the  diastole. 


Fig.  50. — Schema  of  the  cir- 
culation, seen  from  the  dor- 
sal side,  a,  left  auricle;  b, 
left  ventricle;  c,  right  auri- 
cle; d,  right  ventricle;  c, 
pulmonary  circulation  ;  /, 
capillaries  of  the  intestine; 
g,  capillaries  of  the  liver;  h, 
capillaries  of  the  lower  ex- 
tremity; )',  capillaries  of  the 
head  and  upper  extremities; 
k,  hepatic  artery.  Arterial 
blood,  red;  venous  blood, 
blue;  lymph  vessels  shown 
only  in  outline. 


SECOXD    SECTIOX 

THE  MOVEMENTS  OF  THE  HEART 

§    1.     THE    FORM   CHANGES   OF   THE 
HEART   IN   SYSTOLE 


After  opening  the  pericardium  of  a  beating 
heart  it  can  be  seen  that  the  contraction  begins 
at  the  outlet  of  the  great  veins,  which  are  here 
surrounded  by  circular  muscle  fibers,  and  pro- 
ceeds thence  onto  the  auricles. 

The  two  auricles  contract  simultaneously,  and 
immediately  after  the  auricular  systole  the  ventricles  contract,  likewise 
simultaneously.  Xeither  auricles  nor  ventricles  completely  empty  themselves 
bv  their  contractions. 


A.    STRUCTURE  OF  THE   VENTRICULAR  WALL 

The  arrangement  of  the  muscular  mass  which  forms  the  walls  of  the  ven- 
tricles is  verj-  complicated.     Our  description  here  must  be  very  brief. 

Of  the  two  ventricles  the  left  possesses  a  much  stronger  musculature  than 


THE    FORM   CHANGES   OF   THE    HE.IRT    IN    SYSTOLE 


163 


the  right,  a  condition  which  conforms  with  the  much  heavier  work  to  be  done 
by  the  former.  In  fact  the  outer  wall  of  the  right  ventricle  is  formed  for  the 
most  part  of  fibers  which  come 
from  the  left.  To  a  certain  ex- 
tent therefore  the  right  ven- 
tricle may  be  looked  upon  as 
a  cleft  in  the  wall  of  the  left, 
as  shown  in  Fig.  51. 

With  regard  to  the  struc- 
ture of  the  ventricles  the  fol- 
lowing is  worthy  of  mention : 
From  the  fibro-tendinous  rings 
at  the  base  of  the  left  ventricle, 
and  from  the  muscular  sides  of 
the  aorta  superficial  fibers  pass 
obliquely  downward  to  the  apex 
of  the  heart,  enter  for  the 
most  part  the  vertex  of  the  left 
ventricle  and  double  round  into 
its  interior,  to  be  inserted 
either  into  the  papillary  mus- 
cles and  chordte  tcndineae,  or 
into  the  atrio-ventricular  ring. 
The    two    layers    thus    formed 

are  separated  by  a  median  layer,  which,  when  isolated  by  a  special  method 
of  preparation,  has  the  form  of  a  muscular  cone.  It  is  connected  also  by  many 
fibers  with  the  outer  and  inner  layers.  The  fibers  of  this  median  part  describe 
loops,  which,  not  having  any  tendinous  connections,  return  to  their  starting  point 
(Fig.  52).    It  is  obvious  that  this  strongly  developed  median  layer  must  play  a 

prominent  part  in  the  contrac- 
tion of  the  left  ventricle. 

The  synchronism  of  con- 
traction of  the  two  ventricles 
naturally  depends  on  the  fact 
that  the  muscular  fibers  are 
in  part  common  to  both  ven- 
tricles. Xevertheless  various 
observations  indicate  that  this 
synchronism  is  not  an  absolute 
one,  but  that  each  ventricle 
possesses  a  certain  pJii/siolog- 
icat  independence    (Knoll). 


Fig.  51. — Cross-section  through  a  fully  contracted 
human  heart  at  the  junction  of  the  upper  and 
middle  thirds,   after  Krehl. 


B. 


THE  FORM  CHANGES  OF 
THE  HEART 


FiG.  52. — Layer  of  fibers  in  the  left  ventricle  of  the 
human  heart  which  have  no  tendinous  insertions. 
The  more  external  and  more  internal  layers  have 
been  removed.  The  outline  of  the  entire  heart  is 
shown.      After  Krehl. 


In  diastole  the  form  of  the 
ventricles  of  an  empty  heart 
outside  the  body  depends  in  the 
main  upon  the  way  in  which 
they    are   supported,    whereas 


164 


CIRCULATION   OF  THE   BLOOD 


iindor  normal  circumstances  their  form  depends  in  the  main  upon  the  degree 
to  which  they  are  filled.  In  systole  when,  as  Harvey  put  it,  "  the  heart  makes 
tense  all  of  its  fibers,"  the  ventricles  whether  empty  or  filled  have  a  perfectly 
definite  form,  which  is  entirely  independent  of  the  diastolic  form.  Hence  if 
the  heart  is  lengthened  in  any  one  of  its  diameters  during  diastole,  it  is  short- 
ened in  this  diameter  during  systole. 

In  the  living  body  and   in  the  unopened  chest  the  heart  lies  in  the  peri- 
cardium and  is  covered  for  the  most  part  by  the  lungs.     It  is  suspended  upon 


Fig.  53  — Casts  of  the  ventricular  cavities  of  the  ox  heart  in  rigor  mortis,  after  Worm-Miiller 
and  Sandborg.     A,  cavity  of  the  right  ventricle;  B,  of  the  left.      Two-thirds  natural  size. 


the  great  arteries  and  so  far  as  the  pericardium  will  permit,  is  movable  in  dif- 
ferent directions. 

If  one  observes  the  heart  of  a  mammal  in  the  usual  supine  position  of  the 
animal  in  experimentation,  the  diastolic  heart  is  flattened  somewhat  in  the 
anterior-posterior  direction,  while  its  transverse  diameter  is  increased.  Under 
such  circumstances  one  finds  that  the  long  axis  and  the  transverse  diameter 
shorten  in  systole,  while  the  sagittal  axis  becomes  longer. 

In  the  natural  position  of  the  body  the  heart  is  supported  for  the  most  part 
by  the  lungs ;  these  are  to  be  looked  upon  as  air  cushions  which  influence  the 
form  of  the  diastolic  heart  only  to  a  slight  extent.  In  the  natural  position  of 
the  animal  therefore  the  base  of  the  heart  must  be  more  circular  than  in  the 
supine  position  with  the  chest  open.  By  means  of  needles  stuck  through  the 
chest  wall   into   different  parts  of  the  heart,  so  that   their  ends  gave  by  their 


THE   REGULATION    OF   THE   BLOOD  FLOW  THROUGH   THE    HEART      165 

movements  the  directions  of  shortening,  Haycraft  found  that  the  heart  in  its 
natural  position  contracts  in  all  its  dimensions. 

According  to  Braun,  in  the  shortening  of  the  long  axis  of  the  heart  during 
systole  its  conical  end  becomes  blunter  and  the  long  axis  of  the  left  ventricle 
comes  to  form  with  that  of  the  right  a  more  acute  angle  than  during  diastole; 
at  the  same  time  the  apex  of  the  heart  moves  slightly  to  the  right. 

Since  the  apex  of  the  heart  is  its  freest  part,  one  would  suppose  that  on 
contraction  of  the  long  axis  in  ventricular  systole  the  apex  would  approach 
the  base.  But  this  is  not  the  case :  the  base  on  the  contrary  approaches  the 
apex,  and  the  heart  as  a  whole  makes  no  change  in  position.  This  phenomenon 
appears  to  ])e  explained  partly  at  least  by  the  recoil  of  the  blood  when  it 
rushes  out  through  the  arterial  openings.  That  is  to  say,  when  the  ventricles 
drive  the  blood  into  the  great  arteries  the  apex  is  prevented  by  this  recoil 
from  moving  toward  the  base;  and  instead,  presents  a  relatively  fixed  point 
toward  which  the  base  is  drawn  (Chauveau  and  Faivre). 

The  changes  in  form  of  the  heart  cavities  have  been  studied  only  in  heat 
or  in  death  rigor,  where  the  contraction  of  the  heart  muscle  has  proceeded 
much  farther  than  it  ever  does  in  life.  From  such  observations  it  appears 
that  even  in  these  extremely  contracted  conditions  the  cavities  of  the  heart 
are  never  entirely  ohliterated.  In  the  left  ventricle  an  evident  cavity  remains 
above  the  summits  of  the  papillary  muscles ;  while  the  right  ventricle  is  trans- 
formed into  a  narrow  slit,  so  that  the  two  walls  in  the  upper  portion  under- 
neath the  atrio-ventricular  opening  are  still  separated  from  each  other  by  a 
certain  distance  (Hesse,  Worm-Miiller  and  Sandborg;  cf.  Fig.  53). 


§  2.     THE    REGULATION    OF   THE    BLOOD  FLOW    THROUGH    THE 

HEART 

The  normal  course  of  the  blood  through  the  heart  is  determined  chief y 
hy  its  valves,  but  partly  also  by  other  means,  which  prevent  the  blood  from 
flowing  in  the  wrong  direction. 

A.    THE  ATRIO-VENTRICULAR  VALVES 

Between  the  auricle  and  ventricle  we  have  in  the  right  heart  the  tricuspid 
valve,  in  the  left  the  mitral  valve. 

The  trieupsid  is  composed  of  a  tubular  membrane  fastened  around  the  entire 
circumference  to  the  atrio-ventricular  ring.  It  is  divided  by  deep  incisions  into 
three  large  and  one  or  two  small  flaps.  These  are  attached  by  means  of  the 
chordae  tendinse  to  the  papillary  muscles  or  to  the  ventricular  wall.  The  chorda? 
tendinse  run  partly  to  the  free  edge  of  the  valvular  flaps,  partly  to  their  ven- 
tricular surface  where  they  are  attached  broadly  to  the  connective-tissue  frame- 
work of  the  flaps. 

The  mitral  valve  is  similar  in  all  essential  respects  to  the  tricuspid,  only  it 
is  more  firmly  constructed  in  all  its  parts  and  consists  of  but  two  flaps. 

When  the  ventricles  contract  the  blood  is  prevented  by  closure  of  th(^  valves 
from  flowing  back  into  the  auricles,  and  is  forced  to  take  the  right  path  into 


166 


CIRCULATION    OF  THE   BLOOD 


the  arteries.  Without  the  valves  not  a  drop  of  blood  would  reach  the  arteries, 
for  the  resistance  in  the  arteries  is  considerably  greater  than  that  in  the  auri- 
cles and  in  the  great  veins  emptying  into  them. 

During  the  ventricular  diastole  the  atrio-ventricular  flaps  are  more  or 
less  closely  approximated  by  simply  floating  into  position  on  the  blood  as  it 
fills  the  ventricle.  When  the  ventricular  systole  sets  in  and  the  pressure  in 
the  ventricles  rises  suddenly,  the  valvular  flaps  naturally  strike  together  and 
so  cut  off  connection  of  the  ventricle  with  the  auricle. 

Because  the  pressure  in  the  auricle  at  the  systole  of  the  ventricle  is  infini- 
tesimally  small  as  compared  with  that  in  the  ventricle  itself,  the  valves  must 
close  so  quickly  that  at  most  only  a  very  insignificant  quantity  of  blood  can 
get  back  into  the  auricles  before  the  closure  is  complete.  It  appears  even 
that  the  valves  work  so  promptly  that  absolutely  no  regurgitation  of  the  blood 

into  the  auricle  takes  place.  When  the  auricle 
contracts,  the  ventricle  is  somewhat  distended 
owing  to  the  flexibility  of  its  resting  wall  and 
its  contents  are  subjected  to  a  certain  tension. 
At  the  moment  the  contraction  of  the  auricle 
abates  somewhat  or  ceases  altogether  the  pres- 
sure in  the  ventricle  becomes  greater  than  that 
in  the  auricle,  and  by  this  means  the  valvular 
flaps  are  brought  together  even  before  the  ven- 
tricular systole  begins  ( Baumgarten ) . 

The  great  pressure  which  is  brought  to  bear 
on  the  valves  during  the  ventricular  systole 
would  cause  them  to  turn  up  into  the  auricles, 
and  thereby  cause  serious  disturbance  to  the  cir- 
culation, were  it  not  for  the  chordae  tendinae. 
Since  the  chordae  are  attached  not  only  at  the 
free  edges  but  also  on  the  flat  surface  of  the 
valves,  the  latter  are  prevented  not  only  from  turning  up  into  the  auricle,  but 
even  from  bulging  toward  it. 

Because  of  the  chordae  tendinte  the  closed  valve  takes  a  perfectly  definite 
position,  the  central  parts  of  the  flaps  being  pushed  up  to  the  level  of  their 
attachment,  and  their  turned-down  edges  being  applied  to  each  other  as  in  Fig. 
54.  By  this  means  closure  is  established  over  a  greater  surface  and  is  secured 
also  by  the  fact  that  the  bent  portions  of  the  edges  dovetail  into  each  other  by 
toothlike  folds,  so  that  the  valves  are  able  to  sustain  the  great  pressure.  The 
circumference  of  the  base  of  the  heart,  and  at  the  same  time  that  of  the  atrio- 
ventricular opening,  becomes  very  much  smaller  in  ventricular  systole :  the  mus- 
cles surrounding  the  opening  therefore  must  be  credited  with  a  share  in  the 
closure  of  the  passage. 

The  role  of  the  papillary  muscles  in  the  closing  of  the  atrio-ventricular  valves 
has  been  conceived  in  very  different  ways.  The  most  probable  view  is,  that  they 
prevent  swinging  of  the  valves  into  the  auricles,  the  approach  of  the  heart  base 
toward  the  apex  being  compensated  by  their  contraction  and  consequent  pull  on 
the  chordae  tendinae. 

When  the  auricles  contract,  regurgitation  of  blood  into  the  great  veins  is 
prevented  by  contraction  of  the  circular  musculature  passing  around  the  latter. 


Fig.  54. — Position  of  the  atrio- 
ventricular valves  when  closed, 
schematic  drawing,  after  Krehl. 


THE    HEART   SOUNDS  167 

their  openings  being  in  this  way  either  narrowed  considerably  or  actually 
closed. 

B.    THE   SEMILUNAR   VALVES 

Since  the  blood  cannot  flow  back  into  the  auricle  during  the  ventricular 
systole,  it  must  pass  into  the  great  arteries.  The  mouths  of  the  latter  are 
closed  by  means  of  valves,  each  consisting  of  three  pouchlike  flaps. 

These  flaps  are  semicircular  membranes,  fastened  by  their  curved  edges  to 
the  wall  of  the  vessel,  so  that  they  stand  out  with  their  straight  edges  from  the 
wall  and  present  concave  surfaces  toward  the  arteries.  In  this  way  pouches 
are  formed  in  which  the  blood  is  caught  and  dammed  back,  while  at  the  same 
time  the  wall  of  the  pocket  turned  toward  the  lumen  of  the  vessel  is  put  on 
the  stretch. 

In  both  the  aorta  and  the  pulmonary  artery  the  wall  bulges  outward  directly 
above  the  attached  edges  of  the  valve,  forming  in  each  three  enlargements,  the 
sinuses  of  Valsalva.  In  the  aorta  one  sinus  is  directed  backward,  two  forward, 
right  and  left.  From  the  latter  two  the  right  and  left  coronary  arteries  take 
their  origin. 

When  the  pressure  in  the  ventricle  is  lower  than  in  the  corresponding 
artery,  the  semilunar  valves  are  closed  with  their  edges  applied  tightly  to- 
gether. When  the  pressure  in  ventricular  systole  increases  enough  to  exceed 
that  in  the  aorta  or  pulmonary  artery,  the  valves  open  and  the  blood  flows 
out.  When  the  ventricle  again  passes  into  diastole  the  valve  is  closed  once 
more. 

What  position  the  valves  take  in  systole  is  not  yet  definitely  determined, 
although  various  observations  make  it  probable  that  their  free  edges  stand 
out  some  distance  from  the  sinuses,  thtis  narrowing  the  arterial  mouths.  It 
should  be  added  that  there  are  certain  muscular  folds  springing  from  almost 
all  sides  of  the  artery,  which  serve  as  supports  for  the  valves  (Krehl). 

In  consequence  of  this  arrangement  the  blood  is  pressed  through  a  narrow 
muscular  cleft  into  a  wider  space  above  the  valves.  This  must  cause  vortices 
and  eddies  to  be  formed,  which  tend  constantly  to  press  the  flaps  of  the  valve 
together,  and  they  are  unable  so  to  do  only  because  the  blood  is  l)eing  forced 
through  at  high  pressure.  When  the  outflow  ceases,  the  valves  are  pressed 
together  suddenly,  and  without  an;/  regurgitation.  The  closure  is  rigidly 
maintained  by  the  difference  between  aortic  and  ventricular  pressures,  a  dif- 
ference which  is  more  than  sufficient  once  the  muscles  of  the  ventricle  relax 
and  the  above-mentioned  muscular  supports  of  the  valves  give  way. 

§  3.    THE    HEART    SOUNDS 

If  the  ear  be  placed  over  the  breast  wall,  with  every  heart  beat  one  hears 
a  dull,  long-drawn-out  sound,  and  after  this  a  shorter,  clear  sound.  Then 
follows  a  pause,  then  again  the  dull  sound,  and  so  on.  The  long  sound  is 
called  the  first  heart  sound,  the  following  one.  the  second.  The  first  is  hcEird 
throughout  the  entire  ventricular  systole,  and  only  then.  The  second  follows 
immediately  after  the  first,  i.  e.,  immediately  after  the  end  of  the  ventricular 
systole,  and  after  it  comes  the  pause. 


168 


CIRCULATION   OF  THE   BLOOD 


The  cause  of  the  first  heart  sound  is  to  be  sought  chiefly  in  the  so-called 
muscle  tone ;  that  is  to  say,  in  the  tone  or  noise  which  is  to  be  heard  whenever 
a  muscle  contracts  (cf.  Chapter  XV).  The  first  sound  is  clearly  audible  in 
the  ease  of  a  heart  which  is  almost  entirely  empty  of  blood  and  air,  and  in 
which  accordingly  the  valves  cannot  be  stretched  and  cannot  therefore  be  set 
in  vibration  (Ludwig  and  Dogiel). 

Other  factors  cooperate  in  the  production  of  the  first  sound,  notably  the 
closure  of  the  atrio-ventricular  valves  at  the  beginning  of  systole,  and  the  vibra- 
tions set  up  in  them  and  in  the  blood  by  their 
closure.  It  is  not  impossible  that  vibrations 
which  are  caused  by  the  opening  of  the  semilunar 
valves  play  a  certain  part  also  in  the  production 
of  this  sound.  However  the  most  prominent  fac- 
tor of  all  is  a  muscle  sound  with  which  these 
^    V    I    /  other  sounds  are  associated. 

The  second  heart  sound  is  produced  by  the 
sudden  tension  of  the  semilunar  valves,  and  by 
other  simultaneous  vibrations  in  the  blood  con- 
sequent upon  their  closure.  Sudden  stretching 
of  these  valves  in  an  excised  aorta  produces  a 
sound  which  agrees  exactly  in  character  with 
the  second  heart  sound  (Carswell  and  Eouanet). 

It  will  be  apparent  at  once  that  we  have  in 
reality  four  sounds,  two  first  and  two  second. 
Practical  experience  teaches  however  that  the 
first  two  occur  simultaneously  and  the  second  two 
simultaneously :  and  this  is  also  evidence  of  the 
fact  that  both  ventricles  begin  their  contractions 
simultaneously  and  that  the  semilunar  valves  of 
the  two  sides  are  closed  at  the  same  instant. 


4.     PRESSURE     CHANGES    IN    THE 
HEART  DURING  ITS  ACTIVITY 


Fig.  55. — Heart  sound,  after  Chau- 
^'eau  and  Marev. 


A.    TECHNIQUE 

In  order  to  measure  the  pressure  and  its  vari- 
ations in  difi"erent  chambers  of  the  heart,  it  is 
necessary  that  these  should  be  connected  with  a 
manometer.  This  can  be  done  in  the  closed 
thorax  by  passing  a  cannula  or  sound  from  the 
carotid  through  the  aorta  into  the  left  ventricle, 
in  which  one  must  so  far  as  possible  avoid  injurv'  to  the  semilunar  valves  (Chau- 
vcau  and  Marey).  Sounds  can  be  passed  likewise  by  the  jugular  vein  into  the 
right  auricle  and  right  ventricle.  In  the  opened  thorax  sounds  can  be  thrust 
either  directly  through  the  walls  into  the  different  heart  cavities,  or  they  can 
be  passed  into  the  ventricles  first  through  the  walls  of  the  auricles,  then  through 
the  atrio-ventricular  openings. 

Various  instruments  have  been  constructed  for  the  study  of  the  pressure 


PRESSURE   CHANGES   IN  THE   HE.AJIT   DURING   ITS   ACTIVITY     169 

variations.  The  requirements  for  such  an  instrument  are  ver^*  severe :  indeed 
there  occur  in  the  ventricles  variations  of  130  mm.  of  Hg.  in  0.06  of  a  second 
— i.  e.,  2,170  mm.  Hg.  in  a  second.  The  instrument  to  be  used  must  be  capable 
therefore  of  righting  itself  very  quickly,  and  must  be  at  the  same  time  to  a 
high  degree  aperiodic  so  that  it  has  no  oscillations  of  its  own.  The  first  instru- 
ment used  for  this  purpose  was  the  writing  tambour  of  Marey.  This  was  con- 
nected with  a  sound  of  peculiar  construction  (cardiographic  sound)  passed  into 
the  heart  chambers.  Such  a  sound  (Fig.  55)  consists  of  a  tube,  the  end  of 
which,  to  be  placed  in  the  heart  chamber,  carries  a  rubber  bulb.  The  latter  is 
supported  by  a  steel  frame  (a,  v)  so  that  it  is  nnt  oomplptely  compressible.     The 


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Fig.  56. — Intracardial  pressure  curves  of  the  horse,  after  Chauveau  and  Marey. 
auricle;  Vent.  D.,  right  ventricle;  Vent.  G.,  left  ventricle. 


Or.  D.,  right 


free  end  of  the  sound  is  connected  with  the  writing  tambour.  With  the  pressure 
changes  in  the  heart  cavity  the  air  pressure  in  the  bulb  changes  and  the  writing 
tambour  records  these  variations  graphically.  By  suitable  means  the  curves  thus 
obtained  can  be  estimated  in  absolute  terms  (millimeters  of  Hg.). 


B.    PRESSURE   VARIATIONS  IN   DIFFERENT   CHAMBERS   OF  THE   HEART 

As  already  observed  the  auricles  contract  first.  The  duration  of  their 
systole  up  to  the  point  of  maximum  pressure  is,  in  the  horse,  0.1  second:  that 
of  the  ventricles  up  to  the  point  where  the  fall  in  pressure  begins  is  consider- 
ably longer,  namely.  0.4  second  (also  in  the  horse).  The  maximum  pressure 
in  the  right  auricle  of  the  dog  is  given  as  20-22  mm.  Hg.  (Goltz  and  Gaule). 

The  form  of  the  pressure  variations  in  the  heart  chambers  is  variously 
figured,  according  to  the  instruments  used  in  their  graphic  registration.  The 
difference  is  due  to  the  fact  that  not  all  the  difl'erent  instruments  give  the 
rapid  variations  in  pressure  with  sufficient  exactness. 

The  most  correct  form  of  the  intracardial  pressure  curve  appears  to  cor- 
respond to  the  type  represented  in  Fig.  56.  If  we  neglect  details  which  are 
relatively  unimportant,  the  intracardial  pressure  runs  somewhat  as  follows: 


170 


CIRCULATION   OF  THE   BLOOD 


(1)  a  small  elevation,  (2)  a  very  steep  ascent,  (3)  a  subsequent  much  slower 
ascent,  or  a  plateau  almost  parallel  to  the  abscissa,  (4)  a  rapid  fall  from  the 
maximum,  (5)  a  very  gradual  ascent  (Fig.  56). 

The  maximum  pressure  of  the  ventricular  systole  has  been  determined  also 
by  the  Hfi-manometer,  by  interpolating-  between  the  heart  and  the  Hg  a  maxi- 
mum valve  which  opens  with  every  increase  in  the  ventricular  pressure,  but 
prevents  the  return  of  mercury  with  the  fall  of  pressure. 

The  maximum  pressure  in  the  left  ventricle  may  amount  to  200  mm.  Hg. 
(in  the  dog).  The  pressure  in  the  right  ventricle  is  considerably  lower;  in 
the  dog  the  pressure  in  the  pulmonary  arteries  varies  between  10  and  33  mm. 

Hg.,  in  the  rabbit  between  6  and  35,  and 
in  the  eat  between  8  and  25  mm.  Hg. 
A  definite  ratio  between  the  pressures  in  the 
lesser  and  the  greater  circulations  does  not 
obtain,  because  even  with  very  great  varia- 
tions in  pressure  in  the  greater  circulation, 
only  relatively  slight  variations  generally 
occur  in  the  lesser  (cf.  Section  III,  §  8). 

On  the  pressure  curves  given  above, 
various  single  points  are  found  which  are 
sometimes  more,  sometimes  less  clearly 
marked.  Some  of  these — e.  g.,  various  peaks 
which  occur  in  many  tracings  at  the  height 
of  the  plateau — are  doubtless  artifacts  pro- 
duced by  extreme  vibrations,  while  others 
are  definite  expressions  of  events  in  the 
heart.  The  latter  we  must  discuss,  there- 
fore, somewhat  more  in  detail. 

At  the  beginning  of  the  pressure  curve, 
before  the  ascent  which  corresponds  to  the 
strong  rise  in  the  ventricular  systolic  pres- 
sure, a  slight  elevation  is  sometimes  very 
beautifully  shown.  This  elevation,  as  we 
learn  from  Fig.  56.  is  caused  by  the  auricular  contraction  and  the  consequent 
rise  in  pressure  in  the  ventricle. 

In  the  intracardial  pressure  curve  of  the  horse,  Chauveau  has  demon- 
strated between  the  peaks  corresponding  to  the  auricular  systole  and  the  begin- 
ning of  the  true  ventricular  systole  a  more  or  less  clearly  marked  intersystole 
(Fig.  57).  A  similar  elevation  appears  now  and  then  also  in  the  cardiagram 
of  man,  and  represents  doubtless  a  brief  rise  in  the  pressure  inside  the  ven- 
tricle. This  has  been  referred  with  great  probability  to  the  elastic  rebound 
of  the  vei-tricular  wall  after  the  completed  auricular  systole.  Obviously  it  can 
appear  clearly  only  in  case  a  measural)le  time  intervenes  between  the  maximum 
of  the  auricular  contraction  and  the  beginning  of  the  ventricular  systole. 

After  tbc  ventricular  systole  has  begun,  it  requires  a  certain  time  before 
the  power  of  contraction  becomes  sufficient  to  overcome  the  pressure  exerted 
by  the  blood  in  the  vessels  upon  the  semilunar  valves  {period  of  rising  ten- 


FiG.  57. — Pressure  curves  of  the  right 
ventricle  {YD),  of  the  left  ventricle 
{V  G),  and  of  the  aorta  {A  o)  of  the 
horse,  after  Chauveau.  3-4  au- 
ricular contraction;  4-2  intersys- 
tole.     To  be  read  from  left  to  right. 


PRESSURE  CHANGES   IX  THE   HE.\RT   DURING   ITS   ACTIVITY      171 

sion).  It  is  evident  that  the  semilunar  valves  must  open  the  moment  the 
pressure  in  the  aorta  is  exceeded  In'  that  in  the  ventricle.  So  smoothly  is  this 
point  passed  that  it  is  not  marked  on  the  pressure  curve  by  any  special 
fluctuation. 

The  period  of  rising  tension  can  be  determined  on  an  animal  by  recording 
the  pressure  in  the  aorta  and  in  the  left  ventricle  at  the  same  time.     Tt  is 


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Fig.   58. — Pressure   curves   from    the  left  ventricle  ( 

Chauveau  and 


1)    and  the  aorta  (2),    of   the  horse,    after 
Marev. 


found  (cf.  Fig.  58)  that  the  pressure  curve  of  the  ventricle  rises  from  the 
abscissa  in  the  horse  about  0.1  second,  in  the  dog  0.03  second  earlier  than 
does  the  pressure  curve  of  the  aorta.  The  period  shows  but  slight  variation 
with  varying  blood  pressure  or  with  different  rates  of  heart  beat,  which  means 
that  the  heart  possesses  in  a  very  high  degree  the  ability  to  meet  almost  with- 
out loss  of  time  very  different  demands  upon  its  powers. 

In  man  the  period  of  rising  tension  has  been  obtained  by  comparison  of 
the  simultaneous  apex  and  pulse  curves,  and  is  given  by  different  authors  at 
from  O.Oo  to  0.1  second. 

Closure  of  the  semilunar  valves  must  take  place  whenever  the  pressure 
in  the  aorta  exceeds  by  ever  so  little  that  in  the  left  ventricle.  By  simul- 
taneous registration  of  pressure  in  the  aorta  and  in  the  left  ventricle  it  has 
been  found  that  the  moment  of  equal  pre.^^sure  follows  shortly  after  the  begin- 
ning of  the  steep  descent  in  the  ventricle,  but  this  instant  is  not  shown  in 
any  special  manner  on  the  tracing. 

So  long  as  the  pressure  in  the  ventricle  is  higher  than  that  in  the  aorta 
or  pulmonary  arteries,  the  blood  is  being  driven  out  of  the  heart.  The  dura- 
tion of  the  period  of  ejection  depends  on  the  aortic  pressure  at  the  beginning 
of  systole,  or  upon  the  pulse  frequency  only  to  a  very  slight  extent :  it  amounts 
to  about  0.18-0.20  second  in  the  dog. 

At  the  close  of  systole  the  heart  chambers  gradually  fill  with  blood  and 
as  a  consequence  the  intracardial  pressure  gradually  rises  slightly. 
13 


172 


CIRCULATION   OF  THE   BLOOD 


§  5.    THE   APEX   BEAT 

We  have  in  the  apex  beat  a  means  of  studying  the  different  questions  which 
have  to  do  witli  the  pressure  relations  and  the  form  changes  of  the  heart 
in  the  normal  animal  and  in  man.  By  placing  the  hand  on  the  chest  wall, 
where  the  heart  is  not  covered  by  the  lungs — i.  e.,  in  the  fourth  or  fifth  inter- 
costal space — an  impulse  can  be  felt  with 
every  ventricular  systole,  which  is  called  the 
apex  heat.  In  lean  individuals  an  elevation 
of  the  intercostal  wall  can  be  ol)served  with 
the  eye.  This  fact  is  of  itself  sutficient  to 
show  that  the  heart  actually  strikes  against 
the  chest  wall,  but  does  not  on  the  other  hand 
prove  that  the  ventricle  withdraws  from  it 
in  diastole.  In  diastole  the  heart  is  flabby 
and  weak.  If  one  presses  with  the  finger  on 
the  exposed  heart  at  this  time,  only  a  little 
resistance  is  felt,  even  though  the  finger 
does  not  make  a  permanent  imjn-ession. 

As  soon  however  as  the  ventricular  sys- 
tole begins,  the  heart  suddenly  becomes  hard 
and  exerts  a  very  strong  pressure  on  the 
finger.  Everywhere  it  feels  as  if  the  finger 
were  being  pressed  against.  This  sudden 
hardening  is  the  essential  cause  of  the  apex 
heat  (Harvey,  Kiwisch,  Marey).  In  addi- 
tion to  this  however  there  is  an  eifort  on 
the  part  of  the  ventricle  to  assume  such  a 
form  that  the  apex  will  stand  vertical  to  the 
base  (Carlile,  Ludwig).  Consequently  the  heart  in  its  systole  takes  the  posi- 
tion with  reference  to  the  chest  wall  described  by  the  dotted  line  in  Fig.  59. 
The  apex,  therefore,  strikes  against  the  thoracic  wall  and  pushes  it  forward 
to  a  slight  extent. 

In  opposition  to  this,  Shreiber  remarks  that  the  heart  chambers  must  assume 
the  same  form  (a  right  cone)  after  the  auricular  contraction  and  before  the 
beginning"  of  the  systole.  But  this  follows  of  necessity  only  in  case  the  ven- 
tricles become  turgid  with  blood — -a  thing  which  rarely  results  from  auricular 
contraction.  With  an  ordinary  filling  of  the  ventricles  their  diastolic  form  may 
be  very  different,  just  as  an  india-rubber  balloon  may  vary  in  shape  until  it  is 
highly  inflated,  when  it  becomes  spherical. 

Other  factors  also  have  been  brought  forward  for  theoretical  explanation  of 
the  apex  beat.  It  has  been  assumed,  for  example,  that  the  heart  beat  against 
the  thoracic  wall  is  due  chiefly  to  the  rebound  consequent  upon  the  ejection  of 
blood  from  the  ventricle,  or  in  other  words,  has  its  origin  in  the  stretching  and 
elongation  of  the  great  arteries  by  means  of  which  the  heart  is  thrown  forward. 
It  is  possible  that  these  factors  do  in  fact  contribute  to  a  certain  extent  in  pro- 
ducing the  beat.  But  that  they  are  not  the  only  factors,  and  do  not  even  repre- 
sent the  most  important  mechanism  concerned,  appears  from  such  facts  as  these : 
first,  the  forward  movement  can  be  observed  on  an  excised  heart  empty  of  blood 


Fig.  59. — Schema  illustrating  Lud- 
wig's  theorj'-  of  the  apex  beat. 
The  dotted  Hne  represents  the 
position  of  the  heart  in  systole. 


THE   APEX   BEAT 


173 


as  well  as  on  one  with  ligated  arteries;  and  secondly,  the  movement  appears 
immediately  at  the  beginning  of  the  ventricular  systole,  while  the  opening  of 
the  semilunar  valves  and  the  ejection  of  blood  into  the  great  arteries  follows 
appreciably  later  (cf.  page  171). 

The  apex  beat  offers  the  only  possibility  of  studying  the  heart  movements 
on  a  living  man,  and  for  this  reason  much  attention  has  been  devoted  to  its 
graphic  record,  called  the  cardiogram. 

On  animals  the  intracardial  curve  and  the  cardiogram  can  of  course  be 
recorded  simultaneously,  the  latter  by  pushing  in  between  the  chest  wall  and 
the  heart  a  small  balloon  which  communicates  with  the  writing  tambour.  In 
the  two  curves,  as  shown  in  Fig.   60,  we  observe  various  similarities  and  dif- 


FlG. 


60. — Curves  of  pressure  in  the  right  auricle  O,  in  the  right  ventricle  V,  and   of   the   apex 
beat  P  (horse),  after  Chauveau  and  Marey. 


ferences.  In  both  we  have  at  A  the  elevation  caused  by  the  auricular  contrac- 
tion ;  likewise  the  steep  rise  at  the  beginning  of  the  systole.  On  the  cardiogram 
this  reaches  its  maximum  earlier  than  does  the  ascending  limb  of  the  pressure 
curve  (B).  After  the  maximum  is  once  reached  the  pressure  curve  runs  almost 
parallel  with  the  abscissa,  or  it  rises  gradually,  then  sinks  suddenly  at  the  end 
of  the  ventricular  systole.  The  cardiogram  begins  to  fall  much  earlier,  but  does 
so  more  gradually  although  finally  it  shows  also  a  steep  fall. 

At  the  line  C  we  find  almost  at  the  base  of  the  descending  limb  of  both 
curves  a  small  elevation,  which  we  shall  presently  discuss  further.  After  the 
end  of  systole  the  ventricle  is  filled  with  blood,  and  the  pressure  rises  slowly  up 
to  the  succeeding  systole.  At  the  same  time  the  cardiogram  rises  slowly  above 
the  abscissa.  If  the  contraction  of  an  empty  heart  be  recorded  it  has  quite 
another  form  from  that  of  the  cardiogram.  From  which  it  is  evident  that  the 
latter  is  not  a  simple  contraction  curve,  but  must  be  regarded  as  in  fact  a  com- 
bined pressure  and  volume  curs'c  of  the  heart  chambers.  It  is  a  pressure  curve, 
for  the  reason  that  the  button  placed  over  the  breast  wall  exerts  a  pressure 
against  which  the  heart  does  work.  It  is  however  at  the  same  time  a  volume 
curve,  in  so  far  as  it  is  influenced  by  the  volume  changes  of  the  heart. 


174 


CIRCULATION    OF  THE    BLOOD 


Fig.    61. — Receiving  tambour  of 
Marey's  cardiograph. 


While  the  heart  is  filling  during  diastole,  the  curve  rises  gradually  above 
the  abscissa;  but  while  the  ventricles  are  being  emptied,  i.e.,  while  the  semi- 
lunar valves  are  opened,  the  pressure  against  the  breast  wall  is  somewhat  less 
and  the  recording  tambour  cannot  therefore  follow  the  progressive  increase  of 
blood  pressure. 

For  the  graphic  registration  of  the  apex  beat  in  man  the  method  of  air 
transmission  is  generally  used,  as  for  example  with  the  apparatus  represented 

in  Fig.  61  (cardiograph  of  Marey).  A  me- 
tallic box  bears  the  plunger,  p,  fastened 
into  two  small  metallic  disks,  between  which 
the  rubber  membrane  of  the  tambour  is 
placed.  A  spiral  spring  between  the  inner 
of  these  disks  and  the  bottom  of  the  box  gives 
a  suitable  tension  to  the  membrane.  The 
cardiograph  is  placed  over  the  thoracic  wall 
in  such  a  manner  that  the  plunger  presses  on 
the  area  of  the  apex  beat.  The  side  tube,  r, 
leading  out  of  the  box  places  it  in  connection 
with  the  recording  tambour. 

It    is    evident    that    an    apparatus    placed 

over  the  chest  wall  in  this  manner  must  give 

a  curve  which  agrees  essentially  with  the  one 

obtained  by  means  of  a  balloon  inserted  between  the  heart  and  chest  wall ;  for  the 

movements  of  the  chest  wall,  which  is  now  between  the  tambour  and  the  heart, 

are  determined  by  the  movements  of  the  heart. 

The  human  cardiograms  published  in  the  literature  show  considerable 
differences  in  form,  depending'  primarily  upon  the  nature  of  the  recording 
apparatus  employed.  From  what  we  know  of  the  possibilities  of  this  apparatus 
(Hiirthle)  we  may  say  that  the  form  of  the  normal  cardiogram  of  man  is 
about  that  represented  in  Fig.  62.  We  have  here,  as  in  the  animals,  an  ascend- 
ing limb,  a  plateau,  which  inclines  toward  the  abscissa  or  runs  parallel  to  it, 
and  a  descending  limb.  Besides  there  are  some  small  elevations,  which  in  part 
at  least  are  artifacts. 

Often,  if  not  always,  the  cardiogram  begins  with  a  small  elevation  which 
is  caused  by  the  contraction  of  the  auricle.  After  this  follows  the  steep  rise 
caused  by  the  contraction  of  the  ventricle.  In  this  case  the  beginning  of  the 
ventricular  contraction  can  be  clearly  recognized.  It  may  happen  however 
that  the  auricular  contraction  is  not  specially  marked,  but  passes  uninter- 
ruptedly into  the  ascent  produced  by  the  ventricular  contraction,  in  which 
case  it  would  be  erroneous  to  reckon  the  latter  from  the  foot  of  the  ascending 
limb.  This  form  of  the  curve  results  often  from  too  little  tension  of  the 
cardiograph. 

On  the  cardiogram  one  sometimes  finds  at  the  end  of  the  auricular  systole 
the  above-mentioned  (page  170)  elevation,  called  by  Chauveau  the  intersi/stole, 
which  indicates  the  moment  of  closure  of  the  atrio-ventricular  valves.  As  a  rule, 
however,  the  elevation  does  not  occur  on  the  human  cardiogram.  On  the  other 
hand,  the  moment  of  opening  of  the  semilunar  valves  in  some  cases  comes  out 
clearly  at  the  first  turning  point  of  the  cardiogram,  where  the  ascending  limb 
passes  over  into  the  plateau  (Fig.  62,  h).  The  time  intei-val  between  the  base 
and  the  first  turning  point  of  the  cardiogram,  therefore,  represents  the  period 


THE   APEX   BEAT  175 

of  rising  tension  (period  of  closure)  of  the  ventricle.  This  period  is  not  by  any 
means  always  clearly  delimited,  and  could  have  but  small  practical  value. 

In  order  to  determine  the  moment  of  closure  of  the  semilunar  valves  on  the 
human  cardiogram,  the  heart  sounds  have  been  auscultated  and  marked  on  the 
curve  by  means  of  an  electric  signal.  The  exactness  of  this  method  is  not  great 
however,  and  from  observations  of  this  kind  one  can  say  with  certainty  only  that 
the  second  heart  sound  falls  somewhere  in  the  course  of  the  descending  limb  of 
the  cardiogram.  Attempts  have  been  made  therefore  to  determine  this  moment 
by  other  methods. 

In  man  Tliirthle  and  Einthoven  have  registered  the  heart  sounds  automat- 
icallj'  in  various  ways  and  have  found  that  the  second  sound  comes  about  0.02 
second  after  the  beginning  of  the  steep  descent. 

Finally,  Edgren  has  attempted  to  solve  the  problem  by  simultaneous  regis- 
tration of  the  apex  beat  and  the  pulse.  Since  the  pulse  wave  requires  a  certain 
time  to  propagate  itself  from  the  root  of  the  aorta  to  the  place  where  the  pulse 
is  taken,  this  time  must  be  subtracted.  It  is  then  found  that  the  elevation  on 
our  cardiogram  designated  f  corresponds  to  a  similar  mound  on  the  intracardial 
pressure  cui-ve  (Fig.  58,  r'),  and  corresponds  exactly  with  the  well-known  dicrotic 
elevation  of  the  pulse  cui*ve.    This,  as  we  shall  see  later,  is  intimately  connected 


1 

^HS^^^^^^^^^^^^^^^Bc^T/ilaT^^H 

1 

^^■H 

i^^^^H 

1 

Fig.  62. — Cur\L's  of  the  upex  beat  (lower  line)  and  of  the  carotid  pulse  (upper  line)  of  man, 
simultaneously  recorded,  after  Edgren.     b,  b,  and  /,  /,  are  corresponding  points. 

with  the  closure  of  the  semilunar  valves.     On  this  ground  it  appears  justifiable 
to  assert  that  the  mound  is  produced  by  the  stretching  of  the  semilunar  valve. 

In  so  doing  we  do  not  wish  to  assert  tliat  the  valves  are  closed  then  for  the 
first :  for  that  this  event  transpires  much  earlier  is  proved  by  a  comparison 
of  the  pressure  curves  of  the  ventricle  and  of  the  aorta  (Fig.  58).  It  is  not 
improhahlo  that  a  short  time  after  the  noiseless  closure  of  the  valves,  the}'  are 
suddenly  |)ut  on  the  stretch  by  the  aortic  blood  acting  under  great  pressure, 
and  that  they  ])roduce  in  this  way  the  second  sound  of  the  heart.  This  much 
is  certain,  that  the  second  sound  cannot  begin  before  the  closure  of  the  semi- 
lunar valves  (shortly  after  the  beginning  of  the  descending  limb  of  the  cardio- 
gram) and  not  later  than  the  mound  /. 

On  a  typical  cardiogram  we  can  make,  therefore,  a  definite  determination 
of  the  following  points:  auricular  systole,  beginning  of  the  ventricular  systole: 
h,  opening  of  the  semilunar  valves,  beginning  of  relaxation;  /,  stretching  of 
semilunar  valves. 


176  CIRCULATION   OF  THE   BLOOD 

§6.    TIME   RELATIONS   OF   THE   CARDIAC   EVENTS 

The  duration  of  the  auricular  systole  is  very  short.  In  man,  as  in  the 
horse  and  dog,  it  may  amount  to  0.1  second. 

The  duration  of  the  ventricular  systole  shows  hut  slight  variations,  not- 
withstanding considerable  differences  in  the  pulse  frequency.  Thus  in  varia- 
tions between  32  and  124  beats  per  minute  tlie  time  occupied  by  the  systole 
varies  only  between  0.382  and  0.190  second  (man).  In  animals  also  where 
the  pulse  frequency  is  made  to  vary  between  wide  limits  by  stimulation  of  the 
inhibitory  and  accelerator  nerves  (cf.  §  11)  the  systolic  time  varies  only  a 
little,  whereas  the  diastolic  time  presents  considerable  variations.  We  may 
say  therefore  that  the  variations  of  pulse  frequency  in  the  same  individual 
as  well  as  in  different  individuals  of  the  same  genus  are  due  in  the  main  to 
variations  in  the  length  of  diastole.  On  the  average  the  length  of  ventricular 
diastole  in  man  may  be  estimated  at  about  0.4  second. 

§  7.    FILLING   OF  THE   HEART   IN   DIASTOLE 

The  most  important  factor  in  the  filling  of  the  heart  during  diastole  is 
the  impetus  which  the  heart  has  given  the  blood  in  systole.  But  since  the 
blood  meets  with  great  resistance  in  its  passage  through  the  vessels,  the 
residual  driving  power  is  relatively  small,  and  the  accessory  mechanisms  play 
an  important  part. 

One  important  mechanism  is  the  suction  of  the  thoracic  cavity  (cf.  Chapter 
IX).  Almost  the  entire  air  pressure  takes  effect  on  the  great  veins  outside 
the  thorax.  A  small  part  of  it  of  course  is  borne  by  the  skin,  etc. ;  but  it 
may  be  assumed  as  certain  that  the  air  pressure  on  the  extrathoracic  veins  is 
greater  than  the  pressure  which  is  exerted  on  the  organs  inside  the  thorax  by 
the  lungs.  Consequently  in  the  static  position  of  the  thorax  the  intrathoracic 
veins  and  the  heart  are  to  a  certain  extent  expanded. 

In  expiration  the  negative  pressure  inside  the  thorax  decreases  and  both 
the  intrathoracic  veins  and  the  auricles  become  less  distended :  hence  the 
return  flow  of  the  blood  into  the  thorax  becomes  more  difficult.  Quite  other- 
wise is  it  with  inspiration.  The  intrathoracic  pressure  decreases  in  direct 
proportion  to  the  depth  of  inspiration  and  to  the  degree  of  expansion  of  the 
lungs ;  and  since  this  decrease  of  pressure  is  continuous  throughout  the  entire 
act  of  inspiration,  a  continuous  expansion  of  the  intrathoracic  veins  and  of 
the  auricles  must  result,  and  therefore  a  direct  suction  of  the  blood  from  the 
veins  to  the  heart  must  take  place.  Under  certain  circumstances  this  suction 
is  felt  even  by  the  farthest  veins. 

The  return  flow  of  the  blood  is  favored  likewise  by  a  static  inspiratory 
position  of  the  chest  wall;  but  in  this  instance  direct  suction  cannot  result, 
because  this  would  presuppose  that  the  auricles  are  being  continually  ex- 
panded by  extraneous  forces,  which  is  not  the  case  unless  the  chest  wall  is 
actually  moving. 

If  the  air  pressure  inside  the  chest  be  raised  sufficiently  the  return  flow  of 
the  blood  to  the  heart  is  hindered ;  the  circulation  stops,  and  death  may 
result,  if  the  ahnormal  increase  in  pressure  in  the  thorax  is  too  long  continued. 


POWER   AND   WORK   OF   THE    HEART  177 

Furthermore,  the  heart  in  its  own  systole  exercises  a  favorable  influence 
on  the  return  flow  of  the  blood.  During  systole  the  volume  of  the  ventricles 
is  diminished  by  exactly  the  volume  of  the  blood  driven  out.  This  blood  is 
partly  taken  up  by  the  intrathoracic  arteries  and  the  pulmonary  vessels,  but 
part  of  it  leaves  the  thorax.  The  consequence  is  that  the  content  of  the 
thorax  is  smaller.  This  in  its  turn  produces  a  suction  in  the  thoracic  cavity 
which  acts  either  to  draw  air  into  the  lungs  through  the  open  glottis  (cardio- 
pneumatic  movement) ,  or  to  produce  a  sinking  of  the  chest  wall,  or  finally 
to  expand  the  intrathoracic  veins  whereby  blood  is  drawn  into  them. 

Finally,  it  has  been  demonstrated  that  the  heart  exercises  a  suction  on  the 
blood  in  passing  into  diastole.  By  means  of  a  minimum  valve  Goltz  and 
Gaule  and  others  have  observed  in  the  open  thorax  of  a  dog  a  negative  pressure 
of  100-320  mm.  of  water  in  the  left  ventricle,  10-25  mm.  of  water  in  the 
right  ventricle.  Under  the  same  circumstances  (open  thorax)  a  negative 
pressure  can  be  demonstrated  in  the  auricles  (De  Jager  et  al.). 

One  succeeds  however  in  demonstrating  such  a  suction  only  with  a  vigor- 
ously active  heart.  If  the  heart  movement  is  weak  and  if  the  heart  does  not 
empty  itself  well  when  it  contracts,  the  suction  eiTect  is  considerably  diminished. 
What  the  forces  are  which  bring  about  this  suction  is  not  fully  explained. 

Excessive  filling  of  the  left  ventricle  is  prevented  by  its  thick  wall.  In 
the  right  ventricle  the  wall  is  too  thin  to  present  sufficient  resistance  against 
a  very  powerful  flow  of  blood,  but  the  danger  of  overdistention  is  prevented 
in  part  at  least  by  the  fact  that  muscular  cords  are  stretched  across  the  cavity 
of  the  right  ventricle  at  different  levels. 

Moreover  the  pericardium  plays  an  important  role,  as  appears  from  the  fol- 
lowing among  other  observations :  a  cat's  heart  held  12  cc.  when  the  pericardium 
was  uninjured,  when  the  pericardium  was  punctured  11  cc.  more  could  still  be 
driven  into  the  heart  (chiefly  the  right  auricle  and  right  ventricle)  with  the 
same  pressure.  Even  when  beating  normally  the  heart  during  diastole  protrudes 
through  a  slit  made  in  the  pericardium.  Finally  it  should  be  remarked  that  a 
relative  insufficiency  in  the  right  atrio-ventricular  valve  appears  after  opening 
of  the  pericardium.  The  closure  of  this  valve  is  insured  by  the  support  which 
the  pericardium  affords  to  the  heart  (Barnard). 


§8.    POWER   AND    WORK   OF   THE   HEART 
.  A.    POWER 

We  have  already  seen  that  the  left  ventricle  in  its  systole  may  exert  a 
pressure  of  200  mm.  Hg.  and  more  on  the  blood.  A  weight  of  this  size  might 
then  be  said  to  press  upon  the  inner  wall  of  the  ventricle.  Xevertheless  it  is 
able  to  contract,  and  its  power  must  be  everjwhere  sufficient  to  balance  such  a 
maximal  pressure.  In  other  words,  the  power  of  every  square  centimeter  of 
the  internal  surface  of  the  left  ventricle  is  equal  to  the  weight  of  a  column 
of  Hg.  1  sq.  cm.  in  section  and  as  high  as  the  maximal  pressure  expressed 
in  terms  of  Ilg.  If  we  assume  that  the  maximal  pressure  amounts  to  200 
mm.  Hg.,  the  power  of  the  left  ventricle  for  every  square  centimeter  of  its 


178  CIRCULATION    OF   THE   BLOOD 

inner  surface  is  200  mm.  X  100  sq.  mm.  X  13.6  ^  =  272  g.  Jt  is  scarcely 
wortli  while  to  give  a  value  for  the  total  power  of  the  left  ventricle,  since  it  is 
not  possible  to  determine  with  any  accuracy  the  area  of  its  internal  surface 
during  svstole.  In  progressive  contraction  the  residual  power  of  a  muscle 
becomes  smaller  and  smaller.  But  in  the  heart  this  is  compensated  by  the 
fact  that  at  the  same  time  the  internal  surface  of  the  ventricle  is  constantly 
becoming  smaller. 

Since  the  maximal  pressure  of  the  right  ventricle  amounts  to  about  30 
mm.  Hg.,  its  power  per  square  centimeter  of  internal  surface  would  be  suffi- 
cient to  balance  40.8  g. 

B.    WORK 

The  work  of  any  chamber  of  the  heart  at  each  systole  is  expressed  by  the 

formula  W  =  pR  +  -^,  where  p  is  the  weight  of  the  output,  R  is  the  resist- 

y 

ance  or  mean  arterial  blood  pressure  maintained  by  it,  v  the  velocity  per 
second  imparted  to  the  blood,  and  g  the  acceleration  of  gravity. 

In  order  to  estimate  the  work  done  by  the  left  ventricle,  for  example,  we 
must  determine  the  pressure  and  the  velocity  of  the  blood  in  the  aorta,  as  well 
as  the  mass  of  blood  driven  out  at  each  systole.  In  the  following  section  we 
shall  go  into  the  subject  of  blood  pressure  and  velocity  in  the  aorta  more 
fully ;  here  in  order  to  carry  out  the  calculation,  we  shall  say  in  advance  only 
that  the  mean  pressure  may  be  estimated  at  about  150  mm.  Hg.  and  the 
velocity  at  about  0.5  m.  per  second. 

We  cannot  say  as  yet  with  any  definiteness  how  great  is  the  quantity  of 
blood  expelled  from  the  human  heart  at  each  systole.  It  is  very  probable  that 
the  pulse  volume  is  somewhere  between  50  and  100  g.  per  beat.  If  we  adopt 
these  values  and  sid:)stitute  them  in  the  above  formula,  we  olitain  as  the  limits 
of  the  work  necessary  to  force  the  blood  against  the  aortic  pressure:  50  X 
0.150  X  13.61  _-  102  gram-meters;  100  X  0.150  X  13.6  =  204  g-m. 

The  work  which  it  requires  to  impart  a  velocity  of  0.5  meters  to  the  pulse 

1  •  ,.     1      50x0  5*        „„,  100x0.5*        .  „o  rri,    +  X  1 

volume  IS  accordingly    - — —-r-  =  0.64,  or   — -^ — ^r~—  =  1.28  g-m.    The  total 
'=•'2x9.8  2x9.8 

work  of  the  left  ventricle  in  its  systole  would  be  therefore  102. (U  to  205.28 

g-m.    We  see  that  by  far  the  greater  part  of  the  work  of  the  ventricle  is  used 

in  overcoming  the  resistance  in  the  vascular  system  and   that  only  a  very 

small  part  is  necessary  to  give  the  blood  its  mean  velocity.     This  result  is 

perfectly  positive  in  spite  of  the  very  arbitrary  values  used  in  our  calculation, 

for  the  pulse  volume  exercises  no  iniiuence  on  the  reciprocal  relation  of  the 

two  factors,  and  even  if  we  estimate  the  speed  in  the  aorta  much  higher,  and 

the  blood  pressure  there  much  lower,  the  factor  pR  would  still  be  many  times 

greater  than  the  factor  ~— . 

''•^ 
We  have  no  direct  information  as  to  the  quantity  of  blood  expelled  from 

the  right  ventricle  in  its  systole.     But  we  may  assume  that  its  pulse  volume 

is  the  same  as  that  of  the  left  ventricle;  for  the  left  ventricle  drives  the 

blood  through  the  greater  circulation  to  the  right  auricle,  and  the  right  drives 

*  The  specific  gravity  of  mercury. 


PROPERTIES   OF   HEART   MUSCLE 


179 


it  throiiorh  the  lesser  circulation  to  the  left  auricle.  Should  the  two  ventricles 
not  expel  exactly  the  same  quantity  of  blood  at  a  systole  or  in  a  unit  time — 
we  except  accidental  disturbances — the  blood  would  collect  somewhere  in  the 
vascular  system.  Under  the  assumption  that  the  mean  pressure  in  the  pul- 
monary arteries  of  man  is  equal  to  that  of  the  dog,  we  obtain  for  the  work  of 
the  right  ventricle  14.24  to  28.48  g-m. 

In  connection  with  the  subject  of  the  blood  movements  in  the  arteries  we 
shall  discuss  more  fully  how  the  work  of  the  heart  depends  upon  changes  in  the 
vessels  and  upon  their  degree  of  fullness. 


9.    PROPERTIES   OF   HEART   MUSCLE 


A.    THE   NATURE   OF   THE   CARDIAC   CONTRACTION 

If  the  contraction  curve  of  an  empty  heart  be  recorded  graphically,  one 
observes  an  unmistakable  resemblance  to  an  ordinary^  muscular  twitch  produced 
by  a  single  stimulus.  We  have  in  the 
action  current  of  the  heart  (cf.  page  48) 
a  means  of  testing  this  inference.  This 
test  can  be  applied  to  the  human  sub- 
ject also,  if  symmetrical  points  of  the 
body's  surface  be  connected  with  a  gal- 
vanometer, for  the  electrical  currents 
generated  by  the  heart's  activity  diffuse 
according  to  the  usual  laws  throughout 
the  entire  body  (cf.  Fig.  63).  Fig.  64 
represents  the  action  current  of  the 
human  heart  as  recorded  by  the  excur- 
sions of  the  capillary  electrometer.  An 
upward  stroke  signifies  that  the  base  of 
the  heart  is  negative  to  the  apex.  The 
ventricular  systole  begins  with  the  point 
R;  there  follows  a  negative  stroke  S  (the 
apex  negative  to  the  base),  and  finally, 
after  an  inteiwal,  a  positive  stroke  T 
(base  negative  to  apex).  From  this 
curve  of  electrical  variations  we  may 
infer  that  the  contraction  begins  at  the 
base  and  proceeds  from  there  to  the  apex ; 

for  a  certain  time  (a  portion  of  the  stretch  from  S  to  T)  the  ventricle  is  contracted 
in  all  its  parts,  so  that  the  base  and  the  apex  exhibit  no  difference  of  potential. 
The  contraction  ceases  sooner  at  the  apex  than  at  the  base — which  in  all  proba- 
bility is  due  to  the  return  course  of  the  muscular  fibers  (i)age  168) — and  the 
base  becomes  once  more  negative  to  the  apex.  The  inteiwal  of  time  between 
the  beginning  R  and  the  end  T  is  about  0.32  second,  which  corresponds  fairly 
well  to  the  duration  of  a  ventricular  systole. 

From  all  this  it  appears  that  the  ventricular  systole  is  comparable  with 
a  simple  muscular  contraction  and  cannot  be  regarded  as  a  suintnated  con- 
traction (cf.  Chapter  XV). 


Fig.  63. — Schematic  representation  of  varia- 
tions of  electrical  potential  associated 
with  the  beat  of  the  human  lieart,  and 
their  distribution  in  the  body,  after 
Waller. 


180 


CIRCULATIOX    OF   THE   BLOOD 


Before  the  electrical  variations  corresponding  to  the  ventricular  pystolc 
a  small  diaphasic  action  current  is  to  be  observed  (Fig.  64,  PQ),  which  is 
probably  caused  by  the  auricular  contraction.  This  lasts  only  about  0.13 
second  (Einthoven). 


B.    NUTRITION   OF  THE    HEART 

The  heart  gets  its  blood  supply  through  its  coronary  arteries,  for  distribu- 
tion of  which  the  text-books  of  anatomy  should  be  consulted.  Here  it  should 
be  recalled  only  that  they  do  not  anastomose  with  each  other,  and  are  therefore 
terminal  arteries.  Besides,  the  heart  wall  obtains  blood  from  the  heart  cavities 
through  the  veins  of  Thehesius,  which  are  in  connection  with  the  coronary  ves- 
sels (arteries  and  veins)  by  means  of  capillaries,  and  with  the  veins  by  means 
of  somewhat  larger  vessels.  The  capillar^-  network  of  the  heart  is  very  close, 
and  besides  this,  the  smallest  vessels  proceed  directly  from  relatively  large  stems. 
In  those  places  where  several  muscle  fibers  unite,  spiral  vessels  are  found  which 

seem  adapted  to  maintain 
the  blood  supply  when  the 
fibers  shift  their  position 
and  change  their  form 
(Heynemann). 

The  following  is  to  be 
observed  with  regard  to  the 
behavior  of  the  blood  flow 
through  the  coronary  vessels 
in  different  phases  of  the 
heart's  activity.  In  diastole 
of  the  ventricle  the  vessels 
of  the  heart  wall  are  open, 
and  offer  no  hindrance  to 
the  blood  stream.  When  the  ventricles  contract  they  must  sooner  or  later 
exert  such  a  pressure  on  the  capillaries  of  the  heart  wall  that  the  blood  flow 
in  them  is  interrupted  for  a  time,  and  is  only  resumed  at  the  beginning  of 
relaxation.  By  this  compression  of  the  coronary  vessels,  blood  is  driven  out 
into  the  right  auricle.  It  is  found  in  fact  that  the  quantity  of  blood  flowing 
in  the  coronary  veins  increases  during  systole.  The  evacuation  of  the  coronary 
veins  thus  brought  about  has  the  effect  of  diminishing  the  resistance  to  the 
blood,  so  that  at  the  next  relaxation  they  are  filled  more  easily. 

This  variation  in  the  caliber  of  its  vessels  produced  by  the  movements 
of  the  heart — to  which  is  to  be  added  possibly  a  dilatation  of  the  arteries 
taking  place  at  the  beginning  of  systole — causes  a  greater  quantity  of  blood 
to  flow  through  the  coronary  vessels  of  a  beating  heart  than  of  a  quiescent 
one,  the  quantity  being  in  direct  proportion  to  the  force  and  frequency  of 
the  heart  beat  (Porter.  Langendorff).  On  the  other  hand  the  volume  of  blood 
flow  in  a  heart  suffering  from  loss  of  coordination  of  its  muscle  fibers  may 
be  even  greater  than  in  a  normally  beating  heart,  which  is  probably  due  to 
the  fact  that  no  compression  of  the  coronary  vessels  now  takes  place,  while 
the  waving  movements  of  the  cardiac  muscle  fibers  facilitates  the  passage  ^of 
the  blood  by  a  sort  of  light  massage  (Langendorff).     The  quantity  of  blood 


Fig.  64. 


Q  ^S 

-Schematic  representation  of  the  action  current 
of  the  human  heart,  after  Einthoven. 


PROPERTIES   OF   HEART   MUSCLE  181 

flowing  through  the  heart  is  diminished  by  a  greater  internal  pressure  and 
a  consequent  distention  of  the  lieart,  even  when  it  is  beating  ( Hyde) . 

The  flow  of  blood  from  the  coronary  veins  is  temporarily  hindered  by  the 
contraction  of  the  right  auricle,  since  at  this  time  the  mouth  of  the  common 
sinus  is  narrowed — an  effect  which  is  aided  also  by  the  valve  of  Thebesius. 
But  the  same  temporary  stoppage  tends  to  favor  dilatation  of  the  heart  wall, 
thereby  making  the  auricular  systole  that  much  easier.  When  the  auricles 
relax  the  coronary  veins  empty  themselves  again,  and  the  elasticity  of  the 
ventricular  wall,  which  is  important  for  the  prompt  closure  of  the  atrio- 
ventricular valves,  can  the  more  readily  assert  itself  (v.  Vintschgau,  cf. 
page  166). 

Since  the  coronary  arteries  do  not  anastomose  with  one  another,  ligation 
of  one  of  its  branches  deprives  the  corresponding  part  of  the  heart  wall  of  its 
blood  supply,  and  a  coagulation  necrosis  then  makes  its  appearance.  In  such 
a  region  the  power  of  contraction  is  retained  however  for  at  least  eleven  hours ; 
and  in  animals  which  survived  well  the  operation  of  t}dng  off  a  large  arterial 
branch,  the  frequency  and  rhythm  of  the  heart  beats  and  the  heart  sounds 
were  normal  throughout  for  thirty-six  to  fifty-four  hours  afterwards  (Baum- 
garten).     Small  restricted  anaemias  were  in  general  well  borne. 

It  is  evident  that  the  heart  mu.scle  must  eventually  die.  if  one  of  the 
larger  branches  of  the  coronary  arteries  becomes  impassable.  What  is  diffi- 
cult to  explain  however  is  the  circumstance  that  the  coordination  of  the  cardiac 
muscle  fibers,  upon  ligation  of  a  large  arterial  branch,  ceases  almost  imme- 
diately (within  one  hundred  to  one  hundred  and  twenty  seconds)  and  the 
heart  falls  into  fibrillarf/  contractions.  The  same  thing  happens  even  if 
the  ligature  is  loo.<ed  before  the  inception  of  these  disturbances  (Cohnheim 
and  V.  Schulthess-Rec]il)erg).  Since,  however,  one  often  meets  with  cases 
where  such  sudden  disturbance  of  the  heart's  activity  does  not  follow  stoppage 
of  its  blood  supply,  it  has  been  assumed  by  many  that  this  is  traceal^le  to 
some  injury  to  the  ventricular  wall.  Porter  on  the  contrary  has  shown  that 
fibrillary  contractions  appear  if  the  blood  flow  in  an  artery  is  stopped  in  such 
a  way  that  no  possible  injury  to  the  ventricular  wall  can  occur,  and  takes 
the  view  therefore  that  such  contractions  are  caused  by  scanty  nourishment 
to  the  heart  7nu.scle.  That  they  do  not  appear  in  the  heart  at  death  from  all 
manner  of  causes,  he  explains  by  saying  that  the  heart  is  seized  with  fibrillary 
contractions  only  in  case  it  is  working  against  great  resistance  wlien  the  dis- 
turbance to  its  nourishment  occurs.  When  the  resistance  is  not  great  (and 
is  diminishing  gradually)  the  contractility  of  the  heart  muscle  decreases  stead- 
ily, but  gradually,  and  when  finally  the  heart  comes  to  a  standstill  the  residual 
contractility  remaining  in  it  is  no  longer  sufficient  to  produce  well-defined 
fibrilUiry  contractions,  \\niether  this  explanation  is  correct  in  all  points  can- 
not be  definitely  decided  at  this  time. 

The  heart  muscle  can  get  its  nourishment  not  only  through  the  coronary 
arteries  but  also  through  the  veitts  of  Thehesius.  From  observations  on  extir- 
pated hearts,  it  is  seen  that  the  food  which  can  be  supplied  by  these  vessels  is 
sufficient  to  maintain  rhythmical  contractions  for  a  considerable  time.  The 
same  is  true  of  artificial  perfusion  through  the  coronary  veins  (Pratt). 


182  CIRCULATION   OF  THE   BLOOD 

It  has  long  been  known  tliat  1)V  artificially  supplying  blood  to  the  extir- 
pated heart  of  cold-blooded  animals,  activity  can  be  maintained  for  a  con- 
siderable time  (Ludwig).  T^ater  Xewell  ^lartin  and  Langendorff  accom- 
plished the  same  thing  with  the  heart  of  warm-blooded  animals.  For  this 
purpose  blood  is  led  into  the  aorta  by  means  of  a  cannula  tied  in  it  and 
directed  toward  the  heart.  Because  the  semilunar  valves  are  closed  by  the 
pressure  from  the  cannula,  the  blood  flows  through  the  coronary  vessels  to 
the  right  auricle,  whence  it  is  allowed  to  escape.  Numerous  observations  have 
been  made  on  such  preparations  as  to  the  way  a  heart  works  under  different 
conditions  when  separated  from  the  central  nervous  system  and  from  the 
blood  vessels ;  and  as  to  the  effect  which  various  agents  exercise  on  the  per- 
formance of  the  heart. 

However  it  is  not  necessary  to  use  blood  as  the  nutrient  fluid  in  order  to 
keep  the  heart  beating,  for  several  hours  at  least ;  for  both  in  cold-blooded 
(Ringer)  and  in  warm-blooded  animals  (Locke)  a  solution  of  certain  inor- 
ganic salts  has  been  found  sufficient  (0.1  per  cent  XaHCO,,  0.1  per  cent  CaCl.,, 
0.0T5  per  cent  KCl,  eight  per  cent  XaCl).  For  the  warm-blooded  heart  the 
fluid  must  be  saturated  with  oxygen.  By  addition  of  a  small  quantity  of 
dextrose  also  this  artificial  serum  is  still  more  effective. 

The  significance  of  these  sul)stances  has  been  discussed  already  at  page  25. 
Here  it  may  be  added  only  that  the  favorable  action  of  the  XaHCOg  might 
be  due  to  the  COo,  for  with  a  sufficient  supply  of  oxygen,  carbon  dioxide 
actually  increases  the  energv^  of  the  isolated  frog's  heart  (Gothlin). 

The  great  tenacity  of  life  exhibited  by  the  exsected  heart  is  truly  remark- 
able. By  artificial  perfusion  with  the  above-mentioned  solution  (and  dex- 
trose). Kuliabko  obtained  well-marked  contractions  of  the  entire  heart  of 
the  rabbit  five  days  after  the  death  of  the  animal.  He  also  succeeded  in 
completely  reviving  the  heart  of  a  four-year-old  boy  who  had  died  of  pneu- 
monia duplex  and  catarrhus  intestinalis,  twenty  hours  after  death. 

Moreover  the  tenacity  of  life  in  the  different  portions  of  the  heart  is  very 
different.  When  the  heart  is  dying,  the  left  ventricle  stops  first,  then  the  right, 
but  the  auricles  continue  to  beat  for  a  considerably  longer  time.  Finally  the 
pulsations  of  the  left  auricle  cease  and  last  of  all  those  of  the  right.  Even  then 
the  contractions  of  the  great  veins  always  go  on  for  a  time,  and  only  when  these 
have  ceased  is  the  heart  entirely  dead. 

When  the  oxygen  supply  to  the  heart  is  cut  off  the  heart  beats  become  less 
and  less  frequent  as  asphyxiation  comes  on.  and  other  changes  make  their 
appearance  which  cannot  be  discussed  here.  However  it  should  be  observed 
that  the  heart,  especially  of  cold-blooded  animals,  has  great  power  of  resist- 
ance against  oxygen  hunger  (cf.  page  28). 


C.    THE  BEHAVIOR   OF    HEART  MUSCLE   UNDER   DIRECT   STIMULATION 

If  the  heart  muscle  be  stimulated  with  induction  currents  of  different 
strength,  either  it  does  not  contract  at  all,  or  it  contracts  to  its  utmost  extent 
(Bowditch).  The  response  of  the  heart  muscle  therefore  is  always  maximal. 
while  the  contraction  of  skeletal  muscle  is  great  or  small  according  to  the 


PROPERTIES   OF   HEART  MUSCLE  183 

strength  of  the  stimulus.  This  fact  is  often  referred  to  as  the  "  all  or  none  " 
law  of  cardiac  contraction.  The  crustacean  heart  (lobster)  forms  an  excep- 
tion to  this  rule,  since  it  behaves  to  stimuli  of  different  strength  exactly  like 
skeletal  muscle. 

Another  peculiarity  of  heart  muscle  is  that  in  both  cold-blooded  animals 
and  in  Mammalia  it  is  inexcitable  during  its  contraction  up  to  the  maximum 
of  shortening — i.  e..  all  stimuli  which  fall  upon  it  during  this  ("  refractorj/") 
period  are  entirely  without  effect  (Marey).  Only  after  the  maximum  short- 
ening ha.s  been  reached  does  the  heart  muscle  become  excitable  again.  A 
stimulus  applied  then  calls  forth  an  extra  contraction,  which  is  greater  the 
later  in  diastole  it  falls.  After  this  extra  contraction  a  longer  ("compensa- 
tor!/ " )  pause  usually  occurs,  and  the  first  contraction  following  the  pause  is 


Fig.  6.5. — Direct  stimulation  of  the  isolated  heart  of  the  cat  while  beating,  after  Langendorff 
(to  be  read  from  left  to  right;  systole  represented  by  the  downward  stroke).  Stimulation 
at  the  beginning  of  systole  (a)  produces  no  effect.  Stimulation  at  any  time  during  diastole 
(6)  gives  an  extra  contraction.  Following  this  are  seen  the  compensatory  pause  and  con- 
siderable augmentation  in  the  strength  of  the  next  systole. 

considerably  augmented.  The  smaller  the  extra  contraction,  the  longer  is 
the  subsequent  pause  and  vice  versa.  After  such  an  interference  in  the  regu- 
lar rhythm  of  the  beats,  there  is  therefore  a  compensation  by  which  both  the 
frequency  and  the  amount  of  work  done  by  the  heart  are  conserved  (cf. 
Fig.  (55). 

The  compensatory  pause  appears  only  in  those  portions  of  the  heart  which 
beat  in  consequence  of  a  stimulus  communicated  to  them  from  other  portions; 
it  is  not  seen  therefore  in  a  tracing  from  the  venous  sinus  of  the  frog.  In 
explanation  of  this  difference  it  is  supposed  that  the  excitation  of  the  venous 
sinus  is  continuous,  but  that  it  sends  a  discontinuous  stimulus  to  the  other 
chambers  of  the  heart.  When  an  extra  contraction  has  been  induced  in  the 
ventricle,  one  of  these  regular  discontinuous  stimuli  from  the  venous  sinus  would 
fall  at  a  time  when  the  ventricle  is  refraetoiw,  hence  would  produce  no  effect. 
The  ventricle  must  therefore  wait  until  the  next  regular  stimulus,  and  thus  we 
get  the  compensator;v  pause.  It  is  quite  different  with  the  sinus:  as  soon  as 
the  extra  contraction  has  reached  its  maximum,  the  constant  stimulus  again 
becomes  effective  and  produces  the  next  systole  without  an  intervening  pause. 

The  inability  of  the  heart  mu.^cle  to  receive  stimuli  which  fall  on  it  during 
systole,  is  the  reason  why  with  rapidly  repeated  shocks  it  cannot  he  thrown 


184 


CIRCULATION   OF  THE  BLOOD 


into  an  actual  tetanus,  like  skeletal  muscles.  Since  all,  the  stimuli  which 
fall  during  systole  are  entirely  ineffective,  there  can  be  no  superposition  and 
summation  of  eft'ccts. 

This  rule  is  not  strictly  without  exception,  however.  By  simultaneous 
stimulation  of  the  vagus  and  the  venous  sinus  0.  Frank  was  able  to  demon- 
strate a  condition  of  tetanus  in  the  frog's  heart;  Walther  observed  the  same 
thing  on  stimulation  of  a  frog's  heart  poisoned  with  muscarine.  In  the 
latter  case  the  refractory  period  of  the  heart  is  shortened  as  a  result  of  the 
poison,  and  the  l^arrier  to  the  production  of  tetanus  is  thereby  removed. 

Many  other  discoveries  have  been  made  on  the  exsected  heart  concerning 


■20- 


r^   r 


u  u  u  u 


n    n   f 


MAIiJ 


'^mMMM\i\ 


\j\j\j\yj 


Fia.  66 — Influence  of  temperature  on  the  isolated  heart  of  the  cat,    after   Langendorff. 
heart  was  supphed  with  blood  kept  at  the  different  temperatures  indicated. 


The 


the  properties  of  heart  muscle,  but  they  cannot  be  discussed  here.     We  wish 
to  call  attention  only  to  the  following  peculiarities : 

(1)  The  frequency  of  the  heart  beat  varies  directly  with  the  temperature 
— i.  e.,  the  higher  the  temperature  the  greater  the  frequency,  the  lower  the 
temperature  the  less  the  frequency.  Thus  at  40°  C.  it  is  four  times  as  great 
as  at  15°  C.  With  a  fall  in  the  frequency,  the  extent  of  contraction  increases 
up  to  a  certain  limit,  and  at  the  same  time  the  shortening  becomes  slower 
and  more  drawn  out  (Fig.  66). 

(2)  The  quantity  of  blood  which  the  left  ventricle  discharges  at  each 
systole  depends  upon  the  quantity  of  flow  from  the  great  veins:  the  greater 
the  inflow  the  greater  the  amount  discharged,  but  the  latter  increases  more 
slowly  than  the  former. 

(3)  The  quantity  of  blood  flowing  through  the  coronary  vessels  exercises 
but  little  influence  upon  the  frequency,  although  it  is  of  great  importance  for 
the  force  of  the  heart  beat. 

(4)  If  the  heart  has  no  work  to  do  it  has  need  of  only  a  very  small  quan- 
tity of  blood. 


THE  CAUSE   OF  THE   RHYTHMICAL  ACTIVITY   OF  THE   HEART     185 


§  10.    THE   CAUSE   OF   THE   RHYTHMICAL   ACTIVITY   OF   THE 

HEART 

In  warm-blooded  animals  direct  nerve  fibers  to  the  auricles  as  well  as  to 
the  right  and  left  coronary  plexuses,  come  from  the  two  divisions  of  the 
cardiac  plexus,  which  in  turn  is  formed  by  branches  from  the  vagus  and 
sympathetic.  The  threads  of  this  network  are  provided  with  numerous  gan- 
glia, and  the  fibers  radiating  to  the  auricle  and  ventricle  from  the  network 
are  also  interspersed  with  small  ganglia. 

In  the  heart  itself  ganglion  cells  have  been  found  in  the  following  places : 
in  the  auricles  around  the  opening  of  the  great  veins,  along  the  periphery  of 
the  septum,  and,  though  in  smaller  number,  in  the  outer  wall ;  in  the  atrio- 
ventricular groove,  especially  in  the  region  of  the  aorta  and  pulmonary  artery 
at  the  level  of  the  semilunar  valves ;  and  in  the  uppermost  part  of  the  ventricle. 

Fine  nervous  nets  supply  an  abundance  of  nerve  fibers  to  all  parts  of  the 
heart. 

As  appears  from  what  has  been  said  concerning  exsected  hearts,  this  organ 
possesses  the  property  of  acting  quite  independently  of  the  central  nervous 
system.  In  order  to  determine  the  cause  of  this  peculiarity  we  have  to  inves- 
tigate first  the  behavior  of  the  separate  divisions  when  they  are  isolated  from 
the  whole  heart.  In  this  we  shall  consider  chiefly  the  phenomena  appearing 
in  the  Mammalian  heart,  because  a  detailed  discussion  of  those  observed  in 
the  hearts  of  cold-blooded  animals  would  call  for  entirely  too  much  space. 

By  introducing  into  the  auricle  a  small  instrument  provided  with  curved 
plates  on  two  sides,  it  is  possible  to  sever  all  the  nervous  and  muscu- 
lar connections  between  the  auricles  and  ventricles  without  producing 
hemorrhage.  After  this  operation  the  ventricles  continue  to  pulsate  without 
interruption. 

In  this  experiment  the  line  of  separation  can  be  brought  close  to  the  auricu- 
lar boundary.  Since  now  all  the  nerves  which  run  to  the  heart  along  the 
great  arteries  are  aft'erent  in  function  (Wooldridge),  and  since  the  results  are 
the  same  in  case  the  great  arteries  are  pinched  off  directly  above  the  upper 
edge  of  the  semilunar  valves,  it  follows  that  the  isolated  portion  of  the  heart, 
i.  e.,  the  ventricles  and  a  very  small  part  of  the  auricles,  have  ^^^thin  them- 
selves all  the  conditions  necessary  for  rhythmical  activity. 

One  can  go  still  further.  Porter  has  succeeded  by  means  of  artificial  cir- 
culation through  the  coronary  arteries  in  maintaining  regular  rliythmical 
contractions  in  isolated  pieces  of  the  ventricular  wall,  connected  with  the 
rest  of  the  heart  only  by  the  arterial  branch.  We  can  extend  the  proposition 
stated  above  therefore,  and  say  that  every  portion  of  the  ventricular  wall 
possesses  all  the  conditions  necessary  for  rliythmical  activity. 

In  these  experiments  one  meets  with  cases  where  the  rhythm  of  the  sepa- 
rated portion  is  materially  less  than  that  of  the  M'hole  heart  or  that  of  the 
divisions  remaining  after  isolation  of  the  ventricles.  But  under  normal  cir- 
cumstances the  rate  of  the  ventricular  systole  is  determined  by  the  rhythm 
of  those  parts  of  the  heart  which  inaugurate  the  systole  (the  venous  ostia 
of  the  auricles;  cf.  page  1G2). 


186  CIRCULATION   OF  THE   BLOOD 

It  is  most  probable  that  we  have  to  do  here  with  a  chemical  stimulus  of 
some  kind,  which  is  to  be  sought  among  the  products  of  decomposition  formed 
in  the  activity  of  these  parts.  If  this  is  so,  it  follows  that  the  inorganic  con- 
stituents which,  as  mentioned  above,  must  be  present  in  an  artificial  fluid  in 
order  to  maintain  the  heart's  activity,  and  which  occur  in  the  blood,  are  not 
to  be  considered  as  the  real  excitant  of  the  heart  beat,  but  merely  as  a 
condition. 

Since  the  structure  of  cardiac  muscle  agrees  essentially  with  that  of  skel- 
etal muscle,  and  the  latter  is  set  in  action  normally  only  under  the  influence 
of  a  stimulus  communicated  to  it  from  the  central  nervous  system,  it  was 
for  a  long  time  supposed  that  the  rhythmical  contractions  of  the  heart  were 
not  caused  by  any  specific  property  of  the  muscle  fibers,  but  were  discharged 
by  iniracardial  ganglion  cells.  This  view  found  weighty  support  in  the  fact 
that  these  cells  were  demonstrated  in  just  those  parts  of  the  heart  where  the 
systole  l)egins.  In  more  recent  times  various  authors,  notably  Gaskell  and 
Engelmann,  have  advocated  the  view  that  the  spontaneous  contractions  of 
the  heart  are  of  muscular  origin,  and  are  due  to  a  special  property  of  cardiac 
muscle. 

The  following  facts  among  others  have  been  adduced  as  arguments  for  this 
conception.  The  venous  sinus  in  the  frog  contains  a  large  collection  of  gan- 
glion cells,  known  as  Remak's  ganglion,  which  on  the  ganglion  hypothesis  has 
often  been  referred  to  as  the  originator  of  the  heart  beat.  Now  it  has  been 
found  that  normal  pulsations  can  be  started  from  every  other  place  in  the 
sinus  region ;  the  sinus  ganglion  is  not,  therefore,  al)solutely  necessary.  In  the 
frog  in  the  normal  course  of  events,  the  contraction  waves  probably  proceed 
not  from  the  sinus  but  from  the  great  veins.  These  pulsate  spontaneously 
if  they  are  isolated  entirely  from  the  rest  of  the  heart,  even  if  the  isolated 
portion  contains  no  ganglion  cells.  The  same  is  true  of  the  bulbus  arteriosus 
of  the  frog's  heart,  in  which  no  ganglion  cells  are  present.  Moreover  in  the 
heart  of  the  higher  invertebrates,  and  in  the  spontaneously  contractile  veins 
of  the  bat's  wing,  notwithstanding  diligent  search,  no  ganglion  cells  have 
been  found.  Again  the  embryonic  heart  of  mammals  beats  in  a  perfectly 
characteristic  manner  at  a  time  when  no  nerve  or  muscle  cells  have  yet  been 
difl'erentiated. 

All  these  and  still  other  circumstances  go  to  show  that  a  rhythmical,  auto- 
matic activity  of  contractile  tissue  can  be  brought  about  without  the  partici- 
pation of  ganglion  cells ;  and  it  is,  therefore,  possible  that  the  automatism  of 
the  fully  developed  vertel)rate  heart  is  of  muscular  origin.  The  great  tenacity 
of  life  of  the  heart  speaks  strongly  for  this  view  also ;  for  from  all  that  we 
know  of  ganglion  cells  elsewhere,  they  perish  in  much  shorter  time  than  is 
required  for  the  exsected  heart  to  lose  its  power  of  rhythmical  contraction. 

The  fact  that  this  power  is  developed  to  different  degrees  in  different  parts 
of  the  heart,  and  that  individual  parts,  like  the  clamped-off  apex  of  the  frog's 
ventricle,  will  never  pulsate  spontaneously  under  the  influence  of  the  normal 
stimulus,  is  explained  according  to  the  muscular  theory  by  supposing  that 
automatism,  originally  common  to  all  the  cardiac  muscle  cells,  has  disappeared 
in  the  course  of  development  from  some  places,  notably  the  apex,  but  remained 
in  others,  notably  the  region  of  the  venous  sinus. 


THE   CAUSE   OF  THE   RHYTHMICAL   ACTIVITY   OF   THE    HEART     187 

The  number  of  authors  who  have  taken  the  side  of  this  hypothesis  has  con- 
stantly increased — a  fact  not  difficult  to  understand  in  view  of  the  great  logical 
precision  with  which  it  has  been  developed.  Nevertheless  it  appears  that  there 
are  still  certain  difficulties  to  be  overcome.  For  example,  the  questions :  how  it 
transpires  that  the  vena?  cavie  and  the  pulmonarv  veins,  although  separated  by  a 
considerable  distance,  are  roused  to  action  simultaneously;  and  how  the  nor- 
mal coordination  of  the  heart  muscle,  as  well  as  the  disturbances  of  the  same 
by  electrical  stimulation,  by  anaemia  and  by  mechanical  abuse  (cf.  page  183), 
are  brought  about  have  not  yet  been  satisfactorily  answered. 

Any  explanation  of  the  origin  of  the  contraction  must  take  account  also 
of  the  question  as  to  how  the  excitation  is  propagated  through  the  heart, 
whether  through  the  musculature  itself  or  through  a  set  of  nerves ;  because, 
if  the  muscular  theory  of  the  heart  beat  is  correct,  it  follows  almost  of  neces- 
sity that  the  propagation  of  the  stimulus  is  muscular,  and  vice  versa. 

If  the  ventricle  be  artificially  fed  by  the  coronary  arteries,  and  be  divided 
up  into  different  parts  connected  together  Ijy  the  arterial  Ijranches,  and  joined 
by  thin  muscular  bridges,  all  the  portions  beat  s\Tichronously.  no  matter  in 
what  direction  the  cuts  are  made.  After  section  of  the  muscular  bridge,  the 
synchronism  stops  and  each  part  beats  after  its  own  rhythm,  but  does  not 
show  any  signs  of  fluttering  (Porter). 

Xeither  these  phenomena  nor  the  corresponding  observations  made  on  the 
frog's  heart  are,  however,  to  be  regarded  as  conclusive  proof  of  the  muscular 
theory  of  propagation,  inasmuch  as  the  cardiac  muscle  fibers  themselves  are 
surrounded  by  nerves  which  could  only  be  excluded  by  complete  division  of  the 
last  muscular  bridges,  and  might  therefore  cause  the  synchronism. 

The  passage  of  the  excitation  from  the  auricles  to  the  ventricles  once  con- 
stituted a  serious  difficulty  in  the  way  of  a  muscular  theory.  It  was  supposed 
that  the  musculature  of  these  two  divisions  were  completely  separated.  It  has 
been  shown,  however,  that  direct  muscular  connections  are  indeed  present 
between  the  two  (Kent,  His,  Jr.),  and  the  excitation  might  therefore  pass 
from  the  auricle  to  the  ventricle  without  any  participation  of  nerves. 

As  mentioned  above,  a  certain  time  intervenes  between  the  auricular  and 
the  ventricular  systoles.  From  the  standpoint  of  the  ganglion  hypothesis  this 
delay  would  not  be  difficult  to  explain,  since  we  know  from  many  other  ob- 
servations that  ganglia  in  general  do  delay  the  propagation  of  impulses.  But 
the  muscular  theory  also  has  been  able  to  offer  an  explanation  by  supposing 
that  the  transmission  of  the  motor  stimulus  takes  place  very  quickly  within 
each  separate  division  of  the  heart,  while  over  the  cells  which  form  the  con- 
nections between  the  separate  parts,  the  transmission  is  very  slow,  just  as  it 
would  be  over  smooth  or  embryonic  muscles. 

What  appears  to  disprove  conclusively  the  hypothesis  of  nervous  propagation, 
and  is  therefore  a  very  weighty  support  for  the  muscular  hypothesis,  is  the  fol- 
lowing. If  the  auricle  of  a  frog's  heart  bo  injured  by  a  light  pinch,  the  rhythmic 
excitation  travels  just  as  before  over  the  entire  heart.  But  if  the  vagus  be  now 
stimulated,  as  long  as  the  inhibitory  action  lasts,  the  ordinary  excitation  passes 
only  up  to  the  injured  spot  and  stops  there.  If  the  propagation  were  through  a 
nervous  mechanism,  we  should  have  to  suppose  that  the  conductivity  is  tem- 
14 


1S8  CIRCULATION   OF  THE   BLOOD 

porarily  abolished  exactlj-  at  the  injured  place  (F.  B.  Hofmann),  which  however 
could  onb'  be  explained  by  an  action  of  inhibitory  fibers  on  motor  fibers.  Such 
effects  are  entirely  unknown  elsewhere  and  are  therefore  extremely  improbable 
here.  The  phenomenon  presents  no  special  diflSculty,  on  the  other  hand,  if  we 
suppose  that  the  transmission  is  purely  muscular,  and  has  been  rendered  im- 
possible by  the  action  of  the  inhibitors^  nerves  on  the  injured  muscle. 

The  synchronism  of  the  two  ventricles  is  not  effected  by  simultaneous  im- 
pulses from  the  auricles,  but  by  their  muscular  or  nervous  connection  with  each 
other.  For  if  the  two  be  separated  from  one  another,  but  be  left  in  connection 
with  their  respective  auricles,  the  synchronism  is  broken  and  each  beats  in  its 
owni  rhythm  (Porter). 

§  11.  THE  EFFERENT  CARDIAC  NERVES 

The  activity  of  the  heart  is  controlled  bv  impulses  from  the  central  nervous 
system  brought  to  it  over  the  vagus  and  sympathetic  fibers.  Afferent  nerves 
also  pass  to  the  brain  from  the  heart,  and  these  influence  both  the  lieart  itself 
and  the  blood  vessels  of  the  general  system  reflexly.  The  rich  su])ply  of  nerve 
fibers  to  the  ultimate  muscle  fibers  of  the  heart  are  the  terminal  branches  of 
these  same  nerves. 

The  importance  of  these  regulatory  influences  can  scarcely  be  overestimated. 
This  is  well  shown  by  the  following  observations  of  Friedenthal  on  a  dog,  whose 
extracardiac  nerves  were  all  cut,  the  afferent  fibers  from  the  lungs,  and  the  fibers 
to  the  stomach  and  the  oesophagus  being  preserved  on  one  side.  The  animal, 
which  had  survived  the  last  operation  for  more  than  eight  months  and  had  then 
succumbed  to  acute  strophanthus  poisoning,  showed  in  the  meantime  on  super- 
ficial examination  scarcely  any  abnomiality.  The  number  of  heart  beats,  for 
example,  was  not  noticeably  changed.  When,  however,  the  animal  was  required 
to  run,  the  abnormality  became  very  apparent.  Although  he  had  recovered  his 
original  weight  within  two  months  of  the  operation,  he  was  unable  aftero'ards 
to  run  half  a  mile.  The  ability  to  do  even  a  moderate  amovint  of  work  had 
therefore  been  lost,  because  the  mechanism  for  increasing  the  heart  action  was 
wanting. 

A.    THE   INHIBITORY  NERVES 

If  the  vagus  be  cut  in  the  neck  and  its  peripheral  end  be  stimulated  with 
tetanizing  induction  shocks,  slowing  of  the  heart  heat  or  complete  diastolic 
standstill,  according  to  the  strength  of  stimulation,  resiilts.  The  vagus  there- 
fore inhibits  the  heart  movements.  We  owe  this  important  discovery  to  the 
brothers,  E.  H.  and  E.  F.  Weber  (1845). 

If  both  vagi  of  an  animal  be  cut,  the  heart  immediately  beats  faster. 
Under  normal  circumstances  therefore  a  constant  restraint  is  being  exercised 
l)y  the  central  nervous  system  upon  the  heart,  in  consequence  of  which  it  beats 
more  slowly  than  it  otherwise  would. 

The  vagus  influences  not  only  the  frequency  of  the  heart  beats,  but  also 
the  force.  In  fact  it  may  happen  under  certain  circumstances  that  when  the 
vagus  is  stimulated  the  pulse  frequency  remains  entirely  unchanged,  while  the 
size  of  the  contraction  becomes  constantly  smaller  (Heidenhain,  Gaskell). 
According  to  ^luskens,  this  takes  place  in  the  frog  and  turtle  only  in  the 
excised  heart  or  after  loss  of  blood.    The  heart  relaxes  in  diastole  more  during 


THE    EFFERENT   C.\RDIAC    NERVES  '  189 

vagus  stimulation  than  otherwise,   but   this  might  be  caused  by  the  longer 
pause,  affording  more  time  for  relaxation  (0.  Frank,  F.  B.  Hofmann). 

The  following  observations  have  been  made  with  regard  to  the  way  in  which 
the  vagus  acts  upon  the  diiferent  divisions  of  the  mammalian  heart.  The  inhib- 
iting influence  extends  not  only  to  the  heart  itself,  but  also  to  the  central  veins, 
so  that  their  contractions  may  completely  cease  on  vagus  stimulation  (Knoll). 
With  reference  to  the  auricles  it  is  unanimously  asserted  that  it  is  the  force  of 
contraction  which  is  primarily  diminished,  and  that  it  may  even  happen,  in  spite 
of  a  considerable  decrease  in  the  extent  of  the  contraction,  that  the  rhythm 
remains  entirely  unaltered.  On  the  other  hand,  it  invariably  happens  that  a 
fall  in  frequency  is  accompanied  by  a  reduction  in  the  size  of  the  contraction. 

Results  diflFer  somewhat  as  to  the  behavior  of  the  ventricles.  It  seems,  how- 
ever, to  be  pretty  certain  that  with  weak  stimulation  where  the  heart  beats  are 
not  retarded  very  much,  the  contractions  of  the  ventricles  are  somewhat  stronger 
than  otherwise;  and  that  with  stronger  stimulation  and  considerable  retardation 
the  contractions  become  weaker.  The  augmentation  in  the  first  instance  need 
not  be  a  direct  effect  of  the  vagus,  for  it  may  be  due  to  the  fact  that  with  a 
slower  cadence  a  greater  volume  of  blood  is  at  the  disposal  of  the  heart  at  each 
systole;  besides,  it  must  not  be  forgotten  that  with  the  longer  diastole  the  blood 
pressure  in  the  arteries  must  fall,  so  that  the  heart  has  less  resistance  to  overcome. 

The  cause  of  the  reduction  in  frequency,  or  the  complete  standstill  of  the 
ventricle  effected  by  the  vagus  is  to  be  sought  in  a  direct  effect  on  the  ventricles 
themselves.  One  would  think  that  when  the  auricles  are  stopped  they  would 
no  longer  discharge  impulses  to  the  ventricles.  While  this  is  possible  it  does 
not  seem  very  probable,  at  least  for  the  mammalian  heart,  for  under  certain 
circumstances  the  ventricles  may  beat  at  the  rhythm  of  the  great  veins  while 
the  auricles  are  perfectly  quiescent  (Knoll).  Besides,  the  power  of  the  ven- 
tricles to  beat  rhythmically  when  isolated  from  the  auricles  is  so  great  that 
mere  stoppage  of  the  auricles  may  not  necessarily  affect  the  ventricles.  Vagus 
retardation  may,  however,  be  brought  about  in  such  a  way  that  the  impulse 
cannot  be  propagated  from  auricles  to  ventricles.  Thus  there  are  cases  where 
the  auricles  beat  at  a  more  rapid  rhythm  than  the  ventricles,  although  the 
excitability  of  the  latter  is  not  diminished  in  the  least.  Finally,  it  has  been 
shown  that  when  the  heart  is  brought  to  a  complete  standstill  by  strong  vagus 
excitation,  the  cardiac  muscle  is  less  excitable  to  direct  stimulation  and  can- 
not be  roused  to  contractions  so  extensive  as  is  normally  the  case.  All  of 
which  bears  out  the  statement  that  the  vagus  acts  directly  on  the  ventricular 
muscle. 

Engelmann  describes  these  effects  of  vagus  excitation  as  negatively  chrono- 
tropic (retarding),  negatively  inotropic  (weakening),  negatively  dromotropic 
(diminishing  the  conductivity),  and  negatively  bathmotropic  (reducing  the  irri- 
tability);  and  is  inclined  to  the  assumption  that  they  are  brought  about  by  four 
special  sets  of  nerve  fibers.  This  conception,  based  on  the  frog's  heart,  receives 
some  support  from  Pawlow's  observations  on  the  stimulation  of  separate  fibers 
in  the  cardiac  plexus  of  the  dog,  according  to  which  either  the  force  or  the  fre- 
quency of  the  heart  beat  could  be  influenced  either  in  a  positive  or  negative 
direction,  according  to  the  fibers  stimulated.  Other  authors  take  the  view  that 
the  inhibitory  nerves  consist  of  only  one  set  of  fibers,  and  that  the  different 


190  CIRCULATIOX    OF   THE    BI.OOD 

effects   depend    upon    their  condition    at    the    time    of   stimuhition.      A   definite 
decision  of  the  matter  is  not  possible  at  this  time. 

The  view  has  often  been  expressed  that  tlie  vagus  influence  on  the  heart 
is  of  a  nutritive  or  trophic  nature.  The  following  facts  might  he  construed 
in  favor  of  such  a  view:  the  strength  and  working  power  of  the  heart,  as  well 
as  the  ability  of  the  heart  muscle  to  propagate  a  stimulus,  increases  after 
vagus  stimulation;  the  heart's  activity,  if  it  is  weak,  is  materially  raised  by 
vagus  stimulation ;  and  in  the  asphyxiated  animal  the  heart  heats  longer  if 
the  vagi  are  left  intact,  than  if  they  be  cut,  etc.  But  these  phenomena  might 
be  explained  also  by  the  longer  resting  period  after  each  systole. 

Conclusive  proof  of  the  correctness  of  this  view  would  be  afforded,  if 
degenerative  changes  could  be  demonstrated  on  a  heart  whose  vagi  had  l)een 
cut.  Such  have  in  fact  often  been  mentioned,  and  it  has  even  been  asserted 
that  they  are  confined  to  diiferent  parts  of  the  ventricles,  according  as  the 
right  or  left  vagus  is  cut.  But  we  have  the  researches  of  Pawlow  and  Fried- 
enthal  to  the  contrary.  They  find  that  the  heart  of  dogs  which  had  survived 
bilateral  vagotomy  for  several  months  presented  no  anatomical  changes  what- 
soever. The  long  time  during  which  the  animals  remained  alive  in  these 
researches,  as  well  as  in  those  of  Nikolaides  and  Ocaha,  itself  goes  to  show 
at  least  that  the  vagus  cannot  be  exclusively  a  trophic  nerve  for  the  heart. 

That  the  inhibitory  process  is,  nevertheless,  accompanied  by  demonstrable 
molecular  changes,  and  that  the  stoppage  is  not  therefore  a  kind  of  paralysis, 
appears  from  the  electrical  variations  in  the  heart  muscle  which  accompany 
vagus  stimulation.  In  the  turtle's  heart  it  is  possible  to  separate  the  auricles 
from  the  venous  .sinus  without  injuring  the  nervous  fibers  of  the  former.  The 
auricles  stop  for  a  time.  If  now  the  apex  be  killed  by  immersion  in  hot 
water,  and  both  base  and  apex  be  then  led  off  to  a  galvanometer,  the  usual 
demarcation  current  is  observed  with  the  injured  spot.  i.  e.,  the  apex,  negative 
toward  the  base.  If  the  vagus  is  stimulated  the  auricles  remain  at  rest;  but 
the  galvanometer  shows  a  positive  variation  (Gaskell).  This  variation  of  the 
animal  current  is  evidently  opposite  in  sign  to  that  which  takes  place  in 
the  work  of  the  heart  muscle  (cf.  page  179).  Fano  obtained  quite  similar 
results  when  he  stimulated  the  vagus  of  an  active  turtle  heart  so  feebly  that 
it  was  not  stopped  but  only  retarded.  The  positive  phase  of  the  variation 
was  increased,  but  the  negative  was  diminished  or  abolished  altogether. 

Since  now  the  negative  variation  is  quite  certainly  the  expression  of  a 
dissimilatory  process,  one  would  be  forced  by  the  appearance  of  a  positive 
variation  on  stimulation  of  the  vagus  to  the  conclusion  that  this  nerve  calls 
out  processes  of  a  synthetic  nature.  If,  however,  this  is  true,  it  follows  from 
the  above  observations  on  vagotomy  that  these  synthetic  processes  are  not  of 
critical  importance  for  the  maintenance  of  the  normal  structure  of  the  heart. 

In  discussing  the  intracardial  innervation  of  the  heart  (page  186),  the 
significance  of  the  ganglia  was  left  an  open  question.  It  will  be  appropriate 
to  revert  to  the  subject  here,  because  some  observations  on  the  vagus  should 
be  able  to  give  the  desired  answer.  Langley  has  shown  that  nicotine  puts  an 
end  to  the  transmission  of  an  impulse  through  the  sympathetic  ganglion  cells 
with  which  the  nerve  fibers  (preganglionic)  coming  from  the  central  nervous 


THE   EFFERENT  CARDIAC   NERVES 


191 


system  are  connected,  whereas  the  fibers  (postganglionic)  arising  from  these 
cells  retain  their  excitability  (cf.  Chapter  XXV).  This  method  has  been 
employed  also  for  the  study  of  the  ganglionic  connections  of  the  vagus  fibers. 
In  a  frog  poisoned  with  nicotine,  stimulation  of  the  vagus  trunk  produces 
no  inhibition  of  the  heart;  but  stimu- 
lation of  the  nerves  running  in  the 
auricidar  septum  under  certain  cir- 
cumstances gives  very  marked  weaken- 
ing of  the  heart  beat.  The  ganglion 
cells  of  the  venous  sinus  must  there- 
fore be  regarded  as  a  relay  station  for 
the  cardiac  inhibitory  fibers  (F.  B. 
Hofmann). 


B.     THE    ACCELERATOR    NERVES    OF 
THE   HEART 

These  arise  from  the  sympathetic 
(Fig.  67).  They  pass  out  of  the  spinal 
cord  in  the  upper  four  or  five  (most 
of  them  in  the  second  and  third)  thoracic 
spinal  roots,  and  run  in  the  sympathetic 
chain  to  the  first  thoracic  ganglion  (n). 
The  latter  sends  out  two  connecting 
branches  to  the  inferior  cervical  gan- 
glion (0,  or  to  the  vagus  (a),  which 
run  on  either  side  of  the  subclavian  ar- 
tery forming  the  annulus  of  Yieussens. 
Either  from  the  inferior  cervical  gan- 
glion itself,  or  from  the  annulus,  or 
from  the  trunk  of  the  vagus  just  below 
the  inferior  cervical,  the  accelerator 
nerves  (g)  are  given  off  to  join  the  car- 
diac plexus.  Besides,  accelerator  fibers 
are  found  in  the  cervical  portion  of  the 
vagus,  since  with  the  inhibitory  fibers 
thrown  out  of  function  by  atropine 
poisoning  vagus  stimulation  produces 
an  acceleration  of  the  heart  beat.  The 
accelerator  fibers  running  in  the  sym- 
pathetic are  described  by  physiologists 
as  the  accelerator  nerves. 

Stimulation  of  the  accelerator  in- 
creases the  pulse  frequency  more  or  less 
(v.  Bezold,  the  brothers  Cyon)  accord- 
ing as  the  frequency  was  previously 
low  or  high.  The  absolute  maximum 
of  fre<^piency  attainable  l)y  stimulation 
of  the  accelerator  mechanism  is  en- 
tirely independent  of  the  previous  rate 


Fig.  67. — The  cardiac  nerves  of  the  dog, 
after  Ellenberger  and  Baum.  a,  united 
vagus  and  sympathetic;  6,  vagus;  c,  con- 
necting fibers  between  the  vagus  and  the 
inferior  cervical  ganghon  of  the  sympa- 
thetic; (/,  cardiac  nerves  springing  from 
tiie  vagus;  c,  cardiac  ple.xus;  /,  recurrent 
laryngeal ;  y,  y',  pulmonary  plexus ;  /,  in- 
ferior cervical  ganglion;  m,  annulus  of 
Vieussens;  n,  first  thoracic  ganglion  (stel- 
late ganglion) ;  o,  rami  coniniunicantes 
from  tins  ganglion  to  the  lost  cervical 
nerves;  p,  rami  communicantes  to  the 
first  and  second  thoracic  nerves;  y,  car- 
diac branch  from  the  stellate  ganglion; 
r,  trunk  of  the  sympathetic  in  the  thorax ; 
s,  rami  communicantes  to  the  spinal 
nerves;  s',  intercostal  nerves;  v,  phrenic 
nerve;  16,  heart;  17,  innominate  arterj-; 
18,  left  subclavian  vein;  19,  aorta. 


192 


CIRCULATION   OF  THE   BLOOD 


(Baxt).  The  increase  is  accomplished  mainly  l)y  shortening  the  diastole. 
When  stimulation  has  ceased  an  after-effect  remains  which  in  I'avorahle  cases 
lasts  for  as  much  as  two  minutes. 

Just  as  with  the  inhihitorv  nerves,  the  accelerators  appear  to  exerr^ise  a 
tonic  influence  on  the  heart.     Evidence  for  this  we  have  in  the  fact  that 


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Fig.  68. — Graphic  representation  of  the  pulse  rate:  r,  on  stimulating  the  vagus;  a,  on  stimu- 
lating the  accelerator  nerves;  a  v,  on  stimulating  both  simultaneously,  after  Hunt.  Stimu- 
lation lasted  fifteen  seconds  in  each  case,  s — s. 

bilateral  extirpation  of  the  lowermost  cervical  and  uppermost  thoracic  ganglia, 
after  section  of  both  vagi,  diminishes  the  pulse  frequency.  The  normal  rate 
of  the  heart  beat  therefore  is  determined  bv  the  accelerator  nerves  as  well  as 
l)y  the  inhibitory,  and  it  appears  from  Friedenthal's  results,  given  on  page 
188,  that  the  former  are  just  as  necessary  for  the  heart's  activity  as  the 
inhibitory  nerves. 

The  size  of  the  auricular  and  the  ventricular  contraction  in  most  cases 
increases  upon  stimulation  of  the  accelerator.  But  it  may  happen  also  that 
the  extent  of  the  contraction  increases,  while  the  heart  frequency  is  not  influ- 
enced at  all,  and,  vice  versa,  acceleration  may  take  place  without  any  increase 
in  extent.  In  any  case  these  nerves  improve  the  execution  of  the  heart  and 
heighten  the  dissimilatory  processes  going  on  within  it;  hence  the  proposed 
designation  of  them  by  Hofmann  as  the  promoting  nerves  in  contradistinc- 
tion to  the  inhibitory  nerves,  very  aptly  characterizes  their  properties. 

By  way  of  analogy  with  his  conception  of  the  inhibitory  nerves  of  the  heart, 
Engelmann  supposes  that  the  accelerator  neiwes  also  have  several  kinds  of  fibers : 
positively  chronotropic  (increasing  the  rate) ;  positively  inotropic  (increasing 
the  force);  positively  dromotropic  (increasing  the  conductivity);  and  positively 
bathmotropic  (increasing  the  excitability).  The  same  comment  would  apply  to 
this  conception  as  to  that  concerning  the  inhibitory  fibers  (page  1.S9). 

It  has  been  found,  mainly  l:)y  the  use  of  the  nicotine  method,  that  the 
''  promoting  fibers  "  also  unite  with  intracardial  gansflion  cells. 

With  regard  to  the  antagonistic  relations  of  the  vagus  and  accelerator, 
experiments  show  that  the  one  nerve  or  the  other  predominates  according 
to  the  relative  strength  of  its  stimulation,  and  that  with  a  stimulus  of  suitable 
strength  for  each,  the  two  effects  mav  be  made  to  balance  each  other  so  that 


THE   HE.\RT   REFLEXES 


193 


both  the  rate  of  the  heart  beat  and  the  duration  of  its  different  phases  may  re- 
main almost  entirely  unchanged  (Bayliss  and  Starling,  0.  Frank,  Hunt,  et  al.). 
And  yet  we  are  not  to  suppose  that  the  resultant  effect  is  the  algebraic 
sum  of  the  two  when  acting  separately.  For  upon  stimulation  of  the  two 
together,  if  the  vagus  effect  predominates  during  stimulation,  a  characteristic 
after-effect  of  the  accelerator  comes  on  when  stimulation  has  ceased  (Fig.  68). 
The  two  nerves  are  not  therefore  to  be  regarded  as  true  antagonists;  for  if 
they  were,  stimulation  of  the  two  ought  to  give  the  same  result  as  stimulation 
of  neither;  that  is,  the  peculiar  after-effect  of  the  accelerator  ought  not  to 
appear  (Baxt).  In  view  of  these  facts,  it  seems  probal)le  that  the  inhibitory 
and  "  promoting  fibers  "  have  different  modes  of  connection  with  the  cardiac 
muscle  fibers. 


§  12.    THE   HEART   REFLEXES 

The  efferent  cardiac  nerves  are  roused  to  action  retlexly  both  by  the  affer- 
ent nerves  of  the  heart  itself,  and  by  other  nerves,  and  the  heart  is  variously 
influenced. 

On  the  anterior  as  well  as  on  the  posterior  wall  of  the  ventricle  run 
numerous  nerves,  which,  on  stimulation  of  their  central  cut  ends,  reflexly 
raise  or  lower  the  blood  pressure,  and 
accelerate  or  retard  the  rate  of  the  heart 
beat  (Wooldridgo).  The  heart  itself 
therefore  through  its  own  afferent  nerves 
can  set  in  action  mechanisms  l)y  which 
the  circulatory-  apparatus  can  be  changed 
in  one  sense  or  the  other,  according  to 
the  momentary  requirements. 

The  depressor  nerve  discovered  by 
Ludwig  and  Cyon.  which  runs  as  a  sepa- 
rate nerve  in  the  rabbit,  is  the  most  im- 
portant of  the  nerve  trunks  conveying 
fibers  from  the  cardiac  plexus.  It  rises 
as  a  rule  by  two  roots,  one  from  the 
cervical  portion  of  the  vagus,  the  other 
from  the  superior  laryngeal,  and  runs 
parallel  with  the  vagus  to  the  cardiac 
plexus  (Fig.  69).  According  to  Koster 
and  Tschermak.  the  depressor  does  not 
come  from  the  heart  but  from  the  aorta. 
Because  of  its  great  importance  for  the 
action  of  the  heart,  we  shall  discuss  it  in 
this  connection. 

Stimulation  of  its  peripheral  end 
has  no  effect  whatever.     Stimulation  of 

the  central  end  produces  a  fall  in  blood  pressure  and  retardation  of  the  heart 
beat  (Fig.  70).  If  the  vagi  are  cut  the  latter  effect  is  wanting,  but  the  fall 
in  pressure  occurs  just  as  before.     The  retardation  is  therefore  due  to  reflex 


Fig.  69. — The  depressor  nerve  of  the  rab 
bit,  after  Ludwig  and  Cyon.  1,  sympa- 
thetic; 2,  hypoglos.sal ;  3.  descending 
branch  of  the  hypoglossal;  4,  branch 
from  the  cervical  plexus;  5,  vagus;  6, 
superior  laryngeal :  7,  first  and  8,  second 
root  of  the  depressor. 


194 


CIRCri.ATIOX    OF   THE    BLOOD 


excitation  of  tlie  vagus,  the  fall  in  pressure  to  a  reflex  dilatation  of  the  blood 
vessels. 

The  natural  assumption  with  regard  to  the  normal  action  of  the  depressor, 
is  that  it  is  stimulated  bv  dilatation  of  the  aorta,  when  for  example  the  pres- 
sure there  becomes  very  high  ^o  that  it  is  difhcult  for  the  heart  to  empty  itself. 
The  blood  vessels  are  dilated  as  the  result  of  the  depressor  impulses,  and  the 
heart,  working  now  against  less  resistance,  empties  itself  more  easily.  Since 
the  heart  beats  more  slowly  also  as  the  result  of  the  vagus  reflex,  it  has  a 
better  opportunity  to  recover  after  the  previous  overexertion.  These  conclu- 
sions have  been  confirmed  l)y  recent  observations;  e.g..  when  liigh  pressure 


Fig.   70. — Behavior  of  the  blood  pressure  on  stimulation  of  tlie  depressor  nerve.      To  be  read 
from  right  to  left.      The  two  vertical  lines  indicate  the  time  of  stimulation.  ,  |  =  ten 

seconds. 

is  produced  artificially  in  the  arch  of  the  corta,  an  action  current  appears  in 
the  trunk  of  the  depressor  (Tschermak),  and  if  both  depressors  are  cut  when 
the  pressure  is  high,  the  pressure  rise-  still  further   (Pawlov^). 

According  to  Cyon,  the  depressor  has  a  tJiird  root,  central  stimulation  of 
which  produces  an  acceleration  of  the  heart;  this  root  is  connected  with  the 
superior  cervical  ganglion. 

The  heart  does  not  appear  to  have  nerves  which  mediate  tactile  sensations ; 
on  the  other  hand  reflexes  may  l)e  started  from  its  afferent  nerves  which  take 
effect  in  the  skeletal  muscles. 

The  heart  may  be  influenced  reflexly  l)y  a  great  many  other  nerves.  If  one 
vagus  be  cut,  and  the  other  be  left  intact,  central  stimulation  of  the  cut  nerve 
produces  a  slowung  of  the  pulse,  which  disappears  when  the  other  is  cut. 
Among  the  different  afferent  fibers  of  the  vagus,  those  coming  from  the  lungs 
are  most  effective,  those  from  the  heart  much  less  so,  and  those  springing 
from  points  below  the  lung  fibers  are  still  less  effective  (Brodie  and  Eussell). 
The  inhibitorv  nerves  of  the  heart  are  excited   also  bv  stimulation  of  the 


THE  CARDIAC   NERVE  CENTERS  195 

central   end   of   the  superior   laryngeal,   of   the   splanchnic   and   of   the    tri- 
geminal. 

Acceleration  is  obtained  by  inflation  of  the  lungs;  and  in  man  it  has  been 
found  that  any  increase  of  intrabronchial  air  pressure,  as  in  speaking,  sing- 
ing, rapid  and  forced  respiration,  etc.,  accelerates  the  heart  beat. 

The  effect  on  the  heart  of  central  stimulation  of  sensoi-y  nerves  in  the  strict 
sense,  as  well  as  nen-es  of  the  special  senses,  is  twof old :  either  an  acceleration 
or  a  slowing.  Only  the  trigeminal  gives  an  invariable  retardation;  stimulation 
of  the  nasal  mucous  membrane  stops  the  heart  immediately.  It  is  possible  that 
the  result  of  stimulation  depends  upon  its  strength,  inhibition  following  strong, 
acceleration  following  the  weak  current.  We  may  also  suppose  that  such  nei-ves 
consist  of  two  kinds  of  fibers,  one  of  which  brings  about  inhibition  of  the  heart 
beat,  the  other  acceleration ;  but  this  is  improbable.  The  afferent  nerves  from 
the  muscles  appear  to  exercise  but  a  slight  influence  on  the  heart. 

Although  the  heart  reflexes  have  not  been  studied  at  all  sufficiently,  we 
may  affirm  with  a  moderate  degree  of  certainty  that  acceleration  as  well  as 
inhitjition  of  the  heart  beat  can  be  brought  about  reflexly  by  a  great  many 
afferent  nerves. 

Inhibition  is  certainly  to  be  regarded  as  a  reflex  carried  over  to  the  vagus, 
as  appears  unequivocally  from  the  faet  that  when  both  vagi  are  cut  the  heart 
beats  faster.  It  is  generally  supposed  also  that  acceleration  is  mediated  by  reflex 
excitation  of  the  accelerator  nerves.  However,  Hunt  has  made  some  researches 
from  which  he  concludes  that  reflex  acceleration  is  caused  by  a  reduction  in  the 
tonus  of  the  inhibitory  center,  and  he  has  endeavored  with  great  skill  to  prove 
that  in  most  cases  of  augmented  heart  action  the  cause  inheres  in  this  rather 
than  in  excitation  of  the  accelerator,  although  he  admits  that  augmentation  is 
stronger  with  uninjured  accelerators,  than  when  these  are  destroyed,  because 
with  diminshed  tonus  of  the  vagus  they  can  act  on  the  heart  more  powerfully. 

§  13.  THE  CARDIAC  NERVE  CENTERS 

We  designate  as  the  center  of  a  nerve,  that  place  in  the  central  nervous 
system  from  which  its  activity  is  influenced  either  automatically  or  reflexly. 

Nothing  definite  is  known  about  the  location  of  the  augntentor  center  for 
the  heart.  But  since  a  stimulus  applied  to  the  upper  part  of  the  medulla 
produces  acceleration  of  the  heart  beat,  it  is  natural  to  locate  this,  with  the 
other  vegetative  centers  of  the  body,  in  the  medulla. 

It  is  perfectly  certain  that  the  inhibitory  center  is  in  the  medulla.  A 
needle  puncture  halfway  up  the  medulla  and  pretty  well  to  one  side,  causes 
slowing  and  stoppage  of  the  heart. 

The  cardiac  nerves  are  influenced  also  by  portions  of  the  brain  anterior 
to  the  medulla,  including  even  the  cerebral  cortex.  This  is  confirmed  by  our 
daily  experience  that  the  psychic  states — joy,  fear,  hope,  etc. — increase  or 
diminish  the  frequency  of  the  heart  beat.  Most  persons,  however,  find  it 
impossible  to  influence  these  centers  hy  direct  effort  of  the  will. 

The  frequency  of  the  heart  beat  can  he  changed  in  one  direction  or  another 
by  the  so-called  motor  areas-  of  the  cerebral  cortex  and  by  different  lower  parts 
of  the  brain.  But  it  is  not  correct  to  resrard  these  nortions  as  the  seat  of  the 
active  centers  of  the  cardiac  nerves.     It  seems  preferable  to  regard  the  cere- 


196  CIRCULATION   OF   THE    BLOOD 

l)rinn,  etc.,  as  peripheral  organs  ]>}■  wliicli  the  cardiac  centers  are  excited  re- 
flexly,  just  as  they  are  roused  to  activity  hy  afferent  fihers  coming  from  otlier 
parts  of  tlie  body  (Franck).  According  to  this  conception  the  actual  center 
of  the  inhibitory  nerves  would  lie  otily  in  the  medulla.  It  can  be  acted  upon 
by  a  great  many  afferent  nerves — from  the  skin,  from  the  heart  itself,  from 
the  abdominal  viscera,  the  lungs,  the  sense  organs,  and  from  the  different 
parts  of  the  brain. 

The  blood  pressure  also  exercises  an  influence  on  the  rate  of  the  heart  beat. 
It  is  true  that  in  an  exsected  heart,  one  obsei'ves  no  influence  upon  the  pulse- 
frequency  by  variations  of  the  arterial  pressure  within  the  vital  limits,  and  the 
variations  of  the  pulse  produced  by  great  variations  of  the  venous  pressure  are 
not  especially  large.  But  under  normal  conditions  of  the  circulation,  very  evi- 
dent changes  in  frequency  often  occur  as  the  result  of  variations  in  pressure, 
and  this  even  if  every  possible  connection  of  the  heart  with  the  central  nervous 
system  is  broken.  Thus  it  is  found  that  if  an  increase  in  blood  pressure  due  to 
a  local  vasoconstriction  occurs,  there  often  goes  with  it  an  acceleration  of  the 
heart  beat,  the  chief  cause  of  which  is  probably  to  be  sought  in  the  suddenly 
increased  blood  supply  to  the  heart.  By  this  means  those  portions  of  the  heart 
where  the  contraction  starts  are  roused  to  more  frequent  action. 

In  a  heart  completely  isolated  from  the  central  nervous  system  an  increase 
of  pressure  may  produce  also  a  retardation.  The  inhibitory  mechanism  there- 
fore as  well  as  the  motor  mechanism  can  be  excited  by  a  rise  of  blood  pressure. 
The  result  will  depend  upon  the  relativ^e  irritabilitj'  of  the  two  mechanisms. 

When  all  the  cardiac  nerves  are  intact,  the  heart  frequency  decreases  with 
a  rise  in  blood  pressure  and  increases  with  a  fall,  whatever  the  order  in  which 
the  variations  succeed  each  other.  Since  slowing  of  the  heart  is  not  the  usual 
result  of  increased  arterial  pressure  wlien  the  vagi  are  cut,  it  is  clear  that  the 
above-mentioned  phenomenon  is  an  effect  of  the  vagus  center. 

This  excitation  of  the  vagus  center  is  called  out  in  part  by  the  depressor; 
but  is  probably  also  connected  with  a  change  in  the  circulation  of  the  brain, 
excitation  of  the  center  following  an  increase  of  intracranial  pressure. 

Xothing  certain  is  known  as  to  how  the  accelerator  center  acts  with  a  rise 
of  pressure.  The  increase  of  pulse  frequency  obseiwed  in  an  anaemic  condition 
of  the  brain  might  possibly  be  referred  to  an  excitation  of  this  center,  but  it 
can  be  explained  also  by  a  fall  in  the  tonic  influence  of  the  vagus  center. 

From  the  facts  just  discussed,  it  cannot  be  looked  upon  as  fully  established 
that  effects  on  the  efferent  cardiac  nerves,  which  can  be  obtained  by  stimulation 
of  afferent  nerves,  are  caused  exclusively  by  a  reflex  from  the  cardiac  centers, 
for  it  is  not  impossible  that  a  change  in  the  blood  supply  to  the  brain,  brought 
about  by  a  reflex  effect  on  the  vascidar  system,  has  participated  to  some  extent. 

§  14.    THE   RATE   OF   HEART    BEAT 

Xow  that  we  have  studied  the  influence  of  nerves  upon  the  rate  of  the 
heart  beat,  it  remains  for  us  to  inquire  what  are  the  normal  variations  in  man. 

If  all  disturbing  influences  be  removed  as  far  as  possible — i.  e.,  if  the 
individual  be  resting  quietly  in  bed  and  abstain  from  food — only  very  slight 
variations  in  the  pulse  frequency  appear  in  the  course  of  the  day.  But  the 
pulse  rate  is  quickly  affected  by  all  sorts  of  influences. 


THE   RATE   OF    HE.AJIT    BEAT 


197 


Heavy  bed  clothing  sufficient  to  produce  a  growing  sensation  of  warmth 
quickens  the  pulse  frequency  considerably.  Exposure  of  the  naked  bodv  to 
air  at  a  low  temperature  reduces  the  rate;  but  if  the  temperature  of  the  air 
is  high  the  rate  rises.  Hot  and  cold  drinks  have  the  same  effect  as  external 
temperature:  drinking  hot  water  accelerates,  drinking  cold  water  retards  the 
pulse.  A  burning  sensation  or 
sensation  of  pressure,  etc.,  in  the 
stomach  or  intestine  quickens  tiie 
pulse. 

Under  such  circumstances  it  is 
evident  that  a  meal  may  exercise 
an  important  influence  on  the  pulse  ao 
frequency,  and  this  is  confirmed 
by  experience.  The  pulse  rate  as 
a  rule  is  higher  at  meal  times, 
owing  mainly  to  the  addition  of 
heat  to  the  body. 

Bodily  movements  exercise  the 
most  profound  influence  on  the 
pul.se  rate,  and  we  can  almost  say 
that  the  rate  increa.^es  in  direct 
proportion  to  the  effort  required 
and  the  extent  and  vigor  of  the 
movement.  Detailed  experiments 
are  at  hand  showing  that  the  in- 
crease is  due  in  small  part  to  a 
direct  effect  of  products  formed  in 
the  muscular  activity  on  the  heart 
itself,  but  in  by  far  the  greater  part  to  the  fact  that  along  with  the  vol- 
imtary  impulses  from  the  higher  brain  centers  to  the  muscles  there  go  also 
involuntary  impulses  to  the  cardiac  centers,  whereby  the  tonus  of  the  inhibi- 
tory center  is  diminished  or  the  accelerator  center  is  excited  (Johansson; 
cf.  page  195). 

Figure  71  shows  how  the  pulse  rate  varies  with  age.  In  the  first  year  it 
is  highest ;  it  then  falls  to  a  minimum  of  about  seventy  per  minute  near  the 
twentieth  year  (for  males),  where  it  remains  until  the  approach  of  old  age, 
when  it  again  rises  somewhat. 

The  higher  pulse  rate  in  children  is  due  in  part  to  the  smaller  size  of  the 
body,  just  as  we  find  in  grown  animals  of  different  species  that  the  large  ones 
have  a  slow  pulse,  the  small  ones  a  rapid  pul.se  (e.  g.,  horse  and  ox  36  to  50, 
rab])it  200  per  minute).  This  difference  is  without  doubt  connected  with  the 
relatively  more  active  metabolism  of  small  and  young  individuals  (cf. 
page  Wl  et  seq.). 

Figure  71  also  furnishes  information  with  regard  to  the  influence  of  sex. 
The  pulse  frequency  for  all  ages  above  two  years  is  higher  in  the  female  than 
in  the  male.  The  smaller  size  of  the  fenuile  body  is  the  most  important  factor 
in  this  difference.  One  finds  on  comparison  of  the  pulse  rate  in  men  and 
women  of  the  same  height  that  it  is  somewhat  higher  in  the  latter,  but  the 


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Fig.  71. — The  pulse  rate  in  man  at  different  ages, 


after  Guv. 


-,  males; 


•,  females. 


198 


CIRCULATION   OF  THE   BLOOD 


difference  is  much  less  than  when  male  and  female  individuals  of  the  same 
age,  without  regard  to  size,  are  compared. 

Again  we  meet  with  considerable  variation  of  pulse  rate  in  different  indi- 
viduals, a  very  low  (26-20  per  minute)  and  a  very  high  rate  (120  per  min- 
ute) having  been  observed  in  men  of  perfectly  sound  health. 


THIED    SECTION 


THE   BLOOD   FLOW 

§  1.    THE    FLOW   OF   A   LIQUID    IN   RIGID    TUBES 

If  a  reservoir  be  so  arrang'ed  as  to  deliver  a  liquid  through  a  tube  of  uni- 
form diameter  as  represented  in  Fig.  72.  the  mean  velocity  of  the  flow  will  be 
the  same  in  every  cross  section  of  the  tube.  This  follows  from  the  fact  that 
fluids  are  not  compressible.  Moreover,  the  internal  friction  of  the  fluid  creates 
a  resistance  which  causes  it  to  flow  more  slowly  than  it  would  if  it  were  pouring 
directly  from  an  opening  in  the  reservoir;  and  in  consequence  of  this  fi'iction 
the  liquid  in  the  tube  is  subjected  to  a  tension,  which,  however,  is  smaller  than 
it  would  be  if  the  flow  from  the  end  of  the  tube  were  hindered  in  some  way. 
This  tension  manifests  itself  as  a  lateral  pressure  which  can  be  measured  by 
means  of  vertical  tubes  leading  off  at  intervals  along  the  delivery  tube.  If  the 
highest  points  of  the  columns  of  liquid  be  connected  with  each  other,  a  straight 
line  is  obtained — i.  e.,  the  lateral  pressure  decreases  uniformly  in  the  direction 
of  the  current,  to  the  end,  where  it  is  nil.  The  lateral  pressure  at  any  given 
point  along  the  delivery  tube  is  equal  to  that  part  of  the  whole  pressure  which 


J       2  3  u  i  "~^ 

Fig.  72. — The  flow  of  a  liquid  through  a  rigid  tube  of  uniform  diameter. 

is  necessary  to  overcome  the  resistance  of  the  current  from  that  point  onward. 
If  the  system  through  which  the  liquid  flows  consist  of  a  number  of  tubes 
of  different  diameter  fastened  together,  as  in  Fig.  73,  the  same  fundamental 
laws  hold  good.  Because  the  liquid  is  not  compressible  the  same  quantity  must 
flow  through  every  cross  section  of  the  tube,  whatever  its  size,  in  unit  time. 
Consequently  the  velocity  in  the  different  sections  of  the  tube  stands  in  inverse 
relation  to  their  cross  section.  The  lateral  pressure  within  the  different  sections 
falls  at  different  rates — most  rapidly  in  the  narrowest,  most  slowly  in  the  widest. 
In  sections  of  the  same  diameter,  whether  they  are  separated  by  narrow  or  wide 


THE   FLOW   OF  A  LIQUID  IN   ELASTIC  TUBES 


199 


portions,  the  fall  in  pressure  is  the  same,  for  the  velocity  and  hence  the  internal 
friction  also,  are  the  same  in  these. 

When  a  main-deliverj'  tube  is  divided  up  into  a  number  of  small  branches, 
whose  total  cross  section  area  is  greater  than  that  of  the  stem  tube,  and  these 
branches  then  reunite  into  a  single  tube  of  smaller  cross  section  than  the 
branches,  so  as  to  imitate  roughly  the  relationships  of  arteries,  capillaries  and 


Fig.   73.— The  flow  of  a  liquid  through  a  rigid  tube  of  varying  diameter. 

veins,  the  same  quantity  of  liquid  will  flow  through  every  total  cross  section  of 
the  system  in  unit  time,  and  the  velocity  again  will  be  inversely  proportional  to 
the  total  cross  section  area.  In  such  an  enlargement  of  the  total  cross  section  by 
branching  the  superficial  contact  between  the  liquid  and  the  walls  of  the  tubes 
becomes  greater  as  the  diameter  of  the  branches  becomes  smaller,  and  the  resist- 
ance therefore  also  becomes  greater.  Xow  increased  resistance  acts  against  the 
favorable  influence  which  the  mere  widening  of  a  current  bed  produces.  Con- 
sequently the  effect  on  the  flow  of  the  current  produced  by  any  particular  branch- 
ing of  the  bed  will  be  the  resultant  of  these  two  opposing  factors. 


§  2.    THE   FLOW    OF   A   LIQUID    IN   ELASTIC    TUBES 

The  laws  which  apply  to  a  constant  current  in  rigid  tubes  holds  also  for 
tubes  with  elastic  walls.  But  an  important  difference  exists  between  rigid  and 
elastic  tubes,  when  the  fluid  is  driven  into  them  intermittently.  We  leave  out 
of  account  here  for  the  present  wavelike  movements  in  elastic  tubes. 

If  a  fluid  be  pumped  rhythmically  into  one  end  of  a  rigid  tube,  it  will  flow 
out  of  the  other  end  in  jets  of  the  same  rhythm.  But  if  we  use  an  elastic  tvibe 
for  such  an  experiment,  and  if  the  resistance  in  the  tube  is  sufficient  and  the 
rate  of  inflow  rapid  enough,  the  outflow  may  become  continuous.  This  conver- 
sion of  an  intermittent  to  a  constant  flow  is  explained  by  the  fact  that  the  elastic 
wall  of  the  tube  is  put  on  the  stretch  by  the  injecting  force  so  that  a  part  of 
the  energy  is  stored  in  the  wall.  Then  when  the  inflow  ceases  for  a  moment,  the 
stretched  wall  exerts  pressure  on  the  contained  fluid  in  consequence  of  which 
the  latter  flows  during  the  pause  between  jets. 

These  conditions  are  realized  in  the  vascular  system.  The  blood  is  driven 
bv  the  heart  into  the  arteries  in  spurts ;  the  arterial  walls  are  elastic ;  the 
smaller  arteries  and  capillaries  present  a  high  resistance.  Consequently  the 
arterial  wall  is  stretched  bv  the  blood  at  every  systole  of  the  heart,  and  dur- 


200 


CIRCULATION    OF   THE    BLOOD 


ing  diastole  the  elastic  recoil  of  the  wall  drivL's  the  blood  forward  into  the 
capillaries  where  its  flow  becomes  constant. 

The  elasticity  of  the  arteries  spares  the  heart  a  considerable  quantity 
of  work.  If  they  were  rigid  tubes,  it  would  be  necessary  for  the  heart  to 
drive  the  entire  quantity  of  blood  contained  in  them  forward  at  once.  But 
since  they  are  elastic,  the  volume  of  blood  discharged  at  each  systole  is  accom- 
modated by  the  temporary  enlargement  of  the  larger  arteries  and  is   then 


Fig.  74. — An  artificial  schema  for  illustration  of  some  points  in  the  mechanics  of  the  circulation, 
after  Porter.  The  schema  consists  of  an  ''  auricle  "  in  the  shape  of  a  small  cylindrical  reser- 
voir, shown  at  the  left;  a  '"ventricle"  in  the  shape  of  a  small  rubber  pump,  the  pressure 
■within  which  is  varied  by  means  of  a  piston  operated  throug:!!  an  eccentric  wheel  which  is 
rotated  by  a  crank:  a  valve  between  the  auricle  and  ventricle  representing  the  atrio-ven- 
tricular  valves;  another  bej'ond  the  ventricle  representing  the  semilunar  valves;  tubes 
representing  blood  vessels;  a  set  of  "capillaries"  in  the  shape  of  a  section  of  porous  cane 
where  tlie  "peripheral  resistance"  is  high,  and  a  side  tube  provided  with  a  clamp  by  which 
the  peripheral  resistance  can  be  lowered;  and  mercury  manometers  which  exhibit  the 
relative  arterial  and  venous  pressures. 

driven  forward  b}'  the  force  stored  in  tJicir  iraJls,  so  that  only  a  part  of  the 
column  must  be  moved  at  the  time  of  systole  (E.  H.  Weber). 

The  rhythmical  feeding  of  the  vessels  has  still  another  advantage.  The 
blood  corpuscles  are  given  a  kind  of  to-and-fro  motion,  which,  as  experi- 
ment has  shown,  materially  facilitates  the  flow  through  the  capillaries 
( Hamel ) . 

§  3.    THE   FLOW   OF   BLOOD   IN   THE   ARTERIES 
A.    ELASTICITY   OF   THE   ARTERIAL  WALL 

If  a  strip  cut  from  an  artery  be  stretched  by  adding  to  its  load  equal 
increments  of  weight,  the  amount  of  lengthening  produced  l)y  each  successive 


THE   FLOW   OF   BLOOD   L\   THE   ARTERIES  201 

weight  becomes  steadily  less  the  greater  the  total  load.  The  coefficient  of 
elasticity  of  the  arterial  wall  therefore  increases  as  the  stretching  force  in- 
creases, so  that  the  curve  of  elongation  resembles  an  hyperbola  (Wertheim). 

As  to  the  rate  of  cubic  distention  of  the  arteries  caused  by  increasing 
internal  pressures,  which  is  a  matter  of  much  greater  importance  for  under- 
standing the  circulation,  the  results  of  investigators  differ  widely.  While 
Marey  and  others  have  found  that  the  cubic  enlargement  runs  the  same 
course  as  the  elongation  of  the  strip  cut  from  the  wall,  Eoy  asserts  that  this 
is  the  case  only  in  arteries  taken  from  animals  and  men  who  have  suffered 
from  some  wasting  disease,  and  finds  that  with  perfectly  sound  arteries  the 
increase  in  volume  with  equal  increments  of  internal  pressure  rises  at  first 
up  to  a  certain  limit  (variously  given  for  the  dog  from  32  to  120  mm.  Hg.). 
but  with  still  higher  internal  pressure  the  distensibility  falls   (Fig.  75). 

At  any  rate,  it  is  certain  that  the  cubic  enlargement  of  the  arteries  beyond 
that  given  by  a  certain  internal  pressure,  M'hich  as  a  rule  is  not  higher  than 
a  medium,  normal  blood  pressure,  becomes  less  and  less  with  equal  incre- 
ments of  pressure.  From  which  it  follows  that  when  the  arterial  blood  pressure 


Fig.   75. — The  cubic  enlargement  of  the  aorta  of  a  rabbit,  untler  a  uniformly  increasing  internal 

pressure,  after  Roy. 

is  already  high,  any  steady  increase  in  the  quantity  of  blood  discharge  from 
the  heart  will  cause  a  more  than  proportionate  rise  in  the  blood  pressure  and 
will  correspondingly  increase  the  work  of  the  heart. 

From  results  thus  far  at  hand  it  appears  that  with  any  given  increase  in 
pressure  the  arteries  are  distended  relatively  more  the  farther  they  are  situ- 
ated from  the  heart. 

In  the  body  arteries  as  well  as  veins  are  always  on  the  stretch  long:itudiiially, 
whatever  the  internal  pressure;  for  the  moment  they  are  cut  out  of  the  body  they 
at  once  retract,  becoming:  shorter  and  thicker.  It  is  always  possible  to  iind  a 
stretching:  force  which  will  give  an  exseeted  vessel  the  dimensions  it  would  have 
if  it  were  completely  fixed  in  sifu,  when  empty.  This  stretching  force  expressed 
as  pressure  in  millimeters  of  Ilg  is  looked  upon  by  R.  Fuchs  as  the  measure  of 
the  longitudinal  tension  when  there  is  no  internal  i)ressure;  it  amounts  to  from 
50  to  90  mm.  Hg.  in  the  thoracic  aorta  of  the  dog,  and  is  therefore  below  the 
mean  blood  pressure. 

The  elasticity  of  the  arteries  is  perfect — i.  e.,  if  they  be  subjected  to  a  high 
internal  pressure,  and  the  excessive  pressure  be  then  removed,  they  immediately 
return  to  the  original  volume. 

Furthermore,  the  resi,'<t(inre  of  the  arteries  to  high  pressure  is  exceedingly 
great.     The  internal  pressure  necessary  to  rupture  the  carotid  of  the  dog  is  four 


202  CIRCULATION    OF   THE   BLOOD 

to  eleven  atmospheres,  the  carotid  of  man  seven  to  eight  atmospheres  (mean). 
Since  the  maximum  normal  blood  pressure  in  the  carotid  may  be  estimated  at 
one-quarter  atmosphere,  we  see  that  arteries  can  be  ruptured  only  by  a  pres- 
sure twenty-eig-ht  to  thirty-two  times  the  normal.  The  resistance  of  the  smaller 
arteries  is  still  greater.  This  means  that  arteries  can  never  be  ruptured  by 
excessive  blood  pressure,  unless  they  have  first  been  abnormally  weakened  (Hales, 
Grehant  and  Quinquaud). 

B.    METHODS  FOR  THE  DETERMINATION  OF  BLOOD   PRESSURE 

The  mercury  manometer  is  commonly  used  in  determining  arterial  blood 
pressure,  because  it  gives  directly  the  absolute  value  of  the  pressure  without  any 
calculation.  The  elastic  manometer  also  (page  9)  finds  wide  application  where 
it  is  desired  to  follow  exactly  the  variations  of  pressure  accompanying  individual 
heart  beats. 

The  Hg-manometer  is  not  adapted  for  following  rapid  variations  of  pressure 
because  of  the  inertia  of  the  Hg  column,  which  causes  the  maxima  and  minima 
corresponding  to  systole  and  diastole  to  be  incorrectly  reproduced.  With  a 
slow  rhythm  the  maxima  are  too  high,  the  minima  too  low;  while  with  a  quicker 
rhythm  the  maxima  are  too  low,  the  minima  too  high. 

But  a  tolerably  satisfactory  value  of  the  mean  pressure  for  a  given  time  can 
be  obtained  by  means  of  the  Hg-manometer  in  the  following  way  (v.  Kries)  :  In 
the  figure  given  on  page  8  the  smaller  oscillations  on  the  curve  represent  indi- 
vidual heart  beats,  the  larger  represent  pressure  variations  caused  by  the  respira- 
tory movements ;  the  line  a  h  is  the  line  of  no  pressure,  and  the  line  T  gives  the 
time  in  seconds.  When  the  mercury  moves  up  the  free  limb  of  the  manometer, 
it  naturally  falls  just  as  much  in  the  other  limb  (Fig.  3).  If  we  neglect  the 
error  due  to  inertia  of  the  Hg.  column,  the  blood  pressure  at  any  instant  is 
therefore  twice  the  distance  of  the  curve  from  the  line  of  no  pressure.  Hence, 
in  order  to  determine  the  mean  blood  pressure — e.  g.,  during  the  period  a  to  h, 
vertical  lines  are  drawn  from  a  and  &  to  the  curve,  then  the  surface  a  h  d  c, 
is  measured  in  square  millimeters  and  is  divided  by  the  line  a  h.  The  quotient 
is  the  height  of  a  rectangle  of  the  same  surface  as  a  h  d  c,  and  with  a  base  a  h. 
This  height  doubled  is  the  mean  pressure  in  millimeters  of  mercury. 

If  the  pressure  cun'e  presents  no  very  great  variations  but  runs  along  with 
perfectly  regular  oscillations  as  in  Fig.  8  the  mean  pressure  can  be  determined 
by  simply  measuring  the  highest  and  lowest  points  during  the  period,  and  doub- 
ling the  mean  of  these  two. 

The  mode  of  connection  of  the  cannula  with  the  arterj'  must  be  borne  in 
mind  in  interpreting  the  pressure  obtained.  If  a  T-cannula  be  used,  and  the 
unpaired  limb  be  connected  with  a  manometer,  so  that  the  current  in  the  artery 
ia  not  interrupted,  the  manometer  records  the  lateral  pressure  of  the  blood  in 
this  particular  artery  at  the  place  where  the  cannula  is  inserted.  But  as  a  rule 
it  is  more  convenient  to  make  the  cannula  terminal  to  the  central  end  of  the 
artery,  so  that  the  manometer  records  the  lateral  pressure  of  the  larger  artery 
of  which  the  one  used  is  a  branch.  Thus  a  cannula  in  the  central  end  of  the 
carotid  gives  the  lateral  pressure  of  the  blood  in  the  aorta. 

Several  methods,  which  proceed  upon  the  principle  of  finding  the  pressure 
necessary  to  stop  the  blood  flow  in  the  artery  investigated,  have  been  devised  for 
determining  the  Mood  pressure  in  man. 

The  sphygmomanometer  of  v.  Basch  consists  of  a  button  or  plunger,  bound 
to  a  metal  manometer  by  means  of  a  rubber  tube.  The  button  is  placed  over 
some  superficial  artery  (preferably  one  that  is  supported  on  a  solid  substratum — 


THE   FLOW   OF   BLOOD   IX   THE   ARTERIES 


203 


e.g.,  the  radial),  and  pressure  is  applied  until  no  pulse  can  be  felt  by  the  finger 
placed  peripherally  to  the  instrument.  The  pressure  Avhich  the  manometer  now 
shows  is  the  desired  value.  This  instrument  appears  to  be  incapable  of  giving 
an  absolute  value  of  sufficient  accuracy,  although  it  has  proved  admirably  fitted 


Fig.  76. — Erlanger's  apparatus  for  determination  of  the  blood  pressure  in  man.  The  appa- 
ratus is  provided  witli  a  pneumatic  cuff,  C,  which  consists  of  an  inside  rubber  bag  and  an 
outside  leather  band.  The  whole  cuff  can  be  buckled  around  the  arm  above  the  elbow. 
The  air  cavity  within  the  rubber  bag  of  the  cuff  communicates  through  a  thick-walled 
rubber  tube  and  a  four-waj-  connection,  ==^^  with  the  three  other  essential  parts  of  the 
apparatus,  namely:  (1)  downward,  with  the  valved  bulb,  V  B,  by  means  of  which  air  can  be 
forced  into  the  cuff  and  can  thus  be  made  to  compres.s  the  arm;  (2)  to  the  left,  with  the  mer- 
cury manometer,  M,  from  which  the  amount  of  pres.sure  applied  to  the  arm  can  be  read 
directly  in  wwi  of  //</,-  and  (.3)  upward,  with  the  distensible  bag,  B,  inside  the  glass  cham- 
ber, G.  This  bag,  last  mentioned,  responds  to  fluctuations  of  pressure  inside  the  rubber  bag 
of  the  arm,  which  arc  due  to  vibrations  of  the  arterial  wall,  and  the  tambour  at  the  top 
records  such  vibrations  on  the  drum,  D. 

for  the  determination  of   variations   in   prpssure  in  the  same   person,  provided 
neither  too  little  nor  too  much  time  is  covered  by  such  variations. 

Other  authoi*s  compress  a  section  of  a  whole  limb  by  means  of  a  suitably 
constructed  pneumatic  cuff,  and  measure  the  pressure  inside  the  cuff  at  which 
the  pulse  in  some  distal  artery  disappears  or  reappears.  As  H.  v.  Reckling- 
hausen has  shown,  one  must  choose  for  this  purjiose  a  cuff  of  considerable  breadth, 
for  otherwise  a  portion  of  the  pressure  is  consumed  by  the  neighboring  soft  parts 
and  one  obtains  too  high  a  value.     The  broader  the  cuff,  the  more  is  this  disad- 


204  CIRCULATION   OF  THE   BLOOD 

vantage  obviated.  With  a  breadth  of  about  15  cm.  v.  Recklinghausen  observed 
in  eight  trials  a  variation  of  only  3  mm.  Hg.  in  the  blood  pressure  determined 
in  the  brachial  and  the  femoral  arteries  at  the  same  time.  (In  animal  experi- 
ments the  pressure  in  these  two  is  in  general  found  to  be  the  same.)  Such  a 
method  therefore  gives  very  satisfactory  results,  as  it  is  also  much  more  easily 
manipulated  than  other  methods  thus  far  devised  for  this  purpose. 

[With  Erlanger's  apparatus  (Fig.  76)  it  is  possible  also  to  determine  the 
maximum  systolic  and  minimum  diastolic  pressures.  To  determine  the  former  ' 
the  arm  is  compressed  until  no  pulse  can  be  felt  in  the  radial  artery.  Even  at 
this  time  the  tambour  of  the  instrument  shows  vibrations  due  to  pulsations  in 
the  central  stump  of  the  artery;  but  if  the  air  pressure  on  the  arm  be  now 
lowered  gradually  by  means  of  an  escape  valve  (V  in  the  Figure)  these  vibrations 
will  suddenly  become  larger.  The  pressure  which  the  manometer  shows  when 
this  takes  place  is  the  pressure  which  the  pulse  wave  can  just  overcome  and  is, 
therefore,  the  maximum,  systolic  pressure.  If  the  pressure  be  lowered  still  further 
the  vibrations  shown  by  the  lever  of  the  tambour  will  become  still  larger  until 
a  point  is  reached  at  which  they  begin  to  decrease.  The  pressure  at  which  the 
arterial  wall  makes  the  widest  fluctuations,  and  the  lever  therefore  its  largest 
vibrations,   is   the  minimum   diastolic   pressure. — El).] 

C.    HEIGHT   OF  THE   BLOOD   PRESSURE 

Since  the  norma]  blood  pressure  in  the  aortae  of  different  mammals  shows 
but  relatively  slight  differences,  we  can  form  an  approximate  picture  of  the 
blood  pressure  in  man  from  the  numerous  determinations  made  directly  upon 
different  species  of  animals.  The  normal  pressure  in  the  dog  is  130-180 
mm.  Hg.,  in  the  rabbit  80-120,  in  the  horse  150-200.  We  may  say,  there- 
fore, that  the  7nean  normal  blood  pressure  in  man  varies  between  100  and  200 
mm.  Hg.,  and  if  we  Avish  to  use  a  single  figure  we  may  assume  that  150 
mm.  is  the  most  probable  value. 

We  are  not,  however,  to  regard  the  blood  pressiire  as  constant ;  on  the 
contrar}'  very  considerable  variations  make  their  appearance  on  slight  provo- 
cation. We  have,  therefore,  to  study  the  factors  upon  which  the  blood  pressure 
depends. 

These  are  essentially  three :  the  energy  of  the  heart,  the  resistance  in  the 
arteries,  and  the  total  volume  of  the  blood. 

1.  The  Energy  of  the  Heart. — The  quantity  of  blood  which  the  heart 
expels  in  a  given  time  may  be  taken  as  a  measure  of  its  energy.  If,  other 
things  being  equal,  the  quantity  expelled  in  a  given  time  decreases,  the  blood 
pressure  falls  as  is  the  case  for  example  upon  stimulation  of  the  vagus  (Figs. 
7T-79.  If,  on  the  other  hand,  the  decrease  in  pulse  rate  is  only  slight,  and 
is  compensated  by  a  larger  pulse  volume  (cf.  page  189),  the  mean  blood 
pressure  falls  only  a  little  or  not  at  all  (Fig.  77). 

The  quantity  of  blood  expelled  from  the  heart  may  decrease  also  without 
a  fall  in  the  frequency  of  heart  beats  (cf.  page  188),  in  which  case  of  course 
the  blood  pressure  falls. 

On  the  other  hand  the  energy  of  the  heart  may  increase  without  any 
change  in  frequency  of  the  pulse  (cf.  page  192),  and  a  rise  in  pressure  results. 

When  the  heart  is  accelerated  by  division  of  both  vagi,  or  by  stimulation 
of  the  accelerator  nerves,  it  may  or  may  not  expel  more  blood  in  a  given 


THE   FLOW   OF   BLOOD   IN  THE   ARTERIES 


205 


time.  If  it  does,  the  blood  pressure  increases  (supposing  that  the  caliber  of 
the  vessels  has  not  changed)  ;  if  not,  the  pressure  remains  the  same.  For 
a  quicker  rate  does  not  necessarily  imply  greater  energy  of  the  heart  beat, 
and  so  does  not  of  necessity  produce  a  greater  output.  Now  it  is  evident  that 
unless  the  total  output  in  a  unit  time  is  increased,  the  quantity  of  blood 
coming  back  to  the  heart  between  two  systoles  is  less  with  a  rapid  pulse  than 
with  a  slow  one,  or,  in  other  words,  the  pulse  volume  is  less.  Hence,  the 
blood  pressure  following  acceleration  will  depend  upon  the  reciprocal  relation 
between  the  increase  of  pulse  rate  and  the  decrease  of  pulse  volume. 

Direct  investigations  of  this   subject  have  resulted  in   showing  that   no 
general  law  can  be  formulated.     If  a  large  quantity  of  blood  is  found  in  the 


Fig.  77. — Blood  pressure  curve,  showing  a  slight  fall  under  feeble  stimulation  of  the  vagus. 
To  be  read  from  right  to  left.  The  time  of  stimulation  is  indicated  by  the  two  vertical 
lines.   I  1    =   ten  seconds. 

great  veins,  and  is  only  waiting  an  opportunity  to  get  into  the  heart,  and  if 
the  resistance  in  the  arterial  system  is  sufficiently  high,  acceleration  may 
produce  a  considerable  increase  in  blood  pressure.  If  these  conditions  are 
not  fulfilled,  the  increased  frequency  will  occasion  no  rise  in  pressure  worth 
mentioning. 

2.  Resistance  in  the  Arteries. — It  is  evident  that  with  a  given  heart  energy, 
if  the  resistance  in  the  vessels  decreases,  the  pressure  also  must  decrease.  If 
the  resistance  increases  the  pressure  also  must  increase. 

A  fall  in  pressure  in  consequence  of  diminished  resistance  occurs,  if  the 
vessels  in  a  large  vascular  region  lose  their  tonus.  Not  only  the  arteries,  but 
the  veins  as  well  are  to  be  considered  as  taking  a  part  in  this;  for  the  lat- 
ter possess  a  certain  tonus  with  the  disappearance  of  which  they  are  consid- 
erably dilated  and  so  can  contain  more  blood  than  usual.     Hence  the  blood 


206 


CIRCULATION   OF  THE   BLOOD 


stagnates  in  the  veins,  and  its  How  to  the  heart  is  lessened  considerabl}''.  The 
fall  in  blood  pressure,  therefore,  is  occasioned  not  only  by  the  diminished 
resistance  but  also  by  the  deficient  flow  to  the  heart. 

The  7rsistance  in  the  vessels  is  increased  either  l)y  constriction  in  a  large 
vascular  area,  or  Ijy  compression  of  a  large  arterial  stem,  for  example  the 


Fig.  78. — Blood  pressure  curve,  showang  a  pronounced  fall  due  to  slowing  of  the  heart,  as  the 
result  of  vagus  stimulation  of  medium  intensity.  To  be  read  from  right  to  left.  The 
time  of  stimulation  is  indicated  by  the  two  vertical  lines.  |  | 


ten  seconds. 


abdominal  aorta.  In  the  first  case  the  blood  flow  to  the  heart  is  at  the  same 
time  augmented,  since  the  blood  contained  in  the  vessels  is  driven  forward 
by  their  contraction.  It  is  possible  therefore  that  a  larger  quantity  of  blood 
will  he  expelled  hy  the  heart  imder  these  circumstances. 

It  might  bo  su]iposed  that  by  compression  of  the  vessels  the  pressure  could 
be  forced  up  indefinitely.  But  this  is  not  the  case.  The  reflex  mediated  by 
the  depressor  nerve  comes  into  play,  so  that  either  the  vessels  are  dilated  or 
the  heart  beats  are  retarded.  But  even  if  this  reflex  fails,  there  is  an  upper 
limit  to  the  blood  pressure  l)eyond  which  it  cannot  pass.  The  artivitj/  of  the 
tieart  is  not  unlimited,  and  we  have  good  reason,  liased  on  many  ol)servations. 
for  asserting  that  with  a  high  resistance  in  the  vessels  the  quantity  of  blood 
expelled  in  a  given  time  actually  diminishes. 

3.  Quantity  of  Blood. — Investigations  on  the  influence  of  the  blood  volume 
go  to  show  that  when  the  vessels  are  overfilled  the  blood  pressure  does  not 
exceed  the  normal  physiological  limits,  and  that  when  the  vessels  contain  less 
than  the  normal  quantity  mechanisms  are  at  hand  for  the  purpose  of  main- 
taining the  blood  pressure  at  its  normal  height. 

In  what  follows  we  shall  consider  first  the  results  of  adding  to  the  normal 
quantity  of  fluid  in  the  vessels.    Let  us  suppose  that  blood  or  some  other  harm- 


THE  FLOW  OF  BLOOD  IN  THE  ARTERIES 


207 


less  fluid  is  transfused  into  the  veins  of  an  animal.  The  transfused  fluid  does 
not  all  go  to  the  heart  at  once;  a  considerable  part  of  it  remains  in  the  central 
veins,  which  thus  become  overfilled;  and  in  the  liver,  which  after  the  transfusion 
of  a  large  quantity  may  become  almost  as  hard  as  a  board. 

Furthermore,  the  entire  quantity  of  transfused  fluid  does  not  remain  in  the 
vascular  system,  for  the  vessels  relieve  themselves  by  transudation.  The  nature 
of  the  fluid  has  much  to  do  with  the  amount  transuded.  By  means  of  blood 
counts  it  has  been  found,  for  example,  that  after  transfusion  of  blood,  about 
half  the  quantity  transfused  remains  in  the  vessels  at  the  end  of  the  first  day; 
while  if  distilled  water  is  used  in  transfusion  the  blood  quickly  recovers  its 
normal  constitution  (Worm-Miiller,  Regeczy). 

Along  with  transudation  the  secretory  activity  of  the  glands  increases  and 
this  cooperates  to  diminish  the  quantity  of  fluid  in  the  vessels.  Particularly  is 
this  true  of  the  mucous  membrane  of  the  intestine  and  of  the  kidneys.  If  a 
NaCl  solution  bo  transfused  not  too  rapidly  into  a  vein,  after  some  time  trans- 
fusion and  secretion  of  urine  exactly  balance  each  other  (Dastre  and  Loye). 

Thus  by  transudation  and  secretion  the  quantity  of  fluid  is  gradually  brought 
back  to  the  normal.  But  this  takes  place  as  a  rule  rather  slowly,  and  other  fac- 
tors meantime  must  step  in  to  regulate  the  blood  pressure.  One  such  factor  is 
vasodilation,  by  means  of  which  the  resistance  in  the  vessels  is  lowered  (Worm- 
Miiller).     Another  is  the  activity  of  the  heart.     If  transfusion  be   performed 


Fig.  79. — Blood  pressure  curve,  showing  a  sudden  fall  due  to  stoppage  of  the  heart,  as  the 
result  of  strong  stimulation  of  the  vagus.  The  time  of  stimulation  indicated  by  the  two 
vertical  lines.  |  |    =  ten  seconds. 


slowly  enough,  the  heart  is  al)le  to  throw  a  correspondingly  larger  quantity  of 
blood  into  the  vessels  and  so  to  preserve  the  cardiac  pressure  within  safe  limits. 
But  if  the  transfusion  take  place  more  rapidly,  or  if  the  total  quantity  trans- 
fused be  very  large,  the  heart  may  drive  more  blood  into  the  vessels  than  before 
the  transfusion  but  not  enough  to  prevent  stasis  of  blood  in  the  heart.    Finally, 


208  CIRCULATION   OF  THE   BLOOD 

the  quantity  transfused  becomes  so  great  that  sooner  or  later  the  demands  upon 
the  heart  are  excessive,  and  the  arterial  blood  pressure  falls  in  spite  of  the 
abnormally  large  quantity  of  fluid  in  the  vessels.  One  sometimes  meets  with 
cases  where  the  heart  works  powerfully  enough  during  the  transfusion  to  over- 
come the  increased  quantity  of  blood,  but  later  in  the  course  of  the  experiment, 
after  transfusion  has  ceased,  symptoms  of  acute  fatigue  suddenly  appear.  In 
such  cases  the  heart  may  be  relieved  and  death  averted  by  withdrawing  a  suifi- 
eient  quantity  of  blood  from  the  vessels. 

We  have  in  the  circumstances  mentioned  above  the  explanation  of  heart 
weakness  which  sometimes  follows  ingestion  of  very  large  quantities  of  tluid  by 
way  of  the  stomach. 

The  reverse  processes  take  place  in  bloodletting.  The  heart  empties  itself  as 
completely  as  possible  and  drives  the  greatest  possible  quantity  of  blood  into 
the  vessels;  the  vessels  contract  and  thereby  present  a  high  resistance  to  the 
blood  stream;  the  kidneys,  salivary  glands  and  probably  all  the  other  glands 
diminish  their  secretions,  and  there  occurs  an  increased  passage  of  fluid  from 
the  lymph  to  the  blood  vessels. 

By  the  cooperation  of  these  factors  the  blood  pressure  under  normal  cir- 
cumstances varies  in  general  within  rather  narroiv  limits,  notwithstanding 
the  many  influences  which  tend  to  change  it  in  both  directions.  And  yet, 
in  order  to  produce  significant  variations  in  the  pressure  artificially  it  is 
often  necessary  to  use  only  very  weak  stimulation.  In  fact,  the  stimulus 
may  be  so  slight  that  at  times  one  is  wholly  at  a  loss  to  make  out  the  cause 
of  the  sudden  increase  or  decrease  in  pressure  which  results.  More  on  this 
subject  will  be  found  under  the  discussion  of  vasomotor  nerves. 

By  means  of  an  instrument  constructed  on  the  principle  of  the  Basch 
Sphygmomanometer  and  applied  to  the  radial  artery  of  man,  the  blood  pressure 
in  the  sitting  or  reclining  position  was  found  by  Hill  and  Barnard  to  be  100- 
108  mm.  Hg.  It  rose  to  120,  130  or  140  mm.  under  various  influences  such  as 
bodily  movements,  but  sank  again  very  rapidly  toward  the  value  for  rest  when 
the  movements  ceased.  The  blood  pressure  is  raised  also  by  a  cold  bath,  but  is 
depressed  by  a  warm  one  (Edgecombe  and  Bain). 

Blood  pressure  in  the  large  arteries  is  not  much  higher  than  in  those  of 
smaller  caliber,  and  decreases  only  slightly  therefore  with  the  distance  from 
the  heart.  Especially  is  this  true  of  diastolic  pressure,  whereas  differences 
of  systolic  ^  pressure  are  greater.  The  cause  of  this  slow  fall  in  pressure  in 
the  arterial  system  is  purely  hydrodynamic  in  nature.  The  resistance  against 
which  the  blood  pushes  in  the  larger  arteries  is  small  in  comparison  with 
that  to  which  it  is  subjected  in  the  smallest.     The  consequence  is  that  the 

['  From  numerous  comparative  observations  made  on  dogs,  Dawson  concludes  that  "  in 
considering  variations  in  the  systolic  pressure,  it  is  absolutely  essential  to  distinguish 
between  end  pressures  obtained  from  the  branches  of  the  main  arterial  trunk  and  those 
obtained  from  the  main  trunk  itself.  In  the  former  case  the  systolic  pressure  shows  a 
steady  and  considerable  falling  ofT  which  becomes  apparent  in  end  pressures  taken,  for 
example,  in  the  thyroid  arteries,  in  branches  arising  from  the  axillary  and  in  branches 
from  the  lower  part  of  the  aortico-femoral  tnmk.  When,  however,  the  systolic  end 
pressure  is  taken  in  the  main  arterial  tnmk,  it  is  found  that  this  pressure  either  remains 
high  (axillan,^  and  brachial)  or  may  even  greatly  exceed  the  corresponding  lateral  pressures 
in  the  aorta  (iliac  and  femoral)." — Ed.] 


THE   FLOW   OF   BLOOD   L\  THE   ARTERIES 


209 


driving  power  is  not  consumed  rapidly  until  the  smallest  arteries  are  reached, 
and  hence  the  fall  in  pressure  in  the  large  and  medium  sized  arteries  is  only 
relatively  small  (cf.  page  222). 

D.    VELOCITY   OF  THE   BLOOD    IN   THE   ARTERIES 

There  are  two  ways  of  determining  the  velocity  of  the  blood  in  the  arteries, 
according  as  one  wishes  to  obtain  the  mean  velocity  in  unit  time,  or  the  varia- 
tions in  speed  which  take  place  during  a  single  heart  beat. 

The  velocity  can  only  be  determined  by  placing  the  necessary  apparatus 
directly  in  the  path  of  the  blood  without  interrupting  its  flow.     Several  forms 


JL 


'^ 


p' 


Fig.  80. 


Fig.  81. 


Fig.  80. — Ludwig's  Stromuhr  or  "current  clock." 

Fig.  81. — Chauveau's  hsemadromograph  with  air  traiLsmission.  n,  the  needle;  pi,  small  plate 
on  the  pendulum;  k,  a  tambour  influenced  by  the  strokes  of  the  pendulum.  The  blood 
flows  in  the  direction  of  the  arrow,  wi,  a  hard-rubber  membrane  which  serves  as  a  lid  for 
the  vertical  tube  and  as  a  fulcrum  for  the  pendulum. 


of  apparatus  have  been  constructed  for  this  purpose,  the  best  known  of  which 
is  Ludwig's  Strumuhr  or  "current  clock"  (Fig.  80).  It  consists  of  two  glass 
bulbs  of  equal  size  (A,  B)  which  communicate  directly  with  each  other  by  means 
of  the  U-shaped  tube  above.  By  means  of  the  opening  at  the  top  oil  is  placed 
in  one  bulb,  A,  and  salt  solution  in  the  other,  B,  and  the  opening  is  then  closed. 
The  two  fluids  are  in  contact  with  each  other  above.  The  tube  A  is  now  con- 
nected with  the  central  end  and  the  tube  B  with  the  peripheral  end  of  an  artery. 
When  the  arteries  are  undamped  the  blood  flows  into  A  and  drives  the  contained 
oil  over  into  B,  the  salt  solution  meantime  being  forced  into  the  peripheral  end 
of  the  artery.  When  the  blood  has  completely  filled  the  bulb  A,  the  two  bulbs 
are  reversed,  so  that  the  blood  flows  now  into  B,  disjilaeing  the  oil  once  more 
and  driving  the  blood  from  A  into  the  peripheral  end  of  the  artery.  The  capacity 
of  the  bulbs  being  known,  by  counting  the  number  of  reversals  necessary  one 


210 


CIRCULATION   OF  THE   BLOOD 


can  calculate  the  volume  of  blood  whit'h  flows  through  the  artery  in  a  certain 
time.     Refristering  current  clocks  have  been  devised  by  Ludwig  and  Iliirthle. 

In  order  to  determine  the  variations  of  speed  accompanying  a  single  heart 
beat,  Vierordt  employed  a  hydrometric  pendulum.  If  a  pendulum  be  hung  in 
a  current  of  fluid,  the  length  of  its  swing  will  depend  on  the  linear  velocity  of 
the  current,  and  on  a  small  scale  it  will  reproduce  correctly  all  the  variations 
of  speed.  Chauveau  connected  this  pendulum  with  a  writing  tambour  and  by 
this  means  registered  directly  the  variations  in  speed,  and  after  graduating  the 
instrument,  determined  their  absolute  values  (Fig.  81). 

The  following  results  may  be  mentioned.  The  amount  of  hlood  expelled 
per  second  by  the  left  heart  of  a  rabbit  (of  1.59  kg.  body  weight)  into  the 
aorta  is  on  the  average  1.35  c.c.  The  extremes  in  a  series  of  fourteen  experi- 
ments were  0.91  and  3. 76  c.c..  the  mean  was  2.10  c.c.    The  mean  linear  velocitv. 


Fig.  82. — Velocity  curve  T'  and  pressure  curve  P,  carotid  of  the  horse,  after  I.ortet.  The 
lines  1,  2,  3,  4  give  the  corresponding  points  on  the  two  curves.  At  1  the  blood  is  forced 
into  the  aorta;  between  3  and  4  the  semilunar  valves  are  closed. 

calculated  from  the  diameter  of  the  cannula  tied  into  the  aorta  was  128  mm. 
per  second   (extremes  72  and  340  mm.). 

During  systole  it  is  evident  that  the  velocity  is  greater  than  during  diastole 
(ef.  Fig.  82).  In  the  carotid  of  the  horse  Lortet  found  520  mm.  per  second 
in  systole  and  150  mm.  per  second  in  diastole.  At  the  end  of  diastole  the 
velocity  in  the  peripheral  arteries  is  greater  than  in  the  central ;  while  at  the 
beginning  of  systole  it  increases  considerably  in  the  central  and  only  slightly 
in  the  peripheral. 

In  dogs  with  a  mean  Ijody  weight  of  about  14  kg.  Tschuewslcy  found  for 
the  velocity  in  the  carotid  and  crural  arteries  the  values  smnmarized  in  the 
following  table: 


Body  wt. 

Arterj'. 

Vol.  per 
second. 

Lin.  Veloc. 
per  second. 

Diani.  of 
artery. 

Blood 
pressure. 

Remarks. 

13.7  kg. 
14.6  " 
14.1   " 

Crural. 

Crural. 

Carotid. 

0.63  c  c. 
1.69     " 
1.95     " 

128  mm. 
275     •' 
241     " 

2.5  mm. 
2.8     " 
3.3     " 

77  mm.Hg. 
88     "      " 
93     "      " 

Nerves  uniiij. 

Nerves  cut. 

Nerves  uninj. 

THE   FLOW   OF   BLOOD   L\   THE   ARTERIES 


211 


Thus  the  velocity  is  seen  to  increase  considerably  after  section  of  the  nerves 
controlling  the  arteries,  and  to  be  considerably  greater  in  the  carotid  than 
in  the  crural.  One  cannot  therefore  draw  conclusions  as  to  the  velocity  in  one 
artery  from  determinations  made  for  another. 

WHien  one  carotid  is  ligated  the  velocity  in  the  other  increases  materially, 
as  for  example  in  two  dogs  of  13.7  kg.  mean  body  weight,  on  the  average 
from  2.63  c.c.  and  266  mm.  per  second  to  3.47  c.c.  and  350  mm.  per  second. 

Likewise  the  velocity  increases  considerably  after  a  temporary  compression 
of  the  artery,  as  for  example  in  the  crural  (dog  13.2  kg.)  from  0.783  c.c.  and 


Fig.  8.3. — Plethysmograph,  after  Fick.     ae,  the  cylinder;  m,  rubber  cuff  by  which  the  cyUnder 
is  made  to  fit  air-tight  over  the  arm;  r  s,  recording  monometer. 


149  mm.  per  second  before  compression  to  1.252  c.c.  and  255  mm.  after.  The 
pressure  in  both  cases  was  89  mm.  Hg. 

On  account  of  the  dilatation  taking  place  in  the  arterioles  of  an  organ 
during  its  activity,  the  velocity  is  increased  considerably  in  the  arteries  su]i- 
plying  it.  Thus  Chauveau  ob.>*erved  that  the  velocity  in  the  carotid  during 
mastication  ro.se  to  five  or  six  times  its  u.sual  height. 

Finally,  when  the  vessels  are  dilated  as  a  result  of  section  of  the  s|)inal 
cord,  the  velocity  increases  during  systole.  l)ut  is  extremely  small  during 
diastole. 


212 


CIRCULATION   OF  THE  BLOOD 


In  man  the  variations  of  velocity  in  the  peripheral  arteries  can  be  esti- 
mated, but  no  absolute  value  can  be  obtained. 

To  understand  the  principle  of  the  method  employed,  we  must  bear  firmly 
in  mind  that  the  blood  in  the  peripheral  veins  flows  continuously,  exhibiting  as 
a  rule  no  variation  due  to  the  heart  beats  or  to  the  respiratory  movements. 

If  a  part  of  the  body — for  example,  an  arm — be  placed  in  an  air-tight  cylin- 
der the  cavity  of  which  is  connected  with  a  suitable  recording  device,  a  Marey 
tambour  or  manometer  (plethysmograph,  Fig.  83),  a  curve  is  traced  in  which 
the  separate  heart  beats  appear  clearly  marked.  The  variations  thus  recorded 
are  caused  by  the  variations  in  the  volume  of  the  arm,  and  the  so-called  plethys- 
mographic  curve  (Fig.  84)  is  therefore  a  volumetric  curve. 

Since  the  return  flow  in  the  veins  is  constant,  the  variations  are  produced 
by  fluctuations  in  the  arterial  flow.    When  the  curve  rises  the  arterial  inflow  is 


/ 

■-- 

/ 

V. 

^ 

^. 

f 

^ 

V 

/ 

'^- 

^ 

.^^    y 

Fig.  84.- 


-Plethysmographic  curve  (the  upper  black  line).     Pulse  curve  (the  lower  black  Une), 
and  velocity  curve  (red)  in  man,  after  Fick.     To  be  read  from  left  to  right. 


greater  than  the  venous  outflow ;  when  it  sinks,  the  inflow  is  less  than  the  out- 
flow, and  when  the  curve  runs  horizontally  inflow  and  outflow  balance  each  other. 

It  is  clear  however  that  the  volume  changes  of  the  arm  will  follow  more 
quickly  the  more  rapid  is  the  flow  of  blood  to  the  arm.  Thus  if  we  estimate 
the  steepness  of  the  changes  in  different  sections  of  the  curve,  we  can  construct 
a  velocity  curve  from  the  volume  curve  (Fick).  In  Fig.  84  the  red  line 
represents  the  velocity  curve  derived  from  the  volume  curve  (the  upper  line). 
Its  similarity  to  the  curve  recorded  by  means  of  the  hydrometrie  pendulum, 
and  pictured  in  Fig.  82.  is  immistakable.  In  both  we  have,  after  a  sharp 
rise,  a  fall,  upon  which  follows  an  increase  in  velocity  again.  The  latter 
coincides  in  time  with  the  so-called  dicrotic  wave  of  the  pulse  curve  (cf. 
below). 

§  4.    THE   ARTERIAL   PULSE 

A.    THE   MOVEMENT   OF  WAVES   IN   ELASTIC  TUBES 

Imagine  an  elastic  tube,  filled  and  distended  with  water,  to  be  divided  by 
fixed  lines  into  the  segments  a,  h,  c,  d,  e,  f,  g,  h,  i  (Fig.  85).     The  piston,  we 


THE   ARTERIAL  PULSE 


213 


b,. 

c,.^ 

r 

e 

f 

^ 

V 

^y\ 

— -^ 

---.* 

— »■ 

..-■^ 

k 

-* 

:::: 

— 

:::: 

— — 

u 

^^ 

wmmrj^. 

\  — 

— 

:^ 

-^ 

m 

— 

X 

^ 

^ 

"* — 

■~  • 

'^ 

Fig.    85. — Schema   illustrating    E.    H.  Weber's 
theory  of  the  pulse. 


will  suppose,  has  driven  the  water  from  the  rigid  tube  (^-)  into  the  distensible 
tube  {ax),  with  a  velocity  at  first  increasing  and  then  diminishing,  and  has  thus 
dilated  the  tube,  while  the  water  contained  in  the  different  segments  has  been 
given  a  velocity  indicated  bj'  the  number  of  dotted  arrows  in  each.  If  then  the 
ring-shaped  sections  of  the  wall  inclosing  the  segments  exert  a  pressure  upon 
the  contained  liquid,  the  amount  of  which  is  represented  by  the  solid-line  arrows, 
it  is  evident  that  the  particles  of 
water  contained  in  the  segments 
e,  f,  g,  h,  will  be  accelerated  in  the 
direction  i  (since  they  were  already 
moving  in  this  direction).  On  the 
other  hand  the  particles  contained  in 
the  segments  d,  c,  h,  a  will  be  re- 
tarded in  their  movement,  since  the 
pressure  indicated  by  the  solid  ar- 
rows is  exerted  in  the  direction  of  k. 
For  this  reason  the  liquid  in  a  comes 

to  rest  within  the  next  few  moments,  and  the  distended  wall  of  this  segment 
returns  to  its  original  diameter.  During  the  same  time,  the  water  in  segment  i, 
which  until  now  had  not  been  moved,  is  pushed  forward  and  its  wall  is  distended. 
Thus  the  wave  is  propagated  from  one  segment  to  another  in  the  direction  of 
the  dotted  arrows  (E.  H.  Weber).  The  water  presses  upon  the  wall  of  the  tube, 
the  wall  in  turn  presses  upon  the  water,  and  the  wave  spreads  with  a  velocity  (F), 
which  is  inversely  proportional  to  the  square  root  of  the  specific  gravity  (A) 
of  the  liquid,  and  of  the  internal  diameter  of  the  tube  (d)  ;  directly  proportional 
to  the  square  root  of  the  wall's  thickness  (a)  and  of  its  elastic  coefficient   (e) 

(Moens).    The  law  is  expressed  by  the  following  formula  V  ^h  \/-—rr  in  which 

A;  is  a  constant  and  g  is  the  acceleration  of  gravitation. 

The  wave  is  changed  in  form  more  or  less  in  its  propagation  through  the 
tube  by  the  resistance  due  to  friction.  Its  height  is  less  and  its  length  greater 
than  if  there  were  no  friction. 

The  moment  an  elastic  tube,  already  filled  with  an  incompressible  liquid, 
receives  an  extra  quantity,  a  wave  of  increased  pressure  is  started,  and  is  propa- 
gated along  the  tube.  If  the  flow  be  maintained  for  a  time,  the  pressure  keeps 
a  certain  level  for  each  point  along  the  tube,  the  value  of  which  is  determined 
by  the  same  laws  that  apply  to  the  flow  of  a  liquid  in  rigid  tubes  (cf.  page  198). 

If  one  end  of  an  elastic  tube  filled  and  distended  with  water  be  suddenly 
relaxed  by  removal  of  a  quantity  of  water,  a  fall  in  pressure  is  propagated  in 
the  form  of  a  negative  wave  to  the  other  end  of  the  tube.  Likewise  if  a  regular 
current  flowing  through  an  open  elastic  tube  be  suddenly  checked,  a  negative 
wave  is  set  up  which  travels  in  the  direction  of  the  current. 

Besides,  if  the  tube  be  not  so  long  that  waves  thus  set  up  entirely  disap- 
pear, as  the  result  of  friction,  new  ones  will  arise  by  reflection  from  the  end  of 
the  tube,  whioh  will  materially  affect  the  wave  movements.  If  the  end  of  the 
tube  where  the  reflection  occurs  be  closed,  the  wave  will  be  reflected  with  the 
same  sign,  a  positive  wave  as  a  new  positive  wave,  a  negative  wave  as  a  new 
negative  one.  If  the  end  of  the  tube  be  open,  the  wave  will  be  reflected  with 
its  sign  reversed,  a  negative  as  a  positive  and  a  positive  as  a  negative.  The 
same  wave  may  by  repeated  reflection  run  the  length  of  the  tube  several  times. 
If  the  end  of  the  tube  be  only  partially  closed,  every  primary  positive  wave  will 
be  transformed  into  a  reflected  one  which  is  partly  positive  and  partly  negative. 
15 


214 


CIRCULATION    OF  THK    BLOOD 


Since  both  these  reflected  waves  travel  throufih  the  tube  with  the  same  velocity 
and  naturally  interfere  with  each  other,  it  depends  on  the  degree  of  constriction 
whether  the  algebraic  sum  of  the  two  Avill  be  a  positive  or  a  negative  wave,  or 
will  be  nil  (Grashey). 

If  from  a  simi)le  tube  A,  a  side  branch  B  be  given  off,  every  wave  which 
runs  through  A  will  traverse  also  the  branch  /?;  and,  it  matters  not  whether  the 
wave  arises  in  the  wide  or  in  the  narrow  tube,  it  will  traverse  both.  This  state- 
ment holds  also  for  a  complex  system  of  tubes,  and  we  may  say  in  general  that 
when  a  wave  starts  from  any  point  of  a  branching  system  of  vessels,  it  is 
propagated  to  all  the  branches. 

Reflection  takes  place  in  such  a  system  at  every  dividing  place.  But  if  the 
velocity  with  which  the  waves  are  propagated  changes  at  any  point  in  the  same 
proportion  as  the  cross  section  changes,  no  reflection  occurs  (v.  Kries). 

All  the  conditions  for  the  origin  of  primary  and  reflected  waves  and  of  inter- 
ference are  found  in  the  arterial  system.  The  difficulty  consists  only  in  isolating 
from  among  the  theoretically  possible  movements,  those  which  cause  the  peculi- 
arities of  the  arterial  pulse. 


B.    THE   PULSE 

The  ancient  physicians  distinguished  in  the  pulse  a  number  of  different 
qualities,  which  can  be  reduced  to  four:  frequency,  size,  velocitij  and  hardness. 

With  respect  to  frequency,  the  rapidly  repeated  pulse  (pulsus  frequens)  is 
to  be  distinguished  from  the  less  frequent  (rarus).  With  respect  to  size  we 
have  the  large  (magnus)  in  which  the  expansion  of  the  artery  under  the  finger 
is  large,  and  the  small  pulse  (parvus)  in  which  the  expansion  is  small.  With 
respect  to  velucity  the  quick  pulse  (celer)   in  which  the  artery  presses  against 

the  finger  suddenly  and  disappears  sud- 
denly, can  be  distinguished  from  the 
sluggish  pulse  (tardus)  in  which  the  im- 
pact is  more  prolonged.  And  with  re- 
spect to  hardness,  the  pulse  (durus) 
which  can  be  compressed  with  difficulty, 
can  be  distinguished  from  the  one  (mol- 
lis) which  can  be  easily  obliterated  by 
pressure.  On  the  basis  of  these  four 
fundamental  qualities  a  series  of  other 
qualities  can  be  named,  but  we  shall 
not  discuss  them  further. 

Fig.  86.— The  spring  of  Marey's  sphygmo-  Knowledge  of  the  pul.se  ha.s  made 

graph.  rapid  progress  since  E.  H.  Weber  gave 

it  a  mechanical  explanation  (1850) 
and  Vierordt  showed  that  it  could  be  graphically  recorded  (IS.').")).  The  first 
pulse  recorder  (sphygmograplt)  to  give  correct  pulse  curves  was  constructed 
somewhat  later  (18GU)  by  Marey. 

The  most  important  part  of  the  sphygmograph  (Fig.  86)  is  the  steel  spring 
(p)  with  a  contact  surface  to  be  placed  over  the  artery.  This  spring  responds 
to  the  movements  of  the  artery  and  transmits  the  movements  to  the  writing 
lever,  which  magnifies  and  records  them  on  a  writing  surface  driven  by  a  small 
clockwork.  The  movements  of  the  spring  are  transmitted  to  the  lever  by  means 
of  the  screw  s,  jointed  to  the  contact  surface,  and  the  tension  of  the  spring  can 


THE   AIITERL\L   PULSE 


215 


be  regulated  by  means  of  another  screw.  The  whole  apparatus  is  fastened  by 
means  of  a  band  to  the  lower  end  of  the  forearm  (Fig.  ST).  Many  modifications 
of  this  insti-ument  are  in  use. 

The  method  of  air  transmission  is  often  used  also,  especially  when  it  is 
desired  to  register  the  pulse  eui-ves  of  two  or  more  arteries,  or  the  pulse  curve 
and  cardiogram,  at  the  same  time.    A  receiving  tambour  of  about  the  same  con- 


FiG.  87. — Marey's  sphygmograph  as  used. 

struction  as  that  described  for  the  apex  beat  is  fastened  over  the  arteiy  and  is 
connected  in  the  usual  way  with  the  recording  tambour  (cf.  Fig.  10,  page  12). 

The  sphygmograph  has  ofien  been  tested  and  it  has  been  found  to  give  the 
pulse  movements  with  surprising  accuracy.  It  has  been  shown,  for  example, 
that  it  reproduces  very  exactly  the  waves,  already  known,  by  other  means,  to 
occur  in  an  elastic  tube  (Mach) ;  that  the  pulse  curve  has  exactly  the  same 
appearance  when  the  pulsations  are  recorded  without  magnification  and  where 
the  inertia  of  the  lever  is  thus  reduced  to  a  minimum  (Marey)  ;  and  that  pulse 
curves  having  exactly  the  same  form  as  those  recorded  by  the  sphygmograph,  are 
obtained  if  a  very  small  mirror  is  fastened  to  the  skin  over  an  artery,  so  that 
the  light  may  be  reflected  on  a  wall. 

But  we  must  not  suppose  that  every  sphygmograph  records  pulse  waves  so 
perfectly.  It  often  happens  on  the  contrary  that  the  instrument  distorts  the 
curve  considerably.  It  is,  therefore,  necessary-  in  every  exact  study  of  the  pulse 
by  the  graphic  method  to  assure  oneself  of  the  efficiency  of  the  instrument  and 
of  the  maximal  speed  permissible  for  the  lever. 

The  velocity  of  the  pulse  wave  is  measured  by  taking  at  the  same  time 
pulse  tracings  from  two  arteries  separated  by  some  distance  from  each  other. 
The  velocity  of  propagation  found  in  this  way  varies  with  different  individuals, 
and  with  the  same  individual  under  different  circum.>^tances.  In  a  healthy 
man  it  amounts  to  T-10  m.  per  second.  The  velocity  is  greater,  the  greater 
the  coefficient  of  elasticity.  It  increases  therefore  with  a  rise  of  blood  pressure, 
for,  as  we  have  seen  at  page  "^Ol,  the  coefficient  of  elasticity  of  tlie  arterial 
wall  increases,  at  least  within  certain  limits,  as  the  internal  pressure  increases. 

The  length  of  the  pulse  wave  X  is  obtained  from  the  formula  nX=  h; 

or  A  =  — ,  where  7i  is  the  velocity  of  transmission  and  n  the  rhvthm.     Since 

with  each  ventricular  systole  the  blood  is  driven  into  the  aorta  for  0.2  of  a 
second,  the  rhythm  number  is  5.     With  a  velocity  of  8  m.  the  length  would 


be  X  = 


1.6  m.     In  a  grown  man  the  distance  from  the  heart  to  the 


216  CIRCULATION   OF  THE   BLOOD 

farthest  arteries  is  just  about  equal  to  this  wave  length.  Only  the  very  longest 
arterial  paths  in  the  body,  therefore,  are  long  enough  to  include  the  entire 
length  of  a  pulse  wave ;  for  the  end  of  a  wave  enters  the  aorta  only  after  the 
beginning  of  it  has  already  readied  the  periphery. 

Since  the  movements  of  the  contact  surface  of  the  instrument  are  caused 
by  fluctuations  of  pressure  inside  the  artery,  the  pulse  curve  gives  expression 
to  the  rise  and  fall  of  this  pressure.  But  it  does  not  represent  the  variations 
of  arterial  pressure  exactly,  for  the  arterial  pressure  is  exerted  not  only 
against  the  contact  surface  but  also  against  the  arterial  wall  and  the  neigh- 
boring soft  parts. 

The  sphygmograph  is  affected  also  by  other  movements  than  those  of  the 
blood  in  the  arteries — e.  g.,  by  changes  of  turgor  of  that  part  of  the  body  where 
it  is  applied.     If  the  return  flow  of  the  blood  from  the  veins  is  hindered,  the 


Fig.  88. — Radial  pulse  curve  recorded  with  Marey's    sphygmograph,   after    LangendorfF.      To 

be  read  from  left  to  right. 

entire  series  of  curves  in  the  sphygmogram  rises  because  the  swelling  skin 
increases  the  tension  of  the  spring.  One  dare  not  infer  a  rise  of  blood  pressure, 
therefore,  from  such  a  rise  in  the  series  of  curves. 

When  suitable  apparatus  is  employed  the  pulse  curve  presents  a  number  of 
peculiarities,  some  of  which  constantly  recur  more  or  less  well  marked,  what- 
ever the  artery  from  which  the  curve  is  taken. 

The  pulse  curve  (Fig.  88,  cf.  also  Fig.  11)  begins  with  a  rather  steep 
ascent  which  corresponds  to  the  positive  wave  cau.sed  by  the  inflow  of  blood 
into  the  aorta.  This  line  usually  reaches  its  highest  point  without  interrup- 
tion, whence  begins  immediately  the  descending  liml)  of  the  curve.  The  latter 
shows  several  irregidarities,  one  of  which  at  least,  the  second  mound,  occurs 
in  all  pulse  curves  (Fig.  88).  This  mound  is  designated  as  the  dicrotic  eleva- 
tion. That  it  is  not  an  artifact  has  been  shown  by  the  above-mentioned 
tests  to  which  the  sphygmograph  has  been  subjected. 

The  dicrotic  elevation  is  without  doubt  a  positive  wave  running  in  the 
centrifugal  direction;  but  opinions  difPer  as  to  the  way  in  which  it  arises. 
Of  the  two  hypotheses  which  at  present  are  worthy  of  discussion,  one  accounts 
for  the  elevation  l)y  supposing  that  the  primary  pulse  wave  is  reflected  as  a 
positive  wave  from  the  periphery  of  the  arterial  system.  This  reflected  wave 
comes  into  the  aorta,  strikes  against  the  closed  semilunar  valves,  and  is  once 
more  reflected  without  change  of  sign.  The  second  reflection  (that  from  the 
semilunar  valves)  is  the  cause  of  the  dicrotic  elevation  (v.  Kries.  v.  Frey). 

According  to  the  other  hypothesis  the  dicrotic  elevation  arises  in  the 
following  manner.  When  the  cardiac  contraction  ceases,  and  the  semilunar 
valves  are  no  longer  supported  by  the  blood  in  the  heart,  or  by  their  own 


THE   .\RTERIAL   PULSE  217 

muscular  folds  (cf.  page  lOT),  a  negative  wave  starts  from  the  root  of  the 
aorta  running  toward  the  periphery,  and  a  portion  of  the  aortic  blood  flows 
back  toward  the  heart.  When  this  returning  blood  strikes  against  the  semi- 
lunar valves,  which  have  just  been  closed,  a  positive  centrifugal  icave  starts  at 
the  root  of  the  aorta,  producing  the  dicrotic  elevation  (Marey,  Grashey  et  a/.). 
We  cannot  discuss  here  the  principles  underlying  these  two  explanations. 
Both  have  eminent  advocates  and  an  agreement  is  not  yet  in  sight. 

However  we  conceive  the  dicrotic  character  to  be  produced,  it  is  certain 
that  waves  reflected  from  the  periphers'  of  the  arterial  system  have  a  very  mate- 
rial influence  on  the  form  of  the  pulse  curve.  The  reflected  waves  interfere  with 
the  direct  ones ;  they  spread  to  neighboring  arteries  where  again  they  are  propa- 
gated as  direct  waves,  which  in  turn  interfere  with  both  the  direct  and  reflected 
waves  proper  to  these  arteries,  and  so  on.  Thus  a  great  variety  of  pulse  ti*acings 
with  a  varying  number  of  secondary  and  tertiarj'  elevations  on  the  pulse  curve 
may  be  obtained. 

Attempts  have  frequently  been  made  to  draw  conclusions  as  to  the  activity 
of  the  heart,  the  condition  of  the  hlood  vessels,  and  the  blood  pressure  from 
the  character  of  the  pulse  curve.  This  is  possible  to  a  certain  extent,  but 
must  be  done  with  great  caution. 

The  pulse  curve  may  give  some  approximate  information  as  to  the  tem- 
poral course  of  events  in  the  heart.  The  Ijeginning  of  the  pulse  curve  corre- 
sponds to  the  entrance  of  the  blood  wave  into  the  arteries,  and  the  beginning 
of  the  dicrotic  elevation  is  synchronous  with  the  beginning  of  a  corresponding 
elevation  on  the  cardiogram.  Since  this  point  appears  at  a  slight  interval 
after  the  closure  of  the  semilunar  valves  (cf.  page  1T5),  the  time  elapsing 
between  the  beginning  of  the  pulse  curve  and  the  dicrotic  elevation  is  slightly 
greater  than  the  time  during  which  the  left  ventricle  and  the  arteries  are  in 
open  communication  with  each  other. 

It  might  be  supposed  also  that  a  pulse  curve  of  large  amplitude  would 
indicate  a  large  pulse  volume;  but  this  is  true  only  in  a  very  limited  sense, 
for  the  pulse  curve  of  a  given  artery  depends  to  so  great  a  degree  upon  the 
tonus  of  this  artery  and  upon  the  resistance  in  its  peripheral  branches  that 
no  definite  relation  between  volume  and  size  can  be  laid  down. 

^loreover,  a  large  amplitude  of  the  pulse  curve  is  by  no  means  significant 
of  a  high  blood  pressure,  but  at  best  signifies  only  that  the  fluctuation  of 
pressure  is  great.  But  since  we  know  that  the  variation  of  .s3'stolic  pressure 
is  within  certain  limits  less  with  a  high  than  with  a  low  pressure,  we  might 
possil)ly  say  that  under  circumstances  otherwise  the  same  the  greater  ampli- 
tude means  a  lower  blood  pressure.  But  even  this  is  not  invariable.  The  de- 
gree of  constriction  of  the  artery  under  investigation  has  much  to  do  with  it. 

Again  the  height  of  the  dicrotic  elevation  has  often  been  regarded  as  an 
index  of  the  pressure,  a  greater  elevation  being  produced  with  a  low  than 
with  a  high  pressure.  In  many  cases  this  is  true.  But  there  are  exceptions, 
since  the  degree  of  dilatation  of  a  particular  arterial  region  may  influence 
the  production  of  any  particular  dicrotic  pulse. 

All  of  this  shows  how  careful  one  must  be  in  drawing  conclusions  from 
the  pulse  curve  regarding  the  condition  of  the  vascular  system. 


218  CIRCULATION   OF  THE   BLOOD 

The  pulso.  as  a  rult\  can  he  detected  (diUj  in  the  arteries.  This  is  ex- 
plained by  the  fact  that  in  any  ehistic  tul)e  a  Avave  tends  to  be  ol)literated  by 
friction.  Jn  an  unbranclied  lul)e  the  length  necessary  for  this  obliteration 
would  be  very  great,  but  in  one  composed  of  many  branches  like  the  vascular 
system,  the  obliteration  is  favored  by  every  bifurcation,  since  thereby  the 
total  wall  becomes  greater  and  the  active  force  of  the  wave  is  consumed  the 
more  rapidly.  The  wave  is  reflected  also  at  every  point  where  the  vascular 
Avail  changes  direction,  and  on  this  account  it  is  consumed  sooner  than 
otherwise. 

§  5.    FINAL  SURVEY   OF   THE   MOVEMENTS   OF   THE   BLOOD    IN 

THE   ARTERIES 

Now  that  we  have  learned  the  details  of  the  blood  flow  in  the  arteries,  it 
remains  for  us  to  reconstruct  these  details  into  a  connected  whole.  We  shall 
follow  for  this  purpose  the  description  of  E.  H.  Weber. 

Let  us  suppose  that  the  heart  consists  of  only  one  ventricle,  also  that  to 
begin  with  the  blood  in  all  divisions  of  the  vascular  system  is  under  the  same 
pressure.  When  the  ventricle  contracts  the  atrio-ventricular  valves  close  and 
prevent  the  blood  from  flowing  backward.  All  the  blood  must  therefore  take 
the  same  direction  into  the  arteries.  If  these  were  rigid  tubes  no  blood  could 
be  pressed  into  them  without  at  the  same  time  setting  in  motion  the  entire 
column  of  blood  in  all  its  parts.  In  this  case  no  wave  would  be  produced, 
but  only  a  stream  of  ])lood  which  would  last  as  long  as  the  contraction  of 
the  ventricle  continued.  But  since  the  arteries  are  elastic  tubes,  propulsion 
of  the  different  segments  of  the  blood  column  takes  place  successively.  The 
mass  of  blood  discharged  from  the  ventricle  can  find  a  place  for  itself  only 
by  distending  a  portion  of  the  arterial  system,  and  thus  producing  a  positive 
wave  of  high  pressure  which  spreads  through  the  vessels. 

If  there  were  no  semilunar  valves,  and  if  the  ventricular  contractions 
stopped  immediately  after  the  discharge  of  the  blood,  the  distended  arteries 
would  at  once  drive  a  part  of  the  blood  back  into  the  ventricle.  But  since 
this  is  prevented  by  the  semilunar  valves,  the  successive  parts  of  the  blood 
column  are  moved  a  little  farther  forward  in  the  vascular  system  by  each 
ventricular  systole. 

As  soon  as  the  heart  relaxes  at  the  end  of  systole  and  the  atrio-ventricular 
valves  are  open,  the  blood  flows  from  the  veins  into  the  heart  and  produces 
a  negative  wave  which  is  propagated  along  the  veins.  The  valves  connected 
with  the  heart  are  so  arranged  that  with  the  systole  and  diastole  of  the  heart 
periodically  alternating,  positive  waves  pass  out  only  along  the  arteries,  nega- 
tive waves  only  along  the  veins. 

If  the  vascular  system  were  composed  of  a  single  continuous  tube  of  uni- 
form diameter  every  wave  would  run  through  the  entire  system  with  great 
velocity,  and  would  produce  a  state  of  equilibrium  in  the  entire  circuit  before 
the  next  ventricular  systole  could  follow.  But  because  of  the  resistance  in 
the  smallest  arteries,  veins  and  capillaries,  matters  are  quite  otherwise.  On 
account  of  the  friction  in  the  smaller  vessels  the  blood  cannot  pass  through 
as  rapidly  as  would  be  necessary  for  the  propagation  of  a  positive  wave  all 


THE   FLOW   OF   BLOOD   IX   THE  CAPILLARIES  219 

the  way  back  to  the  heart.  The  wavelike  movement  is  reflected,  therefore,  at 
the  capillaries,  etc.,  and  under  normal  circumstances  the  pulse  cannot  be 
perceived  in  the  veins. 

Supposing  now,  as  we  have  done,  that  the  pressure  is  everywhere  the  same 
to  begin  with,  then  if  the  regular  contractions  of  the  heart  were  repeated 
rapidly  enough,  there  would  be  an  accumulation  of  blood  in  the  arteries,  for 
at  each  systole  more  blood  would  be  thrown  into  the  arteries  than  could  be 
pressed  tiirough  into  the  veins  in  the  same  time.  At  every  diastole  of  the 
heart  the  total  quantity  of  blood  in  the  veins  would  be  still  further  reduced, 
because  more  blood  would  pass  from  them  into  the  heart  than  could  come 
into  them  through  the  capillaries  from  the  arteries.  Thus  the  quantity  of 
blood  in  the  arteries  would  go  on  increasing,  and  the  quantity  in  the  veins 
would  go  on  decreasing  until  the  difference  in  pressure  between  the  two  would 
become  so  great  that  from  one  systole  to  another  just  as  much  blood  was 
pressed  through  the  capillaries  as  was  being  discharged  by  the  heart  into  the 
arteries.  Once  this  degree  of  difference  in  pressure  between  the  two  divisions 
of  the  vascular  system  had  been  reached,  if  the  heart  activity  continued  the 
same,  the  difference  would  become  constant — i.  e.,  the  pressure  in  the  arteries 
would  be  permanently  greater  than  in  the  veins. 

It  is  because  of  this  constant  difference  in  pressure  between  arteries  and 
veins  that  the  movement  of  the  blood  from  the  former  to  the  latter  takes 
place  in  a  steady  stream.  For  this  reason  also  the  blood  continues  to  flow 
from  arteries  to  veins  for  some  time  after  the  heart  stops  beating.  Any  sort 
of  influence  which  changes  either  the  resistance  in  the  vessels  or  the  energy 
of  the  heart,  disturbs  this  stationary  condition  and  a  new  equilibrium  is 
established  at  a  different  level  of  arterial  pressure.  Every  variation  in  pres- 
sure is  in  turn  followed  by  a  change  of  one  kind  or  another  in  the  character 
of  the  blood  flow. 

§6.    THE   FLOW   OF   BLOOD   IN   THE    CAPILLARIES 

The  capillaries  are  unquestionably  the  most  important  part  of  the  vascular 
system.  The  purpose  of  the  circulation,  which  consists  in  supplying  com- 
bustil)lo  materials  and  oxygen  to  the  organs,  and  in  relieving  them  of  decom- 
position products,  is  accomplished  in  the  capillaries.  In  them  the  blood  is 
separated  from  the  lymph  by  only  a  thin  wall,  consisting  of  a  single  layer  of 
cells,  through  which  the  exchange  of  diffusible  substances  is  readily  carried 
on.  The  arteries  and  veins  are  only  tubes  conveying  the  blood  to  and  from 
the  capillaries:  the  latter  constitute  the  real  clearing-house  of  tlie  vascular 
system. 

Since  oxygen  is  consumed  in  large  quantities  in  the  tissues,  it  is  evidently 
of  great  importance  that  the  !)loo(l  should  not  flow  too  slowly  through  the 
capillaries.  The  high  pressure  which  prevails  in  the  arteries  is  necessary  in 
order  to  keep  the  blood  ftowing  through  the  capillaries  with  sufficient  speed. 

Whenever  the  pressure  in  the  aorta  falls,  the  pressure  in  the  capillaries 
also  falls.  If  an  artery  becomes  constricted,  the  lateral  pressure  in  this  artery 
central  to  the  place  of  constriction  increases,  but  at  the  same  time  the  pressure 
and  velocity  peripheral   to  that  place,  that  is,  in  the  capillaries,  decreases. 


220 


CIRCULATION    OF   THE    BLOOD 


Whenever,  other  things  being  ('(jual.  an  ark'rv  is  dihited,  the  lateral  pressure 
in  this  artery  may  fall,  hut  a  larger  amount  of  blood  Hows  into  the  capillaries 
and  as  a  result  the  pressure  in  them  increases. 

All  the  complicated  mechanisms  which  help  to  regulate  the  blood  pressure 
have  for  their  immediate  purpose  the  maintenance  of  a  normal  pressure  in 

the  aorta,  in  order  that  the  blood  may  flow  under 
normal  pressvire  through  the  capillaries. 

The  total  quantity  of  blood  in  the  body  is  by 
no  means  sufficient  to  supply  all  the  capillaries  at 
once  with  as  much  blood  as  the  organs  require 
at  their  maximum  activity.  Fortunately  all  the 
organs  are  never  at  their  maximum  at  the  same 
time,  so  that  their  requirements  vary.  In  fact  the 
quantity  of  1)lood  flowing  through  the  capillaries 
varies  incessantly.  An  organ  upon  which  devolves  an  extra  quantity  of  work 
receives  for  the  time  a  greater  supply  of  blood  than  if  it  were  relatively  in- 
active. The  arteries  belonging  to  the  organ  dilate,  while  the  arteries  which 
convey  blood  to  the  other  organs  at  the  same  time  constrict.  By  this  means 
a  fall  in  the  aortic  pressure  is  prevented  and  the  blood  flows  more  copiously  to 
the  capiUarij  si/stem  whose  arteries  have  been  enlarged.  Pressure  and  velocity 
in  this  reofion  increase  togfether. 


Fig.  89. — Branched  contract- 
ile cells  embracing  wall  of 
a  capillary  vessel  in  the 
hyaloid  membrane  of  the 
frog's  eye,  after  Rouget. 


The  length  of  the  capillaries  is  given  as  0.4-0.7  mm.  (in  the  liA^er  as  much 
as  l.i)  ;  their  diameter  is  about  0.009  mm. 

The  capillary  wall  is  composed  of  flattened  cells  which  fit  together  by  their 
edges.  That  they  are  capable  of  constricting  in  many  places  was  first  demon- 
strated by  Strieker.     Rouget  and  S.  Mayer  then  showed  that  this  constriction  is 


Fig.  90. — A,   capillary  when   not   stimulated;  B,   the  same  capillary  stimulated, 
is  entirely  obliterated,   after  Steinach. 


The  lumen 


brought  about  by  contractile  elements  situated  outside  the  basement  membrane 
and  entirely  distinct  from  it.  The  nuclei  of  these  cells  are  arranged  parallel  to 
the  long  axis  of  the  vessel  and  their  cell  substance  is  often  divided  into  little 
strands  which  run  out  at  right  angles  to  the  nucleus  and  embrace  the  capillary 
vessel  like  the  hoops  of  a  barrel  (Fig.  S9).  The  contraction  of  these  elements 
may  entirely  obliterate  the  lumen  of  the  vessel ;   at  the  same  time  fine  longi- 


THE    FLOW   OF   BLOOD   L\   THE   CAPILLARIES 


221 


tudinal  folds  or  wrinkles  appear  in  the  cell  membrane,  which  increase  in  num- 
ber, clearness  and  extent  as  the  capillary  wall  draws  together,  and  entirely 
disappear  when  the  vessel  dilates  again  (Fig.  00).  However,  certain  individual 
capillaries  or  capillary  tracts  are  quite  exempt  from  this  contraction  (Steinach). 

The  most  favorable  object  for  the  demonstration  of  these  phenomena  is  the 
nictitating  membrane  of  the  frog.  Quite  similar  results  have  been  obtained  also 
in  other  capillary  systems  of  the  frog  and  even  of  Mammals. 

Capillaries  are  abundantly  supplied  with  nei-ves,  and  Steinach  has  succeeded 
in  producing  a  contraction  of  the  capillaries  in  the  frog's  nictitating  membrane 
by  stimulation  of  the  sympathetic. 

Since  the  diameter  of  the  capillaries  may  vary  independently  of  the  blood 
pressure,  it  follows  with  great  probability  that  in  virtue  of  their  contractility 
the    capillaries    themselves    participate    to    a    considerable 
extent  in  the  regulation  of  the  blood  supply  to  the  differ-  i 

ent  organs. 

The  blood  in  the  capillaries  flows  in  the  following  man- 
ner. If  the  capillary  vessel  is  not  so  small  that  the  blood 
corpuscles  entirely  fill  it,  the  red  corpuscles  move  along  with 
their  long  diameters  in  the  direction  of  the  current,  and 
keep  to  the  center  of  the  vessel,  so  that  between  them  and 
the  vascular  wall  a  clear  space  is  left  filled  with  plasma. 
In  this  space  are  found  numerous  white  blood  corpuscles 
which  sometimes  come  to  rest  there,  sometimes  roll  along 
very  slowly  making  frequent  pauses.  As  a  rule,  the  cur- 
rent in  the  capillaries  is  continuous.  But  there  are  excep- 
tions to  this  rule.  With  sufficient  dilatation  of  the  small 
arteries  in  a  given  vascular  region  the  blood  stream  in  the 
capillaries  may  exhibit  rhi/thmical  vibrations  synchronous 
with  the  heart  heats.  A  continuous  flow  presupposes  there- 
fore that  the  blood  in  the  small  arteries  meets  with  suffi- 
cient resistance  to  obliterate  these  pulsations. 


Fig.  91. — Apparatus 
for  determining 
the  blood  pressure 
in  the  capillaries, 
after  Ludwig.  The 
small  glass  plate  a 
is  placed  on  the 
skin,  and  the  pan 
b  is  loaded  with 
weights  until  the 
skin  underneath  a 
is  blanched. 


In  the  field  of  the  microscope  the  velociUj  of  blood 
flow  in  the  capillaries  can  be  determined  by  simply  ob- 
serving the  time  consumed  by  a  particular  corpuscle  in 
traversing  a  measured  distance  on  the  eyepiece  microni- 
erer.  The  velocity  determined  in  this  way  is  given  as 
0.5-0.8  mm.  per  second.  These  values  however  are  maximal,  for  they  relate 
to  the  current  in  the  central  part  of  the  vessel.  The  mean  velocity  is  some- 
what less. 

Attempts  have  been  made  to  determine  the  hlood  prcxsurc  in  the  capillaries 
l)y  measuring  the  pressure  upon  the  outer  surface  of  the  skin  or  upon  the 
gums  of  the  teeth  (Fig.  01).  at  which  a  distinct  change  in  color  appears. 
This  is  said  to  indicate  that  the  most  superficial  capillaries  are  completely 
compressed.  The  limits  of  error  of  this  method  are  rather  wide,  and  the 
values  obtained  can  onlv  be  regarded  as  hare  approximations  to  the  truth. 
This  appears  more  clearly  when  we  hear  in  mind  that  the  pressure  thus  de- 
termined is  not  the  total  capillary  pressure,  for  the  lymph  exerts  an  opposite 
pressure  on  the  outer  side  of  the  capillary  wall,  and  this  depends  upon  the 
tension  and  the  turgor  of  the  skin. 

The  capillary  pressure  which  one  obtains  when  the  effect  of  the  hydrostatic 


222  CIRCULATION    OF  THE   BLOOD 

pressure  of  the  blood  column  is  excluded — i.  e.,  when  the  capillary  region 
investigated  lies  at  the  same  level  as  the  heart,  amounts  to  about  33  mm.  of 
mercury  (X.  v.  Kries,  gums  of  the  rabbit).  Since  the  aortic  pressure  in  the 
rabbit  amounts  to  about  100-120  mm.  Hg.,  the  capillary  pressure  would  be 
one-third  to  two-sevenths  of  the  aortic  pressure. 

Poisseuille  ha.<^  given  the  following  formula  for  the  flow  of  a  fluid  through 

a  horizontal  capillary  whose  wall  is  wet  by  the  fluid :  (>  =  tt    '        '  rV  where 

Q  represents  the  volume  of  fluid  flowing  through  the  capillary  in  the  time  t, 
n^  the  hydraulic  pressure  at  the  l^eginning  of  the  capillary,  f.^  that  at  the  end, 
I  the  length,  and  r  the  radius,  t]  is  the  constant  of  internal  friction  If  all 
the  dimensions  are  given  in  millimeters  and  milligrams,  t)  in  milligrams  is 
the  retarding  force  of  the  friction  taking  effect  upon  one  square  millimeter 
of  surface,  when  the  difference  in  velocity  between  two  adjacent  layers  of  the 
fluid  one  millimeter  apart  is  1  mm.  per  second,  the  change  in  velocity  being 
jLiniform.  The  greater  the  value  of  r]  (i.  e.,  the  more  viscous  is  the  fluid),  the 
less  becomes  the  volume  of  fluid  which  will  flow  through  the  tube  in  unit  time. 

It  has  been  sho\\Ti  by  B.  Lewy  that  this  law  is  true  also  for  the  blood. 
At  a  temperature  of  36°-40°  C.  he  found  the  mean  value  of  77  to  be  0.00025 
(swine,  sheep),  whereas  the  corresponding  value  for  distilled  water  is  0.00007. 
The  internal  friction  of  defibrinated  blood  is  thus  on  the  average  3.5  times 
as  great  as  distilled  water.  The  internal  friction  of  normal  blood  is  some- 
what greater.  According  to  the  researches  of  Hiirthle,  at  37°  C.  it  amounts 
to  4.7  for  the  dog,  4.3  for  the  cat,  3.3  for  the  ral)bit.  that  of  distilled  water 
being  taken  as  1.  Moreover  the  internal  friction  of  l)lood  varies  considerably 
under  different  circumstances.  It  decreases  after  bloodletting;  it  is  smaller 
in  starvation  than  after  feeding;  and  in  the  dog  it  reaches  its  highest  value 
after  feeding  meat  (Burton-Opitz).  Belying  upon  data  concerning  the  in- 
ternal friction  of  defibrinated  blood,  and  under  certain  assumptions  as  to  the 
length,  breadth,  etc.,  in  different  parts  of  the  vascular  system,  B.  Lewy  has 
calculated  the  fall  in  pressure  in  the  capillaries  and  has  found  it  equal  to 
20-60  mm.,  or  by  using  the  highest  value  of  -q  (0.00068)  observed  by  him, 
equal  to  150  mm.  of  blood. ^  At  the  most,  therefore,  about  one-fourteentli  part 
of  the  entire  blood  pressure  is  consumed  in  the  capillaries  themselves.  From 
which  it  follows  that  it  is  not  the  capillaries  which  constitute  the  chief  resist- 
ance to  the  blood  stream,  but  rather  the  smaller  arterioles  central  to  them. 

Campbell  also  has  reached  the  same  view  from  altogether  differpnt  con- 
siderations. Among  other  things  he  emphasizes  the  point  that  if  the  resist- 
ance in  the  capillaries  were  very  great,  so  that  the  pressure  at  the  beginning 
of  a  capillary  were  much  higher  than  at  its  end,  the  very  tliin  ca])illaries 
would  be  funnel  shaped  with  the  wide  opening  directed  toward  the  arteries, 
which,  as  we  know,  is  not  the  case. 

With  the  help  of  Poisseuille's  formida,  and  on  the  basis  of  data  already 
at  hand  for  the  internal  friction  of  the  blood,  for  the  quantity  of  blood  flowing 
through  the  aorta,  and  for  the  pressure  therein,  Hiirthle  has  calculated  the 
absolute  resistance  in  the  aortic  path  (rabbit).    As  is  evident  from  the  formula, 


'Approximately  11  mm.  Hg. 


THE   FLOW   OF   BLOOD   IX   THE   VEL\S  223 

this  is  expressed  as  the  length  of  a  tulje  tliroiigh  which  just  as  much  blood 
would  flow  in  unit  time  as  flows  through  the  animal  body.  According  to  this 
calculation  the  resistance  is  equal  to  that  of  a  cylindrical  tube  with  the 
diameter  of  the  aorta  and  with  a  length  of  296  m.  It  need  scarcely  be  re- 
marked that  this  value  relates  only  to  a  special  case,  and  that  it  is  adduced 
here  only  for  the  purpose  of  giving  an  approximate  idea  of  the  amount  of 
resistance  in  the  vascular  system. 

§  7.    THE   FLOW   OF   BLOOD   IN   THE   VEINS 

A.    PRESSURE   AND   VELOCITY 

Tbe  cubic  distention  of  a  vein  to  internal  pressures  increasing  l)y  equal 
increments  is  exactly  like  its  longitudinal  distention  to  loads  increasing  by 
equal  increments — i.  e..  it  Ijecomes  less  the  higher  tbe  total  pressure  becomes 
(Fig.  92).     The  veins,  therefore,  behave  differently  in  this  respect  from  the 


Fig.  92. — The  cubic  enlargement  of  the  inferior  vena  cava  of  the  cat,  luuler  uniformly  increasing 

internal  pressure,  after  Roy. 

arteries  (of.  page  201).  Tlie  resistance  of  tbe  veins  to  rupture  Ijy  internal 
pressure,  is.  under  normal  conditions,  very  great,  just  as  it  is  in  the  arteries. 

The  essential  physiological  purpose  of  the  veins  is  to  return  the  blood  to 
the  heart.  The  force  which  drives  the  blood  forward  in  tbe  veins  is  tbe  force 
of  the  heart  itself.  But  tbe  friction  in  tbe  small  arteries  and  in  tbe  capillaries, 
has  by  this  time  consumed  the  major  part  of  the  heart's  driving  power,  con- 
sequently the  total  energy  with  which  the  blood  flows  in  the  veins  is  but  a 
fractional  part  of  the  energy  which  it  possessed  as  it  left  the  heart.  The 
greater  part  of  that  energy  has  been  transformed  into  heat  during  the  passage 
of  tbe  blood  through  tbe  arteries  and  capillaries. 

The  lateral  pressure  in  the  veins  is,  therefore,  much  smaller  tban  in  tbe 
arteries.  In  tbe  central  veins  of  tbe  thorax  tbe  l)lood  ])ressure  is  negative 
because  of  tbe  aspirating  action  of  the  thorax.  In  more  peripheral  veins  it 
is  positive  and  is  higher  tbe  farther  tbe  vein  from  tbe  beart,  e.g.,  in  the 
right  jugular  of  tbe  sheep,  0.2  mm.  Hg..  in  the  external  facial  3.0,  internal 
facial  5.2,  brachial  4.1,  in  a  branch  of  tbe  latter  9.0,  in  tbe  crural  11.4  mm. 
Hg.  (Jacobson)  ;  in  the  superior  vena  cava  of  the  dog  close  to  its  entrance 
into  the  rigbt  auricle  —  3.0  mm.  Hg.,  in  the  distal  portion  of  tbe  same  vein 
—  1.4,  in  the  rigbt  external  jugular  -0.1,  left  external  jugular  0.5,  in  the 
right  brachial  3.9,  in  the  left  facial  5.1,  left  femoral  5.4,  left  saphena  7.4  mm. 
Hg.  (Burton-Opitz).  Observations  on  the  sheep  and  on  tbe  dog,  as  will  be 
seen,  agree  on  tbe  whole  very  closely. 

After   opening  the  thorax  and    thereby   obliterating   the   negative   intra- 


224  CIRCULATION   OF  THE   BLOOD 

thoracic  pressure,  the  pressure  in  all   the  veins  rises  considerahly,  so  that  a 
negative  pressure  can  no  longer  be  demonstrated. 

In  order  to  determine  the  pressure  in  a  vein  it  is  necessary  to  avoid  stop- 
page of  the  blood;  a  T-eannula  is  used  and  on  account  of  the  low  pressure  a 
soda  solution  is  substituted  for  mercury  in  the  manometer. 

Just  as  in  the  arterial  system,  the  pressure  in  the  veins  is  conditioned  upon 
the  quantity  of  blood  flowing  from  the  heart  in  unit  time,  and  upon  the 
resistance.  If  the  veins  meet  with  great  resistance  in  emptying  their  blood 
to  the  heart,  the  pressure  in  them  increases.  This  happens  for  example  when 
the  heart  is  checked  or  brought  to  a  standstill  by  stimulation  of  the  vagus. 
In  this  case  the  heart  is  unable  to  drive  forward  all  the  blood  which  collects 
in  the  veins,  and  the  consequent  accumulation  raises  the  venous  pressure. 
If  in  spite  of  the  inhibition,  the  right  heart  still  expels  in  unit  time  just  as 
much  blood  as  it  did  before,  the  venous  pressure  suffers  no  change.  The 
pressure  in  the  veins  is  increased  likewise  if  the  lungs  are  highly  inflated, 
for  by  this  means  the  flow  of  blood  into  the  intrathoracic  veins  is  hindered, 
and  it  becomes  more  difficult  for  the  right  heart  to  empty  itself. 

On  the  other  hand,  the  venous  pressure  falls  as  a  result  of  all  conditions 
favoring  the  return  of  the  blood  to  the  right  heart  or  its  discharge  therefrom 
— e.  g.,  acceleration  after  section  of  the  vagus — provided  the  heart  discharges 
in  unit  time  a  larger  quantity  of  blood  than  before. 

These  influences  take  effect  primarily  on  the  central  veins.  In  the  periph- 
ery the  pressure  depends  mainly  upon  the  variations  of  blood  volume  and  of 
resistance  in  the  arteries.  If  an  artery  be  completely  clamped  off,  the  pressure 
in  the  corresponding  vein  sinks  to  the  level  of  the  minimal  pressure  in  the 
larger  vein  to  which  it  is  tributary.  If  a  vein  be  clamped  off,  the  pressure 
increases  peripherally  to  the  ligature  because  in  this  case  the  vein  represents 
only  a  blind  end  of  the  artery. 

The  variations  in  pressure  in  the  venae  cavae  give  rise  to  pulsations  in  the 
larger  veins  of  the  trunk  and  the  extremities,  which  are  transmitted  centrifugally 
with  a  velocity  of  one  to  three  meters  per  second.  The  velocity  of  transmission 
through  the  jugular  vein  is  greater  than  that  through  the  vena  cava  to  the 
crural  vein  (Morrow). 

In  order  that  the  blood  may  flow  uniformly,  it  is  necessary  that  the  same 
quantity  he  delivered  by  the  veins  to  the  heart  in  unit  time  as  is  expelled  by 
the  heart  into  the  arteries,  and  this  has  been  proved  by  the  direct  observations 
of  Cyon  and  Steinmann,  and  of  Burton-Opitz,  to  be  the  case.  The  volume 
of  flow  is,  therefore,  about  the  same  in  corresponding  arteries  and  veins ;  but 
on  account  of  the  greater  cross  section  of  the  veins,  the  linear  velocity  in 
them  is  less  than  in  the  arteries — e.  g.,  in  the  external  jugular  of  the  dog 
147  mm.,  in  the  femoral  62  mm.  per  second.  After  section  of  the  vagi,  the 
volume  of  the  current  in  the  jugular  vein  increases  2.8  times,  but  decreases 
about  fifty-seven  per  cent  on  compression  of  both  carotids  (Burton-Opitz). 

B.    AIDS   TO   THE   BLOOD   FLOW   IN   THE   VEINS 
The  blood  flow  in  the  veins  can  be  very  easily  disturbed  by  all  kinds  of 
external  influences;  but  to  offset  this  we  have  several   special   mechanisms 


THE   FLOW   OF   BLOOD   IX  THE   VEINS  225 

which  favor  the  flow.  One  such  is  the  suction  of  the  thorax  already  discussed 
at  page  176,  as  well  as  that  of  the  heart  itself.  Besides  these,  several  other 
conditions  in  connection  with  the  valves  of  the  veins,  operate  to  prevent  stasis 
of  blood  in  the  veins. 

The  valves  of  the  veins  discovered  by  Fabricius  ab  Aquapeiidente  in  1574, 
are  semilunar  folds  of  the  lining  membrane,  so  arranged  that  they  open  toward 
the  heart  but  prevent  the  flow  of  blood  in  the  opposite  direction.  Two  such 
valves  as  a  rule  stand  opposite  each  other. 

When  external  pressure  of  any  kind  is  exerted  upon  a  vein,  the  backward 
flow  of  Hood  is  checked  by  the  nearest  valve,  and  it  is  compelled  therefore 
to  move  in  the  direction  of  the  heart.  As  a  result  we  find  that  with  every 
muscular  contraction  there  is  an  increase  in  the  quantity  of  blood  flowing 
from  the  corresponding  vein.  If  the  muscle  be  throAvn  into  tetanus,  there 
follows  at  first  an  acceleration,  then  a  retardation  of  the  blood  flow,  which 
lasts  until  the  tetanus  abates,  and  the  pressure  on  the  vein  caused  by  it 
ceases. 

Thus  Burton-Opitz  found  the  volume  of  flow  in  the  femoral  vein  in  one 
experiment  with  a  resting  muscle  to  be  1.1  c.c.  per  second ;  with  a  tetanizing 
stimulus  of  the  sciatic  nerve,  lasting  8.1  seconds,  the  volvune  was  4.0  c.c.  during 
the  contraction,  0.4  c.c.  during  complete  tetanus,  and  after  relaxation  of  the 
muscle  1.3  c.c. 

Under  ordinary  circumstances  clonic,  cramplike  contractions  of  the  mus- 
cles never  occur,  but  with  every  movement  of  the  body  contraction  and  relaxa- 
tion alternate.  Because  of  the  intermittent  pressure  upon  the  veins  which 
such  an  alternation  produces,  the  usual  muscular  contractions  must  materially 
favor  the  movement  of  the  blood  in  them. 

Changing  the  attitudes  of  the  body  also  is  an  important  aid  to  the  flow 
of  venous  blood. 

The  femoral  vein  under  Poupart's  ligament  and  in  the  fossa  ovalis,  becomes 
empty  of  blood  and  collapses  when  the  thigh  is  turned  outward  and  at  the  same 
time  moved  backward  so  as  to  stretch  it  as  much  as  possible.  It  fills  full  again 
as  soon  as  the  leg  is  brought  back  to  its  former  position  or  is  brought  still  fur- 
ther forward  or  flexed  as  much  as  possible.  These  changes  of  position  take  place 
with  every  step  which  we  make  (Braune). 

Finally,  we  have  in  the  stretching  movements  of  the  body  a  means  of 
accelerating  the  blood  in  the  veins.  When  a  vein  is  elongated  without  at 
the  same  time  being  compressed  its  cubic  capacity  is  increased,  and  it  then 
exerts  a  suction  on  the  blood  column.  For  the  venous  system  of  the  upper 
extremities  such  a  suction  is  obtained  when  with  fists  clinched  and  wrists 
bent,  the  arms  are  stretched  horizontally  and  moved  backward  in  a  certain 
plane  of  rotation.  A  general  state  of  relaxation  and  consequent  stagnation 
are  obtained  when  with  fingers  stretched  and  the  hand  flexed  dorsally  the 
arms  are  bent  at  the  elbows  and  brought  close  to  the  thorax.  The  veins 
of  the  lower  extremities  are  stretched  when  the  thighs  are  spread  apart 
and  turned  outward  at  the  hip  joint  as  far  as  possible,  the  knees  and  feet  being 
at  the  same  time  extended.  Flexion,  adduction  and  turning  of  the  thighs 
inward,  bending  of  the  knees  and  dorsal  flexion  of  the  feet  bring  about  a 


226 


CIRCULATION   OF  THE   BLOOD 


Fig.  93. — Position  of  the  body  in  which  the  veins  are  stretched  a?  much  as  possible,  after  Braune. 


Fig.  94. Position  of  the  body  in  which  the  venous  system  is  relaxed  as  much  as  possible, 

after  Braune. 


RESPIRATORY   VARIATIONS   OF   BLOOD   PRESSURE  227 

general  relaxation  of  the  same  chief  trunks.  The  position  in  which  the 
venous  system  is  in  general  stretched  most  strongly  corresponds  well  with 
the  attitude  which  one  takes  involuntarily  when,  after  working  at  a  desk  for 
a  long  time,  he  stands  up  and  stretches  himself  (Fig.  93).  It  is,  therefore, 
to  be  assumed  that  such  a  stretching  of  the  trunk  and  of  the  extremities  acts 
favorably  upon  the  venous  circulation,  which  has  been  disturbed  by  sitting 
too  long  (Fig.  94:).  and  this  quite  independently  of  the  direct  effect  of 
muscles  and  fascia  (Braune). 

It  may  happen  at  times  that  a  greater  quantity  of  blood  flows  to  the  right 
heart  than  can  be  disposed  of.  This  is  possible,  for  example,  when  a  powerful 
vasoconstriction  occurs  throughout  a  large  vascular  region.  A  large  quantity 
of  blood  is  then  forced  from  the  arteries  into  the  veins,  and  from  these  to 
the  right  heart,  while  at  the  same  time  the  discharge  of  blood  from  the  left 
ventricle  becomes  more  difficult  on  account  of  the  high  resistance  in  the  con- 
tracted arteries. 

We  do  not  know  how  often  or  to  what  extent  this  may  happen.  We  only 
know  that  after  extirpation  of  the  liver,  the  portal  vein  having  been  previously 
connected  with  the  inferior  vena  cava,  the  heart  is  found  dilated  to  its  utmost, 
and  the  great  veins  are  filled  swelling  full  of  blood  (Stolnikow).  The  liver 
takes  up  a  considerable  quantity  of  blood  like  a  sponge,  and  protects  the  right 
heart  from  an  oversupply,  just  as  it  aids  in  the  relief  of  the  heart  when  over- 
distention  occurs  as  a  result  of  transfusion  (cf.  page  20?). 


§  8.    THE   LESSER   CIRCULATION   AND   THE    RESPIRATORY 
VARIATIONS   OF    BLOOD   PRESSURE 

A.    THE   PULMONARY   CIRCULATION 

In  general  the  same  laws  which  we  have  learned  in  our  study  of  the  blood 
movements  in  the  greater  circulation  hold  good  for  the  lesser  circulation. 
The  pressure  is  dependent  upon  the  quantity  of  blood  discharged  from  the 
right  heart  and  upon  the  resistance  in  the  pulmonary  vessels.  The  quantity 
of  blood  which  the  right  ventricle  forces  into  the  pulmonary  arteries  depends 
upon  the  quantity  of  blood  which  flows  from  the  greater  circulation  through 
the  venae  cavae  into  the  right  heart.  This  quantity  is  determined  partly  by 
events  in  the  aortic  system,  and  partly  by  the  pressure  changes  in  the  thoracic 
cavity  which  accompany  the  different  phases  of  respiration. 

Thus  every  hindrance  of  any  moment  to  the  flow  of  blood  into  the  vense  cavje 
reduces  the  pressure  in  the  pulmonary  arteries.  An  increased  supply  of  blood 
to  the  riprht  heart,  such  for  example  as  is  brought  about  by  powerful  contraction 
of  the  abdominal  vessels,  increases  the  pulmonaiy  pressure. 

We  have  already  emphasized  the  fact  that  with  each  act  of  inspiration  the 
thoracic  cavity  exerts  suction  on  the  blood  vessels  which  enter  it.  The  right 
ventricle,  therefore,  receives  more  blood  during  inspiration  than  during  expira- 
tion; nevertheless  the  pressure  in  the  ventricle  itself  (Talma)  and  in  the 
pulmonary  arteries  (Knoll)  declines  only  to  rise  again  at  the  next  expiration. 

These  variations  of  blood  pressure  are  caused  partly  by  the  effect  of  varia- 
tions in  the  intrathoracic  pressure  on  the  thin-walled  right  ventricle,  and  partly 


228  CIRCULATION    OF  THE    BLOOD 

by  their  effect  on  the  diameter  of  the  vessels  in  the  lung:s.  The  diameter  of  these 
vessels,  as  d'Arsonval,  De  Jager,  Heger  and  others  have  shown,  increases  with 
the  expansion  of  the  lungs  during  inspiration,  and  decreases  with  the  collapse 
of  the  lungs  during  expiration.  Since  the  two  factors  operate  in  the  same  direc- 
tion, there  remains  for  us  to  determine  to  which  of  them  the  greater  significance 
is  to  be  ascribed.  We  must  first  inquire  to  what  extent  the  resistance  in  the 
pulmonary  vessels  is  changed  by  the  different  phases  of  respiration. 

This  question  does  not  admit  of  a  direct  answer;  but  we  have  certain  well- 
established  facts  which  show  very  clearly  that  the  resistance  in  the  pulmonary 
channels  is  in  general  so  small  that  only  a  considerable  change  in  the  diameter 
of  the  vessels  could  exercise  upon  it  any  very  marked  influence. 

We  should  mention  first  the  results  which  Lichtheim  obtained  by  occluding 
a  large  part  of  the  pulmonaiy  vessels.  It  was  shown  with  dogs  which  received 
artificial  respiration  by  rhythmical  inflation  of  the  lungs,  that  about  three- 
fourths  of  the  territoiy  supplied  by  the  pulmonary  arteries  could  be  shut  out 
without  diminishing  in  the  least  the  flow  of  blood  to  the  left  ventricle.  Again, 
the  left  pleural  cavity  of  a  rabbit  breathing  naturally  has  been  opened  without 
interfering  with  the  respiration  on  the  other  side,  and  the  entire  left  lung  tied 
off  at  the  hilus :  yet  as  a  rule  no  fall  of  blood  pressure  was  observed  in  the  greater 
circulation. 

We  may  say,  then,  that  one-half  (in  curarized  animals  still  less)  of  the  pul- 
monary blood  channel  is  enough  to  supply  the  necessary  quantity  of  blood  to 
the  left  heart.  The  explanation  might  be  sought  in  an  increased  blood  pressure 
in  the  lesser  circulation  and  a  consequent  greater  dilatation  of  the  vessels  which 
remain  open.  But  the  increase  in  pressure  is  so  insignificant  (it  never  amounts 
to  more  than  a  few  millimeters  of  Hg.)  that  it  is  very  doubtful  whether  it  could 
produce  such  an  effect.  Again  we  might  imagine  a  vasomotor  influence  upon 
the  pulmonary  vessels;  but  the  facts  which  we  have  at  present  on  this  subject 
scarcely  point  to  any  considerable  direct  control  of  these  vessels  by  the  central 
nervous  system.  Finally,  it  is  possible  that  under  normal  circumstances  the 
lungs  are  never  uniformly  filled  with  blood,  but  that  certain  regions  remain 
relatively  empty,  being  made  accessible  to  the  blood  only  by  unusual  opportuni- 
ties like  that  just  mentioned. 

Be  this  as  it  may,  it  certainly  follows  from  the  facts  before  us  that  the 
resistance  in  the  pulmonary  vessels  is  very  small.  This  conclusion  is  con- 
firmed also  by  facts  which  we  possess  concerning  the  velocity  of  the  blood  flow 
in  the  lungs.  Stewart  has  shown,  for  example,  that  a  foreign  fluid  injected 
into  the  jugular  vein  passes  the  lesser  circulation  in  three  to  four  seconds. 
When  the  lungs  are  inflated  by  a  positive  internal  pressure  sufficient  to  stop 
the  flow  of  blood  in  -the  pulmonary  vessels,  and  the  lungs  are  then  released, 
the  press-ure  in  the  greater  circulation  retvirns  to  its  normal  height  in  three  to 
four  seconds. 

In  view  of  this  low  pressure  in  the  pulmonary  vessels,  one  hesitates  to  sup- 
pose that  the  changes  in  their  diameter  which  take  place  in  spontaneous  respira- 
tion as  the  direct  result  of  alterations  in  the  lung  tissue  can  play  the  more 
important  part  in  determining  the  variations  of  blood  pressure  in  the  lesser  cir- 
culation. The  changes  in  intrathoracic  pressure  are  much  rather  to  be  assigned 
the  place  of  first  importance.  The  pressure  in  the  right  ventricle  falls  in  inspi- 
ration not  chiefly  because  the  vessels  in  the  lungs  dilate  a  little,  but  because  the 
inspiratory  suction  distends  the  heart,  and  vice  versa. 

The  blood  pressure  in  the  pulmonary  arteries  is  very  low  on  account  of  the 
low  resistance  in  the  smaller  pulmonary  vessels.     On  the  average  it  amounts 


RESPIRATORY   VARIATIONS   OP   BLOOD  PRESSURE  229 

in  the  dog  to  about  20  mm.  Hg.,  in  the  cat  to  about  18  and  in  the  rabbit  to 
about  15  (cf.  page  170). 

As  mentioned  above  (page  208),  the  pressure  in  the  greater  circulation 
in  the  same  individual  may  exhibit  great  variations  from  one  moment  to 
another.  The  puhnonary  circulation  is  entirely  ditferent  in  this  respect,  the 
pressure  variations  there  being  on  the  whole  very  small — scarcely  ever  more 
than  10-15  mm.  under  normal  circumstances. 

It  follows  that  the  work  of  the  left  ventricle  must  vary  in  amount  much 
more  than  that  of  the  right,  and  this  is  borne  out  also  by  the  fact  that  the 
left  ventricle  becomes  more  or  less  fatigued,  when  the  right  is  still  entirely 
capable. 

The  lesser  circulation  is  dependent  upon  the  greater  not  only  because  it 
draws  its  supply  from  the  venae  cavse,  but  also  because  it  must  deliver  its  blood 
to  the  left  ventricle  and  so  is  aifeeted  by  the  conditions  of  the  blood  tlow  from 
that  chamber.  If,  for  example,  the  left  ventricle  is  unable,  because  of  high 
resistance,  to  discharg'e  all  the  blood  coming  to  it,  so  that  a  certain  quantity 
accumulates  within  this  chamber,  a  state  of  affairs  will  finally  be  reached  where 
the  flow  from  the  right  heart  is  hindered,  which  in  fact  has  been  experimentally 
demonstrated  (Waller). 

In  general,  however,  this  reverse  effect  of  the  left  heart  on  the  right  is  only 
slight,  a  fact  associated  with  the  great  capacity  of  the  pulmonary  vessels.  The 
lungs  serve  the  same  purpose  with  respect  to  the  flow  of  blood  into  the  left  heart 
as  does  the  liver  with  respect  to  the  flow  of  blood  to  the  right  (cf.  page  227). 

Moreover,  the  great  capacity  of  the  pulmonary  vessels  has  this  advantage, 
that  in  great  respiratory  distress  where  the  vessels  of  the  greater  circulation  are 
powerfully  contracted,  the  greatest  possible  quantity  of  blood  is  exposed  to  the 
alveolar  air  and  the  greatest  possible  quantity  of  oxygen  is  therefore  absorbed. 
By  this  means  the  blood  is  relieved  of  the  products  of  combustion,  and  the  influ- 
ence which  these  exert  through  their  stimulation  of  ^he  vasomotor  centers  is 
diminished  to  some  extent. 

B.    RESPIRATORY   VARIATIONS  OF  BLOOD  PRESSURE 

Just  as  the  lesser  circulation  is  influenced  in  several  respects  hy  the  greater, 
it  in  turn  exerts  no  less  an  influence  upon  the  greater.     Consequently  there 

I ,    Z'.     ,     /     ,i^. ,    I  ,^JL^ L__^ 

Fig.  95.— Variations  of  the  aortic  blood  pressure  in  the  dog,  due  to  normal  respiratory  move- 
ments, after  De  Jager.     /,  inspiration;  E,  expiration.      To  be  read  from  right  to  left. 

appear  in  the  aorta  variations  of  blood  pressure  which  are  synchronous  with 
the  respiratory  movements  and  are  doubtless  dependent  upon  tbese  and  upon 
the  variations  in  the  pulmonary  circulation.  The  mechanism  by  which  these 
influences  are  brought  to  bear  are  rather  complicated,  and  we  have  to  take 
into  account  the  following  conditions. 

The  following  circumstances  tend  during  inspiration  to  increase  the  Wood 
pressure  in  the  aorta : 

(1)  The  aspiration  of  the  blood  to  the  right  heart  increases; 


230 


CIRCULATION   OF  THE   BLOOD 


(2)  The  diastole  of  the  heart  is  favored; 

(3)  The  flow  of  the  blood  in  the  pulmonary  vessels  is  facilitated  because  of 
their  dilatation ; 

(4)  The  pressure  in  the  abdominal  cavity  increases  because  of  the  descent 
of  the  diaphragm ;  and  the  blood  is  forced  in  greater  quantity  to  the  right  heart. 

The  following  circumstances  tend  to  lower  the  aortic  pressure: 

(1)  The  heart  systole  is  rendered  more  difficult  because  of  the  increased  suc- 
tion in  the  thorax; 

(2)  At  the  beginning  of  inspiration,  while  the  pulmonary  vessels  are  still 
dilating,  a  part  of  the  blood  expelled  from  the  right  ventricle  must  remain  in 


Fig.  96. — Respiratory  variations  of  blood  pressure  in  the  rabbit.  To  be  read  from  right  to 
left.  The  upper  line  represents  the  blood  pressure,  the  middle  line  the  respiratory  move- 
ments (downward  stroke,  inspiration),  the  lower  line  the  time  record  in  seconds. 


them,  and  by  this  means  the  mass  of  blood  flowing  from  the  left  heart  decreases 
until  the  pulmonary  vessels  have  been  filled,  after  which  the  flow  is  increased. 
In  expiration  naturally  these  mechanisms  work  in  the  reverse  direction. 

Among  these  factors  the  alterations  of  hlood  flow  to  the  right  heart  is  of 
the  first  importance.  The  respiratory  variations  of  the  aortic  pressure  wit- 
nessed in  a  dog  breathing  quieth^  (Fig.  95)  could  be  explained  therefore  in  the 
following  manner.  In  expiration  the  right  heart  has  less  blood  at  its  disposal, 
the  left  heart  receives  less  blood,  and  the  aortic  pressure  falls.  When  inspira- 
tion sets  in,  and  the  flow  to  the  right  heart  becomes  greater,  it  can  drive  a 
greater  quantity  to  the  left  heart,  and  the  aortic  pressure  rises.  But  a  short 
time  must  always  elapse  before  this  increased  supply  to  the  right  heart  can 
be  felt  in  the  left  heart  and  in  the  aorta ;  hence  at  the  beginning  of  inspiration 
the  pressure  is  still  falling.  Likewise  at  the  very  beginning  of  the  following 
expiration  the  right  heart  still  has  at  its  disposal  a  portion  of  the  increased 
supply ;  the  rise  in  pressure  in  the  aorta  continues  therefore  for  a  moment 
until  the  diminished  supply  to  the  right  heart  can  be  felt  on  the  left,  when  the 
aortic  pressure  begins  to  fall. 


VASOCONSTRICTOR    NERVES  231 

When  the  rate  of  respiration  is  somewhat  more  frequent  (of.  Fig.  96),  the 
influence  of  expiration  is  felt  for  the  first  during  the  following  inspiration  and 
vice  versa;  the  aortic  pressure  rises  therefore  during  expiration  and  falls  during 
inspiration. 

In  still  more  frequent  and  shallow  breathing  the  variations  of  the  flow  to  the 
right  heart  are  so  slight  that  no  respiratory  variations  of  blood  pressure  appear 
in  the  greater  circulation. 

Besides  these,  certain  nervous  events  exercise  an  unmistakable  influence  on 
the  respiratory  variations  of  blood  pressure  in  the  aorta.  During  expiration  the 
pulse  rate  decreases  in  consequence  of  an  automatic  stimulation  of  the  vagus 
(depressor  effect),  and  the  vascular  tonus  increases  as  the  result  of  an  automatic 
stimulation  of  the  vasomotor  nerves  (pressor  effect).  These  factors  make  them- 
selves felt  only  Avitli  a  rhythm  which  is  not  too  rapid,  and  even  then  tliey  may 
not  be  able  to  alter  the  course  of  variations  in  the  aortic  pressure  produced  by 
the  mechanical  factors  already  discussed. 

Still  other  more  or  less  regular  variations  of  pressure  (Traube-Hering  waves) 
occur  in  the  aortic  system,  which  may  run  parallel  with  certain  periodic  varia- 
tions in  the  frequency  and  depth  of  respiration  extending  over  several  respira- 
tory cycles  (Cheyne-Stokes  breathing.  Chapter  IX)  or  may  be  entirely  inde- 
pendent of  them.  But  further  discussion  of  their  nature  w'ould  lead  us  too 
far  at  this  time. 

Artificial  respiration  gives  in  all  respects  just  the  reverse  effects  of  natural 
respiration.  Thus  with  inflation  of  the  lungs  the  blood  flow  to  the  right  heart 
is  rendered  more  difficult  on  account  of  the  positive  intrapulmonary  pressure, 
and  the  resulting  compression  of  pulmonary  vessels.  The  consequence  is  that  the 
aortic  pressure  rises  at  the  beginning  of  inflation,  and  falls  again  in  the  further 
course  of  the  same  phase. 

The  cause  of  these  artificial  pressure  variations  must  be  mainly  the  altera- 
tions in  diameter  of  the  pulmonary  vessels.  At  the  beginning  of  inflation  the 
blood  pressure  rises  because  of  the  compression  produced  and  the  consequent 
emptying  of  the  blood  toward  the  heart.  The  subsequent  fall  is  the  result  of 
the  increased  resistance  in  the  pulmonary  vessels.  At  the  beginning  of  the  arti- 
ficial collapse  a  certain  quantity  of  blood  remains  behind  in  the  dilated  vessels 
and  the  pressure  sinks  still  farther  until  the  influence  of  diminished  resistance 
in  the  pulmonary  vessels  makes  itself  felt  and  the  left  heart  is  more  abundantly 
supplied. 

§  9.    VASOCONSTRICTOR   NERVES 

The  muscular  coat  of  the  blood  vessels  is  under  tlie  influence  of  two  kinds 
of  nerve  fibers,  namely,  those  through  whose  excitation  the  muscle  fibers  are 
caused  to  contract  (vasoconstrictor  nerves),  and  those  through  whose  excita- 
tion the  muscle  fibers  are  caused  to  relax  (vasodilator  nerves).  The  former 
were  discovered  by  Claude  Bernard  and  Brown-Sequard  (1851.  185'^),  the 
latter  by  Schilf  (1855)  and  Claude  Bernard  (1858).  The  importance  of 
the  vasomotor  nerves  for  the  circiilation  was  first  clearly  established  by  Lud- 
wig  (1864). 

If  the  cervical  sympathetic  he  cut.  one  observes  among  other  things  that 
the  vessels  of  the  ear  dilate  so  that  small  arteries  and  veins  which  were  for- 
merly invisible  now  stand  out  clearly.  If  the  edge  of  the  ear  be  snipped  off, 
blood  flows  more  freely  from  the  wound  than  before  section  of  the  nerve. 
The  temperature  of  the  ear  is  higher  than  that  of  the  other  side.  Blood  flows 
16 


232  CIRCULATION   OF  THE  BLOOD 

more  rapidly  throu<?li  the  organ  and  does  not  have  time  to  undergo  the  changes 
which  it  otherwise  woidd  in  the  capillaries;  the  color  of  the  venous  hlood  is 
therefore  lighter,  apd  its  properties  are  similar  to  those  of  arterial  hlood. 

If  now  the  end  of  the  cervical  sympathetic  toward  the  head  he  stimulated, 
the  arteries  are  constricted — with  powerful  stimulation,  so  much  so  that  their 
lumen  disappears;  the  venous  hlood  flows  slowly  and  has  a  dark  color;  the 
blood  flows  but  feebly  from  a  fresh  cut.  and  the  temperature  of  the  ear  falls. 

Since  section  of  the  cervical  sympathetic  causes  a  vasodilation  of  the  ear, 
and  its  stimulation  constricts  the  blood  vessels  in  the  same  ear,  it  follows  that 
this  nerve  must  contain  fibers  which  preside  over  contraction  of  the  muscular 
coat  in  these  vessels — i.  e.,  which  are  vasoconstrictor  fibers  for  the  ear.  It  fol- 
lows moreover  that  these  nerves  must  be  under  tonic — i.  e.,  continuous — stimu- 
lation from  the  central  nervous  system. 

Now  we  have  nerves  running  to  all,  or  at  least  to  most,  of  the  arterial 
regions  of  the  body,  which  have  the  same  properties  as  those  just  described. 
The  vascular  tonus  maintained  by  their  constant  stimulation  is  of  the  utmost 
importance.  For  should  all  the  vessels  for  any  reason  be  completely  relaxed, 
there  would  collect  in  them,  especially  in  the  veins,  so  great  a  quantity  of 
blood  that  the  volume  flowing  back  to  the  heart  would  not  be  suflficient  to 
maintain  the  necessary  supply;  the  blood  pressure  would  fall  to  a  low  level 
and,  although  the  heart  might  continue  to  act  for  a  time,  it  would  be  unable 
to  accomplish  anything.  All  of  which  means  that  the  total  quantity  of  blood 
in  the  body  is  sufficient  to  fill  the  blood  vessels  to  the  proper  extent,  only  when 
they  are  partially  constricted. 

The  vasoconstrictors  are  given  off  from  the  central  nervous  system  in  the 
anterior  nerve  roots,  and  are  distributed  to  the  sympathetic  paths  throughout 
the  whole  body.  The  following  results  have  been  obtained  so  far  with  regard 
to  their  course; 

Most  of  the  vasoconstrictor  nerves  pass  out  from  the  thoracic  portion  of  the 
spinal  cord.  The  nerves  running  to  the  head  arise  from  the  first  to  the  fifth  tho- 
racic nerves,  pass  over  into  the  cervical  sj^mpathetic  and  are  distributed  to  the 
different  parts  of  the  head.  This  is  attested  by  the  fact  that  stimulation  of  the 
cervical  sympathetic  causes  vasoconstriction  in  all  the  organs  of  the  head.  With 
regard  to  the  brain,  however,  results  are  less  positive.  While  some  authors  assert 
that  they  have  found  vasoconstrictor  nerves  for  the  brain  in  the  cervical  sympa- 
thetic, others  have  come  to  the  conclusion  that  although  nerve  fibers  have  been 
demonstrated  anatomically  for  the  blood  vessels  of  the  brain,  in  general  the  blood 
supply  to  this  organ  is  not  regulated  by  means  of  vasomotor  nerves,  but  by 
alterations  in  the  supply  to  other  organs  of  the  body. 

W^ith  respect  to  the  further  course  of  these  nei'ves  to  the  head,  our  informa- 
tion is  very  incomplete.  According  to  some  they  pass  over  into  the  sympathetic 
plexuses  surrounding  the  blood  vessels,  according  to  others  they  unite  with  the 
cranial  nerves.  The  latter  has  been  demonstrated  for  the  tongue  at  least,  since 
its  vasoconstrictor  nerves  run  for  the  most  part  in  the  hypoglossal. 

The  vasoconstrictor  nerves  of  the  anterior  extremities  pass  out  from  the 
spinal  cord  in  the  third  to  the  tenth  thoracic  nerves,  those  of  the  posterior  ex- 
tremities in  the  eleventh  thoracic  to  the  third  lumbar  nerves.  It  is  stated  also 
that  the  vasoconstrictor  nerves  of  the  toes  are  contained  in  the  sixth  lumbar  to 
the  first  sacral  nerves. 


VASODILATOR   NERVES  233 

The  tail  gets  its  vasoconstrictor  nerves  from  the  third  to  the  fourth  lumbar 
nerves;  and  the  dorsal  side  of  the  trunk  from  the  posterior  branches  of  the  spinal 
nerves  corresponding  to  the  different  segments  of  the  back. 

The  nerves  pass  from  their  origin  through  the  trunk  of  the  sympathetic 
and  from  there  for  the  most  part  to  the  different  organs  of  the  body  by  way 
of  the  chief  nerve  trunks. 

The  vasoconstrictor  nerves  of  the  abdominal  viscera  leave  the  spinal  cord 
by  the  third  thoracic  to  the  first  or  third  lumbar  nerves,  run  for  the  most  part 
in  the  splanchnics,  and  are  distributed  by  them  to  the  different  organs  of  the 
abdominal  cavity.  The  nerves  of  the  large  intestine  pass  out  of  the  spinal  cord 
in  the  seventh  thoracic  to  the  second  lumbar  nerves;  those  of  the  liver  in  the 
sixth  thoracic  to  the  second  lumbar;  those  of  the  pancreas  in  the  fifth  thoracic 
to  the  first  lumbar  nerv'c. 

The  vasoconstrictor  nerves  of  the  organs  of  generation  pass  out  in  the  last 
lumbar  and  in  the  first  sacral  nerves,  and  proceed  to  their  end  arborizations 
through  the  hypogastric  plexus. 

The  lungs  also  possess  vasoconstrictor  nerves;  according  to  the  majority  of 
authors,  they  leave  the  spinal  cord  in  the  second  to  the  fifth  thoracic  nerves,  and 
proceed  by  way  of  the  sympathetic  paths  to  the  lungs.  Recently  the  presence 
of  vasomotor  nerves  in  the  lungs  has  been  absolutely  denied. 

Vasoconstrictor  nerves  appear  to  traverse  other  paths  also.  Thus  we  find 
in  the  second  and  third  nerves  of  the  cervical  plexus  vasoconstrictor  fibers  for 
the  tip  and  lateral  parts  of  the  ear,  which  reach  their  destination  bj'  way  of  the 
auricularis  cei-vicalis  nerve.  It  is  further  asserted  that  the  vagus  conveys  vaso- 
constrictor nerves  to  the  heart,  to  the  stomach,  to  the  intestine  (not  confirmed 
by  all  authors)  and  to  the  kidneys,  and  also  that  in  it  are  contained  vasocon- 
strictor fibers  for  the  lungs.  It  is  indeed  not  impossible  that  these  fibers  might 
arise  from  the  sympathetic  (since  it  is  definitely  asserted  that  the  vasoconstrictor 
nerves  in  the  auricularis  cervicalis  arise  in  the  thoracic  sjonpathetic  and  run 
through  the  stellate  ganglion),  and  it  is  also  conceivable  that  they  actually 
belong  to  the  branches  of  the  vagus. 

Because  of  the  great  vascular  territory  committed  to  their  control  the 
splanchnics  play  the  most  important  part  of  all  vasomotor  nerves.  For  this 
reason  the  blood  pressure  falls  after  bilateral  section  of  these  nerves,  and 
shows  a  very  great  rise  on  stimulation  of  them. 

Constricting  nerve  fibers  have  been  demonstrated  also  for  the  veins.  If  the 
aorta  be  tied  off  immediately  below  the  origin  of  the  left  subclavian,  and  the 
blood  supply  to  the  hinder  part  of  the  body  be  thereby  cut  off,  stimulation  of 
the  splanchnics  drives  through  the  inferior  vena  cava  into  the  right  heart  a 
fluantity  of  blood  which  runs  up  to  twenty-seven  per  cent  of  the  total  quantity 
in  the  animal.  According  to  Mall,  this  is  caused  by  contraction  of  the  portal 
system. 

Constrictor  effects  of  nerve  stimulation  in  other  veins  are  mentioned  by  dif- 
ferent authors;  but  R.  F.  Fuchs  has  published  experiments  in  which  he  obtained 
no  active  constriction  of  the  veins  either  by  direct  stimulation  of  the  veins  them- 
selves or  by  electrical  stimulation  of  nerves,  wherefore  he  denies  entirely  the 
presence  of  vasomotor  nerves  for  the  veins. 

Finally,  the  musculature  of  the  vessels  contracts  under  high  internal  pres- 


234  CIRCULATION    OF  THE    BLOOD 

sure  and  relaxes  in  consequence  of  a  fall  in  pressure.  According  to  Bayliss 
these  changes  are  entirely  independent  of  the  central  nervous  system  and  can 
be  demonstrated  under  natural  conditions  as  well  as  in  exsected  arteries. 


§  10.    VASODILATOR   NERVES 

If  the  lingual  nerve  be  stimulated,  and  attention  be  directed  to  the  sub- 
maxillary gland,  the  vessels  of  the  gland  may  be  seen  to  dilate.  The  veins 
of  the  gland  swell  up.  the  blood  flowing  in  them  takes  on  a  brigliter  color,  and 
sometimes  actual  pulsations  appear  in  them.  From  this  it  follows  that  this 
nerve  contains  fibers,  the  stimulation  of  which  cause  the  vessels  of  the  gland 
to  dilate.     Such  nerves  are  described  as  vasodilator  nerves. 

Where  these  nerves  occur  unmixed  with  vasoconstrictor  nerves,  one  meets 
with  no  difficulty  in  demonstrating  them.  Where  they  are  mixed  with  such 
nerves  for  the  same  organ,  it  is  necessary  to  adopt  a  special  order  of  experi- 
mentation, because  the  vasoconstrictor  effect  of  stimulation  often,  if  not  always, 
predominates.  A  strong  vasodilation  appears  as  an  after-effect  of  the  simul- 
taneous stimulation  of  both  kinds  of  nerves.  The  two  are,  therefore,  not 
strictly  antagonistic,  but  must  affect  the  vessels  at  different  points,  just  as  the 
two  kinds  of  cardiac  nerves  have  different  points  of  application  in  the  heart 
(Y.  Frey;  cf.  page  193). 

On  the  other  hand,  weak  stimulation  of  the  constrictor  nerves  is  overcome 
by  stronger  stimulation  of  the  dilators.  This  appears,  for.  example,  in  the  case 
of  the  submaxillary  gland  with  the  cervical  sympathetic  intact.  Although  the 
vessels  of  the  submaxillary  gland  are  under  the  influence  of  the  constrictor 
fibers  contained  in  this  nerve,  stimulation  of  the  lingual  produces  vasodilation. 

If  a  nerve  trunk  be  cut  in  two  transversely,  and  the  animal  be  allowed  to 
live,  degeneration  of  the  peripheral  stump  appears  in  a  short  time.  If  the 
degenerating  nerve  be  stimulated  some  four  dai/s  after  the  section,  vasodilation 
is  obtained  (Goltz),  whereas  stimulation  of  the  fresh  nerve  causes  vasocon- 
striction. This  means  that  the  dilator  nerves  retain  their  irritability  some- 
what longer  than  the  constrictor  nerves  after  connection  with  the  central 
nervous  system  has  j)een  destroyed. 

By  appropriate  variation  of  the  stimulus  the  presence  of  dilator  fibers  can 
be  demonstrated  also  in  freshly  cut  nerves.  Thus  it  has  been  shown  that  the 
latter  are  more  irritable  than  the  constrictor  nerves  if  the  stimulus  is  weak 
or  is  applied  rlnjtlimically  at  a  stow  rate  (Ostroumoff.  Bowditch). 

Finally,  it  has  been  found  that  even  if  the  two  kinds  of  nerve  fibers  run  in 
the  same  peripheral  nerve  trunk,  they  make  their  exit  by  way  of  different 
roots  of  the  spinal  cord,  and  can  be  separated  one  from  the  other  by  this 
means  (Dastre  and  Morat). 

Other  characteristics  of  the  dilator  nerves  are  the  following:  (1)  the  latent 
period  for  their  stimulation  appears  to  be  somewhat  longer  than  that  of  the 
constrictor  nerves;  (2)  whereas  the  maximum  effect  of  the  constrictors  is  quickly 
reached,  that  of  the  dilators  takes  more  time;  (3)  the  after-effect  is  longer. 

The  Course  of  the  Vasodilator  Nerves. — We  have  already  become  acquainted 
with  the  vasodilator  nerves  which  traverse  the  lingual  nerve  to  the  submaxillary 


VASOMOTOR   REFLEXES  235 

gland.  They  come  from  the  facial  and  pass  by  way  of  the  chorda  tym^pani  to 
the  lingual.  In  the  same  path  are  found  also  the  dilator  nerves  for  the  anterior 
two-thirds  or  three-fourths  of  the  tongue.  The  dilator  fibers  for  the  posterior 
part  of  the  tongue,  for  the  anterior  pillars  of  the  fauces,  and  the  tonsils  run  in 
the  trunk  of  the  glossopharyngeal. 

The  vasodilator  fibers  of  the  mucous  membrane  of  the  lips,  the  cheeks,  the 
hard  palate  and  the  external  nares,  as  well  as  of  the  corresponding  parts  of 
the  skin  of  the  face  comes  from  the  second  to  the  fifth  thoracic  nerves,  traverse 
the  cervical  sjiiipathetic  and  unite  for  the  most  part  with  the  trigeminal,  which 
itself  also  contains  fibers  of  this  kind  for  the  face  and  for  the  eye  (Dastre  and 
Morat). 

The  ear  gets  its  dilator  fibers  from  the  eighth  cervical  and  first  thoracic 
nerves. 

The  dilator  nerves  of  the  anterior  extremities  leave  the  spinal  cord  from  the 
fifth  to  the  eighth  thoracic :  those  of  the  posterior  extremities  probably  in  the 
second  to  the  fourth  lumbar  nei*ves.  Here  we  meet  with  the  remarkable  circum- 
stance that  the  latter  nerves  pass  out  exclusively  in  the  posterior  roots  of  the 
lumbar  nerves  (Strieker,  Bayliss;  cf.  Chapter  XXII).  The  presence  of  vaso- 
dilator nerves  in  the  posterior  roots  of  the  brachial  plexus  has  been  asserted 
also.  We  have  the  following  facts  with  regard  to  the  dilator  nerves  of  the 
abdominal  organs:  Vasodilator  fibers  in  abundance  are  found  in  the  second  to 
twelfth  thoracic  as  well  as  in  the  first  and  second  lumbar  nerves  of  the  dog :  the 
twelfth  and  thirteenth  thoracic  contain  a  number  of  these  in  their  dorsal  roots; 
the  splanchnics  and  the  upper  thoracic  nerves  contain  the  vasodilator  fibers 
for  the  organs  of  the  abdomen. 

The  vagus  is  said  to  convey  vasodilator  nerves  for  the  coronary  arteries  of 
the  heart.  Most  of  the  dilator  nerves  for  the  coronary  vessels  however  traverse 
the  sympathetic  pathways.  They  probably  pass  out  of  the  spinal  cord,  and 
reach  the  heart  by  way  of  the  stellate  ganglion  (cf.  Fig.  67,  page  191). 

According  to  some  authors  the  lungs  receive  dilator  fibers  from  the  cervical 
sympathetic  as  well  as  from  the  vagus. 

The  vessels  of  the  mucous  membrane  of  the  larynx  are  provided  with  dilator 
nerves  from  the  superior  larjTigeal. 

Vasodilator  nerves  which  play  an  essential  role  in  the  erection  of  the  penis 
pass  to  that  organ  by  way  of  the  anterior  roots  of  the  first  to  the  third  sacral 
nerves,  and  the  hypogastric  plexus. 


§  11.    VASOMOTOR   REFLEXES 

Like  the  cardiac  nerves,  the  vasomotor  nerves  are  stiniiilated  refexly,  and 
the  blood  supply  to  the  various  organs  as  well  as  the  arterial  blood  pressure 
is  variously  influenced. 

We  have  ditl'ereut  observations  tending  to  show  that  vasomotor  reflexes  can 
be  discharged  by  the  vessels  themselves,  so  that  the  vessels  may  be  said  to 
participate  in  the  reflex  regulation  of  their  own  functions.  We  know  also 
that  these  reflexes  are  set  up  by  all  other  possible  kinds  of  afferent  nerves. 

The  reflex  lakes  effect  primarily  in  the  same  vascular  region  whence  came 
the  afferent  impulse.  Possibly  the  congestion  which  has  long  been  known  to 
take  place  on  rubbing  or  warming  the  skin  belongs  to  this  class  of  reflexes, 
also  the  congestion  which  is  seen  in  the  intestine  when  the  abdominal  cavity 
is  opened. 


236 


CIRCULATION   OF  THE   BLOOD 


Generally  speaking  the  result  of  these  localized  reflexes  is  a  vasodilation, 
but  under  certain  circumstances  vasoconstriction  may  be  the  result.  The 
reflex  may  spread  to  the  corresponding  part  of  the  body  on  the  opposite  side, 
and  not  infrequently  parts  far  removed  from  the  region  innervated  by  the 
afferent  nerve  show  a  reflex  constriction  or  dilation  of  their  vessels.  Thus 
the  vast  region  innervated  by  the  splanchnics  is  very  easily  constricted  by 
stimulation  of  all  possible  kinds  of  sensory  nerves.  It  may  also  be  dilated 
as  the  result  of  a  sensory  excitation.  The  vessels  of  the  skeletal  muscles  as  a 
rule  appear  to  be  dilated  by  sensory  impulses.  The  dilation  appears  first  in 
the  muscles  which  stand  in  close  functional  relationship  with  the  nerves  stimu- 
lated ;  but  it  may  be  called  out  also  by  excitation  of  distant  afferent  nerves. 

If  these  reflex  effects  are  not  confined  within  too  small  a  vascular  field, 
they  influence  the  general  blood  pressure. 

Since  in  almost  every  afferent  stimulation,  vessels  somewhere  are  con- 
stricted and  others  dilated,  it  is  evident  that  changes  of  pressure  may  take 
place  in  both  the  po.  itive  and  the  negative  direction. 

As  a  rule,  afferent  excitation  produces  a  reflex  rise  of  pressure  (Fig.  97). 
Under  certain  circumstances  a   fall  is  obtained  instead,  for  example:  when 


Fig.   97. — Reflex  rise  of  blood  pressure  in  the  rabbit  (to  be  read  from  riglit  to  left). 

skin  was  stimulated. 


At  a  the 


the  afferent  nerve  stimulated  is  subjected  to  the  cold ;  when  after  having  been 
sectioned  it  is  allowed  to  regenerate  to  a  certain  stage;  if  the  stimulus  is 
weak. 

At  present  it  is  impossible  to  decide  whether  these  different  reflexes  are 
caused  by  two  kinds  of  efferent  nerves  or  by  the  difference  in  l^ehavior  of  the 
vasomotor  center  to  stimuli  of  different  strength.  There  are  nerves  however 
which,  so  far  as  our  present  information  goes,  mediate  only  a  fall  of  pressure, 
whatever  the  strength  of  stimulus.     Such  a  nerve  is  the  depressor,  already 


THE   VASOMOTOR  CENTERS  237 

mentioned  at  page  I'JiJ.     The  afferent  nerves  from  the  muscles  have  the  same 
influence  on  the  blood  pressure  (Fig.  98). 

The  reflex  fall  of  pressure  on  stimulation  of  the  depressor  appears  with  both 
vagi  cut;  hence,  it  is  independent  of  changes  in  the  heart  frequency  and  is 
caused  essentially  by  a  vasodilation.  This  involves  primarily  the  region  of  the 
abdominal  cavity  innervated  by  the  splanchnics,  although  other  parts  of  the  body 
may  take  part  in  it. 

The  reflex  rise  of  pressure  is  produced  primarily  by  a  contraction  of  the 
vascular  region  innervated  by  the  splanchnics,  even   though  other  regions  also 


Tig.  9>^. — Reflex  fall  of  blooil  pressure  in  the  rabbit  produced  by  stimulation  of  an  afferent 
muscular  nerve  (to  be  read  from  right  to  left).  The  period  of  stimulation  is  indicated  by 
the  vertical  lines.   |  1    =  ten  seconds. 

may  be  concerned.  Xot  all  the  vascular  regions  of  the  body  are  constricted,  at 
least  not  to  the  same  extent,  when  the  pressure  rises;  for  vasodilatation  has  often 
been  observed  in  dilTerent  organs,  especially  in  the  muscles. 

It  is  difficult  to  decide  in  many  cases  whether  a  given  dilator  effect  is  active 
or  passive.  It  may  be  that  with  an  increase  of  pressure  produced  by  an  extensive 
contraction  of  the  splanchnic  region,  various  other  regions  dilate  only  because 
of  the  high  pressure.  Or  it  may  be  that  dilatation  is  actively  produced,  either 
by  a  decline  in  the  tonus  of  the  constrictor  nerves  or  by  stimulation  of  the 
dilator  nerves. 

A  fall  in  pressure  obtained  reflexly  is  caused  by  a  reduction  of  tonus  in  some 
of  the  great  vascular  regions.  But  as  in  the  case  of  a  rise  of  pressure,  the  reduc- 
tion may  be  due  either  to  stimulation  of  dilator  nerves,  or  to  diminished  activity 
of  the  constrictors.  After  excluding  all  the  vasoconstrictor  nerves  of  the  hind 
limb,  Bayliss  succeeded  in  demonstrating  vasodilatation  in  the  same  region  by 
stimulation  of  the  vagus.  In  this  case,  therefore,  the  dilatation  took  place 
through  the  activity  of  the  vasodilator  nerves. 

§  12.    THE   VASOMOTOR   CENTERS 

We  have  no  positive  data  as  yet  for  the  location  of  centers  for  the  vaso- 
dilator nerves.    These  nerves  have  been  followed  far  into  the  central  nervous 


238  CIRCULATION   OF  THE   BLOOD 

system,  and  it  is  very  prol)able  that  their  chief  center,  like  the  centers  of  the 
other  vegetative  functions,  lies  in  the  medulla  oblongata. 

The  chief  center  for  the  vasoconstrictor  nerves  is  positively  known  to  lie 
in  the  medulla.  In  the  rabbit  it  occupies  on  each  side  a  small  prismatic 
space;  in  man  in  a  cross  section  taken  at  the  level  at  which  the  facial  nerve 
passes  off.  it  appears  as  one  or  more  aggregations  of  gray  matter  on  the 
median  side  of  the  facial  tract.  From  this  center  the  vasoconstrictor  nerves 
descend  chiefly,  but  not  exclusively,  in  direct  paths  along  the  cord  and  pass 
out  in  the  nerve  roots  already  mentioned  (page  232).  As  we  have  seen,  the 
center  is  under  tonic  stimulation.  If  by  transecting  the  cord,  its  influence 
be  cut  off,  the  vascular  tonus  falls  and  as  a  consequence  the  blood  pressure 
becomes  considerably  less. 

But  the  vascular  tonus  is  not  entirety  ohHternted  by  this  operation.  On 
the  contrarv,  it  has  been  shown  that  throughout  the  entire  length  of  the 
spinal  cord,  with  the  exception  only  of  the  cervical  region,  and  the  lowest 
part  of  the  lumbar,  there  are  centers  for  the  vasoconstrictor  nerves  which  can 
be  stimulated  both  reflexly  and  by  asphyxiation.  These  centers  appear  to  be 
less  excitable  than  the  vasomotor  center  in  the  medulla  (although  this  is 
denied).  They  do  not  react  so  promptly  as  that  center;  but  their  activity 
lasts  longer;  and  in  virtue  of  their  greater  endurance  they  appear  to  be  of 
no  less  importance  for  the  maintenance  of  vascular  tonus. 

Experiment  has  shown  also  that  after  destruction  of  a  targe  part  of  the 
spinal  cord,  the  tonus  of  the  vessel  may  be  gradually  restored.  The  vessels 
which  receive  their  constrictor  nerves  from  the  destroyed  part  of  the  spinal 
cord  are  at  first  entirely  paralyzed,  and  they  are  dilated  to  their  maximal 
extent.  But  gradually  their  tonus  returns;  they  react  to  local  application  of 
cold  and  heat  much  the  same  as  in  the  normal  condition,  but  are  not  influ- 
enced by  distant  parts  of  the  body  (Goltz  and  Ewald).  Either  the  vascular 
wall  itself  must  have  the  property  of  contracting  in  a  tonic  manner,  when  it 
is  entirely  isolated  from  the  central  nervous  system,  or  this  tonic  contraction 
is  caused  by  ganglion  cells  strewn  along  the  peripheral  course  of  the  vasomotor 
nerves,  which  then  serve  as  vasomotor  centers  of  a  third  order.  A  definite 
decision  between  these  two  alternatives  is  not  possible,  and  the  inherent  prob- 
ability of  the  one  or  the  other  naturally  shapes  itself  according  to  one's 
inclination  to  ascribe  greater  or  less  importance  to  the  peripheral  ganglia. 

The  fact  remains  however  that  vessels  entirely  isolated  from  the  central  ner- 
vous system  can  recover  their  tonus.  And  the  action  of  the  vasodilator  nerves 
favors  the  idea  that  vascular  tonus  is,  at  least  in  part,  of  peripheral  origin.  We 
know  of  no  muscles  whose  contraction  could  cause  the  vessels  to  dilate.  Dilata- 
tion must  be  caused  therefore  by  diminishing  the  activity  of  the  circular  muscle 
fibers — i.e.,  vasodilator  nerves  must  be  a  kind  of  inhibitory  nerves.  They  can 
even  exercise  their  characteristic  influence  upon  the  vessels  when  all  the  vaso- 
constrictor nerves  to  the  same  part  of  the  body  have  been  cut.  In  other  words, 
a  certain  tonus  of  the  vessels  remains  after  section  of  the  constrictor  nerves, 
which  however  is  entirely  obliterated  by  stimulation  of  the  vasodilator  nerves. 

We  can  form  the  following  conception,  therefore,  of  the  innervation  of  the 
blood  vessels.  The  musculature  of  the  vessels  is  under  the  influence  of  the 
central  nervcms  <iystem  and  of  peripheral  strxictures.     In  the  former  is  found 


DISTRIBUTION   OF   BLOOD   IN   THE   BODY  239 

the  vasomotor  center  located  in  the  medulla,  which  constitutes  the  chief  center 
of  the  vasoconstrictor  nerves.  The  centers  distributed  in  the  spinal  cord 
represent  centers  of  the  second  order,  and  the  peripheral  ganglia  or  the  muscu- 
lature of  the  vessels,  as  the  case  may  be,  represent  centers  of  the  third  order. 
The  last  named  can  exert  a  powerful  influence  even  when  they  are  isolated 
from  the  others.  As  a  rule,  the  musculature  of  the  vessels  is  in  a  state  of 
tonic  contraction  because  of  impulses  passing  out  over  this  chainlike  series 
of  centers.  The  contraction  is  more  or  less  weakened  by  stimulation  of  the 
vasodilator  nerves,  since  they  exert  an  inhibitory  influence  on  the  peripheral 
mechanism. 

The  parts  of  the  brain  above  the  medulla,  especially  the  motor  zone  of  the 
cerebrum,  influence  the  blood  vessels.  With  regard  to  this  influence,  I  believe 
with  Fr.  Franck  that  it  is  to  be  conceived  in  the  same  way  as  that  produced  by 
the  same  parts  upon  the  cardiac  nerves — i.  e.,  that  the  vasomotor  center  of  the 
medulla  is  set  in  action  by  these  parts  of  the  brain  in  exactly  the  same  way  as 
it  is  stimulated  by  the  other  parts  of  the  body  throug^h  their  afferent  nerves. 
And  just  as  we  have  seen  that  in  muscular  activity  the  acceleration  of  the  heart 
is  conditioner!  by  this  influence  of  the  cerebrum  upon  the  medulla,  we  may  infer 
from  the  facts  which  we  already  have  that  the  change  in  vascular  tonus  taking 
place  in  muscular  work  are  produced  by  a  similar  influence. 


§    13.      GENERAL    CONSIDERATIONS    ON    THE    DISTRIBUTION    OF 

BLOOD   IN   THE   BODY 

The  distribution  of  blood  in  the  body  depends  partly  upon  mechanical 
conditions,  but  chiefly  upon  the  vasomotor  nerves. 

A.    MECHANICAL  IMFLUENCES 

To  these  belong  first  the  caliber  of  the  afferent  arteries ;  the  greater  the 
caliber,  the  greater,  other  things  being  equal,  must  be  the  supply  of  blood  to 
the  part.  Moreover  the  attitude  of  the  body  plays  a  prominent  part  especially 
in  the  flow  of  blood  in  the  veins.  In  the  upright  position,  for  example,  the  veins 
of  the  lower  extremities  are  dilated  because  of  the  hydrostatic  pressure  of  the 
blood  column,  and  they  contain  a  large  quantity  of  blood.  In  changing  to  the 
horizontal  position  the  rich  supply  of  blood  to  the  lower  extremities  decreases. 
The  quantity  which  is  shifted  in  this  way  amounts  in  a  grown  man  to  about 
100  g.  (Mosso). 

The  influence  of  the  respiratory  movements  on  the  circulation  has  already 
been  discussed.  With  a  positive  pressure  in  the  thoracic  cavity,  for  example,  in 
severe  muscular  effort,  when  the  lungs  are  inflated  and  the  glottis  is  closed,  the 
return  flow  of  blood  to  the  heart  is  hindered  and  the  quantity  in  the  extremities 
increases. 

If  with  the  body  in  a  vertical  position,  the  head  being  upward,  the  splanch- 
nics  be  cut  so  as  to  paralyze  the  great  vascular  region  of  the  abdominal  viscera, 
and  the  respiration  be  then  interrupted,  the  circulation  stops  at  once.  The 
dilated  vessels  of  the  abdomen  contain  so  much  blood  that  the  heart  no  longer 
receives  a  sufficient  supply.  In  such  cases,  however,  the  circidation  can  be 
restored  to  some  extent  by  respiratory  movements,  the  blood  being  drawn  by  the 
aspiration  of  the  thorax  from  the  venae  cavaj  to  the  heart  (Hill  and  Barnard). 


240  CIRCULATIOX    OF  THE    BLOOD 

An  increase  or  decrease  of  turgor  in  a  certain  part  incident  to  diflFerent 
positions  of  the  body  must  evidently  produce  in  other  parts  changes  of  an  oppo- 
site character.  The  volume  of  one  arm  is  greater  when  the  other  is  held  pas- 
sively above  the  head ;  the  volume  of  the  hand  increases  when  both  femoral 
arteries  are  compressed,  etc.  Keflex  activity  of  the  vasomotor  nerves  often  comes 
in  here  to  influence  the  result. 

B.    THE  INFLUENCE  OF  VASOMOTOR  NERVES 

In  general  one  may  say  that  under  normal  circu7n stances  every  part  of 
the  body  receives  exactly  as  much  Mood  as  it  has  need  of,  and  that  by  dilata- 
tion of  vessels  a  particular  part  receives  more  blood  the  more  active  it  is. 
At  the  same  time  blood  vessels  in  other  parts  of  the  body  are  constricted,  and 
in  this  M'ay  the  normal  blood  pressure  necessary  for  life  is  maintained  by  an 
incessant  reciprocity  between  the  different  vascular  regions. 

In  the  state  of  bodily  rest  the  organs  of  the  thorax  and  abdomen  contain  a 
relatively  large  part,  as  a  rule  more  than  half,  of  the  total  quantity  of  blood 
in  the  bod3^  The  content  of  blood  in  these  organs  amounts  to  al)out  twenty 
per  cent  of  their  weight,  Avhile  the  blood  content  of  the  skin,  skeleton,  muscles 
and  the  nervous  substances  amounts  to  only  two  to  three  per  cent  of  their 
weight  (Kanke  et  ol.).  The  blood  stored  up  in  the  internal  organs  is  always 
at  the  disposal  of  any  organ  which  has  need  of  a  larger  supply. 

Thus  in  muscular  work  the  vessels  of  the  muscles  and  skin  are  dilated,  while 
at  the  same  time  the  vessels  innervated  by  the  splanchnic  nerve  are  constricted 
to  a  greater  extent.  Consequently  the  blood  pressure  as  a  rule,  if  not  ahvays, 
increases. 

By  the  use  of  apparatus  constructed  for  the  purpose  of  determining  the 
velocity  of  the  blood,  the  quantity  flowing  through  some  of  the  organs  in  a  given 
time  has  been  measured  directly  (cf.  also  page  211).  In  the  dog  Tschuewsky 
found  the  quantity  per  minute  and  per  100  g.  of  organ  to  be  3.4  c.c.  for  the  hind 
limbs  with  the  nerves  intact,  and  9.9  c.c.  after  section  of  the  nerves.  The  head 
received  16.6  c.c,  muscles  with  uncut  nerves  13  c.c,  the  thyroid  gland  590.9 
c.c.   (!),  all  per  minute  and  per  100  g.  of  organ. 

In  the  researches  of  Chauveau  and  Kaufmann  the  quantity  of  blood  flowing 
through  the  levator  superiorus  proprius  muscle  of  the  horse  was :  in  rest,  on  the 
average,  17.5  c.c  per  100  g. ;  in  activity,  it  rose  to  85  c.c  According  to  Bohr  and 
Henriques,  the  dog's  heart  receives  on  the  average  30  c.c.  per  minute  per  100  g. 

In  view  of  its  function  of  removing  from  the  body  the  nitrogenous  products 
of  metabolism,  the  kidney  receives  a  relatively  large  quantity  of  blood,  especially 
if  great  demands  are  made  upon  it  by  transfusion  of  a  diuretic  agent  (cf.  Chap- 
ter XIII).  There  then  flows  through  the  kidney  (dog)  per  minute  a  quantity 
of  blood  which  amounts  to  one  hundred  and  forty  per  cent  of  its  own  weight 
(average  ninety-six  per  cent).  In  the  same  animal  the  quantity  of  blood  expelled 
from  the  left  heart  per  minute  may  be  estimated  at  about  ten  per  cent  of  the 
body  weight.  Hence,  in  strong  diuresis  the  blood  supply  to  the  kidney  would  be 
relatively  fourteen  times  as  great  as  to  all  the  organs  talcen  together. 

Furthermore  the  distribution  of  blood  to  the  different  parts  of  the  body 
exhibits  incessant  fluctuations  produced  by  the  vasomotor  nerves,  which  are 
connected  either  with  the  activity  of  the  organs,  or  with  the  heat  regulation  of 
the  body;  for  the  heat  regulation  is  controlled  in  the  main  by  vasomotor  nerves 
(cf.  Chapter  XIV). 


DISTRIBUTION   OF   BLOOD   IN   THE   BODY  241 

The  hlood  flow  to  the  brain  calls  for  a  special  discussion.  In  the  child 
while  the  skull  is  not  yet  completely  ossified,  the  great  fontanel  exhibits  pulsa- 
tions which  are  undoubtedly  caused  by  the  heart  beats  and  by  the  respiratory 
movements,  and  which  show  moreover  that  the  blood  supply  to  the  brain  may 
vary  under  different  circumstances. 

How  far  this  is  true  in  the  mature,  uninjured  shidl  has  been  much  debated. 
Were  the  skull  cavity  rigidly  closed  on  all  sides,  and  were  the  brain  substance 
nearly  incompressible,  the  same  quantity  of  blood  should  be  present  in  the  brain 
at  all  times.  But  this  would  not  be  true,  if  water  or  other  material  were  secreted 
from  the  blood  vessels  or  otherwise  extravasated ;  for  then  the  quantity  of  blood 
equivalent  to  the  volume  of  material  poured  out  of  the  vessels  would  be  dis- 
placed. Otherwise  blood  flowing  away  by  the  veins  would  always  make  room  for 
the  blood  flowing  in  by  the  arteries. 

But  it  has  been  shown  that  this  conclusion  is  not  strictly  correct,  and  that 
the  quantity  of  hlood  in  the  hrain  can  in  fact  increase  and  decrease.  The  skull 
cavity  is  not  surrounded  on  all  sides  by  solid  bony  walls.  It  communicates  with 
the  spinal  canal,  between  the  inner  surface  of  which  and  the  outer  surface  of 
the  dural  sac  are  numerous  venous  plexuses  connected  with  the  veins  of  the 
general  system.  The  foramina  intervertebralia  are  filled  with  a  vacuolated  tissue, 
which  can  be  pressed  outward.  The  subdural  space  communicates  with  the  deep 
lymph  vessels  and  glands  of  the  neck,  as  well  as  with  the  lymph  tracts  of  the 
peripheral  nerves. 

The  subarachnoid  spaces  are  likewise  in  connection  with  the  lymph  tracts 
of  the  peripheral  nerves.  The  cerebrospinal  canal  therefore  must  be  regarded  as 
a  rigid-walled  cavity  with  an  elastic  door. 

Now  it  has  been  found  both  by  experiments  on  animals,  and  by  physical 
(Grashey)  and  mathematical  (Lewy)  calculations,  that  the  regulation  of  the 
hlood  flow  to  the  hrain  takes  place  in  exactly  the  same  way  as  in  the  other 
organs — i.  e.,  dilatation  of  the  arteries  produces  an  increase  in  the  flow,  con- 
striction a  diminution.  Any  stasis  of  venous  blood  causes  an  arterial  antemia, 
just  as  does  a  severe  compression,  as  for  example  by  a  foreign  body  forced  into 
the  skull  cavity.  So  long,  therefore,  as  it  is  a  question  only  of  the  alterations 
in  arterial  volume,  which  correspond  to  the  physiological  needs,  the  circum- 
stance that  the  brain  is  inclosed  by  a  solid,  unyielding  capsule  is  of  no  essential 
importance. 

Jensen  has  found  that  the  quantity  of  blood  flowing  to  the  brain  of  a  rabbit 
is  on  the  average  130  c.c.  per  100  g.  per  minute  (extremes  60-278  c.c).  In  the 
dog  he  found  as  a  mean  of  two  researches  138  cc.  The  hrain  receives  relatively 
more  hlood  than  any  of  the  other  organs  thus  far  studied  except  the  thyroid  gland. 

Eeferences. — R.  Tiegerstedt,  "  Lehrbuch  der  Physiologic  des  Kreislaufes," 
Leipzic,  1893. 


CHAPTER    VII 


DIGESTION 


The  purpose  of  digestion  is  to  so  change  the  foodstuffs  that  they  can  pass 
into  the  blood  and  be  utilized  in  metabolism.  To  this  end  the  food  is  sub- 
jected to  mechanical  division  and  chemical  transformation  in  the  digestive 
organs. 

Of  all  the  combustible  constituents  of  our  diet,  onlv  sugar  is  soluble  in 
water.  Starch  and  coagulated  proteid  are  insoluble  in  water ;  but  by  digestion 
they  are  so  changed  that  they  can  be  taken  into  solution.  Fat  also,  which  is 
insoluble  in  water,  is  transformed  so  that  it  can  be  absorbed  from  the  ali- 
mentary tract  into  the  Ijlood. 

The  organic  foodstuffs,  which  are  already  soluble,  undergo  transformations 
in  the  alim'^ntary  canal  which  adapt  them  to  the  requirements  of  metabolism. 
The  noneombustible  constituents  of  the  diet,  water  and  the  salts,  do  not  require 
to  be  digested  in  order  to  be  taken  into  the  blood. 

In  man  the  work  of  the  digestive  system  is  materially  aided  by  the  prepa- 
ration of  "  dishes  "  of  food,  since  the  foodstuffs  are  thereby  rendered  more 
easily  accessible  to  the  digestive  fluids. 

The  heat  necessary  to  boil  or  roast  meat  swells  the  connective  tissue,  which 
holds  the  muscle  fibers  together,  and  changes  it  partly  into  gelatin.  The  meat 
at  the  same  time  becomes  less  compact,  and  so  is  the  more  readily  reduced  to 
fine  bits  bj'  our  teeth.  In  the  cooking  of  vegetable  foods,  the  cell  membranes 
are  ruptured  by  the  heat  and  the  starch  granules  are  transformed  into  a  soluble 
modification.  In  bread  baking  the  dough  is  rendered  spongy  by  the  carbon 
dioxide  formed  in  "  raising,"  and  this  is  carried  still  further  by  the  heat  of  the 
oven,  by  which  also  the  starch  granules  are  transformed  in  the  same  way  as  in 
ordinary  cooking. 

FIRST    SECTION 

THE   DIGESTIVE   FLUIDS 

§  1.    GENERAL    SURVEY 

The  fluids   secreted  by  the  digestive  glands  serve  either  to   change  the 

chemical  nature  of  the  foodstuffs  so  that  they  shall  be  fit  for  absorption,  or 

they  aid  the  processes  going  on  in  the  alimentary  canal  in  some  other  way. 

Certain  products  also  which  are  given  off  with  the  digestive  fluids  are  des- 

242 


GENERAL   SURVEY  243 

tined  merely  to  be  eliminated  from  the  body.     In  this  section  we  shall  con- 
sider in  the  main  only  the  constituents  important  in  digestion. 

In  order  to  study  the  chemical  properties  and  the  action  of  the  diflEerent 
digestive  fluids,  one  may  use  either  extracts  of  the  appropriate  glands  or  the 
natural  secretion  collected  from  their  ducts.  In  the  latter  case  the  duct  is 
shifted  from  its  normal  connections  and  is  made  to  open  as  a  fistula  on  the 
outer  surface  of  the  body,  so  that  it  conveys  the  secretion  to  the  exterior. 

The  first  fistula  of  a  digestive  grland  to  be  the  subject  of  a  thoroughly  scien- 
tific investigation  was  one  resulting,  from  a  gunshot  wound  in  the  stomach  of 
a  Canadian  hunter.  As  a  consequence  of  his  accident,  the  hunter  had  all  the 
rest  of  his  life  a  stomach  fistula  opening  at  the  upper  part  of  the  abdomen, 
through  which  the  interior  of  the  stomach  could  be  observed  and  gastric  juice 
could  be  obtained.  From  observations  on  this  man  extending  over  a  number  of 
years  (1825-1833)  Beaumont  collected  a  large  number  of  important  facts  con- 
cerning the  digestive  process  in  the  stomach,  and  concerning  the  movements  of 
that  organ.  Later  Bassow  and  Blondlot  (1842)  showed  how  a  stomach  fistula 
may  be  made  on  an  animal.  Since  that  time  such  fistulae  have  been  made  for 
therapeutic  purposes  on  man  himself,  and  they  have  been  used  to  good  advan- 
tage for  the  study  of  gastric  digestion. 

The  pancreatic  juice  is  obtained  by  means  of  a  cannula  fastened  in  the  duct 
of  Wirsung,  or  from  the  open  duct  sutured  to  the  abdominal  wall,  or  finally  by 
isolating  that  portion  of  the  intestine  into  which  the  duct  opens  and  bringing 
it  forward  to  the  abdominal  wall. 

In  order  to  study  the  secretion  of  bile,  fistulte  are  made  in  the  gall  bladder. 
The  ductus  choledochus  can  be  tied  off  and  the  bile  can  thus  be  entirely  shut  out 
of  the  intestine,  or  the  duct  can  be  left  open,  so  that  the  bile  flows  as  usual  to 
the  intestine  except  when  the  fistula  is  open  (amphibolous  biliary  fistula).  The 
intestinal  loop  containing  the  mouth  of  the  duct  can  also  be  resected  and  brought 
forward  to  the  abdominal  wall.  By  the  last  method  especially  it  is  possible  to 
observe  how  the  bile  flow  is  affected  by  different  kinds  of  food. 

To  obtain  pure  intestinal  juice  a  loop  of  the  intestine  is  isolated,  one  end 
of  it  is  sutured  to  the  skin  and  the  other  is  closed  (Thiry's  fistula)  ;  or  both 
ends  may  be  sutured  to  the  skin  (Vella's  fistula),  in  which  case  the  intestine  is 
of  course  more  accessible. 

The  most  important  constituents  of  the  digestive  fluids  are  certain  en- 
zymes which  may  be  classified  in  three  groups:  proteid  dissolving  (proteo- 
lytic), sugar  forming  (diastatic  or  aniylolytic)  and  fat  splitting  (lipolytic). 
All  of  the  digestive  enzymotic  processes  agree  in  this,  that  the  organic  food- 
stufi's  acted  upon  absorb  the  constituents  of  water  and  are  split  into  simpler 
compounds  (hydrolytic  cleavage). 

The  enzymes  are  formed  in  the  different  glands  of  the  alimentary  canal ; 
namely,  the  proteolytic  in  the  glands  of  the  stomach  and  in  the  pancreas; 
aniylolytic  in  the  salivary  glands,  in  the  pancreas  and  in  the  glands  of  Lieber- 
kiihn  of  the  small  intestine,  lipolytic  in  the  mucous  membrane  of  the  stomach 
and  in  the  pancreas. 

Two  enzymes  which  act  on  the  same  foodstuffs  are  not  necessarily  identical. 
For  example,  pepsin  from  the  gastric  glands  acts  on  proteid  in  an  acid  medium, 
while  tr:\psin  from  the  pancreas  acts  on  proteid  in  neutral  and  alkaline  media. 


244  DIGESTION 

The  enzymes  are,  so  far  as  we  know,  formed  in  the  glands  themselves. 
During  the  intervals  between  meals  they  are  deposited  in  the  glands,  to  be 
poured  out  when  required  for  digestion.  But  we  do  not  find  the  finished 
product  in  the  glands :  instead,  precursors  of  the  enzymes,  the  so-called  zymo- 
gens, are  elaborated  in  them  and  are  transformed  into  the  enzymes  either 
during  the  act  of  secretion  or  in  the  secretory  product  after  it  is  given  off 
(Fig.  99). 

Artificial  digestioji  is  often  employed  in  studying:  the  action  of  the  digestive 
fluids  on  the  foodstuffs — i.  e.,  a  given  food  is  mixed  either  with  the  fluid  secreted 
by  a  gland  or  with  an  extract  of  the  gland,  and  the  mixture  is  kept  for  a  time 


-i^'-, 


'...■•;,V- 


••■H'^.i  '   ••"•.■•.    JV.  "■*.  ♦•. 

-    ^^V-Lji*  •■  i   ■■"•V'  «•.  •«•«_,    ...^■. ■■■.,/ 


Fig.  99. — Transverse  section  of  the  hepato-pancreas  of  an  isopod  crustacean,  fixed  in  osmic 
acid,  showing  the  gradual  transformation  of  zymogen  granules  into  secretion  droplets, 
after  Murlin.  The  zymogen  granules  appear  first  immediately  about  the  nucleus  (Zym'g.). 
As  the  cell  grows  in  size  the  granules  increase  in  number  so  as  to  almost  fill  1  he  cell  ( 1'.  sym.). 
Still  later  they  absorb  fluid  from  the  protoplasm  and  swell  up,  being  finally  discharged 
from  the  free  border  of  the  cell  as  secretion  droplets  (-1/.  zym.).  Fray.,  fragment  of  a  cell  broken 
off  and  lying  in  the  lumen  of  the  gland;  A'mc,  nucleus  of  a  mature  cell. 

at  body  temperature.  A  great  mass  of  important  facts  has  been  obtained  in 
this  way;  but  we  cannot  apply  the  results  of  artificial  digestion  to  the  natural 
process  in  the  body  without  some  reservation.  For,  even  neglecting  the  me- 
chanical work  of  the  alimentary  canal,  there  are  several  important  differences 
between  the  two.  (1)  In  natural  digestion  the  fluid  is  always  adapted  in  quan- 
tity and  quality  to  the  quantity  and  character  of  the  food  acted  upon,  while  in 
artificial  digestion  both  the  quantity  and  the  character  are  fixed  for  a  given 
experiment.  (2)  In  the  natural  process  the  products  of  digestion  are  removed 
by  absorption  as  soon  as  they  are  formed ;  in  artificial  digestion  they  remain  in 
the  mixture.  This  is  of  no  small  consequence ;  for  in  the  one  case  the  course  of 
digestion  is  affected  by  the  presence  of  these  products  (cf.  page  38),  while  in 
the  other  this  is  prevented  by  their  prompt  removal  from  the  sphere  of  action. 
(3)  Finally,  in  the  normal  course  of  digestion  the  different  secretions  may  influ- 
ence each  other  so  that  the  final  result  may  be  essentially  modified. 


SALIVA  245 

Mett  employs  the  following  method  of  determining  the  strength  of  a  pro- 
teolytic enzyme  in  a  digestive  fluid.  Fresh  white  of  egg  is  sucked  into  a  narrow 
glass  tube,  the  tube  is  dipped  into  water  at  95°  and  is  then  allowed  to  cool 
slowly.  The  tube  is  now  broken  into  small  pieces  and  one  of  them  is  placed 
in  the  fluid  to  be  tested.  The  number  of  millimeters  of  the  coagulated  albumin 
dissolved  in  a  unit  of  time  affords  a  measure  of  the  enzymotic  action.  Amyloly- 
tic  action  can  be  determined  in  a  similar  way  by  means  of  tubes  containing 
colored  starch  paste,  and  lipolytic  action  by  finding  the  amount  of  fatty  acids 
set  free  in  a  given  time  from  a  known  quantity  of  neutral  fat. 

§  2.    SALIVA 

Saliva  is  secreted  b}'  the  three  pairs  of  large  salivary  glands  located  in 
the  neighborhood  of  the  buccal  cavity  and  opening  into  it  by  their  several 
ducts,  and  also  by  small  glands  embedded  in  the  mucous  membrane  of  the 
mouth. 

The  product  has  a  varying  constitution  according  to  the  gland  by  which  it 
is  formed,  and  on  the  basis  of  the  characteristic  properties  of  their  secretions 
the  salivary  glands  may  be  divided  into  two  chief  groups.  One  group,  called 
albuminous  glands,  produce  a  thin,  watery  secretion,  which  contains  only  pro- 
teids,  salts,  and  in  certain  cases  a  diastatic  enzyme.  Here  belong  the  parotid 
gland  of  all  mammals,  the  submaxillary  of  the  rabbit,  some  of  the  glands  in 
the  nose  and  tongue,  and  the  lachrymal  glands.  The  other  group — the  mucous 
glands — secrete  a  more  or  less  viscid  fluid,  which  contains  mucin  as  its  char- 
acteristic ingredient,  besides  salts  and  small  quantities  of  proteid.  This  group 
includes  the  submaxillary  glands  (with  few  exceptions),  the  sublingual,  part 
of  the  buccal  glands,  those  in  the  mucous  membrane  of  the  pharynx,  the 
larynx,  trachea  and  a^sophagus.  There  are  also  mixed  glands — e.  g.,  the  sub- 
maxillary of  man — in  which  a  part  of  the  gland  conforms  to  one  of  these  types, 
and  a  part  to  the  other. " 

The  mixed  saliva  of  man  is  a  colorless  or  light-bluish,  turbid,  odorless, 
slippery  and  viscid  fluid,  which  upon  standing  for  a  time  separates  into  an 
upper,  transparent  and  a  lower,  turbid  layer,  the  latter  consisting  of  mucous 
flakes,  salivary  corpuscles,  epithelial  scales  from  the  mouth,  etc.  The  reaction 
as  a  usual  thing  is  weakly  alkaline  although  it  may  be  neutral,  or  even  weakly 
acid.  It  is  asserted  that  the  reaction  early  in  the  morning  is  weakly  acid, 
neutral  or  amphoteric,  that  after  every  meal  it  becomes  alkaline  and  then 
gradually  returns  to  the  neutral  or  weakly  acid  reaction.  The  specific  gravity 
is  1. 002-1. OOJ). 

The  chief  constituents  of  mixed  saliva  are:  proteid,  mucin,  a  diastatic 
enzyme  (ptyalin),  and  potassium  sulphooyanide  (KCNS).^  Besides,  we  find 
inorganic  salts,  gases  and  traces  of  ammonia,  nitrous  acid,  urea,  etc.  Certain 
drugs  also  are  removed  from  the  blood  in  the  salivary  secretion. 

According  to  recent  analyses,  the  human  saliva  contains  98.8-99.5  per  cent 
water,  and  0.5-0.3  per  cent  solids  of  which  0.1-0.4  per  cent  is  organic;  the 

*  We  can  only  .say  with  regard  to  this  substance  that  its  N  and  S  probably  come  from 
proteid.  It  has  been  assumed  to  confer  an  antiseptic  action  on  the  saliva,  but  this  is  not 
confirmed. 


246  DIGESTION 

salt  content  is  0.1-0.2  per  cent  and  the  KCXS,  0.003-0.01  per  cent.  The 
quantity  of  mixed  human  saliva  secreted  in  twenty-four  hours  is  about 
1.500  c.c. 

The  Diastatic  Enzi/me. — In  1831  Leuchs  found  ihat  saliva  gradually 
dissolves  starch  and  converts  it  into  the  soluble  carboliydrates,  dextrin  and 
sugar.     This  action  is  to  be  ascribed  to  an  enzyme,  called  ptijalin. 

Dry  starch  is  not  soluble,  but  it  swells  up  in  warm  water,  forming  starch 
paste.  On  heating  starch  with  glycerin  up  to  190°,  or  by  acid  fermentation 
of  the  paste,  it  is  rendered  soluble.  Soluble  starch  is  also  the  first  product  of 
digestion  under  the  action  of  ptyalin.  In  the  further  course  of  this  action 
soluble  starch  is  split  by  absorption  of  water  into  dextrin,  isoraaltose,  and 
maltose.  There  is  present  in  saliva  a  trace  of  an  inverting  enzyme,  maltase,^ 
which  converts  a  small  quantity  of  maltose  into  dextrose  (Rohmann). 

More  in  detail,  this  transformation  of  starch  into  sugar  proceeds  al)0ut 
as  follows:  First  the  solul)le  starch  is  split  into  eri/fhrodr.rtrin  (red  color 
with  iodine)  and  maltose.  Then  from  the  erythrodextrin  is  formed  an  achro- 
odextrin  (no  color  with  iodine)  and  more  maltose,  and  achroodextrin  in  its 
turn  yields  another  achroodextrin  and  more  sugar,  etc. 

In  artificial  digestion  starch  can  never  be  completely  changed  into  sugar. 
But  if  the  experiment  be  so  arranged  that  the  sugar  can  be  removed  by  dial- 
ysis as  it  is  formed,  the  transformation  may  be  carried  much  farther  than  is 
possible  otherwise  (Lea).  Since  provision  for  removal  of  the  sugar  is  made 
in  the  digestive  system,  it  is  probable  that  all  the  starch  is  transformed, 
provided  only  that  the  ptyalin  has  the  opportunity  of  acting  long  enough. 

Human  saliva  acts  very  rapidly.  When  equal  volumes  of  saliva  and  starch 
paste  are  mixed,  at  body  temperature  the  starch  disappears  in  about  two  and 
a  half  hours.  Cooked  starch  is  digested  more  rapidly  than  raw,  and  pulver- 
ized starch  more  rapidly  than  nonpulverized. 

Ptyalin  appears  to  act  more  powerfully  in  a  nputrai  or  u-eal-li/  acid  medium  ; 
hence  best  results  are  obtained  when  the  alkaline  saliva  is  carefully  neutralized 
bv  addition  of  a  A'erv  small  quantitv  of  acid  (not  more  tlian  ().000T-0.0012  per 
cent  HCl;  Cole). 

§3.    GASTRIC   JUICE 

Gastric  juice  cannot  be  obtained  pure  from  an  ordinary  gastric  fistula,  for 
even  if  the  particles  of  food  could  be  excluded,  it  would  be  mixed  with  some 
saliva  which  had  been  swallowed.  In  the  dog,  however,  these  difiiculties  can  be 
overcome,  by  making  both  a  stomach  fistula  and  an  opsophageal  fistula  (Pawlow). 
The  stomach  can  also  be  cut  off  from  both  oesophagus  and  duodenum,  the  lat- 
ter two  sutured  together,  and  the  juice  collected  from  the  isolated  stomach 
(Fremont). 

Gastric  juice  obtained  in  this  way.  when  it  is  freed  from  the  stomach 
mucus,  is  perfectly  clear  in  color,  acid  in  reaction  and  is  devoid  of  foreign 
taste.  Its  specific  gravity  is  1.003-1.0039.  In  a  layer  20  cm.  long  it  rotates 
the  plane  of  polarized  light  0.T0°-0.73°  to  the  left.     Its  dry  residue  amounts 

'  In  general  the  enzymes  are  named  by  adding  the  suffix  ase  to  the  name  of  the  sub- 
stance on  which  it  acts.     Exceptions  to  this  rule  are  older  names  still  in  use. 


GASTRIC  JUICE  247 

to  0.29-0.60  per  cent,  the  ash  to  0.10-0.1?  per  cent.  It  contains  neither 
peptone,  nor  leiicin,  nor  tyrosin,  but  always  contains  proteid,  and  at  times 
traces  of  fatty  acids.  At  a  low  temperature  it  becomes  turbid,  and  sepa- 
rates into  three  layers:  an  upper  clear  layer,  a  median  turbid  layer,  and  a 
lower  one  consisting  of  a  sediment  of  small,  homogeneous,  strongly  refractive 
granules. 

The  analysis  by  Schumow-Simanowsky  of  the  pure  gastric  juice  of  the 
dog  is  as  follows: 

Acid 0 .  46  -0 .  58  per  cent. 

Chlorine 0.49-0.63        " 

Dry  residue 0.43-0.60 

Ash 0.09-0.16 

Coagulation  by  alcohol 0.14-0.19        " 

Coagulation  by  heat 0.13-0.18 

Precipitation  at  0°  C 0.011-0.003      " 

Phosphoric  acid 0 .  004      " 

Gastric  juice  inverts  cane  sugar,  digests  proteid,  gelatin  and  gelatin- 
forming  substances,  coagulates  milk  and  splits  emulsified  fats  into  fatty  acid 
and  glycerin. 

The  inversion  of  cane  sugar  is  accomplished  by  the  acid,  the  digestion 
of  proteid,  etc.,  by  pepsin,  the  coagulation  of  milk  by  rennin,  the  cleavage 
of  emulsified  fats  probably  by  a  third  enzyme,  the  gastric  steapsin.  We  have 
now  to  study  more  closely  the  acid  and  these  enzymes  of  the  gastric  juice. 

A.    THE  ACID   OF  THE  GASTRIC  JUICE 

Proof  was  given  by  Prout  as  early  as  1844  that  the  acid  reaction  of 
the  gastric  juice  is  due  to  free  HCl  ^ ;  but  it  was  not  incontestably  established 
until  C.  Schmidt  (1852)  by  his  convincing  analyses  showed  that  more  chlorine 
is  secreted  by  the  mucous  membrane  of  the  stomach  than  can  unite  with  all 
the  inorganic  bases,  including  ammonia,  present  in  the  gastric  juice. 

The  percentage  of  HCl  in  the  gastric  juice  is  very  different  in  different 
animals.  In  the  dog  it  amounts  to  0.46-0.58  per  cent;  and  in  the  case  of 
a  boy  with  a  complete  oesophageal  stricture  and  a  stomach  fistula,  it  was  found 
to  be  0.39-0.5?  per  cent.  In  other  fistulous  patients  0.05-0.3  per  cent  has 
been  observed. 

When  proteids  are  taken  into  the  stomach,  the  HCl  unites  with  them, 
and  later  with  the  products  of  their  digestion  (Sjoquist).  On  this  account 
and  l)ecause  the  HCl  reacts  with  the  phosphates  of  the  food  with  liberation 
of  pliosphoric  acid,  great  difficulty  is  experienced  in  determining  the  quantity 
of  HCl  in  the  stomach  contents,  and  in  following  its  quantitative  varia- 
tions. N^evertheless.  the  mucous  membrane  secretes  more  acid  than  is  neces- 
sary to  combine  with  the  proteid,  consequently  free  acid  can  always  be  demon- 
strated, at  least  in  certain  stages  of  digestion. 

The  HCl  combined  with  proteids  seems  to  insure  their  digestion ;  the 
conception  that  only  free  acid  could  be  of  importance  is  therefore  not  sound. 

'  Lactic  acid  found  in  the  stomach  is  probably  formed  by  bacterial  decomposition  of 
carbohydrates. 
17 


248  DIGESTION 


B.    PEPSIN 


After  Spallanzani  (about  1T80)  luul  showTi  that  the  gastric  juice  can 
produce  chemical  changes  outside  the  hodv.  Eberle  (1834)  was  the  first  to 
demonstrate  the  same  effects  with  extracts  of  the  gastric  mucosa,  and  Schwann 
(183())  pointed  out  that  a  substance  formed  in  the  mucosa,  which  he  named 
pepsin,  is  involved  in  this  action. 

Under  this  name  is  described  the  enzyme  which  acts  in  acid  medium  upon 
proteid.  gelatin  and  connective  tissues,  causing  them  to  absorl)  water  and  to 
split  into  simpler  compounds.  Pepsin  has  no  effect  in  neutral  solution,  and 
is  destroyed  in  soda  solution. 

From  pure  gastric  juice  of  the  dog,  Xencki  and  Sieber,  also  Pekelharing, 
have  prepared  by  dialysis  a  very  pure  pepsin.  This  is  a  proteid  body,  con- 
taining 51-52  per  cent  C.  6.7-7.1  per  cent  H,  14.4  per  cent  X,  1.5-1.6  per 
cent  S,  and  0.5  per  cent  CI.  and  some  Fe.  On  cleavage  it  yields  a  pentose, 
purin  bases,  and  an  acid  (pepsinic  acid,  50.8  per  cent  C,  7.0  per  cent  H.  14.4 
per  cent  X,  1.1  per  cent  S).  Since  in  a  strongly  active  preparation  no  trace 
of  phosphorus  could  be  demonstrated,  pepsin  cannot  be  numbered  among  the 
nucleoproteids.  On  the  other  hand,  it  is  possible  that  it  unites  with  lecithin 
to  form  a  compound  analogous  to  jecorin   (page  79). 

Pepsin  occurs  in  the  mucous  membrane  only  in  the  preliminary  form  of 
its  zymogen,  pepsinogen.  We  have  seen  that  pepsin  is  destroyed  by  soda. 
If  hoAvever  the  mucous  membrane  be  extracted  with  a  iveak  soda  solution 
and  the  extract  be  then  acidified  with  HCl,  a  pepsin-containing  fluid  of  good 
digestive  properties  is  obtained  (Langley).  Therefore  there  must  be  in  the 
mucosa  a  substance  which  is  not  destroyed  by  soda,  and  which  is  transformed 
into  pepsin  by  treatment  with  acids. 

In  artificial  digestion  the  quantitative  results  depend  upon  the  following 
factors:  temperature;  the  amount  of  pepsin;  the  amount  and  the  kind  of  acid; 
the  kind  and  the  amount  of  proteid;  the  presence  of  the  products  of  digestion; 
and  the  presence  of  certain  inorganic  salts. 

The  quantity  of  enzyme  necessary  to  produce  a  very  powerful  digestive 
action  is  very  small.  Thus  in  a  certain  artificial  gastric  juice  of  very  excellent 
digestive  power,  there  was  found  for  example  only  0.067  per  cent  of  nonvolatile 
organic  matter. 

If,  however,  the  quantity  of  HCl  and  of  proteid  remaining  the  same,  the 
quantity  of  pepsin  be  increased,  the  rate  of  digestion  is  increased,  so  that  up  to 
a  certain  limit  the  action  is  proportional  to  the  square  root  of  the  concentration 
of  the  enzyme  (Schiitz).  The  same  law  holds  also  for  the  enzymes  contained  in 
the  pancreatic  secretion  (Walther). 

The  acidity  of  the  digest  is  a  matter  of  particular  importance.  We  find : 
(1)  that  the  optimum  acidity  is  very  different  for  different  proteids;  (2)  that 
too  much  or  too  little  acid  stops  all  digestive  action.  The  most  powerful  action 
on  fibrin,  for  example,  is  said  to  be  obtained  with  an  acidity  of  0.09  per  cent 
HCl ;  at  0.13  per  cent  and  0.02  per  cent  the  action  is  very  feeble.  But  on  coagu- 
lated white  of  egg  the  best  effect  is  obtained  with  0.16-0.25  per  cent  HCl. 

In  the  transformation  of  proteid  under  the  influence  of  pepsin  a  number 
of  different  substances  arise  by  cleavage,  the  composition  of  which  becomes 
simpler  and  simpler  the  farther  the  cleavage  progresses. 


GASTRIC   JUICE  249 

These  substances  may  be  separated  one  from  another  by  fractional  pre- 
cipitation with  ammonium  sulphate.  Those  precipitated  by  a  degree  of  satura- 
tion of  twenty-four  to  forty-two  per  cent  are  called  primary  albumoses  (hetero- 
aWumose,  protoalbumose).  Those  precipitated  by  stronger  concentration  of 
the  sulphate  are  designated  dcitteroalhumoses.  Those  easily  diffusible  prod- 
ucts not  precipitated  by  the  salt,  but  still  giving  the  biuret  reaction,  are  known 
as  peptones.  After  acidification  of  the  solution  the  peptones,  in  an  impure 
condition,  can  be  separated  from  other  end  products  by  precipitation  with 
picric  acid. 

We  have  then  from  peptic  cleavage  of  proteid  (besides  acid  albuminate) 
first,  two  primary  albumoses  (hetero-  and  protoalbumose),  and  then  deutero- 
albumose  (Pick.  Zunz).  Primary  albumoses  show  a  higher  percentage  of 
C  and  X  and  a  lower  percentage  of  0  than  the  original  proteid  (e.  g.,  in 
fibrin,  there  are  52.7  per  cent  C.  16.9  per  cent  X,  1.1  per  cent  S,  and  22.5  per 
cent  0,  while  in  the  primary  albumoses  derived  from  it  we  find  55.4  per  cent 
C,  17.8  per  cent  X,  1.2  per  cent  S,  and  19.1-18.7  per  cent  0).  Heteroalbu- 
mose  from  fibrin  contains  thirty-nine  per  cent  of  the  total  nitrogen  in  basic 
form  and  fifty-seven  per  cent  as  monoamino  acids,  while  the  corresponding 
numbers  for  protoalbumose  are  twenty-five  and  sixty-eight  per  cent  respec- 
tively. Heteroalbumose  contains  only  a  small  quantity  of  the  aromatic  groups 
which  yield  tyrosin  and  indol,  but  it  is  rich  in  those  groups  which  yield  leucin 
and  glycocoll.  Protoalbumose,  on  the  other  hand,  yields  abundance  of  tyrosin, 
indol  and  skatol,  but  only  a  little  leucin  and  no  glycocoll. 

The  third  direct  product  of  digestion  is  a  deuteroaJbumose  (synalbumose) 
which  is  characterized  chiefly  by  the  fact  that  it  contains  a  carbohydrate  group, 
whenever  such  a  group  occurs  in  the  parent  proteid  molecule.  Its  quantita- 
tive composition  differs  materially  from  that  of  the  primary  albumoses :  thus 
48.7  per  cent  C,  13.8  per  cent  X,  30.5  per  cent  S  +  0. 

On  further  cleavage  with  pepsin,  primary  albumoses  yield  secondary  albu- 
moses which  appear  to  be  very  numerous.  Among  them  thioalbumose  should 
be  especially  mentioned  on  account  of  its  high  content  of  S  (three  per  cent). 

Deuteroalbumoses  are  transformed  into  peptones,  the  molecular  weight 
of  which  is  relatively  small — only  about  500  by  the  depression  of  the  freezing 
point,  whereas  the  molecular  weight  of  deuteroalbumose  is  about  3,200. 

According  to  Kiihne,  peptic  cleavage  of  proteid  could  proceed  only  as  far 
as  the  fonnation  of  peptones.  Later  it  was  found  that  from  the  beginning  of 
the  cleavage,  substances  separate  off  which  no  longer  give  the  biuret  reaction. 
Among  these  are  certain  intermediary  substances,  the  pepioids,  comparable  in 
their  structure  to  the  peptones,  from  which  after  long-continued  digestion  the  end 
products  finally  appear.  Probably  all  of  the  hydrohjtic  cleavage  products  (of. 
page  72)  belong  here,  for  already  the  following  have  been  demonstrated  in  such 
digestive  mixtures:  leucin,  asparatic  acid,  cadaverin,  putrescin,  glutamic  acid, 
tyrosin,  amino-valerianic  acid,  dihexosamin,  lysin,  penta-methyl-endiamin,  phe- 
nylalanin,  cystin,  a-pyrrolidin-earboxylic  acid,  tryptophan  (Pfaundler,  Lawrow, 
Langstein,  Salaskin,  Fischer,  and  Abderhalden). 

The  relative  proportion  of  primary  digestive  products  olitained  from  dif- 
ferent kinds  of  proteids  is  very  different.     The  kind  of  albumoses  formed  is 


250  DIGESTION 

likewise  very  different,  though  they  are  all  included  under  the  common  name 
proteoses.     The  glutin-forming  substances  are  changed  by  gastric  juice  into 
gelatin,  and  this  into  gelatin  peptones. 
• 

The  same  decompositions  which  proteids  suffer  in  digestion  they  exhibit  also 
when  treated  with  acids  or  alkalies  or  superheated  steam,  and  when  they  fall 
under  the  influence  of  putrefactive  Bacteria.  In  fact,  weak  salt  solutions  have 
a  digestive  action  on  proteids  (Dastre).  The  action  of  the  enzymes  is  not  to 
be  regarded,  therefore,  as  particularly  exceptional. 

Loss  of  the  power  of  coagulation  on  the  part  of  the  blood  and  other  harmfvd 
effects  which  have  long  been  known  to  follow  intravenous  injection  of  albumoses 
have  lately  been  attributed  to  other  substances — e.g.,  peptozymes — mixed  with 
them  (Pick  and  Spiro).  Peptozymes,  acting  mainly  in  the  liver,  cause  the 
production  of  a  substance  which  prevents  coagulation  (Contejean,  Gley). 

C.    RENNIN 

It  has  long  been  known  that  milk  coagulates  by  precipitation  of  its  casein 
when  it  comes  in  contact  with  the  mucous  membrane  itself,  or  is  mixed 
with  an  extract  of  the  membrane.  Since  acids  produce  the  same  effect  it  was 
supposed  that  this  precipitation  was  due  to  the  acid  reaction  of  the  mucosa. 
But  the  investigations  of  Selmi  and  Heinz,  and  especially  those  of  Ham- 
marsten  (1872)  and  of  Alex.  Schmidt  showed  that  coagulation  takes  place 
in  a  neutral  or  alkaline  reaction,  that  the  acid  is,  therefore,  quite  superfluous, 
and  finally  that  coagulation  of  milk  is  effected  by  a  special  enzyme  called 
rennin  or  cliymosin. 

Rennin  occurs  in  the  mucous  membrane  as  a  precursor,  rennin-zymogen, 
which  like  pepsinogen  is  more  resistant  to  alkalies  than  its  enzyme,  can  be 
extracted  from  the  mucosa  with  water,  and  is  transformed  into  the  active 
enzyme  by  addition  of  acids.  In  its  action  rennin  resembles  the  other  digestive 
enzymes.  One  part  of  the  impure  enzyme  can  coagulate  400.000  to  800,000 
parts  of  casein. 

In  the  coagulation  of  milk  produced  by  rennin,  casein  first  suffers  cleavage 
into  paracasein,  and  whey  proteid,  a  substance  resembling  albumose;  the  for- 
mer, which  is  the  chief  product,  then  precipitates  out  in  solid  form,  provided 
Ca  salts  are  present  in  the  solution.  If  Ca  salts  are  absent,  cleavage  occurs 
under  the  influence  of  rennin,  but  no  coagulation. 

D.    GASTRIC   STEAPSIN 

After  Marcet,  Cash  and  Ogata  had  demonstrated  the  decomposition  of  neu- 
tral fat  in  the  stomach,  Volhard  made  further  investigations  on  the  subject 
and  established  this  property  of  gastric  juice  beyond  doubt — with  the  limita- 
tion, however,  that  it  acts  only  on  emulsified  fats,  but  on  these  very  powerfully. 

The  rule  holds  for  stomach  steapsin,  as  for  other  enzymes,  that  its  action 
is  proportional  to  the  square  root  of  concentration.  It  is  quickly  destroyed  in 
a  strongly  acid  gastric  juice.  The  pure  pepsin  of  Pekelharing  has  no  fat- 
splitting  action,  a  fact  which  speaks  decisively  for  the  independence  of  the 
gastric  steapsin. 


PANCREATIC   JUICE      -  251 


§  4.    PANCREATIC   JUICE 

Pancreatic  juice  presents  different  properties  according  as  it  is  obtained 
from  a  long-established  fistula  or  a  recent  one  (page  243).  In  the  latter  case 
it  is  viscid  or  almost  ropy,  and  at  a  low  temperature  passes  over  into  a  trans- 
parent jelly  from  which  a  thin  fluid  separates  out.  At  0°  C.  there  is  formed 
a  gelatinous,  flocculent  precipitate,  readily  soluble  in  dilute  acids.  Under 
some  circumstances  the  secretion  is  so  rich  in  proteid  that  the  whole  fluid 
coagulates  when  heated.  The  secretion  from  a  permanent  fistula  is  thinner 
and  contains  a  smaller  quantity  of  solids. 

According  to  Pawlow  the  latter  is  to  be  regarded  as  the  normal  secretion. 
In  his  experience  the  thick,  sirupy  secretion  is  due  to  the  effects  of  the  opera- 
tion on  this  uncommonly  sensitive  gland. 

The  quantity  of  pancreatic  juice  secreted  daily  is  no  more  to  be  estimated 
witli  exactness  than  is  the  quantity  of  gastric  juice.  In  cases  of  pancreatic 
fistula  in  man  a  daily  secretion  of  from  293  to  840  c.c,  with  an  average  of 
something  more  than  400  c.c,  has  been  observed. 

Pancreatic  juice  is  always  alkaline  in  reaction  and  often  contains  an 
abundance  of  proteid  as  the  following  analyses  show: 


Man  (Glaessner). 

Dry  residue 13 .  59  per  cent.  1 .  25-1 .  27  per  cent, 

Orfjanic  substance 13.25        "  0.50-0.54 


Proteid *. 9^21        "  o!l3-0.17 

Ash 0.34       "  0.57-0.70 


Kudrewetsky  has  found  that  the  alkalinity  as  determined  by  the  quantit;^  of 
IICl  in  g.  necessary  to  neutralize  100  c.c.  of  dog's  pancreatic  juice  is  0.05-0.89. 

Its  most  important  constituents  are  the  enzymes :  two  or  three  amylolytic, 
one  proteolytic  and  one  lipolytic.  Probably  all  of  these  occur  in  the  gland 
as  zymogens.  That  they  are  actually  different  enzymes  prol)ably  follows  from 
the  fact  that  the  am3dolytic,  proteohi:ic  and  lipolytic  effects  either  of  the 
secretion  or  of  the  pancreatic  extract  do  not  keep  pace  one  with  another. 

A.    THE   AMYLOLYTIC   ENZYMES 

Valentin  (1844),  also  Bouchardat  and  Sandras  (184fi)  found  that  pan- 
creatic secretion  transforms  starch  into  sugar.  The  very  same  cleavages  appear 
in  this  as  in  the  action  of  ptyalin  on  starch.  Besides,  pancreatic  juice  contains 
an  enzyme  (malta.'^e)  which  changes  maltose  to  dextrose  (Rohmann)  and 
according  to  Weinland,  another  (lactase)  M^hich  splits  milk  sugar  into  dex- 
trose and  galactose. 

Glaessner  was  unable  to  demonstrate  any  action  of  human  pancreatic  juice 
on  cane  sugar,  maltose  or  milk  sugar. 

The  action  of  the  amylolytic  enzyme  is  favored  by  small  quantities  of  hydro- 
chloric acid  and  of  bile  (Rachford). 


252  DIGESTION 


B.    THE   PROTEOLYTIC   ENZYME,   TRYPSIN, 

is  distinguished  from  pepsin  mainly  by  the  fact  that  it  digests  proteids  in 
an  alkaline  medium.  Purkinje  and  Pappenheim  as  early  as  183G,  and  CI. 
Bernard  later  alluded  to  the  proteolytic  action  of  the  pancreatic  juice,  but 
Corvisart  (1857)  must  be  looked  upon  as  its  real  discoverer.  Later  Kiihne, 
especially,  did  large  service  for  our  knowledge  of  this  enzyme. 

Trypsin  as  such  does  not  occur  in  the  pancreas,  but  instead  a  zymogen, 
which,  like  those  of  the  other  enzymes,  is  more  resistant  toward  all  kinds 
of  injurious  agents  than  the  enzyme  itself.  But  even  the  secreted  juice  does 
not  contain  any  trypsin  and  is  entirely  without  effect  on  proteid,  if  it  is  not 
first  activated  by  an  enzyme,  called  enterol'inase  (Pawlow),  found  in  the 
intestinal  juice.  The  formation  of  trypsin  from  its  zymogen  presupposes 
therefore  t'he  presence  of  this  special  enzyme,  and  according  to  Delezenne, 
Popielski,  Bayliss  and  Starling,  there  is  no  other  means  of  bringing  about 
this  change.  (The  unactivated  secretion,  nevertheless,  will  digest  boiled 
fibrin  and  casein,  though  ver}'  slowly.) 

Opposed  to  these  observations  however  are  others  according  to  which  a 
powerfully  active  extract  is  obtained,  if,  for  example,  the  gland  be  allowed  to 
lie  twenty-four  hours  before  extraction.  Hekma  is  of  the  opinion  that  this  is 
a  case  of  bacterial  action,  since  with  antiseptic  fluids  no  formation  of  trypsin 
could  be  observed. 

According  to  SchifF  and  Herzen,  the  spleen  may  have  much  to  do  with  the 
formation  of  trypsin,   since  addition  of  splenic  infusion  or  of   splenic  venous 
blood  activates  the  pancreatic  extract.     This  in  Herzen's  opinion  is  due  to  an  . 
internal  secretion  of  the  spleen. 

The  cleavage  of  proteids  l)y  trypsin  goes  on  in  the  same  way  as  that  pro- 
duced by  pepsin,  saving  only  that  the  end  products  are  formed  in  less  time 
in  tryptic  than  in  peptic  digestion.  However,  hydrolytic  cleavage  of  proteid 
may  be  carried  further,  if  peptic  digestion  precedes  the  tryptic  digestion 
(Giirber).  Siegfried  finds  two  peptones  (CioHj-XgOg,  C11H19X3O5,  molecular 
weights,  259  and  273  respectively),  and  Fischer  and  Abderhalden  find  a  more 
complex  residue  containing  all  the  monamino  acids,  which  stubbornly  resist 
further  cleavage  with  trypsin. 

Trypsin  also  dissolves  gelatin,  elastic  substance  and  structureless  membranes ; 
likewise  the  gelatin-forming  tissues,  if  they  first  be  treated  with  acids  or  wanned 
to  90°  C.  Bokai  states  that  tiypsin  does  not  act  upon  the  nucleins;  but  after 
autodigestion  of  the  pancreas,  Kutscher  found  xanthin,  hypoxanthin,  and  guanin 
— just  the  cleavage  products  of  nucleic  acids.  Blood  serum  and  serum  globulin 
are  not  attacked  by  trj^psin,  although  both  are  digested  without  difficulty  by 
gastric  juice. 

The  pancreatic  juice  of  many  mammals  (human  pancreatic  juice  uncertain) 
also  coagulates  milk,  and  according  to  Vernon  the  action  is  due  to  a  special 
enzyme.  Instead  of  paracasein,  however,  the  clot  contains  a  substance  known 
as  metacasein,  which  may  represent  a  product  of  tryptic  digestion  of  casein 
(Roberts). 


BILE  253 

C.    LIPOLYTIC   ENZYME,   STEAPSIN 

In  1846  CI.  Bernard  observed  that  in  the  dog  fat  suffered  digestive  changes 
immediately  after  its  entrance  into  the  duodenum,  whereas  in  the  rabbit  it 
took  place  somewhat  farther  from  the  pylorus.  The  cause  of  this  difference 
he  found  to  he  the  fact  that  in  the  dog  the  chief  pancreatic  duct  opens  into 
the  intestine  in  common  with  the  ductus  choledoehus  quite  close  to  the  pylorus, 
while  in  the  rabbit  it  opens  some  30-35  cm.  farther  down.  It  follows  that  the 
pancreatic  secretion  must  have  a  determining  influence  upon  the  digestion 
of  fat.  Further  researches  have  shown  that  this  effect  consists  in  a  cleavage  of 
the  fat  into  glycerin  and  free  fatty  acid.  We  shall  discuss  the  importance  of 
this  cleavage  more  fully  in  our  study  of  digestion  in  the  intestine. 

§  5.    BILE 

Human  bile  as  it  flows  from  the  liver  is  a  ])eautiful  reddish-yellow  or 
yellowish-brown,  or  green,  alkaline  fluid,  which  on  standing  for  some  time 
in  contact  with  the  air  assumes  a  green  or  greenish-yellow  color.  It  contains 
a  not  insignificant  amount  of  mucin,  and  the  quantity  of  solids  amounts  to 
1.5—1  per  cent  or  more,  of  which  0.7-0.8  per  cent  is  mineral. 

The  daily  output  of  bile,  taken  from  men  with  biliary  fistulas,  has  been 
found  to  vary  from  500  to  1,100  c.c. 

During  the  intervals  of  digestion  the  bile  does  not  flow  into  the  intes- 
tine, but  collects  in  the  gall  bladder,  where  ])y  absorption  of  its  water  and 
mixture  with  bladder  mucus,  it  becomes  more  concentrated,  so  that  its  con- 
tent in  solids  may  rise  sixteen  or  seventeen  per  cent  higher.  The  specific 
gravity  of  bile  is  1.01-1.04. 

The  most  important  constituents  are  mucin,  the  bile  acids,  and  bile  pig- 
ments. The  bile  acids  never  occur  free,  but  always  as  salts  of  the  alkalies. 
They  are  compounds  of  glycocoll  and  taurin  (amino-ethyl-sulphonic  acid: 
NH,.CoH,.SOoOH)  with  cholic  acid.  Glycocholic  acid  (C.eH.jXOe)  and 
taurocholic  acid  (Cor,H4..,XS0-)  occur  in  different  biles  in  relatively  different 
quantities.    In  man  the  former  is  alwavs  present  in  greater  quantity.     Besides 

rCHOH 
the  usual  cholic  acid,  whose  formula  is  C00H31  i  (CH,OH),,  two  other  acids, 

[CHOH 
choleic  acid  (Cn4H4oOJ,  and  fellic  acid  (CogH^oO^)  have  been  demonstrated 
in  human  bile.     Numerous  derivatives  can  be  obtained  from  the  bile  acids. 

The  bile  pigments  are  very  numerous  and  they  can  be  changed  by  various 
means  into  still  others.  Under  physiological  conditions  we  have,  properly 
speaking,  only  two  such  pigments — the  reddish-yellow,  hilirubin,  and  the 
green,  bilivcrdin.  The  former,  which  is  easily  crystallized  in  rhombic  tablets, 
is  to  be  regarded  as  the  mother-substance  of  biliverdin  and  all  other  bile 
pigments. 

Bilirubin  has  the  formula  C,„II,,]Srj03  (Maly).  It  is  transformed  by  oxida- 
tion into  biliverdin  C,JI,„N,0„  land  vice  versa  the  latter  can  pass  by  reduction 
into  bilirubin  aprain.  Biliprasi'n,  according  to  Dastre  and  Floresco,  is  to  be 
regarded  as  an  intermetliate  stage  between  the  two.     Bilirubin,  acted  upon  by 


254 


DIGESTION 


nascent  hydrogen,  is  reduced  to  hydrobiliruhin  C32H4,!N'407  which  also  occurs  at 
times  in  the  human  bile.  Since  bilirubin  and  biliverdin  are  commonly  present 
together  in  the  bile,  the  color  of  the  fluid  is  somewhere  between  red  and  green, 
and  varies  toward  one  or  the  other  according  as  one  pigment  or  the  other  pre- 
dominates. 

The  bile  contains  also  mucin,  cholesterin,  jecorin,  lecithin,  neutral  fats  and 
soaps,  ethereal  sulphuric  acids,  paired  glycuronic  acids,  cholin,  glycerin-phos- 
phoric acid  (both  the  latter,  decomposition  products  of  lecithin),  and  various 
mineral  constituents,  namely:  the  alkalies  in  combination  with  the  bile  acids, 
sodium  chloride,  potassium  chloride,  calcium  and  magnesium  phosphate  and 
iron.  Sulphates  occur,  if  at  all,  in  very  small  quantities.  A  diastatic  and  a 
fibrin-splitting  ferment  have  been  demonstrated  in  the  bile  of  certain  animals; 
but  it  is  not  quite  certain  that  they  are  formed  in  the  liver,  for  they  might  rep- 
resent enzymes  only  reabsorbed  into  the  bile. 

The  following  summary  of  analytical  results  with  regard  to  the  quantita- 
tive composition  of  bile  may  be  given : 


Bladder  bile. 

Liver  bile. 

W^ater     

82.3  -89.8 

10.2  -17.7 

1.3  -  2.5 

3.0  -  6.8 
0.9  -  1.9 

2.1  -  4.9 
1.6  -  0.8 
0.3  -  0.4 

[    1.2  -  0.4 

per  cent. 

it 

96.5    -98.8  percent. 
1.2    -  3.5 

Solids 

Mucin  and  ijiginents      

0  1-05        " 

Alkaline  salts  of  the  bile  acids 

0  2-18 

Taurocholate 

0.05  -  0.3 

Glycocholate     

0  2-16        " 

Patty  acids  derived  from  soaps 

0.02  -  0.14      " 

Cholesterin    ....          

0.05  -  0.16      " 

Lecithin     

0.005-  0.13      " 

Fat 

0.01  -  0.10      " 

Soluble  salts ....          

0.7    -  0.9 

Insoluble  salts        

0.02  -  0.05      " 

The  chief  importance  of  bile  in  digestion  appears  to  be  that,  in  virtue 
of  its  bile  salts  it  has  the  power  to  dissolve  the  free  fatty  acids  and  to  increase 
the  solubility  of  soaps ;  but  more  on  this  under  the  subject  of  absorption  from 
the  intestine. 

Proof  that  the  bile  pigments  are  formed  for  the  most  part  in  the  liver  is 
found  in  the  fact  that  when  this  organ  is  extirpated  from  birds,  or  when  all 
the  blood  vessels  of  the  liver  and  the  bile  ducts  are  ligated,  not  a  trace  of  bile 
pigments  can  be  demonstrated  anj^vhere  in  the  animal. 

The  bile  pigments  are  universally  regarded  as  derivatives  of  hsemoglobin. 
The  following  facts  among  others  speak  for  this  view.  A  pigment  called  hcemo- 
toidin  found  in  old  blood  stains  is  closely  related  to  hilirithin  and  probably  is 
identical  with  it.  Hcematinic  acid,  CsHoNO^,  which  is  the  first  oxidation  product 
of  hcematin  when  oxidation  takes  place  at  the  lowest  possible  temperature,  appears 
to  be  identical  with  biliverdinic  acid,  an  oxidation  product  of  bilirubin  (Kiis- 
ter). — When  dissolved  haemoglobin  is  injected  into  the  blood,  or  when  substances 
which  liberate  haemoglobin  from  the  corpuscles  are  taken  into  the  body,  the  quan- 
tity of  pigments  excreted  in  the  bile  increases  materially. 

Since  it  has  been  shown  in  these  and  other  researches  that  the  secretion  of 
bile  pigments  never  runs  parallel  to  that  of  the  bile  acids,  it  follows  that  these 
two  chief  constituents  are  not  derivatives  of  the  same  substance. 


INTESTINAL  JUICE  255 


§  6.     INTESTINAL   JUICE 

The  intestinal  juice  of  man  is  a  thin,  clear,  alkaline  fluid  containing 
epithelial  cells,  Bacteria  and  fat  crystals,  which  effervesces  on  addition  of 
acids.  Freed  of  solid  bodies  by  means  of  the  centrifuge,  it  contains  from  0.2 
to  0.5  per  cent  Xa^COa,  0.2-0.6  per  cent  CI,  and  about  1.1  per  cent  dry  residue. 
Its  specific  gravity  is  in  the  neighborhood  of  1.007  (Hamburger  and  Hekma). 

Intestinal  juice  acts  but  feebly  on  starch.  It  inverts  cane  sugar,  splits 
maltose,  and,  in  young  animals  at  least,  also  milk  sugar.  According  to  Koh- 
mann  and  Nagano,  the  action  of  secreted  intestinal  juice  on  cane  sugar  and 
malt  sugar  is  much  less  than  that  of  the  intestinal  mucosa:  it  might  be 
therefore  that  the  cleavage  of  these  sugars  takes  place  in  the  mucosa  itself, 
or  that  mere  contact  with  the  surface  of  the  mucous  membrane  is  sufficient 
for  this  purpose. 

Emulsified  fats  appear  to  be  attacked  to  some  extent  by  the  intestinal  juice. 

The  native  proteids,  with  the  exception  of  casein  and  fibrin,  are  not 
digested  by  the  intestinal  juice.  On  the  other  hand,  an  extract  of  the  intes- 
tinal mucosa  in  weakly  alkaline  or  neutral  reaction  splits  albumoses  and  pep- 
tones into  simpler  compounds:  XHg,  leucin,  tyrosin,  lysin,  arginin,  histidin, 
etc.  (Cohnhcim).  This  action  is  heightened  by  warming  the  solution,  and 
it  is  regarded  therefore  as  the  effect  of  a  special  enzyme  called  erepsin.  The 
normal  secretion  (man,  dog)  has  the  same  effect,  only  to  a  less  extent,  from 
which  we  may  perhaps  conclude  that  this  cleavage  of  the  primary  products 
of  digestion  really  takes  place  in  the  mucous  membrane. 

The  nucleic  acids  are  not  decomposed  by  trypsin;  but  when  they  are 
exposed  to  the  action  of  erepsin  they  are  split  into  phosphoric  acid  and  the 
purin  bases.  This  fact  speaks  very  strongly  for  the  specific  nature  of  erepsin 
(Xakayama). 

Pawlow  has  discovered  a  new  enzyme  in  the  intestinal  juice  which  he  calls 
enterokinase,  and  which,  as  mentioned  on  page  252,  transforms  the  raw  mother- 
substance  of  trypsin  in  the  pancreatic  juice  into  the  active  enzyme.  We  know 
that  this  is  not  identical  with  erepsin  from  the  fact  that  (in  the  human  intes- 
tinal juice)  the  latter  is  destroyed  by  a  temperature  of  59°  C,  whereas  the 
enterokinase  is  not  destroyed  below  67°  C. 

Gachot  and  Pachon,  as  well  as  Glaessner,  assert  that  the  glands  of  Brunner, 
which  have  an  entirely  different  structure  from  that  of  the  glands  of  Lieberkiihn, 
secrete  a  proteolytic  enzyme. 

The  glands  of  the  large  intestine  produce  no  enzymes,  but  secrete  a  mucus 
which  is  of  importance  as  a  lubricant  for  the  fecal  mass. 


256  DIGESTION 


SECOND    SECTION 


SECRETION   OF  THE   DIGESTIVE   FLUIDS 

§  1.    GENERAL    SURVEY 

The  secretory  process  presents  many  points  of  similarit}'  in  all  ditrestive 
glands.  For  this  reason,  it  is  desirable  to  consider  the  process  in  broad  out- 
line before  taking  up  in  detail  the  peculiarities  of  the  individual  glands. 

In  the  year  1851  Ludwig  showed  that  section  of  the  cerebral  nerve  supply 
to  the  salivary  glands  was  followed  by  complete  cessation  of  the  flow  of  saliva 
(submaxillary,  parotid).  For  hours  there  was  not  the  least  trace  of  fluid 
in  the  cannula  which  had  been  inserted  into  the  duct.  As  soon  however  as 
the  cerebral  nerve  was  stimulated,  saliva  gushed  out  of  the  duct.  In  a  thor- 
oughgoing investigation,  which  is  to  be  reported  more  fully  under  §  2,  Ludwig 
demonstrated  that  this  secretion  is  not  a  filtrate  from  the  blood,  but  is  pro- 
duced by  the  specific  activity  of  the  gland  cells  under  the  influence  of  the 
nerves. 

These  discoveries  stood  quite  alone  for  several  decades.  It  is  true  that 
soiue  observations  were  collecting,  from  which  it  appeared  with  a  certain 
degree  of  probaljility  that  the  secretion  of  the  gastric  glands  and  of  the  pan- 
creas Avere  influenced  considerably  b}^  secretory  nerves  (Heidenhain,  Kichet 
ct  ah).  But  the  existence  of  such  nerves  was  conclusively  proved  by  Pawlow 
only  a  few  years  ago.  We  do  not  know  definitely  even  yet  whether  the  other 
digestive  glands,  those  of  Lieberkiihn,  of  Brunner,  and  the  liver,  are  under  the 
influence  of  secretory  nerves  in  the  same  way  as  those  already  mentioned. 

It  would  be  a  matter  of  the  greatest  interest  to  know  exactly  the  anatomical 
connection  between  the  secretory  nerves  and  the  g'land  cells.  The  many  efforts 
of  histologists  in  this  direction  have  not  been  entirely  successful  as  yet,  although 
it  has  been  stated  recently  that  the  nerves  penetrate  the  membrana  propria  of 
the  acini  and  terminate  in  end  organs  lying  in  direct  contact  with  the  secreting 
cells.  The  end  organs  are  said  to  have  either  the  form  of  mulberrylike  clumps 
or  of  small  twigs  beset  with  nodules. 

Under  normal  circumstances  the  secretion  of  those  glands  which  are 
plainly  under  the  control  of  the  central  nervous  system  is  evoked  by  reflex 
action,  set  up  in  many  cases  by  perfectly  definite  chemical  substances  (Paw- 
low)  (cf.  page  264).  These  reflexes  as  a  rule  stand  in  a  very  close  relation- 
ship with  the  ingestion  of  food,  and  in  general  it  may  be  said  that  in  the 
intervals  of  digestion  when  there  is  no  desire  for  food,  the  digestive  fluids  are 
secreted  only  in  very  small  quantities. 

Bile  forms  an  exception  to  this  rule,  since  even  in  the  fasting  condition  it 
is  produced  and  is  given  off  by  the  liver.  Possibly  this  is  due  to  the  fact  that 
bile  is  not  only  a  digestive  fluid,  but  contains  also  various  substances  which,  so 
far  as  our  knowledge  at  present  goes,  have  no  signifieance  whatever  in  diges- 
tion, and  must  be  looked  upon  as  real  waste  products.  As  such  they  would 
naturally  be  produced  continuously,  just  as  in  the  case  of  urea  and  the  decom- 


THE   SALIV.IRY   GLANDS  257 

position  products  found  in  the  expired  air.  However,  the  bile  passes  into  the 
digestive  canal  only  after  the  ingestion  of  food;  in  the  meantime  it  is  being 
stored  in  the  gall  bladder. 

In  1868  Heidenhain  published  the  important  observation  that  after  long- 
continued  activity  the  submaxillary  gland  exhibits  morphological  changes, 
and  some  years  later  he  ascertained  that  the  same  is  true  of  the  parotid  and 
of  the  fundus  glands  of  the  stomach.  Investigation  in  this  direction  was 
extended  by  several  other  authors,  and  it  has  been  proved  by  their  work  that 
while  the  gland  is  resting — i.  e.,  is  not  pouring  out  secretions — a  substance 
is  being  laid  down  within  it  in  the  form  of  small  granules,  which  to  a  greater 
or  less  extent  disappears  during  the  activity  of  the  gland.  This  substance 
must  be  regarded  as  the  source  of  the  specific  constituents  of  the  glandular 
secretions. 

Heat  is  generated  by  the  glands  in  the  act  of  secretion.  CI.  Bernard 
(185G)  found  the  temperature  of  the  hepatic  l)lood  constantl}^  higher  than 
that  of  the  portal  blood.  At  the  time  of  active  secretion  of  bile  the  difference 
rose  to  0.7'°-0.9°  C.  The  following  year  Ludwig  and  Spiess  observed  that 
the  temperature  of  the  submaxillary  saliva  may  be  more  than  1°  C.  higher 
than  that  of  the  l)lood  in  the  carotid  of  the  same  side.  The  increase  in  oxygen 
consumption  and  of  carbon-dioxide  production  indicate  a  highly  active  metab- 
olism going  on  in  a  working  gland;  both  are  three  to  four  times  as  great  in 
a  strongly  active  condition  of  the  submaxillary  as  in  a  resting  condition 
(Barcroft). 

Attention  has  already  been  directed  to  the  electric  phenomena  of  glands 
(page  48).  Bayliss  and  Bradford  report  that  on  stimulation  of  the  cerebral 
secretory  nei-ves  of  the  dog,  a  strong  electric  variation  is  produced  both  in  the 
submaxillary  and  in  the  parotid,  since  the  surface  of  the  gland  becomes  negative 
to  the  hilus.  Stimulation  of  the  sympathetic  produced  an  opposite  variation — 
the  surface  becoming  positive  to  the  hilus.  Moreover,  they  showed  that  these 
electrical  variations  arc  not  due  either  to  alterations  of  the  blood  flow  or  to  the 
flow  of  the  secretion  through  the  duct.  On  the  basis  of  these  and  other  observa- 
tions, the  authors  conclude  that  the  negativity  of  the  surface  toward  the  hilus 
is  the  result  of  a  passage  of  fluid  through  the  wall  of  the  acini  or  is  the  result 
of  changes  in  the  gland  cells  set  up  by  stimulation,  which  precede  the  passage  of 
the  fluid.  The  positivity  of  the  surface  would  be  the  expression  of  those  changes 
in  the  gland  cells  by  which  the  organic  constituents  of  the  secretion  are  formed. 

§2.    THE    SALIVARY   GLANDS 
A.    SECRETORY   NERVES 

The  salivary  glands  receive  their  nerves  by  two  different  pathways,  namely 
the  cerebral  and  the  sympathetic.  The  former  were  demonstrated  by  Ludwig  as 
mentioned  on  page  256;  while  the  discovery  that  the  syiniiathetic  can  cause 
secretion  of  saliva  we  owe  to  Eckhard. 

In  the  dog  the  cerebral  nerves  to  the  submaxillary  and  sublingual  glands 
proceed  from  the  facial  nerve  through  the  chorda  tympani  to  the  lingual  branch 
of  the  trigeminal,  and  from  this  along  the  ducts  to  the  gland.  The  cerebral  sup- 
ply to  the  parotid  of  the  dog  springs  from  the  glossopharyngeal  and  reaches  the 


258  DIGESTION 

aiirieiilo-temporal  branch  of  the  fifth  nerve  through  the  nerve  of  Jacobson,  the 
small  superficial  petrosal,  and  the  otic  ganglion. 

The  sympathetic  fibers  run  in  the  cervical  sympathetic  trunk  to  the  superior 
cervical  ganglion,  and  from  there  follow  the  blood  vessels  to  the  hilus  of  the 
appropriate  gland. 

Ganglion  cells  are  interpolated  in  the  course  of  these  nerves — those  of  the 
sj'mpathetic  fibers  for  the  sublingual  and  submaxillary  being  located  in  the  supe- 
rior cervical  ganglion.  The  ganglion  cells  of  the  cerebral  secretory  fibers  for 
the  sublingual  gland  are  distributed  as  small  ganglia  over  the  entire  gland  (to 
these  belong  also  the  sublingual  ganglion)  ;  those  for  the  submaxillary  lie  for 
the  most  part  in  the  hilus  of  the  gland  itself  (Langley). 

On  stimulation  the  different  secretory  nerves  give  different  results,  which 
vary  with  the  species  of  animal  experimented  upon.  We  shall  consider  here 
only  the  results  obtained  in  the  dog. 

Stimulation  of  the  cerebral  fibers  to  any  of  the  glands  causes  almost  immf>- 
diately  a  copious  secretion  of  a  fluid  poor  in  solids,  which  may  continue  for 
hours,  if  the  stimulation  be  maintained  at  the  proper  strength.  The  secre- 
tion produced  from  the  submaxillary  by  excitation  of  the  sympathetic  appears 
later.  At  first  a  few  drops  of  a  fluid  rich  in  solids  come  from  the  duct,  then 
the  secretion  ceases,  but  reappears  on  continued  stimulation.  The  parotid 
as  a  rule  gives  no  secretion  on  stimulation  of  the  sympathetic,  probably 
because  the  tliick  fluid  stops  up  the  duct. 

Since  stimulation  of  the  cerebral  fibers  causes  a  considerable  dilatation  of 
the  blood  vessels  of  the  gland  and  a  consequent  increase  of  blood  flow  (as  much 
as  six  times  the  original)  (cf.  page  234),  whereas  stimulation  of  the  sympathetic 
causes  vasocontraction  and  a  considerable  decrease  of  blood  flow,  it  might  be 
thought  that  the  difference  in  the  secretion  in  the  two  cases  is  due  to  the  differ- 
ence in  the  amount  of  blood  supplied.  But  this  is  not  true.  For  if  the  arteries 
of  the  gland  be  entirely  closed  off  and  the  cerebral  fibers  be  then  stimulated,  the 
quantity  of  secretion  obtained  is  smaller,  but  it  has  all  the  properties  of  the  nor- 
mal cerebral  saliva  and  its  percentage  content  of  solids  is  not  greater  than  when 
the  circulation  is  unhindered. 

Heidenhain,  with  some  reseiwation  it  is  true,  has  sought  to  explain  these 
phenomena  as  follows.  He  supposes  that  every  gland  is  provided  with  two  kinds 
of  nerve  fibers:  (1)  those  which  preside  over  the  transudation  of  water  and  of 
the  salts,  the  "secretory  fibers,"  and  (2)  those  which  control  the  formation  of  the 
soluble  constituents  and  the  growth  of  the  protoplasm,  the  "  trophic  fibers." 
These  fibers  occur  in  the  different  nerves  of  the  glands  in  different  numbers. 
Thus  the  cerebral  fibers  in  the  dog  would  be  relatively  poor  in  trophic  but  rela- 
tively rich  in  secretory  fibers,  while  the  sympathetic  would  contain  only  a  few 
secretory  but  many  trophic  fibers. 

It  is  not  to  be  denied-that  Heidenhain  has  brought  many  facts  to  the  support 
of  this  view.  For  example,  simultaneous  stimulation  of  the  sympathetic  and 
the  glossopharyngeal  in  the  dog  increases  considerably  the  percentage  composi- 
tion of  solids  in  the  parotid  saliva.  But  it  is  not  possible  to  explain  all  the 
known  facts  concerning  the  influence  of  nerves  on  the  salivary  secretion  from 
this  point  of  view.  Thus  if  the  glands  be  poisoned,  not  too  severely,  with  atropine, 
stimulation  of  the  chorda  is  entirely  without  effect  at  a  time  when  stimulation 
of  the  sympathetic  is  still  effective.  Now  it  is  very  probable  that  atropine  acts 
so  as  to  paralyze  the  end  organs  of  the  cerebral  fibers,  and  from  the  fact  just 


THE   SALIVARY   GLANDS  259 

given  we  know  that  this  poison  acts  upou  the  end  organs  of  the  two  nerves  in 
an  entirely  different  way.  Hence  we  can  scarcely  say  that  the  sympathetic  and 
the  chorda  are  composed  of  the  same  kinds  of  fibers  in  relatively  different  num- 
bers (Langley). 

The  discovery  of  Gerhardt  with  regard  to  morphological  changes  in  the  sub- 
maxillary after  section  of  the  sympathetic  and  of  the  chorda,  speaks  to  the  same 
effect.  In  the  former  case  the  protoplasm  remains  unchanged,  whereas  the 
nucleus  shrinks,  although  not  in  all  cells;  after  section  of  the  chorda  the  nu- 
cleus remains  normal,  but  the  protoplasm  in  many  cells  undergoes  significant 
changes,  becoming  turbid,  finely  granular  and  opaque. 

A  further  difficulty  for  Heidenhain's  theory  is  the  so-called  paralytic  secre- 
tion discovered  by  CI.  Bernard.  Some  twenty-four  hours  after  section  of  the 
cerebral  nerves,  the  submaxillary  gland  begins  to  secrete,  slowly  at  first,  then 
faster  and  faster  until  within  a  week  a  drop  issues  from  the  duct  every  twenty 
m.inutes.  It  makes  no  difference  whether  the  sympathetic  is  injured  or  not; 
section  of  this  nei-ve  produces  no  paralytic  secretion.  In  the  course  of  time 
after  section  of  either  nerve  the  size  of  the  gland  gradually  diminishes,  and 
the  gland  acquires  a  waxlike  appearance. 

A  priori  it  might  be  supposed  that  secretion  is  only  a  process  of  filtration 
from  the  blood  through  the  capillary  walls.  But  we  have  great  dit!iculty  on 
such  an  hypothesis  to  account  for  the  chemical  properties  of  the  secretion; 
for  several  substances  found  in  the  secretion  and  in  the  glands  are  not  found 
at  all  in  the  blood,  and  must,  therefore,  be  formed  in  the  gland  cells.  This  is 
attested  also  by  facts  to  be  discussed  later  with  regard  to  morphological  changes 
appearing  in  the  glands.  But  more  convincing  is  the  following.  If  the  duct 
of  the  submaxillary  gland  be  connected  with  a  Hg-manometer  and  the  cerebral 
nerve  be  then  stimulated,  the  mercury  in  a  very  short  time,  even  within  twenty- 
five  seconds,  rises  100  mm.  higher  than  the  mercury  in  a  manometer  connected 
with  the  carotid.  That  is.  the  secretion  pressure  becomes  higher  than  the 
blood  pressure.  Finally,  the  remotest  possibility  of  regarding  the  secretion 
as  a  process  of  filtration  is  excluded  by  the  fact  that  stimtilation  of  a  secretory 
nerve  causes  a  flow  of  saliva  in  animals  which  have  been  bled  to  death. 

^Tien  a  nerve  is  stimulated,  the  constituents  already  deposited  in  the 
gland  cells  during  rest  are  not  only  given  off.  but  there  is  at  the  same  time 
an  increased  production  of  them.  This  is  plainly  indicated  by  the  fact  that 
the  quantity  of  nitrogen  in  both  the  secreting  gland  and  its  secreted  saliva  is 
greater  than  that  of  the  resting  gland  on  the  other  side  (Pawlow).  When 
the  nerves  are  excited  with  stimuli  of  increasing  strength,  not  only  does  the 
absolute  quantity  of  the  secretion  and  of  its  solid  constituents  increase,  but 
the  percentage  content  of  the  latter  rises  higher  the  more  rapid  the  rate  of 
secretion  becomes.  This  increase  always  affects  the  inorganic  constituents, 
but  not  the  organic,  unless  care  be  taken  not  to  fatigue  the  gland  by  over- 
work. If  the  gland  be  fatigued,  the  percentage  content  of  organic  substances 
may  even  decline  in  the  face  of  an  increased  rate  of  secretion. 

We  may  summarize  the  effects  produced  in  the  glands  by  stimulation  of 
their  nerves  as  follows:  (1)  A  change  takes  place  in  the  gland  cells  develop- 
ing certain  forces  which  are  expressed  by  the  act  of  secretion ;  ( 2 )  at  the 
same  time  an  increased  formation  of  the  specific  constituents  of  the  secretion 
appears;  and  (3)  if  the  stimulation  continue  for  a  long  time,  the  gland  gradu- 
17* 


260 


DIGESTION 


ally  becomes  fatigued,  so  that  the  delivery  of  secretory  products  exceeds  the 
new  formation  of  specific  constituents. 

Under  normal  circumstances  the  secretion  of  saliva  is  caused  l)y  a  reflex  act 
induced  chiefly  from  the  mouth,  and  Pawlow  has  shown  that  the  quantity  as 
well  as  the  quality  of  saliva  in  the  dog  is  adapted  with  extraordinary  nicety 
to  the  properties  of  the  substances  introduced  into  the  mouth. 

Mechanical  stimulation  of  the  buccal  mucous  membrane  does  not  always 
produce  a  flow  of  saliva.     If,  for  example,  a  haiulful  of  pebbles  be  thrown  into 


Fig.  100. — Parotid  gland  of  the  rabbit  a.s  seen  in  a  fresh,  unstained  preparation,  after  Langley. 
A,  resting  state.  B,  after  injection  of  a  sHght  quantity  of  pilocarpine.  C ,  after  stimulation 
of  the  cervical  sympathetic.     D,  the  same,  only  a  stronger  effect. 


a  dog's  mouth,  the  dog  moves  them  to  and  fro  in  his  efforts  to  get  rid  of  them, 
but  no  saliva,  or  at  most  only  a  drop  or  two,  is  poured  out.  If  on  the  other  hand 
sand  be  used  instead  of  pebbles,  a  copious  flow  of  saliva  is  set  up,  because  the 
sand  cannot  be  removed  from  the  mouth  without  a  stream  of  fluid.  Xor  is  there 
any  discharge  of  saliva  from  application  of  water  or  snow,  but  with  acid,  salty, 
bitter  or  caustic  substances  which  require  to  be  diluted  or  washed  out  of  the 
mouth,  a  discharge  at  once  occurs. 

In  all  these  cases  the  saliva  is  thin,  watery  and  contains  only  a  trace  of 
mucin.  But  with  all  kinds  of  edibla  substances  a  viscid,  mucous  saliva  is 
secreted  such  as  is  necessary  to  facilitate  swallowing  the  bolus.  Besides,  the 
quantity  of  saliva  depends  upon  the  dryness  of  the  food :  the  drier  it  is,  the 
more  saliva. 

It  is  unnecessary  actually  to  place  the  stimulant  into  the  mouth  in  order 
to  produce  a  flow  of  saliva.  Sight  or  smell  of  it  is  sufficient,  or  indeed,  as 
our  own  experiences  prove,  imngination  even  of  savory  substances  will  produce 
the  effect.  With  regard  to  the  quality  and  quantity  of  saliva,  the  same  differ- 
ences are  observed  as  when  the  stimulus  is  applied  to  the  mouth  cavity:  from 
which  we  may  conclude  that  a  psychical  influence  of  no  small  value  is  involved, 
although  this  cannot  be  exercised  by  direct  effort  of  the  will. 


THE   SALIVARY   GLANDS  261 

The  salivary  nerve  centers  are  located  in  the  medulla;  for  reflex  secretion  is 
obtained  after  transsection  of  the  brain  in  the  pons.  A  puncture  in  the  medulla 
is  followed  likewise  by  secretion.  Unilateral  injury  to  the  floor  of  the  fourth 
ventricle  a  little  behind  the  origin  of  the  trigeminal  nerve  causes  secretion  in 
both  submaxillary  glands  and  in  the  parotid  of  the  same  side.  Both  cerebral 
and  symi)athetic  nerves  are  roused  to  activity  in  this  case.  It  is  possible  that 
the  glands  on  each  side  of  the  body  have  their  own  centers,  and  that  these  are 
connected  together  by  commissures  (Beck). 

The  salivary  glands  can  be  set  in  action  also  by  artificial  stimulation  of  that 
part  of  the  cerebral  cortex  which  corresponds  roughly  to  the  motor  zone.  It  is 
very  probable  that  the  above-mentioned  psychical  influence  on  the  salivary  glands 
depends  upon  this  cortical  field. 

B.    MORPHOLOGICAL  CHANGES  DURING  SECRETION 

The  more  recent  investigations  of  this  subject  have  been  made  upon  prac- 
tically fresh  material  instead  of,  as  formerly,  upon  preserved  material.  We 
shall  follow  the  descriptions  given  by  Langley  and  by  Biedermann. 

In  the  albuminous  glands  (Fig.  100)  Langley  found  that  in  the  resting 
state,  the  cells  are  filled  with  a  collection  of  granules  so  alnindant  as  to  ob- 
scure the  cell  boundaries.  When  the  gland  has  secreted  for  some  time,  the 
cells  increase  in  size,  the  granules  gradually  disappear  especially  from  the 
outer  zone,  or  the  side  toward  the  meml^rana  propria,  while  the  inner  zone 
or  the  side  toward  the  lumen  of  the  gland  still  contains  granules.  These 
changes  are  constant  whether  the  gland  l^e  caused  to  secrete  by  the  natural 
stimulus,  by  injection  of  pilocarpine,  or  by  stimulation  of  its  nerves. 

According  to  E.  Miiller,  there  occurs  here  a  conversion  of  strongly  refractive 
granules  into  feebly  refractive  ones,  which  pass  into  the  secretion  as  small 
spherical  drops — the  so-called  secretion  vacuoles  (Fig.  101;  cf.  also  Fig.  99). 
In  very  active   secretion   the  first-named  granules   pass  directly   over  into   the 


Fig.   lOL — Parotid  gland  of  the  cat,  after  E.  Miller.     Sublimate  fixation.     A,  after  twenty-four 
hours'  fast.     B,  during  active  discharge  of  the  secretion. 

secretion  vacuoles.  When  they  leave  the  gland  cells  they  pass  first  into  the 
secretory  capillaries  running  between  the  cells  where  they  are  dissolved  and 
whence  the  secretion  flows  into  the  ducts  of  the  gland. 


262  DIGESTION 

We  meet  with  similar  phenomena  in  fresh  preparations  of  the  mucous 
glands.  A  ghind  from  the  tongue  of  Raua  csculenta  teased  in  a  0.6-per-cent 
salt  solution  (Biedermann)  almost  always  shows  cells,  which  in  the  ends 
turned  toward  the  lumen  are  thickly  set  with  dark,  strongly  refractive  gran- 
ules. When  the  same  object  is  observed  in  active  secretion  the  dark  granules 
have  disappeared  for  the  most  part,  or  form  only  a  narrow  border  along  the 
inner  edge  of  the  cells.  The  latter  contain  also  clear,  vacuolar  drops 
(Fig.  102). 

From  these  observations  it  appears  that  in  the  albuminous  as  well  as  in  the 
mucous  glands,  a  substance  is  formed  during  the  resting  state,  which  in  the 
fresh  gland  has  the  form  of  small  granules.  This  substance  is  liberated  from 
the  cells  in  the  act  of  secretion  and  as  a  consequence  the  cells  decrease  in  size, 
especially  after  a  copious  discharge;  the  main  part  of  the  cell  is  now  clear. 

Are  the  specific  constituents  of  the  secretion  derivatives  of  the  living  proto- 
plasm, or  are  they  to  be  regarded  as  products  of  its  activity?  This  question 
cannot  be  answered  definitely  at  present.  Heidenhain  conceived  that  in  the 
mucous  glands  at  least  the  cells  as  a  whole  are  converted  into  the  secretion,  and 
that  the  so-called  demilume  cells  of  Gianuzzi  are  young  cells  destined  to  replace 


^^^ 
^^-?#% 


Fig.  102. — Parts  of  a  tongue  gland  of  the  frog  (Rana  esculenta),  fresh  condition,  after  Bieder- 
mann.    A,  resting  state.     B,  after  stimulating  the  glossopharyngeal  nerve  for  three  hours. 

the  mucous  cells  after  their  disintegration.  This  assumption  however  is  not  in 
accord  with  the  fact  that  cell  divisions  are  very  rarely  met  with  in  secreting 
glands.  That  cells  do  occasionally  perish  in  very  active  secretion  and  can  be 
replaced  by  division,  has  nothing  whatever  to  do  with  the  process  of  secretion 
as  such.  And  as  for  the  demilumes,  they  appear  from  recent  researches  (Stcihr, 
Noll)  to  be  simply  empty  mucous  cells. 

Other  investigators,  with  Altmann  at  their  head,  regard  the  granules  as 
morphological  derivatives  of  formed  constituent  elements,  and  claim  that  the 
manner  of  their  origin,  their  growth  and  their  transformation  indicate  that  they 
are  vital  units. 

From  all  that  we  know,  however,  the  granules  found  in  the  resting  gland 
might  just  as  well  represent  products  of  the  metabolic  activity  of  the  proto- 
plasm; hence  no  destruction  of  living  substance  would  be  involved  in  their  for- 
mation. The  material  at  hand  is  by  no  means  sufficient  to  decide  a  question 
fundamentally  so  important. 


THE   GLANDS   OF  THE   STOMACH  263 

§  3.    THE   GLANDS   OF   THE    STOMACH 

A.    SECRETORY   NERVES 

Early  observations  on  the  secretion  of  gastric  juice  for  the  most  part 
tended  to  show  that  this  process  scarcely  came  within  the  control  of  the 
central  nervous  system.  Some  few  o1:)servations  there  were,  it  is  true,  which 
indicated  such  an  influence,  but  they  were  rather  scattered  and  were  outnum- 
bered by  other  observations  which  made  it  more  likely  that  the  extrinsic  nerves 
to  the  stomach  had  no  influence  of  a  direct  kind  upon  its  secretory  activity. 
In  the  year  1889,  however,  Pawlow  and  Schumow-Simanowsky  demonstrated 
that  the  vagus  contains  secretory  fibers  for  the  gastric  glands. 

Richet  had  found  in  the  case  of  a  man  with  an  esophageal  stricture  and 
upon  whom  a  stomach  fistula  had  been  made,  that  chewing  strongly  sapid  foods 
produced  immediately  a  flow  of  gastric  juice  from  the  fistula.  It  was  natural 
to  regard  this  secretion  as  a  reflex. 

The  above-named  authors  undertook  to  establish  this  conclusion  experiment- 
ally, and  for  the  purpose  made  on  dogs  an  oesophageal  fistula  besides  the  usual 
stomach  fistula.  When  the  animal  received  something  to  eat  and  swallowed  a 
bolus,  it  of  course  came  out  through  the  opening  in  the  neck  without  ever  reach- 
ing the  stomach  ("  fictitious  feeding  ").  Nevertheless,  after  a  latent  period  of 
five  to  six  minutes  a  copious  secretion  of  gastric  juice  made  its  appearance.  In 
this  way  it  was  proved  that  the  secretion  can  in  fact  be  called  out  reflexly. 

The  efferent  nerves  concerned  in  this  reflex  are  the  vagi.  If  the  vigi  be 
cut,  the  reflex  fails.  If  they  be  stimulated  a  clear  fluid  begins  to  trickle  from 
the  fistula,  which  in  comparison  with  the  normal  gastric  juice  shows  a  lower 
acidity,  but  digests  proteids.  In  addition  to  these  the  vagus  appears  to 
contain  also  fibers,  which  inhibit  the  glands  of  the  stomach. 

But  the  secretion  of  gastric  juice  is  not  dependent  alone  upon  the  vagus. 
There  are  perfectly  trustworthy  statements  in  the  literature  which  show  that 
the  secretion  does  not  cease  after  section  of  the  vagi,  although  the  reflex  from 
the  mouth  be  excluded;  but  that  animals  thus  operated  upon  digest  their 
food  in  the  stomach.  Besides,  analysis  of  the  urine  reveals  no  products  of 
abnormal  putrefaction  in  the  alimentary  canal  of  such  animals,  and  we  may 
conclude  that  a  real  gastric  juice  is  secreted  which  contains  just  as  much 
hydrochloric  acid,  but  considerably  less  pepsin,  than  the  normal  juice. 

Thus  there  are  two  modes  of  gastric  secretion,  namely,  one  under  the 
influence  of  the  secretory  nerve  fibers  which  traverse  the  vagus,  and  the  other 
independent  of  those  fibers. 

(1)  The  Secretion  under  the  Influence  of  the  Vagus. — Neither  excitation  of 
the  nerves  of  taste,  nor  the  act  of  chewing,  nor  the  movements  of  deglutition 
have  of  themselves  any  power  to  cause  a  reflex  secretion  of  gastric  juice.  Only 
when  the  animal  exhibits  some  desire  for  food  does  secretion  result.  The  imagi- 
nation of  savory  substances  would  seem  therefore  to  be  of  special  importance, 
and  this  is  confirmed  by  the  fact  that  gastric  secretion  occurs  when  one  merely 
offers  a  dog  a  piece  of  meat  without  giving  it  to  him.  This  "  psychical "  secre- 
tion is  at  times  very  abundant;  but  if  not,  the  amount  of  secretion  is  consider- 
ably increased  by  fictitious  feeding.  From  these  and  similar  facts  it  appears 
that  although  excitation  of  the  afferent  nerves  from  the  mouth  and  the  a?sopha- 


264  DIGESTION 

gus  does  not  of  itself  produce  any  gastric  secretion,  yet  when  the  animal  has 
some  desire  for  food  this  excitation  intensifies  considerably  the  psychical  secre- 
tion which  would  otherwise  take  place,  and  raises  both  the  acidity  and  the 
digestive  power  of  the  secretion. 

In  the  case  of  a  five-year-old  boy  with  a  complete  oesophageal  stricture  and 
a  gastric  fistula,  Hornborg  found  that  chewing"  palatable  foods  induced,  after 
an  average  latent  period  of  seven  minutes,  a  secretion  which  lasted  for  forty 
minutes  or  more,  whereas  chewing  disagreeable  foods,  or  chemically  active 
(lemons)  or  indifferent  substances  (rubber)  was  without  any  influence  on  the 
gastric  glands.  It  is  worthy  of  note  that  the  secretion  failed  when  the  boy  was 
not  permitted  to  eat  immediately  food  particularly  palatable  to  him,  and  began 
to  cry;  also  that  every  time  he  was  fed  through  the  stomach  fistula  he  wished 
for  something  edible  to  chew.  Mere  sight  of  food  was  not  effective  in  provoking 
the  secretion. 

(2)  The  Secretion  Independent  of  the  Vagus. — Mechanical  stimulation  of  the 
stomach  mucosa,  even  when  it  is  very  energetic,  causes  no  secretion  of  gastric 
juice  whatever;  only  an  alkaline  mucus  flows  from  the  fistula  (Pawlow).  The 
secretion  not  mediated  by  the  vagus  must  be  the  result,  therefore,  of  chemical 
stimulation.  In  order  to  study  this  question  more  closely  and  to  prevent  mixture 
with  foreign  substances,  Heidenhain  separated  the  fundus  portion  from  the  rest 
of  the  stomach  by  a  surgical  operation,  and  thus  prepared  an  isolated  "  fundus 
fistula."  In  this  operation  the  branches  of  the  vagus  which  mediate  the  secretory 
reflex  were  cut.  Nevertheless,  when  the  animal  received  something  to  eat  secre- 
tion appeared  in  the  blind  sac.  It  began  fifteen  to  thirty  minutes  after  eating 
and  continued  for  a  longer  or  shorter  time  according  to  the  quality  and  quantity 
of  the  food — after  a  moderately  full  meal,  thirteen  to  fourteen  hours;  after  a 
very  full  one,  sixteen  to  twenty  hours.  When  the  dog  was  given  very  slightly 
digestible  food,  such  as  coarsely  chopped  ligamentum  nuchse,  no  secretion  ap- 
peared, but  began  when  he  was  subsequently  allowed  to  drink.  Even  then  the 
secretion  continued  for  onlj'  a  short  time,  one  and  one-half  to  four  hours  at  most. 

Pawlow  and  Chigin  carried  out  even  more  detailed  experiments  on  dogs  in 
which  the  blind  sac  was  prepared  without  section  of  the  vagus  branches.  The 
substances  whose  effects  on  the  mucous  membrane  were  to  be  tested  were  intro- 
duced (without  the  dog's  knowledge)  through  a  fistula  directly  into  the  main 
part  of  the  stomach.  Water,  0.1-0.5-per-cent  HCl  solutions,  etc.,  in  quantities 
of  100-150  c.c.  exerted  only  a  very  slight  influence  on  the  process  of  secretion  in 
the  isolated  sac.  In  quantities  of  500  c.c.  pure  water,  ten-per-cent  solutions  of 
cane  sugar  or  starch,  or  egg  albumin  provoked  a  somewhat  stronger  secretion. 
This  began  in  a  majority  of  cases  after  thirteen  to  twenty-nine  minutes.  Since 
distilled  water  evoked  just  as  much  secretion  as  the  solutions,  it  is  assumed  that 
the  effects  here  are  only  those  of  the  solvent.  Weak  soda  solutions  reduced  the 
effect  of  water.     Fats  also  exerted  an  inhibitory  influence. 

When  meat  gravy,  meat  juice  and  meat  extract  or  milh,  or  a  solution  of 
gelatin  in  water  were  introduced  into  the  stomach  in  the  same  way,  results  were 
very  different.  An  abundant  secretion  began  after  an  average  latent  period  of 
thirteen  minutes,  which  continued  for  about  three  hours.  Neither  egg  albumin 
nor  albumose  nor  bread  had  any  such  effect.  It  appears  therefore  that  certain 
extractives  contained  in  meat,  to  which  however  creatin  and  creatinin  do  not 
belong,  certain  constituents  of  milk,  etc.,  are  specific  stimuli  for  the  stomach. 
Furthermore,  there  are  experiments  which  show  that  once  the  secretion  is  started 
by  these  substances,  it  is  considerably  augmented  when,  for  example,  egg  albu- 
min, of  itself  but  slightly  active,  is  introduced.  In  the  same  way  starch  intro- 
duced with  meat  can  intensify  the  secretory  process  considerably. 


THE  GLANDS  OF  THE  STOMACH 


265 


From  these  observations  we  can  form  provisionally  the  following  concep- 
tion of  the  conditions  for  secretion  in  the  stomach.  Secretion  of  gastric  juice 
is  started  by  a  complicated  reflex  process,  which  is  set  in  operation  by  the 
sight  of  food  as  well  as  by  its  passage  through  the  mouth  and  oesophagus,  and 


Hours    12    3    4 


3    4    5    0 


8     y    10    1     2    3    4    5    6 


mmBSSSSSSSS 


Mt-at.  Bread.  Milk. 

Fig.  103. — Hourly  course  of  secretion  of  gastric  juice  in  the  dog's  stomach,  after  Pawlow.     Ex- 
clusive diets  of  meat,  bread,  and  milk  were  given. 

is  mediated  by  the  vagus.  This  secretion  itself  lasts  for  a  fairly  long  time; 
but  it  is  augmented  by  the  stimulating  influence  on  the  mucous  membrane  of 
ingested  water  and.  al)ove  all,  of  certain  extractives,  etc..  contained  in  the  food. 

Chigin's  experiments  on  the  course  of  the  secretion  in  the  blind  sac  with 
the  vagi  preserved  show  very  instructively  how  the  activity  of  the  mucous  mem- 
brane under  the  influence  of  the  vagus  reflexes  and  the  excitation  of  the  food, 
is  adapted  to  the  momentary  requirements  upon  it.  With  all  the  articles  of 
food  thus  far  tested  the  secretion  began  at  about  the  same  time.  It  reached  its 
maximum  during  the  first  or  the  second  hour  (with  milk  during  the  third  hour). 
After  the  maximum  was  reached  the  secretion  fell  immediately  and  became 
gradually  less  and  less  until  it  finally  ceased.  The  absolute  quantity  of  gastric 
juice  with  the  same  article  of  food  was  greater,  the  greater  the  mass  of  food 

Hours     1     234567     12345G78     12345 


etc    •^ 
^        3 


■■■■^^[■■■■■■■■■■H 


:Mpat.  nrcad.  Milk, 

Fig.  104. — Houriy  course  of  the  digestive  action  of  gastric  juice  on  proteid,  after  feeding  exclu- 
sively meat,  breed,  and  milk  (Pawlow). 

introduced.  The  quantity  secreted,  for  example,  was  greater  with  200  g.  of 
meat  than  with  200  g.  of  bread  or  GOO  g,  of  milk  (Fig.  103).  The  digestive 
power  of  the  fluid  secreted  with  the  articles  of  food  just  mentioned,  when  tested 
from  hour  to  hour,  shows  characteristic  variations   (Fig.  104).     Feeding  meat. 


266  DIGESTION 

milk  and  bread  with  the  same  N-eontent  (about  3.4  g.),  there  appeared  in  the 
isokited  sac  27,  34  and  42  c.c.  respectively  of  gastric  juice  having*  a  digestive 
power  of  4.0,  3.1  and  O.IG  mm.  of  egg  albumin  (cf.  page  245).  Since  the  di- 
gestive power  is  proportional  to  the  square  root  of  the  quantities  of  pepsin,  the 
quantities  in  this  series  would  be  to  each  other  as  430,  340,  and  1,600. 

The  center  of  these  reflexes  mediated  by  tlie  vagus  probably  coincides  with 
the  vagus  nucleus.  The  psychic  influence  on  the  secretion  is  exercised  natu- 
rally through  the  cerebrum.  In  the  dog  Bechterew  obtained  a  secretion  of 
gastric  juice  and  of  gastric  mucus  on  stimulating  a  region  lateral  to  the 
anterior  portion  of  the  gyrus  sigmoides  just  at  the  forward  end  of  the  third 
convolution.  Stimulating  for  four  to  five  minutes  tlie  secretion  continued 
for  thirty  to  fifty  minutes  and  exhibited  an  unmistakable  similarity  with  that 
obtained  by  fictitious  feeding.  After  extirpation  of  this  cortical  field  no 
secretion  appeared  on  offering  food. 

The  mechanism  of  the  secretion  which  is  independent  of  the  vagus  is  much 
more  difficult  to  explain.  It  might  be  caused  either  by  some  reflex  process  or 
by  the  direct  exciting  effects  of  absorbed  substances  upon  the  glands  themselves. 
There  are  difficulties  in  the  way  of  both  hypotheses  and  the  matter  cannot  be 
regarded  as  settled. 

B.    THE   GASTRIC   GLANDS 

The  mucous  memhrane  of  the  stomach  presents  considerable  differences  be- 
tween the  fundic  and  pyloric  portions.  The  pyloric  portion  is  pale  and  whitish 
in  color  and  is  beset  by  a  few  high  folds,  here  and  there  united  together.  The 
rest  of  the  mucous  membrane  has  a  reddish-yellow  or  reddish-gray  color,  and 
possesses  numerous  folds  bound  together  into  an  irregular  network,  and  in  addi- 
tion to  these,  fine  secondary  folds  likewise  arranged  as  a  net.  Into  the  depres- 
sions formed  by  the  folds  open  the  gastric  glands,  whose  epithelial  cells  are 
continuous  with  the  epithelium  which  clothes  the  free  surface  of  the  mem- 
brane. 

This  superficial  epithelium  secretes  the  gastric  mucus  and  behaves  prob- 
ably like  similar  cells  of  the  salivary  glands. 

The  glands  of  the  mucous  membrane  are  tubular  and  belong  to  two  dif- 
ferent types,  one  constructed  of  one  kind  of  cells,  the  other  of  two  kinds. 
The  spatial  distribution  of  the  two  kinds  presents  certain  differences  in  dif- 
ferent mammals.  In  the  dog  and  man  the  glands  formed  of  one  kind  of 
cells  occur  only  in  the  pylorus ;  those  with  two  kinds  occur  only  in  the  fundus. 
For  this  reason  they  are  named  pyloric  and  fundic  glands  respectively.  The 
boundary  between  the  two  divisions  of  the  mucous  membrane  is  not  however 
very  sharp. 

The  secreting  elements  of  the  pyloric  glands  are  cylindrical  cells  arranged 
in  a  single  layer  upon  the  basement  membrane  of  the  glands.  The  fundic 
glands  contain  similar  cylindrical  cells  similarly  arranged.  These  cells  were 
discovered  by  Eollet  and  Heidenhain,  and  are  called  the  chief  or  adelomor- 
phous cells. 


THE  GLANDS  OF  THE  STOMACH 


267 


In  addition  to  the  chief  cells  and  situated  outside  of  them  are  other  so- 
called  parietal  or  delomorphous  cells.  These  lie  between  the  chief  cells  and 
the  membrana  propria,  but  do  not  form  a  continuous  layer.  Just  as  in  the 
salivary  glands,  there  are  fine  secretory  capillaries  between  the  gland  cells. 
Those  belonging  to  the  parietal  cells  surround  them  in  a  basketlike  fashion 
and  are  connected  bv  cross  ducts  with  the  lumen  of  the 
gland  (Fig.  105).     "'  |H^  Vj 

It  has  been  known  for  a  long  time  that  the  pepsin  is  /n.it-i 

formed  in  the  chief  cells   (Wassman,  1839). 

If  small  pieces  of  the  fundus  mucosa  be  digested  in  a 
warm  place  with  dilute  hydrochloric  acid,  they  dissolve  leav- 
ing only  small  flakes  behind.  Boiled  white  of  egg  digested 
at  35°^0°  C.  in  acidulated  water,  to  which  a  small  piece 
of  the  fundic  mucosa  has  been  added,  dissolves  in  one  to 
one  and  one-half  hours. 

Since  it  had  been  observed  further  that  the  pylorus 
mucosa  withstood  digestion  much  longer  on  similar  treat- 
ment, and  since  the  chief  cells  had  not  yet  been  discov- 
ered, it  was  supposed  that  the  fundic  glands  were  the  only 
seat  of  pepsin  production,  and  that  the  pyloric  glands  pro- 
duced only  mucus  like  the  superficial  epithelium.  It  has 
since  been  proved  that  the  pyloric  glands  also  produce 
pepsin. 

Simply  to  make  an  extract  of  pylorus  mucosa  and  dem- 
onstrate pepsin  therein,  would  not  be  a  fair  test,  for  it 
might  be  that  the  pepsin  came  from  the  gastric  juice  and  had 
only  been  absorbed  by  the  pyloric  mucosa.  The  matter  takes 
quite  another  aspect  however  when  we  discover  that  the 
pyloric  mucosa  is  not  completely  freed  of  its  pepsin  by 
washing  for  forty-eight  hours  in  running  water.  Several 
other  observations  show  the  same  thing,  and  conclusive  evi- 
dence is  furnished  by  the  following:  By  an  operation  the 
pyloric  portion  can  be  isolated  from  the  rest  of  the  stomach 
in  the  same  way  as  has  already  been  described  for  the 
fundic  portion,  and  a  pyloric  fistula  be  thus  established 
(Klemensiewicz,  Heidenhain.  Akerman).  The  animals  re- 
cover and  exhibit  no  sort  of  disturbance  in  their  general 
health.  From  this  pyloric  sac  a  fluid  is  obtained  which 
always  contains  pepsin  even  if  collected  weeks  or  months 
after  the  operation.  There  can  be  no  question  here  of  absorpt 
trie  juice. 


K 


\A 


y^\ 


^rt 


Fig.  105. — Secretion 
capillaries  s  u  r  - 
rounding  the  pa- 
rietal cells  of  the 
gastric  glands  in 
a  basketlike  net- 
work. The  capil- 
laries also  pene- 
trate the  cells, 
after  E.  Miiller. 

ion  from  the  gas- 


We  have  still  to  decide,  however,  whether  the  pepsin  is  formed  in  the 
chief  or  the  parietal  cells  of  the  fundic  glands.  Several  facts  indicate 
the  former. 

(1)  If  freshly  isolated  fundic  glands  bo  warmed  in  a  drop  of  dilute  hydro- 
chloric acid  under  the  microscope,  the  chief  cells  may  be  seen  to  disintegrate 
rapidly,  whereas  the  parietal  cells  only  swell  up  and  become  transparent. 
(2)  In  sheep  embryos  it  has  been  observed  that  the  parietal  cells  appear  first 
in  the  course  of  development  and  the  chief  cells  much  later.     Pepsin  produc- 


268  DIGESTION 

tion  can  be  demonstrated  in  the  mucous  membrane  only  after  the  hitter  appear. 
(3)  If  different  parts  of  the  stomach  mucosa  be  extracted,  it  is  found  that  the 
quantity  of  pepsin  shows  no  dependence  upon  the  number  of  parietal  cells 
in  the  different  parts,  but  varies  in  direct  proportion  to  the  number  of 
chief  cells. 

How  far  the  parietal  cells  participate  in  the  formation  of  pepsin  must  be 
regarded  as  still  an  open  question.  In  various  lower  vertebrates  whose  gastric 
glands  possess  cells  of  only  one  kind,  it  has  been  observed  that  both  pepsin  and 
hydrochloric  acid  are  produced.  But  we  cannot  draw  any  positive  conclusion 
with  respect  to  the  more  differentiated  gland  of  the  higher  vertebrates  from 
this  discovery. 

Weight  for  weight  the  pyloric  mucosa  produces  much  less  pepsin  than  does 
that  of  the  fundus — which  is  quite  intelligible  when  we  consider  that  the  fundic 
glands  are  much  more  thickly  set  than  the  pyloric  glands,  and  also  that  the 
length  of  the  former  is  considerably  greater  than  that  of  the  latter. 

The  amount  of  rennin  of  the  gastric  juice  during  the  different  stages  of 
digestion  always  runs  parallel  to  the  amount  of  pepsin.  From  this  and  other 
facts  it  appears  permissible  to  conclude  that  although  rennin  is  not  identical 
with  pepsin  (])age  550).  it  is  formed  in  the  pyloric  glands  as  well  as  in  the 
chief  cells  of  the  fundus  glands.  Whether  it  originates  in  the  parietal  cells 
also  cannot  yet  be  decided. 

Views  are  widely  divergent  as  to  the  seat  of  hydrochloric  acid  production. 
While  some  assume  that  it  is  produced  in  all  the  gland  cells  of  the  stomach, 
others  suppose  that  it  originates  only  in  the  parietal  cells  of  the  fundic  glands. 

As  a  matter  of  fact  it  appears  to  be  shown  with  a  fair  degree  of  certainty 
that  the  pyloric  glands  do  not  produce  hydrochloric  acid,  for  in  the  secretion 
of  the  isolated  pyloric  sac  one  finds  in  exceptional  cases  an  alkaline  reaction 
and,  what  is  important  also,  the  mucous  membrane  of  the  blind  sac  exhibits 
at  such  times  perfectly  normal  properties  throughout.  Moreover,  it  is  stated 
that  the  free  surface  of  the  mucosa  gives  an  acid  reaction  only  in  places 
where  glands  with  two  kinds  of  cells  are  found ;  at  other  places  it  reacts 
alkaline. 

After  considering  all  the  facts  obtainable  bearing  on  this  subject.  Heiden- 
hain  came  to  the  conclusion  that  hydrochloric  acid  is  formed  in  the  parietal 
cells  of  the  fundic  glands.  It  must  be  stated,  however,  that  he  reached  this 
conclusion  by  the  process  of  exclusion  and  not  by  direct  evidence. 

The  cells  of  the  gastric  glands  in  the  process  of  secretion  undergo  morpho- 
Jogical  changes  which  have  been  followed  by  Langley  on  fresh  preparations.  In 
the  fasting  condition  the  chief  cells  are  strongly  granular,  but  during  digestion 
are  clear — i.  e.,  the  outer  zone  (about  one-third  to  one-half  of  the  entire 
cell)  shows  no  granules;  they  occur  only  along  the  luminal  border  of  the 
cell.  Extracts  from  different  parts  of  the  mucosa  yield  pepsin  in  greater 
abundance,  the  richer  the  glands  in  granules. 

We  find  therefore  the  same  state  of  affairs  in  the  cells  of  the  gastric  glands 
as  in  the  salivary  glands.  During  the  fasting  period  a  substance  is  laid  down 
in  the  chief  cells,  which  in  fresh  preparations  appears  in  the  form  of  granules. 
During  the  act  of  secretion  this  substance  is  gradually  used  up ;  at  the  same 


SECRETIOX  OF   PANCREATIC   JUICE  269 

time  a  new  formation  of  the  substance  is  going  on,  as  we  know  from  the  fact 
that  the  percentage  of  pepsin  of  the  mucosa  increases  again  after  the  ninth 
hour  of  digestion. 

C.    WHY  DOES  THE  STOMACH   NOT  DIGEST  ITSELF? 

Several  hypotheses  have  been  put  forward  to  account  for  the  fact  that  the 
stomach  does  not  digest  itself.  The  mucus  of  the  stomach  might  act  as  a  kind 
of  varnish  to  protect  the  mucosa  itself  from  the  action  of  the  gastric  juice,  or 
the  epithelium  of  the  mucosa  might  preserve  the  underlying  parts  in  some  way, 
or  the  gastric  juice  might  be  neutralized  by  the  alkalinity  of  the  blood,  or  the 
mucosa  might  be  absolved  from  the  destructive  action  of  the  gastric  juice  by 
its  absorption.  However,  many  objections  can  be  urged  against  all  of  these 
hypotheses  as  well  as  the  experimental  facts  underlying  them,  and  the  question 
was  left  to  a  certain  extent  undecided  by  simply  assuming  that  the  proteolytic 
enzymes  cannot  act  upon  the  living  cells  of  the  same  body. 

A  nearer  approach  to  an  explanation  seems  to  have  been  attained  in  Wein- 
land's  discovery  of  an  antipeptic  and  antitryptic  action  of  the  stomach  and  intes- 
tinal mucosa.  This  action  is  probably  due  to  antienzymes  which  are  found 
throughout  the  whole  animal  scale,  and  occur  not  only  in  the  intestinal  tract 
but  also  in  cells  of  other  organs.  As  mentioned  at  page  155,  such  antienzymes 
are  present  also  in  the  blood. 

§  4.    SECRETION  OF   PANCREATIC   JUICE 

A.    SECRETORY  NERVES 

That  the  secretion  of  pancreatic  juice  is  to  a  certain  extent  under  the 
control  of  the  central  nervous  system  was  rendered  very  probable  by  the  fact, 
ascertained  by  Heidenhain,  that  it  can  be  started  up  or  accelerated  by  elec- 
trical stimulation  of  the  medulla  oblongata.  Later  Pawlow  succeeded  in  com- 
pleting the  evidence  of  secretory  nerves  to  the  pancreas. 

These  nerve  fibers  traverse  the  vagus.  If.  with  the  observance  of  certain 
precautions  which  are  necessary  to  shut  out  the  restraining  influence  of  vari- 
ous sensory  stimuli,  the  vagus  be  stimulated,  a  more  or  less  active  secretion 
of  pancreatic  juice  is  plainly  demonstrable.  The  vagus  also  conveys  fibers 
which  inhibit  the  pancreatic  secretion. 

The  splanchnic  likewise  contains  secretory  fibers  for  the  pancreas,  but  its 
action  is  much  less  powerfid  than  that  of  the  vagus  (Kudrewetsky). 

Secretion  of  tlie  pancreatic  juice  in  the  herbivorous  animals  is  continuous 
— a  condition  doubtless  connected  with  the  continuous  character  of  digestion 
in  these  animals.  In  the  carnivora  it  is  intermittent,  and  (in  the  dog)  the 
first  drops  flow  from  the  duct  one  and  one-half  to  three  and  one-half  minutes 
after  eating.  In  man  also  a  rise  occurs  after  eating  and  reaches  its  maximum 
in  the  fourth  hour,  from  which  time  on  it  gradually  falls  (Glaessner;  Fig. 
106). 

To  what  extent  the  secretion  of  pancreatic  juice  is  caused  like  that  of  the 

gastric  juice  by  stimuli  from  the  mouth,  or  what  role  the  psychic  factor  plays 

in  the  process  must  remain  for  the  present  undecided.     However,  still  another 

influence  is  of  far-reaching  importance  here.     If  an  acid  (no  matter  what 

18 


270 


DIGESTION 


Proteid 


Fig.  lOG.— The  course  of  pancreatic  secretion  in  man, 
after  a  meal  consisting  of  soup,  meat,  and  rolls,  after 
Glaessner. 


Hours    12    3    4    5     1 


3    4    5    6 


8     1 


3    4    5    6 


one)  be  introduced  into  the 
duodenum,  after  a  short 
latent  period,  a  copious  se- 
cretion of  pancreatic  juice 
is  poured  out.  The  acid 
gastric  juice  flowing  through 
the  pylorus  obviously  must 
have  exactly  the  same  effect 
( Gottlieli.  Pawlow) .  As  soon 
as  the  pyloric  sphincter  opens 
and  gastric  juice  pours  out 
into  the  small  intestine,  the 
conditions  are  present  for  an 
abundant  flow  of  pancreatic 
juice. 

This  influence  of  acids  is 
beautifully  confirmed  by  the 
fact  that  a  flow  of  pancreatic 
juice  caused  by  the  gastric  secretion  is  reduced  considerably  when  the  stomach 
contents  are  neutralized  by  administration  of  alkaline  fluids. 

Since  the  vagus  causes  the  flow  of  gastric  juice  also,  it  might  be  thought 
that  the  secretion  of  the  pan- 
creas under  the  influence  of 
this  nerve  begins  only  under 
the  stimulating  action  of  the 
acid  gastric  juice.  But  this 
is  not  true,  for  on  artificial 
stimulation  of  the  vagus  the 
pancreas  begins  to  secrete 
sooner  than  the  stomach,  and 
besides,  the  pancreatic  secre- 
tion makes  its  appearance 
even  if  the  pylorus  be  firm- 
ly ligated  so  as  to  prevent 
any  passage  of  gastric  juice 
(Popielski). 

Water  and  neutral  fats 
in  the  intestine  are  men- 
tioned by  Pawlow  as  special 
excitants  of  the  pancreatic 
secretion  (in  man  adminis- 
tration of  fat  was  without 
effect) ;  other  authors  have 
succeeded  in  inducing  a  se- 
cretion by  means  of  mus- 
tard, pepper,  chloral  hy- 
drate, ether,  etc. 

Formerly  it  was  supposed 
that  this  secretion  is  in  the 
nature  of  a  reflex  and  is 
mediated     by     the     afferent 


50 
48 
46 
44 
42 
40 
38 
36 
34 
32 

-J  30 
6 

a  -^ 

t  2(5 

S    24 

a 

d    oo 

^  20 
IN 
16 
14 
12 
10 
8 
6 
4 

0 


■■■■—■—■■■■■■— 

r 


Meat.  Bread.  Milk. 

Fig.  107. — The  course  of  secretion  in  the  pancreas  of  the 
dog,  after  feeding  exclusively  with  meat,  with  bread 
and  with  milk,  after  Walther. 


SECRETION  OF  P.AATREATIC   JUICE 


271 


Hours 


nerves  of  the  small  intestine.  It  could  .be  pointed  out  in  support  of  this  view 
that  injection  of  acids  into  the  rectum  or  directly  into  the  blood  .evoked  np  secre- 
tion, and  that  therefore  the  glands  could  not  be  stimulated  from 'the.  blood.  '  Bay- 
liss  and  Starling,  however,  observed  that  an  extract  of  the  intestinal  mucous 
membrane  with  HCl,  injected  into  a 
vein,  called  forth  the  pancreatic  secre- 
tion at  once.  The  acid  dissolves  out  of 
the  mucous  membrane  a  substance,  not 
destroyed  by  boiling  and  called  by  the 
authors  secretin,  which  in  their  opinion 
acts  specifically  upon  the  pancreas  and 
constitutes  the  only  natural  cause  of  its 
secretory  activity. 

Beyond  all  doubt  secretin  is  a  pow- 
erful excitant  of  the  pancreatic  secre- 
tion ;  but  its  specific  nature  is  denied 
by  several  authors.  Since,  however,  CO. 
from  the  small  intestine  also  produces  a 
flow  of  pancreatic  juice,  and  there  is 
of  course  no  secretin  extract  of  the 
mucosa  in  this;  since,  further,  the  acid 
introduced  into  an  intestinal  loop  has 
an  exciting  action  on  the  pancreas,  even 
when  the  venous  blood  of  this  loop  is 
diverted  and  the  thoracic  duct  is  tied 
off,  one  is  justified  in  the  assumption 
that  on  introduction  of  acid  into  the  in- 
testine the  secretion  is  produced  partly 
by  a  reflex  set  up  by  the  acid,  and  partly 
through  the  secretin  in  the  blood. 

Nothing   definite   can   be   said   con- 
cerning the  nerve  centers  of  pancreatic 
secretion.     The  observations  which  pur- 
ported to  demonstrate  reflex  centers  in  the  gland  itself  are  no  longer  convincing 
since  the  discovery  of  secretin. 

Tlie  hourly  course  of  the  secretion,  which  appears  to  be  connected  with 
variations  in  the  discharge  of  the  stomach  contents  into  the  intestine,  as  well 
as  the  amount  of  the  different  enzymes  present  in  the  secretion,  shapes  itself 
according  to  the  food  ingested,  as  may  best  be  seen  from  the  diagrams  in 
Figs,  la?  and  108.^ 

:r  From  these  diagrams  it  is  evident  that  the  absolute  rate  of  secretion  fol- 
lowing milk  is  different  from  that  following  the  ingestion  of  meat  and  bread: 
that  the  content  of  amylolytic  enzyme  is  considerably  greater  for  broad  than 
for  meat  and  milk,  and  that  the  content  of  steapsin  is  much  greater  for  milk 
than  for  meat  and  bread. 

The  total  quantity  of  nitrogen  which  is  given  off  in  the  pancreatic  juice 
during  a  period  of  digestion  varies  much  with  different  foods.    In  fact  with  the 

'  With  regard  to  Fig.  108  it  should  be  said  that  the  observations  there  represented 
were  made  before  the  discovery  of  enterokinase ,  ahd  give  therefore  only  the  manifest 
trypsin  content  of  the  juice. 

18* 


Meat. 


Bread. 


Milk. 


Fig.  108. — The  enzymes  of  panceratic  juice, 
after  feeding  exclusively  with  meat,  with 
bread  and  with  milk,  after  Walt  her. 


272 


DIGESTION 


same  amount  of  N  in  the  food,  it  is  about  twice  as  great  for  bread  as  for  milk 
or  meat,  and  in  the  former  case  rises  to  about  one-fifth  the  amount  of  N  ingested. 
In  a  carnivorous  animal  like  the  dog,  the  digestion  of  bread  seems  to  call  for  a 
much  greater  effort  on  the  part  of  the  pancreas  than  the  digestion  of  meat  or 
of  milk  (Walther). 

B.    MORPHOLOGICAL   CHANGES  IN  THE  PANCREAS 

Kiihne  and  Lea  observed  directly  on  the  living  rabbit  the  changes  which 
take  place  in  the  cells  of  the  pancreas  during  secretion  (Fig.  109).  When 
secretion  Ijegins  a  change  of  form  comes  over  the  cells,  which  is  expressed  in 
a  striking  change  of  configuration  of  the  tubule.  While  in  the  inactive  state 
the  latter  appears  perfectly  smooth  on  the  outer  edge,  during  activity  convex 
swellings  which  correspond  to  the  separate  cells  become  visible.  The  resting 
cells  form  an  optically  continuous  picture  within  the  tubule,  but  the  active 


-<^:M.^ 


Fig.   109. — The  pancreas  of  the  rabbit,  as  observed  in  the  living  animal,  after  Kiiline  and  Lea. 

A,  resting  state;    B,  secretion. 

cells  are  marked  off  from  one  another  by  sharp  and,  for  the  most  part,  double 
boundary  lines.  Likewise  during  the  active  condition  the  striations  in  the 
outer  zone,  running  from  the  base  toward  the  inner  border,  stand  out  more 
clearly.  The  granules  of  the  inner  zone  withdraw  gradually  from  the  region 
of  the  nucleus  toward  the  lumen,  become  smaller  and  softer,  and  finally 
disappear  altogether. 


§  5.    THE   LIVER  AND   THE   SECRETION   OF   BILE 
A.    GENERAL   PHENOMENA   OF   HEPATIC   SECRETION 

The  secretion  of  bile  differs  from  the  other  secretory  processes  thus  far 
studied,  primarily  by  being  continuous,  but  also  by  the  fact  that,  notwithstand- 
ing many  researches,  secretory  nerves  have  not  yet  been  found  for  the  liver. 

In  this  respect  there  is  complete  agreement  between  the  bile  and  the  urine, 
and  one  might  suppose  that  these  two  secretory  processes  do  not  require  the 
cooeration  of  secretory  nerves,  since  in  order  to  discharge  their  function  of 
removing  excretory  products  from  the  body  they  must  go  on  continuously.     As 


THE   LIVER   AND  THE   SECRETION   OF   BILE  273 

far  as  the  kidneys  are  concerned,  we  know  indeed  that  certain  diuretic  substances 
in  the  blood  intensify  the  secretion  of  urine  quite  independently  of  the  nervous 
system.  It  is  possible  that  the  same  thing  is  true  of  the  liver  and  that  here,  as 
probably  in  the  kidneys,  the  regulation  of  secretion  is  the  result  of  a  vasomotor 
influence.  However,  this  conclusion  does  not  exclude  the  possibility  of  some 
controlling  influence  by  secretory  nerves,  for  experience  with  the  secretory  nerves 
of  the  stomach  and  pancreas  teaches  that  the  results  of  stimulation  may  be 
entirely  masked  by  various  different  circumstances. 

Although  the  secretion  of  bile  goes  on  continuously,  it  shows  certain  varia- 
tions which  are  not  yet  satisfactorily  explained.  Indeed  the  statements  of 
facts  themselves  exhibit  a  difference  in  many  points,  which  is  but  little  gratify- 
ing. This  much  appears,  however,  from  the  observations  at  hand,  that  the 
food  exerts  an  important  influence.  The  quantity  of  bile  secreted  is  least  in 
fasting  and  declines  steadily  as  the  period  is  prolonged.  The  increase  effected 
by  the  food  depends  in  the  first  place  upon  the  kind :  meat  causing  a  consider- 
able increase,  carl)ohydrates  causing  little  or  none  at  all. 

Even  in  fasting  the  secretion  of  bile  varies  from  hour  to  hour.  After 
feeding  meat  the  rise  mentioned  above  does  not  appear  at  once,  but,  as  a  rule, 
only  after  the  lapse  of  twenty  to  thirty  minutes.  The  latent  period  is  still 
longer  after  feeding  fat.  Statements  disagree  as  to  when  the  maximum 
occurs. 

This  long  latent  period  is  of  great  importance  for  our  theoretical  con- 
ception of  the  causes  of  the  secretion,  and  seems  to  speak  decisively  for  the 
view  that  the  increase  results  from  an  exciting  influence  of  sulistances  absorbed 
from  the  alimentary  canal,  and  that  these  substances  act,  therefore,  directly 
on  the  liver.  Whether  this  view  actually  represents  the  truth  of  the  matter, 
or  whether  the  increase  in  the  secretion  of  liile  which  is  to  be  observed  after 
feeding  is  due  to  a  reflex  effect  upon  vasomotor  or  secretory  nerves,  must  for 
the  i)resent  be  regarded  as  another  open  question. 

The  direct  stimulation  of  the  liver  by  l)ile-producing  (cholagngic)  sub- 
stances is  illustrated  further  by  the  following  facts  to  which  Schiff  first 
directed  attention.  If  both  a  biliary  and  an  intestinal  fistula  have  been 
established  in  a  dog,  and  the  bile  obtained  from  the  former  be  injected  into 
the  latter,  or  if  ox  bile  be  used  for  the  same  purpose,  a  considerable  increase 
in  the  amount  of  bile  flowing  from  the  biliary  fistula  is  obtained.  Schiff 
explained  these  facts  by  saying  that  the  injected  bile  was  absorbed  from  the 
intestine,  came  to  the  liver  and  was  again  secreted. 

We  have  direct  proof  of  the  correctness  of  this  view  in  the  fact  that  sheep's 
bile,  when  injected  into  a  mesenterial  vein  of  a  dog  whose  hepatic  arteries  have 
been  tied  off.  is  secreted  in  the  bile  of  the  dog  and  can  be  demonstrated  by  the 
spectroscopic  test  for  cholohematin,  which  occurs  normally  only  in  the  bile  of 
the  sheep.  At  the  same  time  the  absolute  quantity  of  bile  rises.  Bile  or  bile 
salts  given  by  the  mouth  have  the  same  effect.  The  percentage  content  of  solids 
rises  at  the  same  time  (Spiro  and  Voit). 

B.  DEPENDENCE  OF  THE  SECRETION  OF  BILE  UPON  THE  BLOOD  SUPPLY 

The  supplji  of  blood  to  the  liver  manifestly  influences  the  secretion  of 
bile  to  a  considerable  extent.    If  the  general  hln<vl  pressure  be  reduced  mark- 


274  DIGESTION 

edly  by  bleeding,  the  quantity  of  bile  secreted  is  diminished;  at  the  same 
time,  however,  the  percentage  of  solids  increases.  Cutting  down  the  supply 
of  blood  by  tying  oif  several  branches  of  the  portal  vein  likewise  diminishes 
the  secretion.  And  when  the  vena  cava  inferior  is  compressed — so  that  the 
volume  of  blood  passing  through  the  liver  in  a  unit  of  time  is  materially 
reduced — the  same  result  is  obtained. 

The  secretion  of  the  bile  declines  on  stimulation  of  the  spinal  cord,  because 
of  excitation  of  the  vasoconstrictor  nerves  to  the  abdominal  viscera,  and  a  con- 
sequent fall  in  the  blood  supply  to  the  liver.  Section  of  the  cervical  cord  pro- 
duces a  general  fall  of  pressure  throughout  the  vascular  system  and  is  accom- 
panied by  a  decline  in  the  output  of  bile.  The  output,  on  the  other  hand, 
increases  after  section  of  the  splanchnic,  because,  in  spite  of  the  fall  in  general 
blood  pressure,  the  blood  supply  to  the  liver  increases  on  account  of  the  dilatation 
of  the  portal  vessels. 

These  and  other  kindred  facts  can  be  fully  explained  by  variations  of  blood 
supply  and  contain  no  proof  whatever  that  the  secretion  of  bile  is  directly 
affected  by  secretory  nerves.  It  is  possible  also  that  the  rise  of  the  secretion 
mentioned  by  some  authors  as  beginning  shortly  after  the  ingestion  of  food,  is 
produced  by  the  dilatation  of  stomach  and  intestinal  vessels  during  digestion. 

We  may  summarize  the  facts  thus  far  discussed  as  follows :  The  liver 
secretes  bile  continuously.  This  secretion  is  intensified  by  abundant  supply 
of  blood,  also  by  certain  bile-producing  substances,  especially  the  digestive 
products  of  proteids.  There  is  yet  at  hand  no  single  observation  which  would 
permit  us  to  speak  of  any  influence  of  secretory  nerves  on  the  liver.  Like 
the  other  digestive  fluids,  bile  represents  an  elaborated  product  of  the  secret- 
ing cells  of  the  gland,  for  its  specific  constituents  do  not  occur  in  the  blood. 
The  secretion  pressure  of  the  bile  also  is  higher  than  the  blood  pressure  in  the 
portal  vein. 

Since  the  liver  receives  blood  from  several  sources  (hepatic  arteries,  portal 
vein  and  by  return  flow  from  the  inferior  vena  cava),  it  is  of  interest  to  inquire 
whether  any  one  of  these  vessels  is  indispensable  to  the  production  of  bile,  or 
whether  all  three  can  maintain  the  secretion  independently.  On  closing  off  the 
hepatic  arteries,  secretion  still  takes  place  in  abundance.  Likewise  after  liga- 
tion of  the  portal  feeding  one  of  the  lobes  of  the  liver,  the  arterial  branch  sup- 
plying the  same  lobe  alone  mediates  the  secretion.  Eck  has  shown  that  by  an 
operation  (Eck  fistula)  the  portal  blood  can  be  conducted  directly  to  the  inferior 
vena  cava,  thus  evading  the  liver  altogether;  and  Stolnikow  has  found  that 
secretion  of  bile  continues  after  such  an  operation.  This  secretion  occurs  at 
least  in  part  at  the  expense  of  blood  flowing  backward  in  the  hepatic  veins.  For 
if  the  hepatic  artery  is  tied  off  after  the  new  route  for  the  blood  is  established, 
the  secretion  still  continues.  It  ceases  however  when  the  hepatic  vein  in  addi- 
tion is  tied.     Either  kind  of  blood  therefore  seems  to  be  sufficient  to  produce  bile. 

The  hepatic  artery  supplies  the  gall  bladder,  the  bile  ducts  and  the  inter- 
lobular branches  of  the  portal  vein  with  blood  through  its  vasa  nutritia.  When 
these  are  ligated  and  the  arterial  blood  supply  thus  completely  stopped,  multiple 
necrotic  foci  make  their  appearance  in  the  liver.  From  the  larger  foci  cysts 
develop;  the  smaller  ones  become  transformed  into  connective  tissue,  and  are 
followed  finally  by  an  hepatic  cirrhosis. 

When  the  discharge  of  bile  into  the  intestine  is  prevented,  the  bile  is  reab- 


THE   LIVER  AND  THE  SECRETION   OF   BILE 


275 


sorbed.  It  does  not  pass  directly  from  the  biliary  ducts  into  the  blood,  but  is 
taken  up,  in  part  at  least,  by  the  lymphatic  vessels.  If  the  thoracic  duct  as  well 
as  the  bile  duct  be  tied  off,  it  may  happen  that  no  constituents  of  the  bile  will 
pass  into  the  blood  (Harley)  ;  but  there  are  statements  to  the  effect  that  even 
under  these  circumstances  they  may  find  their  way  into  the  general  circulation 
(Wertheimer  and  Lepage). 

C.    THE  DISCHARGE  OF  BILE  IN  DIGESTION 

When  digestion  is  not  going  on  the  secreted  bile  collects  in  the  gall  blad- 
der; there  it  loses  water  and  becomes  thicker.  Neither  bodily  movements, 
nor  movements  of  the  alimentary  canal,  fasting,  nor  appetite  have  any  effect 


Fig.  110. — The  hourly  covirse  of  the  discharge  of  bile  into  the  intestine  of  the  dog,  following  in- 
gestion of  different  foods,  after  Bruno.  meat ; bread; milk. 

in  causing  the  gall  bladder  to  empty  its  contents :  the  bile  begins  to  flow  from 
the  bladder  into  the  intestine  only  at  the  beginning  of  digestion. 

The  outflow  of  bile  into  the  intestine  is  adapted  to  the  immediate  require- 
ments by  the  following  mechanisms.  The  discharge  of  bile  from  the  ductus 
choledochus  is  controlled  by  a  special  sphincter.  The  gall  bladder  and  the  bile 
duct  possess  muscles  which  are  under  the  influence  of  the  splanchnic  nerve.  It 
is  said  that  the  duodenal  sphincter  of  the  ductus  choledochus  is  innervated  by 
the  vagus.  Phenomena  witnessed  on  stimulation  of  the  splanchnic  show  fur- 
ther that  the  gall  bladder,  as  well  as  the  ductus  choledochus  and  the  sphincter, 
may  be  reflexly  dilated.  Again  by  central  stimulation  of  the  vagus,  reflex  con- 
traction of  the  gall  bladder  and  relaxation  of  the  sphincter  may  be  produced. 

The  evacuation  of  the  gall  bladder  and  the  discharge  of  bile  in  dig-estion, 
according  to  Bruno,  are  elicited  by  the  passage  of  the  stomach  contents  into  the 
intestine.  The  substances  active  in  this  are  the  digestive  products  of  proteids, 
extractives  of  meat  and  fats.  The  carbohydrates  evoke  no  discharge  of  bile. 
Since  the  passage  of  the  stomach  contents  into  the  intestine  is  governed  by  the 
kind  of  food,  the  discharge  of  bile  is  naturally  different  for  different  foods,  as 
appears  also  from  the  diagram  in  Fig.  110. 

With  respect  to  the  properties  of  the  l)ile.  it  should  be  mentioned  that  the 
portions  first  di.'^charged  are  tliicker  tlian  tliat  wliicli  comes  later,  liecau.-ie  the 
former  comes  from  the  gall  bladder,  while  the  latter  is  freshly  secreted. 


276  DIGESTION 

§6.    THE    GLANDS   OF   THE   INTESTINE 
A.    GLANDS   OF  THE  SMALL  INTESTmE 

In  fasting  animals  scarcely  any  secretion  of  intestinal  juice  takes  place. 
But  if  the  intestinal  mucosa  be  stimulated  directly,  either  by  mechanical, 
electrical  or  chemical  means,  or  if  food  be  ingested,  it  makes  its  appearance. 
Whether  an  isolated  loop  of  the  intestine  into  which  no  food  can  pass  begins 
to  secrete  without  direct  stimulation,  must,  in  view  of  recent  discoveries,  be 
regarded  as  very  doubtful. 

If  the  nerve  fibers  running  in  the  mesentery  beside  the  blood  vessels  to  an 
intestinal  loop  be  cut,  either  immediately  or  after  some  time,  an  extremely  abun- 
dant secretion  appears  in  the  loop,  whereas  the  adjacent  parts  of  the  intestine 
outside  of  the  tract  deprived  of  its  nerves  show  nothing  of  the  kind.  This  secre- 
tion, which  may  reach  the  enormous  value  of  one-eleventh  of  the  body  weight, 
continues  for  some  hours,  becomes  somewhat  scanty  after  four  or  five  hours,  but 
does  not  cease  within  twenty-four  hours.  At  first  the  secretion  is  quite  clear, 
containing  no  solid  flakes,  or  at  least  only  a  few;  but  as  time  goes  on  the  quantity 
increases  so  that  finally  a  veritable  "  pap  "  is  produced.  At  times  the  secretion 
is  milky,  like  a  thin  gruel,  and  contains  an  abundance  of  intestinal  epithelia 
(Moreau).  Somewhat  similar  phenomena,  more  or  less  degenerative  in  character, 
make  their  appearance  after  extirpation  of  the  co^liac  plexus. 

It  is  not  easy  to  explain  this  secretion.  We  might  regard  it  as  primarily  a 
transudation  of  fluid  caused  by  the  vasodilatation,  and  not  as  a  true  process 
of  secretion  at  all  if  our  knowledge  of  transudation  in  general  did  not  speak 
decisively  against  such  an  explanation.  If  it  were  an  actual  secretion  of  the 
glands  of  Lieberkiihn — a  view  which  is  confirmed  by  the  properties  of  the  fluid — 
it  were  easy  to  assume  that  the  nerves  whose  seetion  produced  the  hypersecretion 
exert  a  tonic  influence  which  inhibits  the  glands.  When  the  glands  escape  from 
this  inhibitory  influence  they  fall  into  the  condition  described.  This  hypothesis 
assumes  that  in  the  intestine  itself  conditions  are  present  which  would  set  the 
glands  in  excessive  action,  if  they  were  not  restrained  by  the  nerves.  But  we 
know  nothing  more  about  it.  Meantime  let  it  be  remembered  as  was  remarked 
concerning  the  other  digestive  glands — the  paralytic  secretion  of  the  salivary 
glands,  etc. — that  certain  phenomena  have  been  observed  which  point  to  such  an 
inhibitory  influence. 

Other  than  this  we  have  no  knowledge  of  an  ultimate  influence  of  the  ner- 
vous system  upon  the  secretion  of  the  intestinal  juice.  Vagus  stimulation  thus 
far  has  given  only  negative  results. 

So  far  as  the  few  scattered  observations  on  this  subject  go.  the  secretion 
of  the  lower  part  of  the  small  intestine  seems  to  be  more  abundant  than  that 
of  the  upper.  It  is  stated  also  that  the  quantity  of  slimy  flakes  in  the  upper 
parts  is  greater.  These  flakes  consist  essentially  of  swollen  cellular  elements 
(epithelial  cells  and  leucocytes)  and  of  desquamated  cells  undergoing  fatty 
degeneration. 

If  the  two  ends  of  an  isolated  loop  of  the  intestine  be  sewed  together  and 
the  intestinal  ring  thus  formed  be  lowered  into  the  abdominal  cavity,  one  finds, 
when  the  animal  is  killed  some  months  later,  that  the  intestinal  ring  is  filled 
full  of  a  semisolid  mass  (Hermann).  This  mass,  like  the  above-mentioned  flakes 
in  the  intestinal  juice,  consists  of  dead  cellular  elements.    It  appears  therefore 


THE   GLANDS   OF  THE   INTESTINE 


277 


as  if  cells  of  the  mucous  membrane  perish  in  great  numbers,  even  if,  as  in  this 
case,  no  food  or  anything  of  the  kind  comes  into  the  intestine.  Xevertheless, 
this  conclusion  is  not  quite  definitely  established,  for  it  cannot  be  maintained 
that  the  isolated  loop  is  in  a  perfectly  normal  condition.  And,  in  fact,  Klecki 
has  observed  that  if  he  washed  the  intestinal  ring  tolerably  free  of  Bacteria 
with  boracic  acid  and  artificial  gastric  juice  before  sewing  it  up,  and  if  in  the 
further  course  of  the  experiment  no  pathological  changes  of  any  kind  made 
their  appearance,  he  found  after  the  lapse  of  more  than  two  months  only  a 
scanty  deposit  of  yellowish,  sticky,  waxlike  substance  adherent  to  the  surface  of 
the  membrane.  This,  like  the  contents  mentioned  above,  consisted  mainly  of 
desquamated  intestinal  epithelial  cells, 
but  was  by  no  means  so  abundant.  /> 

Histological  studies  of  the  glands  a 

of  Lieberkiihn  have  shown  that  their  ^ 

fundic  cells  have  the  same  morpho-  f; 

logical  character  as  the  cells  of  the  ^ 

other  digestive  glands.     Likewise  in  ^ 

these  the  preliminary  stages  of  the  ^ 

secretion  appear  in  the  form  of  gran-  fs^. 

nles  which  gradually  increase  in  size  ^ 

and  finally  pass  over  into  the  secretion.  \S 

These  cells  are  very  sharply  distin-  '^ 

guished  by  their  properties  from  the  '^ 

mucous   cells    (goblet   cells)    of   the  -^0 

intestinal  epithelium   (W.  ^I oiler).  ^ 


B.     THE 


GLANDS    OF    THE 
INTESTINE 


LARGE 


A  B 

Fig.  111. — Glands  of  the  large  intestine  of 
the  rabbit,  after  Heidenhain.  .4,  after 
very  active  secretion;  B,  after  a  long 
period  of  rest. 


The  glands  of  Lieberkiihn  in  the 
large  intestine  do  not  secrete  a  digest- 
ive fluid.  The  properties  of  their 
secretion  have  been  studied  by  mak- 
ing an  opening  into  the  large  intes- 
tine and  introducing  various  sub- 
stances   inclosed    in    small    sacs    of 

network.  It  has  been  found  in  this  way  that  neither  fibrin  nor  starch  is 
digested.  The  secretion,  which  is  Iiut  scanty,  is  a  water-clear,  odorless,  thickly 
gelatinous  and  sticky  mass  of  neutral  reaction,  containing  turbid  flakes  of 
various  sizes  (Klug  and  Koreck). 

The  secretion  of  the  large  intestine,  therefore,  jihujs  no  purl  in  digestion. 
The  mucus  contained  in  it  probal)ly  serves  to  facilitate  the  passage  of  the 
intestinal  contents  which  have  become  thicker  by  the  absorption  of  water. 

If  the  mucous  membrane  of  the  large  intestine  be  studied  under  the  micro- 
scope, after  injection  of  pilocarpine  into  the  animal,  the  glands  are  seen  to 
be  composed  of  cells  which  are  strikingly  like  those  of  the  glands  in  the  small 
intestine.  In  alcoholic  preparations  the  cells  of  both  are  small,  longitudinally 
striated,  and  contain  round  or  oval  nuclei  (Fig.  Ill,  A).  After  prolonged 
rest  the  glands  of  the  large  intestine  present   quite  another  picture.     The 


278  DIGESTION 

great  majority  of  the  tubes  are  clothed  from  base  to  mouth  with  cells 
which  have  gone  through  a  process  of  mucous  degeneration,  and  have  taken 
the  form  of  goblet  cells — i.  e.,  swollen  structures  with  the  nuclei  in  the  basal 
end  (Fig.  Ill,  B).  The  contents  of  these  cells  behave  exactl}^  like  those  of 
the  typical  mucous  cells  (Heidenhain). 

Likewise  in  the  glands  of  the  small  intestine  are  found  goblet  cells  be- 
tween the  true  epithelial  cells;  but  they  are  often  wanting.  Frequently  they 
occur  separately  in  the  region  of  the  upper  end  of  the  tube,  rarely  also  at 
the  lower  end. 

From  these  facts  it  follows  that  the  cells  during  rest  undergo  mucous 
degeneration  ;  in  activity  the  mucus  is  discharged  and  the  cell  itself  often 
perishes  in  the  process.  Just  to  what  extent  the  latter  takes  place  has  not 
been  finally  determined.  At  the  base  of  the  epithelium  are  found  here  and 
there  small  round  cells  \yhich  are  looked  upon  as  substitutes  for  the  cells 
which  disintegrate. 


THIRD    SECTION 

MOVEMENTS   OF   THE   ALIMENTARY   CANAL 

§  1.    MASTICATION 

The  movements  of  mastication  are  for  the  purpose  of  dividing  the  food 
mechanically  and  of  saturating  it  with  saliva,  so  that  a  bolus  may  be  pre- 
pared suitable  for  swallowing.  Mastication  is  accomplished  by  movements 
of  the  lower  jaw  against  the  upper,  the  morsel  of  food  being  placed  by  appro- 
priate movements  of  the  tongue  and  cheeks,  between  the  two  rows  of  teeth, 
and  l>eing  ground  up  by  the  latter  acting  against  each  other  under  the  force 
of  the  powerful  jaw  muscles. 

The  teeth  and  the  mode  of  chewing  are  unmistakably  adapted  to  the  kind 
of  food  eaten,  so  long  as  regard  is  had  to  the  animals  whose  natural  food  is 
exclusively  animal  or  exclusively  vegetable.  In  man  the  teeth  and  movements 
of  the  jaw  present  no  pronounced  characteristics,  doubtless  because,  with  the 
assistance  of  the  art  of  cooking,  he  has  learned  how  to  subsist  upon  so  many 
different  articles  of  diet.  Raw  meat  cannot  be  properly  reduced  by  the  teeth  of 
man ;  but  if  properly  boiled  or  roasted  so  that  the  connective  tissue  binding  the 
muscle  fibers  together  is  loosened,  it  is  easily  masticated.  Likewise  the  seeds 
of  cereals,  which  are  otherwise  incapable  of  being  attacked  by  the  human  digest- 
ive apparatus,  are  rendered  fit  for  food  by  boiling  or  by  baking.  Among  all 
the  articles  of  diet  which  are  generally  accessible  to  the  higher  animals,  strictly 
speaking  only  grass  and  hay  are  incapable  of  serving  man  as  food. 

The  actual  grinding  of  the  food  is  attended  to  primarily  by  the  molar 
teeth,  those  in  the  front  of  the  mouth  serving  only  for  biting  off  morsels  of 
suitable  size.  The  lower  jaw  is  drawn  upward  by  the  masseter  and  temporal 
muscles,  forward  and  upward  by  the  internal  pterygoids,  forward  by  the 
external  pterygoids.  It  is  drawn  downward  by  the  digastric,  the  mvlohyoid 
and  the  geniohyoid,  and  backward  by  the  posterior  belly  of  the  digastric. 


DEGLUTITION  279 

By  contraction  of  the  external  pterygoid  muscle  of  one  side  the  jaw  is  moved 
toward  the  opposite  side.  In  the  depression  of  the  lower  jaw,  the  articular 
tubercle  is  moved  forward  in  a  line  which  is  concave  upward,  at  first  slowly, 
then  rapidly  and  at  last  slowly  again. 

The  lips,  cheeks,  and  tongue  cooperate  to  bring  the  new  or  incompletelv 
masticated  portions  of  the  morsel  between  the  teeth,  to  facilitate  saturation 
of  it  with  the  saliva  and  finallv  to  form  the  mass  into  a  bolus  to  he  swallowed. 


§  2.    SUCKING 

The  buccal  cavity  is  capable  of  being  closed  air-tiglit.  It  can  also  be 
enlarged  without  admission  of  air,  and  in  this  way  suction  can  Ije  produced 
by  which  fluids  may  be  drawn  into  the  mouth. 

When  the  buccal  cavity  is  closed  so  as  to  be  air-tight,  the  tip  of  the  tongue 
lies  against  the  teeth  and  the  alveolar  process  of  the  upper  jaw;  the  base  of  the 
tongue  is  raised  on  both  sides  against  the  back  teeth  and  the  neighboring  parts 
of  the  upper  jaw;  the  lower  surface  of  the  tongue  rests  on  the  edge  of  the  lower 
jaw,  and  the  soft  palate  hangs  down  loosely  over  the  root  of  the  tongue.  Holding 
the  jaws  perfectly  still  with  the  parts  in  this  position,  a  negative  pressure  of 
from  2  to  4  mm.  of  Hg.  prevails  in  the  mouth  (Mezger,  Bonders).  One  can 
easily  convince  himself  that  the  cavity  is  really  air-tight,  for  if  he  depress  the 
lower  jaw  without  opening  the  mouth,  the  cheeks  are  drawn  between  the  rows 
of  teeth. 

By  drawing  the  tongue  back  or  by  lowering  the  jaw,  the  buccal  cavity  is 
enlarged  and  a  suction  is  thus  produced,  which  becomes  still  stronger  if  the 
tongue  be  drawn  downward. 

The  space  inclosed  by  the  mouth  parts  in  the  act  of  sucking  is  about  ?7  c.c, 
three-eighths  of  which  is  due  to  the  depression  of  the  jaw,  and  five-eighths 
to  the  lowering  and  flattening  of  the  tongue. 

The  power  of  suction  in  the  human  mouth  is  very  great.  It  is  possible 
by  repeated  efforts  to  develop  a  negative  pressure  of  700  mm.  of  Hg. 

A  child  in  nursing  grasps  the  nipple  of  the  breast  with  the  lips  in  such 
a  way  that  the  mouth  is  closed  air-tight.  In  the  absence  of  teeth  this  is 
facilitated  by  special,  membranous,  and  very  vascular  prominences  on  the 
edge  of  the  gums  of  both  jaws.  These  structures  are  found  in  the  position 
of  the  four  canines  and,  especially  in  the  lower  jaw,  are  united  by  a  mem- 
branous seam  projecting  1-3  mm.  high. 


§  3.    DEGLUTITION 

We  include  under  deglutition  all  those  processes  by  which  the  bolus  of 
food  is  propelled  from  the  mouth  into  the  stomach.  It  is  a  very  complicated 
reflex  process  in  which  many  muscles  cooperate. 

After  the  bolus  is  formed  and  is  placed  on  the  back  of  the  tongue,  the 
swallowing  reflex  is  elicited  by  stimulation  of  the  sensory  nerves  in  the  back 
of  the  mouth.  In  the  ape  the  bolus,  thrown  into  the  ]iharynx,  excites  the 
reflex  act  in  gliding  over  the  tonsils   (Kahn).     In  man  no  definite  part  of 


280  DIGESTION 

the  mouth  cavity  from  which  the  reflex  can  invarial)ly  be  started  has  yet  been 
made  out.  We  can  only  say  that  it  is  induced  when  the  bolus  is  forced  back 
of  the  soft  palate  into  the  region  of  the  tonsils.  Thus  far  the  process  is  under 
control  of  the  will  and  the  swallowing  reflex  therefore  is  inaugurated  volun- 
tarily, but  thereafter  it  is  independent  of  the  will. 

The  first  muscles  to  contract  are  the  mylohyoids,  and  the  pressure  in  the 
mouth  cavity  is  raised  by  their  contraction  alone  to  about  20  c.c.  of  water. 
Almost  at  the  same  instant  the  hyoglossi  contract  causing  the  free  surface 
of  the  base  of  the  tongue,  which  in  rest  is  directed  backward  and  upward, 
to  execute  a  movement  backward  and  downward.  By  this  contraction,  ac- 
cording to  Kronecker  and  ]\Ieltzer,  fluid  foods  are  spirted  through  the  whole 
length  of  the  oesophagus  to  its  lower  end  jjefore  the  contractions  of  the  phar- 
yngeal and  oesophageal  muscles  can  be  brought  to  bear  on  them.  Against  this 
view,  however,  it  may  be  observed  that  at  the  moment  of  the  mylohyoid  con- 
traction the  oesophagus  is  still  closed  by  an  elastic  pressure  exerted  by  the 
larynx.  This  closure  is  broken  only  when  the  larynx  is  drawn  upward  and 
forward,  which  takes  place  some  0.2  (Schreiber)  to  0.3  of  a  second  (Eykman) 
after  the  inception  of  the  act — i.  e.,  at  a  time  when  the  effect  of  the  mylo- 
hyoid is  already  past.  If  this  be  true,  the  movements  of  the  above-named 
muscles  of  the  tongue  can  only  force  the  food  mass  into  the  pharynx  (cf. 
Fig.  112,  in  which  a  sagittal  section  of  the  floor  of  the  mouth  and  of  the 
neck  in  both  the  normal  position  (A)  and  the  open  position  (B)  of  the  pas- 
sageway is  represented  after  X  ray  photographs ;  from  B  it  is  plain  that  the 
tongue  in  swallowing  lies  against  the  posterior  wall  of  the  throat). 

When  the  food  reaches  the  pharynx  there  follows  in  order  the  contractions 
of  the  pharyngeal  and  the  oesophageal  muscles.  In  the  oesophagus  the  move- 
ment is  executed  at  two  different  rates  of  speed.  The  muscle  fibers  in  the 
cervical  part  of  the  oesophagus  are  cross-striated  and  the  movement  conse- 
quently is  rapid ;  in  the  thoracic  portion  the  cross-striated  muscle  layers  are 
replaced  more  and  more  by  smooth  muscles  and  the  movement  of  the  food 
is  consequently  slower.  The  total  time  from  the  beginning  of  the  act  of 
deglutition  until  immediately  before  the  opening  of  the  cardia  is  about  seven 
to  eight  seconds. 

If  the  cpsophagus  be  cut  in  the  neck  or  even  if  a  long  piece  of  it  be  extir- 
pated, and  the  superior  laryngeal  nei-ve,  which  very  easily  discharges  the  swal- 
lowing reflex,  be  stimulated,  a  perfectly  regular  act  of  swallowing  results  in 
which  the  contraction  not  only  extends  over  the  upper  part,  but  appears  just  as 
usual  in  the  part  lying  below  the  section  (Mosso).  The  peristaltic  wave  of  con- 
traction therefore  runs  from  above  downward,  under  the  direct  control  of  the 
central  nervous  system.  In  deeply  antesthetized  dogs  this  experiment  does  not 
succeed  (Wild) ;  but  if  in  such  animals  the  anatomical  continuity  be  preserved, 
the  contraction  wave  travels  over  the  entire  oesophagus.  From  this  it  follows 
that  the  contraction  can  be  propagated  through  the  oesophagus  without  the 
cooperation  of  the  central  nervous  system,  a  circumstance  which  Meltzer  sup- 
poses to  be  due  to  the  action  of  peripheral  reflex  centers. 

We  have,  therefore,  to  conceive  the  act  of  deglutition  as  taking  place  in 
such  a  way  that  once  the  reflex  is  induced,  the  different  divisions  of  the 
passageway   (floor  of  the  mouth  and  tongue,  pharynx,  the  various  divisions 


DEGLUTITION 


281 


of  the  oesophagus)  are  excited  in  a  perfectly  definite  order  by  impulses 
coming  from  the  central  nervous  system. 

The  nerves  for  the  upper  part  of  the  oesophagus  are  found  in  the  recurrent 
laryngeals,  for  the  lower  part  in  the  pulmonary  and  oesophageal  plexuses. 

Since  the  phar}Tix  is  in  open  communication  not  only  with  the  oesophagus 
but  with  the  nose  and  the  larynx,  the  pressure  developed  in  swallowing  might 
easily  force  the  food  into  the  wrong  opening.  But  because  of  the  different 
protective  mechanisms  brought  into  play  this  does  not  happen.  The  return 
of  the  bolus  into  the  mouth  cavity  is  prevented  l)y  contraction  of  the  palato- 
glossal muscles,  which  approximates  the  tongue  to  the  palate  and  narrows  the 
isthmus  of  the  fauces.  This  is  assisted  also  by  the  styloglossal  muscles,  which 
raise  the  tongue  and  press  it  forward  against  the  soft  palate.  The  nasal 
cavity  is  shut  off  from  the  mouth  and  pharynx  by  elevation  of  the  soft  palate. 


A  B 

Fig.  112. — Sagittal,  optical  sections  of  the  floor  of  the  mouth  and  of  the  neck,  reconstructed  from 
X  ray  photographs,  after  P.  H.  Eykman.  A,  position  of  quiet  inspiration;  B,  position  in 
swallowing;  the  passageway  for  food  into  the  tesophagus  is  open.  The  observer  is  supposed 
to  be  looking  into  the  left  half  of  the  lar\Tix.  In  A  the  epiglottis  is  shown  in  the  erect  posi- 
tion. In  B  it  is  depressed,  by  the  backward  motion  of  the  tongue,  against  the  posterior  wall 
of  the  phar^-nx  (only  the  edge  of  the  epiglottis  is  seen).  In  B  the  cricoid  cartilage  is  raised  to 
the  upper  border  of  the  fourth  cervical  vertebra. 

When  the  palate  muscles  are  paralyzed,  water  sometimes  passes  out  the  T^Tong 
way  through  the  nose. 

The  larynx  is  raised  in  swallowing  both  for  the  purpose  of  releasing  the 
pressure  on  the  oesophagus  so  that  it  may  be  freely  open,  and  for  the  purpose 
of  preventing  the  passage  of  food  into  the  lar\'nx  itself.  This  movement  may 
be  described  as  follows: 

Tho  geniohyoid,  mylohyoid  and  anterior  belly  of  the  digastric  muscle  draw 
thp  hyoid  bono  and  the  larynx,  the  lower  jaw  being  fixed,  forward  and  upward. 
The  hyothyroid  muscles  serve  to  keep  the  larynx  close  up  to  the  hyoid  bone.  At 
the  same  time  the  base  of  the  tongue  moves  downward  and  backward,  a  move- 
ment already  described  as  the  effect  of  the  hyoglossal  and  genioglossal  rnuscles. 
By  this  means  the  cushion  of  fat  which  is  found  immediately  over  the  epiglottis 
is  pressed  together  from  above  downward,  so  that  with  the  epiglottis  it  is  pushed 
in  as  far  as  the  bottom  of  the  supraepiglottidean  space,  and  the  aryepiglottidean 


282 


DIGESTION 


folds  are  applied  to  the  posterior  side  of  the  epiglottis  (Fig.  112,  B).  The- 
epiglottis  itself  cannot  play  any  great  part  in  the  closure  of  the  pharj^nx;  for 
it  can  be  extirpated  without  interfering  with  the  act  of  swallowing.  Nor  do  the 
muscles  of  the  epiglottis  appear  to  be  of  any  importance. 

This  extremely  complicated  process  of  swallowing  is  in  all  probability 
presided  over  and  controlled  by  the  medulla.  According  to  Marckwald  the 
center  lies  lateral  to  and  above  the  summit  of  the  ala  cinera\ 

When  the  bolus  has  reached  the  lower  end  of  the  o?sophagus  it  is  forced 
into  the  stomach.  The  cardia  is  normally  closed  by  tonic  contraction  of  its 
sphincter  muscle,  as  is  evident  from  the  fact  that  no  regurgitation  of  food 
takes  place  even  when  the  pressure  in  the  abdominal  cavity  is  very  greatly 


Gl-jOu 


/inh  J- 


'VCL.. 


'Lar.s. 


Mcnc.    Mstemcl. 


Fig.  113. — Tlie  motor  nerves  of  the  throat  and  palate  of  the  monkey,  after  Rethi.  1,  upper;- 
2,  middle;  3,  lower  bundle  of  roots.  Gl-ph.,  glossopharyngeal  nerve;  Va,  vagus;  Lar.s, 
superior  laryngeal;  Ac.  accessory  nerve;  R.  ph.,  v.  pharjTigeal  root  of  the  vagus;  St.  ph.,  the 
motor  nerves  of  the  stylopharyngeal  muscle;  P.  yl.,  motor  nerves  of  the  palatoglossal  muscle; 
P  ph.,  the  motor  nerves  of  the  palatophar>Tigeal  muscle;  C,  motor  nerves  of  the  constrictor 
muscles  of  the  pharynx;  L.,  motor  nerves  of  the  levator  veli  palatini;  Az.,  those  of  the  azygos- 
uvul». 

increased.  The  cardia  is  opened  by  the  action  of  its  dilator  nerves  (cf.  §4). 
and  the  bolus  of  food  is  pushed  into  the  stomach  by  contraction  of  the  lower- 
most .section  of  the  cesophagus.  Wlien  the  cesophagus  is  paralyzed  bv  section 
of  its  nerves,  food  remains  in  it.  and  may  be  sucked  into  the  lungs,  producing 
inflammations  which  result  fatally. 

By  auscultation  of  the  region  over  the  cardia  in  man  two  sounds  may  be 
heard  after  deglutition,  the  one  almost  immediately  after  the  inception  of  the 
act,  the  other  some  six  to  seven  seconds  later.  The  first  sound  is  seldom  heard 
and  appears  to  be  caused  by  an  abnormal  gaping  of  the  cardia.  In  this  case 
the  food  is  probably  spirted  by  contraction  of  the  muscles  in  the  upper  passages, 
directly  into  the  stomach.  The  second  sound  corresponds  in  its  occurrence  to 
the  time  when  the  food  is  being  forced  into  the  stomach,  and  it  is  probably 
caused  by  this  procedure. 


MOVEMENTS   OF  THE   STOMACH  283 

§  4.    MOVEMENTS   OF   THE    STOMACH 
A.    KNEADING  MOVEMENTS 

The  purpose  accomplished  by  the  movements  of  the  stomach  is  to  mix 
the  food  with  the  gastric  juice  and  to  reduce  it  mechanicalhj  by  kneading 
and  grinding.  B}'  this  means  the  chemical  changes  to  be  wrought  by  the 
gastric  juice  are  aided  materially.  The  digestion  of  proteid  in  an  artificial 
gastric  juice  requires  much  less  time  if  the  proteid  is  kept  moving  than  if  it 
is  allowed  to  remain  quiet.  The  proteid  is  more  accessible  to  the  gastric  juice 
by  reason  of  the  movement,  and  the  kneading,  such  as  takes  place  in  natural 
digestion,  easily  reduces  to  small  pieces  the  masses  already  rendered  brittle 
by  the  preliminary  effect  of  the  gastric  juice. 

With  reference  to  the  musculature  of  the  stomach,  we  have  to  distinguish 
the  two  openings,  the  cardia  and  pylorus,  as  well  as  the  main  body  or  fundus, 
and  the  antrum  pylori.  The  openings  are  surrounded  by  strong  muscular  fibers 
and  are  as  a  rule  closed.  The  fundus,  or  body  of  the  stomach,  has  a  relatively 
weak  musculature,  the  antrum  a  very  strong  one. 

Observations  on  the  movements  of  the  stomach  after  the  ingestion  of  food 
all  agree  in  finding  the  contractions  of  the  pyloric  portion  much  more  powerful 
than  those  of  the  body  of  the  stomach.  The  former  is  marked  off  from  the 
fimdus  by  a  ring  muscle  called  the  spJtincfer  of  the  antrum.  Relatively  weak 
peristaltic  waves  sweep  over  the  fundus  from  the  cardiac  end,  and  are  con- 
tinued by  the  very  powerful  contractions  of  the  antrum,  beginning  at  the 
sphincter  of  the  antrum  and  spreading  toward  the  pylorus. 

Meltzer  found  that  the  fundic  portion  does  not  respond,  even  to  very  strong 
stimulation  with  easily  recognizable  contractions,  whereas  the  pyloric  portion 
with  the  same  stimidus  contracts  more  energetically  the  closer  the  stimulus  is 
applied  to  the  pylorus  itself. 

In  a  patient  with  a  stomach  fistula,  a  pressure  of  14  to  35  mm.  Hg.  has  been 
observed  in  the  body  of  the  stomach,  and  130  mm.  in  the  antrum.  The  antrum, 
it  seems,  may  be  closed  off  completely  by  contraction  of  its  sphincter  or  by  local 
contractions  of  separate  sections,  from  the  parts  of  the  stomach  lying  to  the  left. 

Since  the  pressure  exerted  by  the  fundic  wall  is  commonly  not  very  strong 
and  the  antrum  is  filled  therefore  during  the  dilatation  which  follows  its  own 
contractions  under  a  very  weak  vis  a  tergo,  the  coarser  portions  of  the  food 
are  probably  not  pressed  into  the  antrum,  but  only  the  easily  mobile,  more 
fluid  and  more  gruelly  portions.  If  this  is  true,  it  follows  further  that  the 
changes  which  the  food  undergoes  in  the  body  of  the  stomach  are  principally 
of  a  chemical  nature,  while  the  antrum  represents  the  truly  motor  part  of 
the  stomach,  where  the  bits  of  food  already  more  or  less  comminuted  are 
intimately  mixed  with  the  gastric  juice  and  still  more  thoroughly  ground  up 
by  powerful  contractions. 

Experiment  shows  that  the  stomach,  deprived  entirely  of  nerves,  or  even 
cut  out  of  the  body,  undergoes  spontaneous  contractions:  that  like  the  heart, 
the  stomach  has.  therefore,  within  itself  all  the  necessary  conditions  of  its 
movements — which  is  probably  due  to  the  ganglion  cells  found  in  the  stomach 


284 


DIGESTION 


wall  (cf.  page  288).  But  those  movements  are  presided  over  and  regulated 
in  many  ways  by  the  central  nervous  system.  The  very  complicated  relations 
of  the  nerves  concerned  in  this  control  will  be  evident  from  the  scheme  devised 
by  Openchowski   (Fig.  114). 

The  stomach  receives  its  moior  nerves  in  part  from  the  vagus,  in  part  from 

the  sympathetic  nerves.  These 
nerve  paths  have  been  fol- 
lowed up  to  the  cerebrum  as 
follows : 

a.  The  Cardia:  (1)  From 
the  region  of  the  posterior  cor- 
pora quadrigemina  constrictor 
fibers  run  for  the  most  part 
through  the  vagi ;  some  run  in 
the  sympathetic  paths,  reach- 
ing their  destination  by  way  of 
the  spinal  cord  and  the  fifth 
to  eighth  thoracic  roots,  thence 
through  the  two  splanehnics. 
In  the  thoracic  sympathetic 
the  fibers  are  only  sparingly 
represented.  (2)  The  cardia 
is  dilated  by  fibers  which 
emerge  from  that  region  of  the 
brain  where  the  anterior  lower 
end  of  the  nucleus  caudatus  is 
united  with  the  nucleus  lenti- 
formis,  and  join  the  vagus.  In 
the  spinal  cord  also  as  far  as 
the  fifth  thoracic  root,  there 
are  centers  for  the  opening  of 
the  cardia  which  send  their 
fibers  by  sympathetic  path- 
ways. 

h.  The  Body  of  the  Stom- 
ach between  the  cardia  and  the 
pylorus:  (1)  The  brain  centers 
for  the  contraction  of  this 
part,  lie  in  the  corpora  quadri- 
gemina,  and  the  paths  traverse 


Fig.  114. — The  nerves  of  the  stomach  musculature, 
after  Openchowski.  Red,  the  paths  to  the  cardia; 
blue,  the  patli.s  to  the  body  of  the  stomach  ;^ree77,  the 
patlis  to  the  pylorus.  C,  the  cerebrum;  V,  stom- 
ach; MO,  medulla;  MS,  spinal  cord;  5-10,  thoracic 
roots;  VRS,  right  vagus;  VS,  left  vagus;  XD,  dilators 
of  the  cardia;  XC,  constrictors  of  the  cardia;  a, 
Auerbach's  plexus;  S.  S,  fibers  from  the  sympathetic 
plexus.  1,  sulcus  cruciatus;  2,  corpus  striatum;  3, 
corpus  quadrigemina;  4,  centers  in  the  .spinal  cord. 


both  the  vagi  (chiefly)  and  the 
spinal  cord,  thence  by  way  of 
the  lower  thoracic  cord  through  the  sympathetic  trunks.     (2)   Inhibitory  cen- 
ters he  in  the  upper  part  of  the  cord  and  the  paths  traverse  the  sympathetic 
and  splanehnics  (according  to  Langley  also  the  vagus). ^ 

c.  The  Pylorus  and  Pyloric  Atitrum:  (1)  Contraction  centers  are  found  in 
the  corpora  quadrigemina  for  both  the  pyloi-us  and  its  antrum.  The  chief  parh 
IS  the  vagus,  but  the  constrictor  fibers  run  also  through  the  spinal  cord.  (2)  The 
dilator  center  for  the  cardia  gives  inhibition  of  the  pyloric  movements,  but  no 

Cannon  has  shown  that  distress  inhibits  gastric  movements  not  only  in  the  normal 
animal,  but  after  the  two  vagi  are  cut,  and  after  the  four  splanehnics  are  cut.— Ed. 


MOVEMENTS   OF  THE   STOMACH  285 

opening.  The  path  lies  through  the  cord  as  far  as  the  tenth  thoracic  root,  then 
through  the  splanchnics.  Inhibitory  centers  for  the  antrum  are  present  in  the 
corpora  quadrigemina ;  and  opening  of  the  pylorus  can  be  induced  from  the 
olivary  body  over  a  pathway  which  runs  through  the  cord.  The  dilator  nerve 
of  the  cardia  under  all  circumstances  proves  to  be  a  closing  nerve  for  the  pylorus. 
Opening  of  the  cardia  and  contraction  of  the  pylorus  occur  simultaneously. 
Langley  finds  inhibitory  fibers  for  the  pylorus  also  in  the  vagus. 

B.    EVACUATION  OF  THE  STOMACH 

When  the  stomach  contents  have  been  changed  by  the  united  action  of  the 
gastric  juice  and  the  movements  of  the  stomach  into  a  gruelly  mass  kno\\Ti 
as  chi/me,  the  object  of  gastric  digestion  is  fulfilled;  the  pylorus  is  opened 
and  the  chyme  is  forced  into  the  intestine. 

The  length  of  time  the  food  is  retained  in  the  stomach  depends  to  a  great 
extent  upon  the  kind  of  food  eaten.  In  dogs  having  a  duodenal  fistula,  Moritz 
has  shown  that  pure  fluids  (water  and  uncoagulated  milk)  leave  the  stomach 
very  quickly.  With  coagulated  milk  the  evacuation  is  considerably  slower. 
It  is  longest  of  all  wdth  the  solid  foods  (meat,  sausage).  The  consistency 
of  the  stomach  contents  therefore  determines  primarily  when  the  food  will 
be  evacuated.  But  its  chemical  properties  also  are  of  considerable  importance 
in  this  respect.  The  experiments  of  Moritz  upon  himself  tended  to  ^show  that 
water,  weak  salt  solutions,  and  bouillon  leave  the  stomach  very  quickly,  but 
water  containing  CO2,  weak  acid  solutions,  milk  and  beer  remain  considerably 
longer.  If  meat  or  bread  be  eaten  the  expulsion  of  water  ingested  at  the 
same  time  is  delayed  considerably. 

[Cannon  fed  fat,  carbohydrate  and  proteid  foods,  uniform  in  amount  (25  c.c.) 
and  consistency  and  mixed  with  a  small  quantity  of  subnitrate  of  bismuth,  to 
cats,  and  with  the  aid  of  the  fluoroscope  observed  the  rate  of  their  discharge 
from  the  stomach.  He  found  that  fats  remain  longest  in  the  stomach,  proteids 
next,  and  carbohydrates  a  very-  short  time.  When  carbohydrates  and  proteids 
were  mixed  in  equal  parts,  the  mixed  food  did  not  leave  the  stomach  so  slowly 
as  proteids  alone  or  so  rapidly  as  carbohydrates  alone.  Fat  mixed  in  equal 
amounts  with  proteids  and  with  carbohydrates  caused  both  these  to  be  discharged 
more  slowly  than  when  each  was  fed  alone. — Ed.] 

Even  with  a  diet  of  firm  consistency,  small  portions  having  the  consistency 
of  gruel  are  forced  into  the  duodenum  as  they  are  formed,  and  thus  the 
evacuation  of  the  stomach  goes  on  gradually.  It  has  been  shown  further  that 
the  pylorus  closes  and  the  expulsive  movements  of  the  stomach  cease  tem- 
porarily when  a  certain  portion  of  the  contents  has  been  emptied  (Hirsch, 
V.  Mering).  Not  only  the  degree  of  fullness,  but  the  reaction  of  the  intestinal 
contents  is  of  importance  in  this  connection.  A  slight  stream  of  HCl  oi*  pure 
gastric  juice  poured  steadily  through  a  fistula  into  the  duodenum,  will  cause 
a  soda  solution  previously  introduced  into  the  duodenum  to  be  kept  there 
for  an  indefinite  time.  A  soda  solution  poured  into  the  duodenum  in  the 
same  way  has  no  such  effect.  From  this  it  follows  that  each  outflow  of 
stomach  contents  into  the  intestine  stops  further  evacuation  until  the  HCl 
of  the  gastric  juice  is  neutralized  by  the  alkaline  fluids  of  the  intestine 
(Pawlow). 


286  DIGESTION 


C.    VOMITING 

A'oiiiitinu:  is  an  abnonnal  process  by  which  the  stomach  contents  are  emp- 
tied tlirough  the  cardia  instead  of  througli  the  pylorus.  Several  muscles  are 
concerned  in  vomiting,  but  chiefly  those  of  the  diaphragm  and  al)domen. 
These  contract  all  at  once,  producing  a  high  intraabdominal  pressure  which 
naturally  takes  effect  on  the  stomach  wall.  When  the  cardia  is  closed  vomiting 
does  not  result.  We  know  that  this  must  be  true  Ijecause  when  simultaneous 
contractions  of  the  diaphragm  and  abdominal  muscles  take  place  under  other 
circumstances,  for  example  in  defecation,  the  stomach  is  not  emptied  through 
the  cardia.  The  stomach  wall  itself  plays  little  part  in  the  process,  for  the 
entire  stonuich  may  be  replaced  by  a  swine's  bladder  and  vomiting  therefrom 
may  be  produced  (Magendie).  And  yet  it  must  be  observed  that  the  pyloric 
portion  of  the  stomach  contracts  powerfully  in  vomiting  and  expels  its  con- 
tents into  the  fundus. 

In  vomiting  the  larynx  and  nasal  passages  are  protected  in  the  same  way 
as  in  swallowing,  and  the  mass  of  stomach  contents  ejected  from  the  stomach 
under  high  pressure  must  therefore  take  its  way  through  the  mouth.  The  tongue 
is  not  raised  as  in  swallowing,  but  is  pressed  down  and  held  out  in  the  form 
of  a  groove. 

Vomiting  is  induced  either  by  certain  dioigs  or  by  reflexes  set  up  from  the 
base  of  the  tongue,  the  throat,  the  stomach  or  the  uterus.  It  may  be  caused  also 
even  by  the  imagination  or  sight  of  something  nauseating,  or  by  excessive  dis- 
turbances of  the  brain. 

As  appears  from  the  foregoing,  a  large  number  of  muscles  cooperate  in  the 
act  of  vomiting  in  a  perfectly  definite  manner,  and  our  current  views  of  the 
action  of  the  central  nervous  system  make  it  very  probable  that  this  coordina- 
tion is  obtained  by  a  special  center  (the  vomiting  center).  In  fact  it  is  stated 
that  in  the  dog  the  destruction  of  an  area  lying  in  the  midline  of  the  medulla 
in  the  region  of  the  calamus  scriptorius  prevents  vomiting — i.  e.,  that  this  place 
is  the  vomiting  center.  This  center  is  bilateral  and  lies  in  the  deep  layers  of 
the  medulla  (Tumas).  Whatever  the  facts  as  to  the  actual  presence  of  such  a 
center,  this  much  appears  certain,  that  the  vomiting  center  and  respirator^'  cen- 
ter are  not  identical,  as  has  often  been  assumed.  For  while  certain  respiratory 
nniscles  take  part  in  vomiting,  many  other  movements  supervene  which  have 
nothing  to  do  with  respiration.  Besides,  simultaneous  inspiratory  contraction  of 
the  diaphragm  and  expiratory  contraction  of  the  abdominal  muscles  never  takes 
place  in  respiration. 

§  5.    MOVEMENTS   OF   THE   INTESTINE 

The  purpose  of  the  intestinal  movements  is  to  mix  thoroughly  the  contents 
of  this  division  of  the  alimentary  canal  with  the  digestive  fluids  poured  into 
its  cavity,  and  to  move  the  contents  gradually  along  in  the  direction  of  the 
anus. 

According  to  Oriitzner,  antiperistaltic  contractions  occur  normally  in  the 
intestine,  by  Avhich  the  intestinal  contents  may  be  driven  upward  for  some 
distance. 

In  the  fasting  state  the  intestine  appears  as  a  rule  to  be  quiet.  But  about 
one-quarter  hour  after  eating  it  begins  to  move.     These  movements  are  induced 


MOVEMENTS    OF   THE    INTESTINE 


287 


also  by  swallowing,  by  brief  inhalations  of  ether,  by  psychic  influences,  applica- 
tion of  cold  to  the  abdomen  and  by  direct  stimulation  (cf.  infra). 

Attempts  have  been  made  by  investigation  of  intestinal  fistulse  to  deter- 
mine the  rate  of  propagation  of  the  intestinal  contractions,  and  different  rates 
have  been  observed — which  really  was  to  be  expected  a  priori,  if  one  but  con- 
siders how  much  the  degree  of  fullness  and  the  nature  of  the  contents  rnust 
affect  the  results.  This  consideration  is  confirmed  by  the  observation  made  iipon 
an  exsected  intestine,  that  a  contraction  locally  produced  is  propagated  along 
the  intestine  only  when  it  is  induced  by  the  moving  contents. 

By  observations  on  Vella  fistukie  a  value  of  1  cm.  in  two  to  ten  minutes,  and 
1  cm.  in  thirty  to  forty  seconds,  have  been  found  for  the  rate  of  propagation  of 
intestinal  contractions,  the  latter  value  after  ingestion  of  food.  According  to 
other  observations  the  peristaltic  wave  would  travel  the  entire  length  of  the 
intestine  of  a  dog  in  about  ninety  minutes.  Again,  the  velocity  of  the  intestinal 
movement  has  been  estimated  by  passing  a  little 
balloon  fastened  to  a  string  through  a  stomach 
fistula  into  the  duodenum  and  measuring  on  the 
string  the  rate  at  which  the  balloon  was  forced 
along.  In  the  uppermost  parts  the  rate  was 
greater  than  in  the  lower  parts,  and  in  the  former 
reached  the  high  value  of  10-18  cm.  in  a  minute. 
In  view  of  the  long  time  the  food  sojourns  in  the 
intestine  this  appears  abnormally  high. 

The  intestine  is  of  course  constricted  by  the 
contraction  of  its  circular  muscles;  it  is  short- 
ened and  at  the  same  time  dilated  by  contraction 
of  its  longitudinal  muscles.  Suppose,  e.  g.,  that 
in  Fig.  115  the  small  circles  lying  side  by  side 
represent  cross  sections  of  the  longitudinal  mus- 
cle fibers.  When  they  contract,  they  become 
thicker;  each  fiber  therefore  claims  more  space, 
and  the  fibers  lying  side  by  side  becoming  thicker 

all  at  once  must  have  the  effect  of  making  the  circumference  larger — i.  e.,  of 
dilating  the  lumen.  This  conclusion  has  been  confirmed  also  experimentally 
(Exner). 


Fig.  115. — Schema  to  illustrate 
the  relation  of  the  lon^itiulinal 
niu.'iciilar  fibers  of  the  intestine 
to  each  other. 


With  re<jard  to  the  movements  actually  takinp;  place  in  the  intestine  within 
the  body.  Cannon  observed  with  the  hel])  of  tlie  Rontgen  rays,  after  feeding  a 
food  mixed  with  bismuth  subnitrate,  that  the  food  in  an  intestinal  loop  is 
divided  all  at  once  into  small  segments.  From  these  segments  new  ones  are 
continually  being  formed  by  rln/tlnniral  confractlons  [what  Cannon  calls 
"rhythmical  segmentation"],  at  the  rate  of  about  thirty  per  minute.  By 
this  means  the  food  is  very  intimately  mixed  with  the  intestinal  fluids  and 
is  brought  into  close  contact  with  the  intestinal  wall.  The  contents  are  then 
pushed  along  and  the  process  is  repeated  over  and  over  (Fig.  116). 

The  intestinal  movements  are  to  a  certain  extent  independent  of  the 
central  nervous  system,  for  an  exsected  intestine  may  contract  spontaneously. 
In  animals  whose  nerves  to  the  intestine  have  all  been  cut.  two  kinds  of 
contractions  may  be  observed. 

(1)  The  intestinal  loops  execute  pendulum  movements — i.e.,  movements 
to  and   fro,   in  which   the  longitudinal,   and,  to  a  less  extent,   the  circular 


288  DIGESTION 

muscles  are  active.  V>y  virtue  of  the  latter,  small  waves  arise  in  the  intestinal 
wall,  which  are  propagated  I'alher  I'apidly  ('^-5  cm.  per  second),  usuall)'  from 
above  downward. 

(3)  In  separate  parts  of  the  intestine  powerful  contractions  occur  which 
proceed  much  more  slowly  than  the  above-meutioned  small  waves,  but  like 
them  from  above  downward.  These  are  the  true  peristaltic  movements.  In 
the  propagation  of   these   contractions   the   intestine   is  always   dilated   just 

below    the    place    which    at    that 
moment  is  contracted. 

The  peristaltic  movements  may 
be  ]n-oduced  on  an  e-nervated  intes- 
tine by  a  weak  mechanical  stimu- 

bet- 
the  introduction  of  a 


3     A 


O  GJ)  ^-^  Y^  *^-— ^  (j)  r-\  l^^s  of   the  outer   surface,   or 

^       l-^  (^  (^  ^-— ^       ■'    i   /  ter  still   by  the  introduction  oi  a 

4       O  ^—-^  ^-^  ^-^  ^-^  O  Q  balloon  into  the  intestine.     Every 

F.G.    I16.-Schema   to   illustrate   the   rhythmical  ^^^^    stimulus    eXciteS    the    Section 

segmentation  of  the  small  intestine,  after  Can-  lying   aboVC    the    point    at    which    it 

non.      1,  the  contents  of  the  intestine  unseg-  ig    applied    and    VCloxeS    that    lying 

mented;     2,     the    contents     constricted     into  •  Tii        ii  /-ni-        '        i 

.separate  masses;    3,  the  next  phase,  the  origi-  IJ^^l^t^iately     bcloW      (BayllSS     and 

nal  segments  are  split  in  half  by  new  constric-  btarlmg). 
tions  and  become  fused  into  new  masses,  as  a 
and  6  into  c;   4,  the  first  segmentation  restored.  Peristalsis     in     the     intestine    is 

therefore  a  tolerably  complicated 
phenomenon  which  calls  for  a  definite,  regular  coordination  of  different  portions 
of  the  intestine,  and  in  all  probability  requires  for  its  excitation  the  participa- 
tion of  a  nervous  mechanism.  Since  this  can  be  observed  in  all  its  regularity 
both  in  an  exsected  intestine  and  in  the  intestine  deprived  of  extrinsic  nerves, 
the  mechanism  concerned  must  lie  within  the  intestinal  wall  itself,  and  we  have 
probably  to  regard  the  plexus  myentericus  as  that  mechanism. 

Magnus  is  authority  for  the  statement  that  the  spontaneous  movements  con- 
tinue unchanged  in  their  character  in  surviving  portions  of  the  intestine,  or  in 
those  preserved  in  Ringer's  solution,  after  removal  of  the  submucosa  and  of 
Meissner's  plexus.  But  separation  of  the  circular  layers  from  Auerbuch's  plexus 
stops  their  movements,  whereas  the  longitudinal  muscles  left  in  connection  with 
this  plexus  continue  as  before  to  contract.  From  these  results  it  would  appear 
that  all  the  automatic  movements  of  the  intestine  depend  upon  the  action  of 
Auerbuch's  plexus. 

The  intestinal  movements  are  regnlated  in  many  ways  by  the  central 
nervous  system;  and  we  can  say  fin-ther  that  the  small  intestine  receives  its 
efferent  nerves  partly  through  the  vagus  and  partly  through  the  splanchnic. 
But  with  regard  to  the  action  of  these  nerves,  until  very  recently  there  was 
absolutely  no  unanimity  of  opinion.  Indeed  one  may  say  without  exagger- 
ation that  every  conceivable  possibility  has  been  represented  by  the  different 
authors. 

However,  most  authors  noM^  agree  that  the  splanchnics  contain  inhihiting 
fibers  for  the  intestine  (Pfliiger,  1857).  If  the  abdomen  of  a  fasting  dog, 
having  the  splanchnics  still  intact,  be  opened,  the  above-mentioned  contrac- 
tions are  not  observed — the  intestine  is  perfectly  quiescent.  A  local  stimulus 
is  either  entirely  without  effect  or  it  produces  only  a  circumscribed  contrac- 


MOVEMENTS   OF  THE   INTESTINE  289 

tion.  If  now  the  splanchnics  be  cut,  after  some  fifteen  to  twenty  minutes 
the  intestine  begins  to  move  as  above  described  (page  288).  These  results 
show  that  the  splanclinic  under  normal  circumstances  exercises  a  tonic  re- 
straining influence  on  the  intestinal  musculature.  This  inhibition  appears 
still  more  clearly  if  the  splanchnic  be  stimulated  while  the  intestinal  move- 
ments are  in  progress :  the  contractions  immediately  cease,  and  the  tonus  of 
the  wall  decreases. 

Since  the  splanchnic  conveys  vasoconstrictor  fibers  for  the  intestinal  vessels, 
it  might  be  supposed  that  the  cause  of  the  intestinal  calm  following  stimulation 
is  to  be  found  not  in  a  specific  inhibition,  but  in  the  resulting  anaemia.  But  it 
is  to  be  observed  against  this  hypothesis  that  the  necessary  parallelism  is  want- 
ing between  the  two  phenomena.  The  increase  in  blood  pressure  is  sometimes 
very  considerable  while  the  inhibition  at  the  same  time  is  only  slight.  The 
inhibitory  effect  is  not  evident  at  the  first  stimulation  of  the  splanchnic  and 
decreases  with  each  succeeding  stimulation,  while  the  blood  pressure  goes  on 
increasing.  And  finally,  inhibition  of  the  intestinal  movements  can  be  demon- 
strated even  after  the  circulation  is  completely  stopped  by  extirpation  of  the 
heart. 

Many  authors  agree  also  that  the  vagus  is  a  motor  norve  for  the  intestine, 
while  others  have  obtained  no  effect  at  all  on  the  intestine  by  vagus  stimula- 
tion. It  is  possible  that  this  failure  is  dtie  to  the  inhibiting  influence  of  the 
splanchnics,  wherefore  it  is  recommended  to  sever  the  splanchnics  first  in  such 
experiments  (Jacobi).  In  order  to  prevent  disturbances  to  the  circulation 
resulting  from  stoppage  of  the  heart  by  stimulation  of  the  vagus,  either  the 
stimulation  must  be  applied  below  the  cardiac  branches,  or  the  latter  must 
be  paralyzed  by  atropine.  Under  such  circumstances  Bayliss  and  Starling 
and  also  Bunch  have  observed  as  the  typical  result  of  vagus  stimulation,  first 
a  brief  inhibition  and  then  a  contraction  which  be- 
comes stronger  and  stronger.  It  wotild  thus  seem 
that  the  vagus  contains  both  inhibitory  and  motor 
fibers,  tlie  former  with  a  short  and  the  latter  with  a 
long  latent  period.  In  the  opinion  of  some  authors 
these  effects  extend  to  both  muscle  layers ;  in  the 
opinion  of  others  the  vagus  inhibits  the  longi- 
tudinal fibers  and  excites  the  circular  fibers  (Ehrman, 
Winkler).  "» 

As  soon  as  the  intestinal  contents  pass  into  the       Fi«-  117.— Schema  illus- 

1  •     .      I-  c    1  11-  i>   xi  trating       antiperistalsis 

large  intestine  a  powerful  contraction  of  the  caecum  .^^  ^^^  ascending  colon, 

and  colon  can  be  seen  with  the  Eontgen  rays  (Can-  after  Cannon, 

non)    to    take    place,    and   the    contents    are    moved 

toward  the  rectum.  A  moment  later  peristalsis  is  succeeded  by  antiperistalsis, 
and  the  latter  in  rhythmical  order  now  represents  the  usual  form  of  move- 
ment of  the  ascending  and  transverse  colon.  Finally,  however,  it  ceases,  the 
contents  collect  in  the  transverse  colon  and  are  driven  into  the  descending 
colon. 

As  for  the  innervation  of  the  large  intestine  and  rectum,  Bayliss  and  Star- 
ling'have  shown  that  the  former  deprived  of  its  nerves  acts  just  as  does  the  small 
intestine  under  the  same  circumstances.     The  vagus  is  said  to  contain  motor 


290  DIGESTION 

fibers  for  the  first  part  of  the  larg'e  intestine.  The  other  parts  and  the  rectum 
are  supplied  by  the  lumbar  and  the  sacral  nerves.  The  former  arise  from  the 
second  to  the  fourth  lumbar  roots,  pass  through  the  sympathetic  to  the  inferior 
mesenteric  ganglion  and  so  to  the  intestine.  The  sacral  nerves  arising  from  the 
II-IV  sacral  roots  traverse  the  so-called  nervi  errigentes  (Langley,  cf.  page  233). 
[According  to  Elliott  the  large  intestine  also  receives  inhibitory  fibers  from 
the  sympathetic. — Ed.] 

FOURTH    SECTION 

DIGESTION   IN   THE   DIFFERENT   DIVISIONS  OF  THE 
ALIMENTARY   CANAL 

Now  that  we  have  become  acquainted  with  the  properties  of  the  different 
digestive  fluids,  and  the  processes  by  which  they  are  formed,  as  well  as  with 
the  movements  of  the  alimentary  canal,  there  remains  vet  for  ns  to  consider 
the  digestive  process  itself  in  the  different  divisions  of  the  canal,  and  to  study 
the  relative  importance  of  each  division. 

By  way  of  general  remark  it  must  be  emphasized  here  once  more  that 
appetite  is  of  great  and  deep-seated  importance  for  the  entire  activity  of  the 
digestive  apparatus.  Only  under  its  influence  does  a  plentiful  secretion  of 
gastric  juice  take  place  immediately  after  the  ingestion  of  food.  The  acid 
of  the  gastric  juice  in  turn  rouses  the  secretion  of  the  pancreas  which  then 
without  delay  pours  its  secretion  into  the  intestine;  Avhen,  after  a  longer  or 
shorter  time,  the  stomach  is  emptied,  the  intestine  is  immediately  prepared 
to  continue  the  work  of  digestion  and  to  carry  it  forward  to  the  end. 

Our  knowledge  of  the  conditions  which  control  the  movements  of  the 
alimentary  canal  are  still  too  meager  to  permit  us  to  say  anything  as  to  the 
importance  of  appetite  and  of  eating  for  them.  Certain  observations  of 
Pawlow  show  that  desire  for  food  does  exert  an  actual  influence  on  the  move- 
ments of  the  stomach.  Thus  spontaneous  movements  of  this  organ  are  sup- 
pressed when  the  animal  is  greatly  excited  by  the  sight  of  food :  the  stomach 
is  preparing  itself  for  the  reception  of  food  "(cf.  also  note,  page  284). 

§  1.    DIGESTION   IN   THE   MOUTH 

The  most  important  function  of  the  mouth  with  reference  to  digestion 
is  the  mechanical  reduction  of  the  food,  and  the  admixture  of  saliva  with  it. 
Substances  soluljle  in  water  are  dissolved  by  the  saliva  and,  what  is  more 
important,  the  morsel  of  food  is  rendered  slippery  by  the  mucin  therein 
coDtained,  and  thus  is  the  more  easily  passed  through  the  gullet  to  the  stomach. 

The  latter  function  is  confirmed  by  the  following  observation  of  01.  Bernard. 
An  oesophageal  fistula  was  made  in  the  neck  of  a  horse  and  the  animal  was  given 
mouthfuls  of  wet  oats.  In  one  minute  there  came  through  the  opening  of  the 
fistula  55  g.  of  the  oats.  After  the  ducts  of  the  two  parotid  glands  were  cut  off 
so  as  to  shut  out  the  saliva  from  the  mouth,  only  14.4  g.  came  through  in. one 
minute. — The  mucus  secreted  by  the  glands  of  the  pharynx  and  oesophagus  also 
aids  the  passage  of  the  bolus. 


DIGESTION   IN   THE   STOMACH  291 

In  several  species  of  animals  a  diastatic  enzyme  is  wanting  in  the  saliva, 
and  in  these  the  physiological  importance  of  saliva  is  restricted  to  the  above- 
mentioned  purely  mechanical  action.  In  general  it  has  been  supposed  that 
even  v/here  the  ptyalin  is  present  the  formation  of  sugar  induced  by  it  plays 
only  a  subordinate  part  in  digestion,  either  because  of  the  short  time  the 
food  remains  in  the  mouth,  or  because  the  swallowed  saliva  would  quickly 
lose  its  diastatic  power  on  account  of  the  acid  of  the  gastric  juice.  The  latter 
conclusion  presumes  either  that  the  acid  content  of  the  gastric  juice  is  suffi- 
ciently high  to  neutralize  the  alkaline  reaction  of  the  saliva  at  once  or  that 
the  stomach  contents  are  very  quickly  permeated  by  the  gastric  juice.  But 
neither  presumption  is  warranted  by  the  facts.  Hensay  has  shown  that  as 
much  as  eighty  per  cent  of  the  carbohydrates  raised  from  the  human  stomacli 
at  the  end  of  half  an  hour  is  maltose  or  the  closely  related  dextrin.  Accord- 
ing to  Cannon  and  Day,  an  acid  reaction  in  the  interior  of  the  stomach  con- 
tents of  the  cat  can  only  be  observed  after  one  to  one  and  one-half  hours  from 
the  time  of  feeding,  and  during  this  time  the  ptyalin  has  every  opportunity 
to  act  on  the  starch.  This  was  confirmed  also  by  direct  experiments  in  which 
human  saliva  was  given. 

§  2.    DIGESTION   IN   THE    STOMACH 

The  first  division  of  the  alimentary  canal  in  which  the  food  is  chem- 
ically changed  to  any  considerable  extent,  is  the  stomach.  Here  the  carbo- 
hydrates are  split  up  partly  by  the  ptyalin  of  the  swallowed  saliva,  partly  by 
the  acid  and  the  Bacteria  of  the  stomach  contents.  Starch  paste  is  changed 
by  the  acid  of  the  stomach  to  soluble  starch,  and  from  this  with  the  help  of 
acid  fermentation  under  the  influence  of  Bacteria,  dextrin,  sugar  and  lactic 
acid  are  formed. 

Emulsified  fat  is  split  to  a  considerable  extent  by  the  stomach  steapsin 
(of.  page  250),  Casein  is  coagulated  under  the  influence  of  the  rennin,  and 
the  curd  thus  formed  is  dissolved  again  by  the  gastric  juice.  Moreover,  what 
is  of  particular  importance  for  the  noiirishment  of  children,  almost  the 
entire  quantity  of  phosphorus  from  the  curd  passes,  according  to  experiments 
in  vitro,  into  solution  in  organic  combination.  The  passage  of  the  casein, 
which  is  the  most  important  constituent  of  milk,  into  the  intestine  is  delayed 
by  its  coagulation  in  the  stomach. 

The  pcpsln-hijdrochJoric  acid  dissolves  all  kinds  of  true  ])i'oteids,  the  gela- 
tin-forming substances  and  elastic  tissues;  but  keratin  is  not  acted  upon. 
The  influence  of  gastric  juice  on  the  gelatin-forming  substances  appears  to  be 
especially  significant  for  the  whole  process  of  digestion;  it  is  even  said  that 
they  are  dissolved  more  easily  and  more  completely  by  the  gastric  juice  than 
are  proteids  (Bikfalvi). 

This  is  quite  in  line  with  all  that  we  know  about  the  function  of  the  stomach. 
This  function  in  brief  is  to  transform  the  invested  food  into  a  soupy  mass,  the 
chyme — to  prepare  it,  in  other  words,  for  entrance  into  the  intestine.  The  abil- 
ity of  the  gastric  juice  to  dissolve  gelatin-forming  substances  aids  in  this  direc- 
tion; for  the  tissue  elements  which  bind  together  the  cells  of  the  animal  foods 
are  composed  of  just  s\ich  substance,  and  as  soon  as  they  are  dissolved  the  cells 
are  set  free  and  the  chyme  is  formed. 


292  DIGESTION 

It  is  naturally  a  matter  of  groat  interest  to  determine  how  the  transforma- 
tion of  proteid  actually  goes  on  in  the  stomach;  for  one  can  never  form  any 
definite  conclusion  about  the  cleavages  actually  taking  place  in  life  from 
experiments  in  vitro  (page  244).  Among  the  more  recent  contributions  to 
our  knowledge  of  this  subject  are  the  researches  of  Zunz  on  the  digestion  of 
meat  in  the  stomach  of  the  dog.  At  whatever  time  between  one-half  hour 
and  six  hours  after  feeding,  the  stomach  contents  were  obtained,  they  con- 
sisted in  by  far  the  greatest  part  (eighty-six  to  ninety-eight  per  cent  of  the 
total  nitrogen)  of  albumoses.  Acid  albumin  was  present  only  in  small  quan- 
tities and  the  total  quantity  of  peptones,  poptoids  and  end  products  only  ex- 
ceptionally reached  more  than  ten  per  cent  of  the  total  nitrogen.  Among  the 
latter  was  found  only  a  very  sparing  quantity  of  crystalline  products,  leucin, 
tyrosin,  etc.,  and  these  might  have  been  formed  previously  in  the  meat  fed. 

These  results  are  to  be  explained  in  one  of  two  ways:  either  the  cleavage 
of  proteid  in  the  stomach  proceeds  only  so  far  that  about  ten  per  cent  of  the 
proteid- N"  is  transformed  into  end  products,  or  the  end  products  as  they  are 
formed  are  absorbed  more  rapidly  through  the  stomach  wall  than  the  albu- 
moses. It  is  not  easily  conceival)le  that  the  end  products  already  in  solution 
should  pass  into  the  duodenum  more  rapidly  than  the  albumoses  present  in 
the  same  solution. 

Looking  to  a  decision  between  these  two  possibilities,  Eeach  made  experi- 
ments on  surviving  stomachs.  The  animals  were  killed  at  the  end  of  the 
second  hour  of  digestion;  the  stomach,  tied  off  at  both  ends  and  cut  out  of 
the  body,  was  maintained  for  four  hours  longer  in  a  moist  chamber  at  blood 
temperature.  Since  no  absorption  could  take  place,  this  experiment  was  well 
calculated  to  show  how  far  the  cleavage  of  proteid  had  actually  gone.  The 
result  was  that  thirty-two  to  fifty-six  per  cent  of  the  total  N"  in  solution  (aver- 
age forty-four  per  cent)  was  present  in  the  form  of  albumoses,  and  fifty-six 
per  cent  in  the  form  of  peptones  and  end  products,  the  latter  alone  containing 
some  thirty-two  per  cent  of  the  total  nitrogen.  It  appears  therefore  that  the 
reason  for  the  ninety,  per  cent  and  more  of  albumose  nitrogen  foimd  in  the 
intravital  digestion  is  not  that  the  enzyme  action  stops  at  the  albumose  stage, 
but  that  absorption  going  on  at  the  same  time  removes  the  simpler  products 
very  rapidly. 

Partly  because  of  its  hydrochloric  acid,  and  partly  quite  independently 
thereof  (London),  the  gastric  juice  plays  no  small  role  as  an  antiseptic.  This 
property  of  the  gastric  juice  is  by  no  means  sufficient  to  destroy  all  the  Bac- 
teria which  find  their  way  into  the  stomach ;  for  very  many  are  found  through- 
out the  alimentary  canal,  and  in  certain  species  of  animals  they  play  a  very 
important  part — of  which  more  under  the  discussion  of  intestinal  digestion. 

Since  the  food  always  remains  for  a  tolerably  long  time  in  the  stomach, 
this  organ  most  of  all  must  suffer  the  harmful  effects  of  an  ill-adapted  diet. 
We  speak  also  of  a  digestible  or  indigestible  article  of  food  according  as  it  is 
digested  with  greater  or  less  ease  in  the  stomach.  It  would  be  very  impor- 
tant, therefore,  if  general  rules  could  be  established  as  to  what  is  digestible 
and  what  is  not.  Unfortunately,  however,  this  can  be  done  only  to  a  very 
limited  extent,  for  the  stomach  is  very  capricious,  and  what  is  well  suited  to 
one  stomach  is  unsuited  for  another. 


DIGESTION   IN  THE   STOMACH  293 

Attempts  have  been  made  to  determine  the  digestibility  of  different  articles 
of  diet  and  dishes  by  subjecting  the  stomach  contents  obtained  from  fistulous 
patients  or  from  healthy  individuals  by  means  of  the  stomach  tube,  to  investi- 
gation at  certain  intervals  after  eating.  But  it  has  been  shown  that  in  the  same 
person  the  same  food  on  different  occasions  requires  a  very  different  time  for 
its  formation  into  chyme.  A  presentation  of  these  results  would  call  for  a  dis- 
cussion of  a  mass  of  details  which  would  be  out  of  place  here.  Besides,  the 
fact  just  stated  has  lost  much  of  its  strangeness  in  view  of  the  recent  contribu- 
tions on  the  conditions  of  secretion  in  the  stomach  (page  263). 

Nevertheless,  the  following  general  principles  as  to  the  digestibility  of  a  diet 
in  the  stomach  may  be  laid  down : 

(1)  A  too  voluminous  meal  is  harmful  to  the  stomach;  for  in  order  that  it 
may  be  properly  saturated  with  gastric  juice,  a  very  copious  secretion — i.  e,,  a 
great  effort  on  the  part  of  the  gastric  glands — is  required,  and  in  order  to  knead 
and  mix  it  thoroughly,  an  unusual  demand  is  made  upon  the  stomach  mus- 
culature. 

(2)  Poorly  masticated  or  very  compact  food  will  likewise  call  for  too  great 
an  effort  on  the  part  of  the  stomach ;  for  the  larger  and  more  compact  the  pieces 
swallowed,  the  longer  will  be  the  time  required  to  saturate  them  with  gastric 
juice  and  dissolve  them. 

(3)  Animal  foods  which  are  tough — e.g.,  meat  from  old,  poorly  nourished 
animals — are  difficult  to  chew,  and  offer  great  resistance  to  the  action  of  the 
stomach.  The  looser  and  more  porous  the  food,  the  more  easily  is  it  digested 
in  the  stomach;  a  sick  or  weakly  stomach,  therefore,  receives  best  a  soft  or 
gruelly  food. 

(4)  Fat  in  the  food  has  a  great  influence,^  partly  through  its  inhibitory  action 
on  the  glands  of  the  stomach.  But  not  only  so;  if  it  permeates  the  food  thor- 
oughly, it  forms  a  kind  of  protective  film,  which  prevents  the  entrance  of  the 
gastric  juice  to  the  proteid  or  gelatin  constituents.  This  is  especially  true  if 
the  fat  eaten  be  not  fluid  at  the  body  temperature. 

(5)  Strong  spices,  alcohol,  etc.,  act  unfavorably  on  digestion  in  the  stomach, 
partly  because,  as  with  alcohol  in  great  concentration  at  least,  they  reduce  the 
action  of  the  gastric  juice  on  the  food  in  some  way  or  other, 

(6)  Digestion  in  the  stomach  is  influenced  also  by  other  circumstances  than 
the  character  of  the  food.  Thus  the  digestive  power  of  the  gastric  juice  is 
reduced  for  a  time  by  intense  sweating,  since  both  the  IICl  and  the  absolute 
quantity  of  the  secretion  are  thereby  diminished.  Again  exhaustion  from  intense 
muscular  work  causes  a  decrease  in  the  quantity  of  gastric  juice,  which  becomes 
thick,  ropy  and  strongly  mucous.  It  has  even  been  observed  that  stomach  diges- 
tion ceases  entirely  under  heavy  muscular  work. 

Since  the  function  of  the  stomach  is  to  change  the  food  into  a  semifluid  or 
gruelly  mass,  one  might  suppose  a  priori  that  the  stomach  could  be  dispensed 
with  entirely,  if  the  food  taken  were  already  of  this  gruellike  nature.  And  this 
is  in  fact  the  case.  The  stomach  has  been  successfully  removed  from  dogs 
(Czerny),  cats,  and  even  from  men  suffering  from  carcinoma  of  the  stomach, 
without  endangering  life  or  preventing  digestion.  It  is  only  necessary  to  admin- 
ister food  in  small  portions  and  in  a  very  finely  divided  state  in  order  to  main- 
tain life  as  usual. 

Our  knowledo^e  of  gastric  digestion  and  related  phenomena  show  there- 
fore that  the  essential   function  of  the  stomach,   aside  from   the  antiseptic 


*  See  also  page  285. 
19 


294  DIGESTION 

action  of  the  gastric  juice,  is  that  of  transforming  the  food  into  a  gruelly- 
mass;  l)ut  that  its  work  can  be  replaced  by  careful  comminution  of  the  food 
before  eating.  And  yet  this  role  of  the  stomach  is  of  very  great  importance; 
for  it  is  owing  to  the  gastric  digestion  that  we  can  utilize  all  possible  kinds 
of  food  for  our  nourishment,  and  can  limit  our  eating  to  a  few  meals  per 
day.  If  the  food  were  to  be  introduced  immediately  into  the  intestine,  we 
would  be  compelled  to  eat  only  fluid  or  semifluid  foods,  and  it  would  be 
necessary  to  eat  much  more  frequently  than  we  do.  More  than  that,  the 
stomach  protects  the  intestine  from  excesses  of  temperature  whether  high  or 
low  and  from  all  kinds  of  harmful  substances.  It  brings  all  the  food  to  the 
temperature  of  the  body  and  dilutes  harmful  substances  with  the  gastric 
juice  before  allowing  them  to  pass  into  the  intestine.  In  short,  the  stomach 
is  a  protecting  organ  for  the  intestine,  and  permits  us  to  derive  our  sus- 
tenance from  a  very  great  variety  of  foods. 

§  3.    DIGESTION   IN   THE   INTESTINE 

Comparative  anatomy  teaches  us  that  the  length  and  diameter  of  the 
intestine  are  intimately  related  to  the  character  of  the  food  of  the  animal 
species.  In  carnivorous  animals  the  intestine  is  considerably  shorter  than 
in  herbivorous  animals;  while  in  man  its  length  is  intermediate  between 
these  two  extremes. 

The  most  important  part  of  the  work  of  digestion  is  carried  out  in  the 
intestine,  and.  as  it  appears,  chiefly  under  the  influence  of  the  pancreatic 
secretion. 

When  the  chyme  enters  the  intestine  from  the  stomach  it  is  subjected  to 
the  action  of  this  secretion,  of  the  bile  and  of  the  intestinal  juice. 

The  pancreatic  secretion  continues  the  transformation  of  proteids  begun 
in  the  stomach.  As  we  have  already  seen,  the  proteolytic  enzyme  of  the  pan- 
creas is  essentially  different  from  that  of  the  stomach.  We  may  add  to  what 
was  said  before  that  the  pancreatic  juice  acts  rather  feebly  on  the  gelatin- 
forming  suljstances  (cf.  page  291).  whereas  it  acts  very  powerfully  on  the 
true  proteids.  This  fact  is  in  perfect  agreement  with  the  condition  already 
emphasized,  that  the  food  must  be  of  a  gruelly  nature  in  order  to  be  adapted 
for  digestion  in  the  intestine.  The  proteolytic,  the  amylolytic  and  especially 
the  lipolytic  action  of  the  pancreatic  juice  are  assisted  in  some  way  not  fully 
understood  l)y  the  bile  (Rachford  and  Southgate.  Bruno.  Ussow). 

The  action  of  pepsin-HCl  on  proteid  is  soon  stopped  in  the  intestine.  In 
the  first  place  the  bile  hinders  the  swelling  of  proteid  necessary  for  pepsin  diges- 
tion; moreover  it  has  the  property  of  precipitating  proteids  in  acid  solution, 
whence  the  pepsin  is  removed  from  the  fluid  with  the  precipitate.  This  precipi- 
tation of  proteids  by  the  bile  can  be  ver^'  prettily  demonstrated  in  vitro ;  but  in 
natural  digestion  it  appears  to  transpire  only  to  a  slight  extent ;  for  the  bile- 
acid  precipitate  is  easily  redissolved  by  the  bile  salts,  and  by  other  salts  like 
sodium  chloride,  lactate  or  acetate.  It  is  stated  also  that  one  never  finds  any 
such  precipitate  in  the  intestine  of  an  animal  killed  during  digestion. 

Hydrochloric  acid  in  small  quantities  has  no  harmful  effect  on  tryptic  diges- 
tion and  is  even  said  to  favor  it  in  the  presence  of  bile. 


DIGESTION   IX   THE   INTESTINE  295 

With  regard  to  the  extent  of  digestion  of  proteids  in  the  intestine.  Zunz 
has  found  that  in  the  uppermost  50  cm.  of  its  length  the  relative  quantities 
of  albumose  and  end  products  varies  in  favor  of  the  latter,  the  longer  diges- 
tion continues.  After  four  hours,  the  nitrogen  in  the  form  of  albumose 
amounts  to  seventy-six  to  ninety-five  per  cent  of  the  total  nitrogen ;  after  six 
hours,  seventy-one  to  eighty-three  per  cent;  after  eight  hours,  forty-four  to 
forty-six  per  cent;  and  after  ten  hours,  thirty-two  to  forty-four  per  cent. 
The  end  products  increase  therefore  with  the  duration  of  digestion.  We 
cannot  draw  from  this  any  positive  conclusion  as  to  the  form  in  which  the 
digested  proteid  is  chiefly  absorbed,  for  it  might  very  well  be  that  the  albu- 
moses  are  more  quickly  absorbed  from  the  intestine  than  are  the  end  products. 
We  shall  discuss  this  question  more  fully  in  our  study  of  absorption. 

Proteid  and  its  digestive  products  are  attacked  also  by  the  Bacteria  pres- 
ent in  the  intestine.  To  judge  from  observations  on  men  with  intestinal 
fistulae,  this  action  is  only  very  slight;  and  this  is  probably  the  reason  why 
the  contents  of  the  small  intestine  have  no  fecal  odor.  In  the  large  intes- 
tine the  Bacteria  act  much  more  extensively  on  the  proteid.  and  as  a  result 
we  find  there  besides  carbon  dioxide  and  marsh  gas,  sulphureted  hydrogen, 
methyl  mercaptan,  skatol,  phenol,  etc.,  which  give  the  faeces  their  character- 
istic odor.  The  bile  pigments  are  destroyed  in  the  large  intestine  by  Bacteria, 
and  l)ilirubin  is  changed  into  sterkobilin,  which  is  probably  identical  with 
urobilin. 

The  putrefactive  products  arising  in  the  intestine,  which  in  so  far  as  they 
are  basic  in  character  (like  cholin  and  the  different  uric  acid  and  creatin  deriva- 
tives), are  called  leucomaines,  are  taken  up  by  the  blood  and  are  there  changed 
by  chemical  reactions  into  relatively  harmless  substances,  and  are  finally  elimi- 
nated in  the  urine.  Formed  in  too  large  quantities  and  absorbed,  however,  they 
may  remain  in  the  body  and  cause  a  kind  of  poisoning,  autointoxication,  which 
produces  more  or  less  profound  disturbances  of  the  system. 

Moreover,  the  body  strives  in  many  ways  to  overcome  alt  kinds  of  poisonous 
substances  which  maj'  be  taken  up  with  the  food.  Some  are  not  absorbed  from 
the  intestine,  some,  as  in  the  case  of  the  different  Bacterial  decomposition  prod- 
ucts, are  destroj-ed  by  the  digestive  fluids,  some  are  retained  and  rendered 
innocuous  by  the  liver  and  the  mesenteric  glands.  It  is  plain  that  these  proc- 
esses, which  cannot  be  discussed  more  fully  here,  are  of  the  very  greatest  im- 
portance for  the  body,  although  the  protection  provided  by  them  is  not  in  all 
cases  sufficient  to  save  the  body  from  poisoning. 

Until  recently  it  was  rather  generally  assumed  that  fat  is  partly  broken 
down  by  the  pancreatic  juice  into  the  fatty  acids  and  glycerin,  that  the  former 
unite  with  the  alkalies  of  the  intestine  to  form  soaps,  and  that  the  soaps 
bring  about  an  emulsification  of  the  fat.  On  account  of  its  alkalies  bile  was 
said  to  play  a  prominent  part.  Unlike  the  other  nutritive  substances  fat 
would  then  pass  from  the  intestinal  cavity  into  the  mucous  membrane,  not 
in  solution  but  in  the  form  of  an  emulsion.  The  following  two  facts  support 
this  view :  rancid  fat  is  emulsified  easily  by  alkalies,  and  the  absorption  of 
fats  from  the  intestine  is  very  considerably  reduced  by  exclusion  of  the  bile. 

But  by  more  exact  investigation  of  the  phenomena  accompanying  absorp- 
tion of  fat  several  facts  have  come  to  light  which  speak  strongly  against  this 


296  DIGESTION 

conception.  Free  fatty  acids  are  very  well  absorbed  from  the  intestine  even 
when  their  melting  point  is  higher  than  50°  C.  and  when  they  cannot  there- 
fore become  fluid  in  the  body  (I.  Munk).  The  fine  emulsion,  known  by  the 
name  of  chyle,  is  in  many  cases  entirely  wanting  from  the  intestine  of 
the  dog:  and  even  when  chyle  is  introduced  into  the  intestine,  the  fine  emul- 
sion entirely  disappears  after  three  hours,  and  there  is  found  now  only  larger 
fat  drops  surrounded  by  a  turbid  granular  mass.  Lanolin  which  is  a  mixture 
melting  at  40°-42°  C,  made  up  of  compounds  of  fatty  acids  with  cholesterin, 
isocholesterin,  etc.,  very  difficult  to  split  into  their  constituents,  is  not  ab- 
sorbed at  all  from  the  intestine  of  the  dog  (Cohnstein).  Finally  the  histolog- 
ical findings  in  preparations  of  the  intestinal  mucosa  made  during  absorption 
of  fat  are  of  such  a  character  that  they  can  scarcely  be  explained  from  the 
standpoint  of  the  emulsion  hypothesis    (cf.  page  304). 

Against  the  emulsion  hypothesis  it  has  been  observed  also  that  in  the  dog 
the  reaction  throughout  the  greater  part  of  the  small  intestine  is  acid  in  spite 
of  very  active  absorption  of  fat ;  and  in  man  the  reaction  of  the  small  intestine 
is  said  to  be  acid.  This  reaction,  however,  is  caused  by  an  excess  of  organic 
acids  and  of  carbon  dioxide,  and  cannot  be  adduced  as  proof  against  an  eventual 
formation  of  soaps  (Moore  and  Rockwood). 

In  the  light  of  these  facts  the  emulsion  theory  cannot  be  looked  upon  as 
sufficiently  well  founded,  and  in  fact  another  possibility  is  at  hand  to  explain 
the  absorption  of  fats.  This  is,  that  the  fats  are  completely  decomposed  in  the 
intestine  and  that  the  fatty  acids  formed  are  absorbed  either  as  soaps  or  in  a 
solution  brought  about  by  the  bile. 

This  view,  advocated  especially  by  Altmann,  Pflliger,  Moore  and  Eatch- 
ford,  and  supported  by  many  histological  facts,  is  not  contradicted  by  anything 
known  concerning  the  extent  of  the  decomposition  of  fats  in  the  intestine, 
for  that  decomposition  is  in  fact  very  great.  To  find,  after  feeding  neutral 
fat,  that  some  of  it  is  not  decomposed,  of  course  proves  nothing  against  the 
assumption,  for  the  free  fatty  acids  are  absorbed  as  they  are  formed,  and  if 
the  absorption  goes  on  properly  they  might  never  be  present  in  large  quantity 
in  the  intestine. 

It  has  been  known  since  Strecker's  time  (1848)  that  bile  and  bile  salts  dis- 
solve fatty  acids  quite  easily.  One  hundred  c.c.  of  dog's  bile  can  dissolve  6  g. 
of  mixed  fatty  acids  from  swine's  fat,  5.5  g.  from  ox  fat  and  2  g.  from  sheep's 
fat.  The  solubility  of  the  fatty  acids  in  the  bile  depends  therefore  essentially 
on  the  presence  of  oleic  acid,  which  has  been  shown  also  by  direct  experiment. 
The  bile  salts  of  themselves  have  a  much  smaller  solvent  power  than  the  bile, 
among  whose  constituents  lecithin  must  be  the  most  important  for  this  action. 
The  solubility  of  soaps  is  increased  also  by  the  bile. 

After  exclusion  of  bile  from  the  intestine,  the  absorption  of  fats  declines 
considerably — a  fact  very  easily  understood  in  the  light  of  the  conception  now 
under  discussion.  But  even  under  these  circumstances  a  certain  quantity  is 
absorbed,  probably  in  the  form  of  soaps.  In  the  intestinal  contents  there  is 
always  found  under  normal  circumstances  more  alkali  than  is  necessary^  for  the 
neutralization  of  the  inorganic  acids  present,  and  there  occurs  as  a  consequence 
a  certain  amount  of  saponification.     The  soaps   as  they  are  taken   up  by  the 


DIGESTION   IX   THE   INTESTINE  297 

intestinal  mucosa  are  again  decomposed  into  fatty  acids  and  alkalies,  and  the 
alkalies  would  then  be  at  the  disposal  of  the  intestinal  contents  once  more. 

Likewise  when  the  pancreas  is  extirpated,  the  utilization  of  fats  is  usually 
much  diminished  if  not  entirely  stopped;  fatty  acids  are  then  found  in  abun- 
dance in  the  faeces.  The  pancreas  may  be  caused  to  waste  away  slowly,  if  its 
duct  be  ligated  and  0.2  per  cent  sulphuric  acid  be  injected  into  the  g'land.  In 
this  case  the  absorption  of  fat  declines,  but  not  to  any  considerable  extent  until 
a  longer  time  has  elapsed  than  in  the  case  of  extirpation.  The  cleavage  of  fat 
under  such  circumstances  might  be  brought  about  either  by  the  enzyme  (formed 
in  cells  which  are  still  functional)  being  absorbed  and  reaching  the  intestine  by 
some  roundabout  way,  or,  as  after  extirpation,  through  the  agency  of  Bacteria 
(Eosenberg).     But  the  question  is  not  yet  finally  settled. 

If  the  conception  here  presented  is  in  the  main  correct,  then  the  principle 
upon  which  the  transformation  of  foodstuffs  in  the  alimentary  canal  proceeds 
would  be  the  same  for  all,  namely:  they  are  changed  by  liydrohjtic  cleavages 
into  substances  which  can  be  brought  into  solution  by  the  fluids  present  in 
the  alimentary  canal,  or  l)y  fluids  poured  into  it  from  the  glands. 

The  carbohydrates  are  changed  into  soluble  carbohydrates  principally  in 
the  intestine.  The  pancreatic  juice  plays  the  chief  part  in  this,  although  it  is 
assisted  by  the  bile  and  the  intestinal  juice.  Besides,  the  Bacteria  present 
act  upon  the  carbohydrates  to  a  considerable  extent.  In  this  way,  particu- 
larly in  the  small  intestine,  alcohol,  lactic  acid^  acetic  acid  and  succinic  acid 
among  other  things  (Xencki  and  his  pupils)  are  formed.  The  acid  reaction 
of  the  intestinal  contents  depends  in  part  on  these  products. 

Tlie  intestinal  Bacteria  have  a  very  special  part  to  play  in  the  herbivorous 
animals ;  for  by  their  agency  cellulose  is  decomposed  and  the  foodstuffs  locked 
up  by  it  are  made  accessible  to  the  digestive  fluids  (Tappeiner). 

The  participation  of  Bacteria  does  not  appear  to  be  necessary  in  the  digestion 
of  animal  foods,  for  various  polar  animals  have  no  Bacteria  at  all  in  the  intes- 
tinal contents  (E.  Lewin).  Thierfelder  and  Xuttal  have  demonstrated  the  same 
thing  for  guinea  pigs  fed  on  milk  and  finely  prepared  vegetable  food,  such  as 
cakes.  Schottelius  succeeded  also  in  maintaining  chicks  for  a  time  on  perfectly 
sterile  food.  But  from  twelve  days  on  the  animals  decreased  in  weight  and  died 
of  hunger  at  about  the  seventeenth  day.  From  this  it  seems  that  a  coarse  vege- 
table diet  cannot  be  properly  and  continuously  disposed  of  by  the  higher  animals 
without  Bacteria.  And  yet  it  must  be  added  that  the  facts  are  by  no  means 
sufiieient  to  warrant  definite  conclusions,  for  Lewin  finds  the  intestine  perfectly 
sterile  in  herbivorous  polar  animals. 

In  the  lower  animals  enzymes  (cji:ases)  have  been  demonstrated  which  them- 
selves destroy  cellulose.  The  secretion  of  the  snail's  liver  is  an  instance  (Bieder- 
mann  and  Moritz;  cf.  page  110). 

The  putrefactive  processes  in  the  intestine  are  generally  restricted  within 
very  moderate  limits.  The  reason  lies  partly  in  the  action  of  the  hydrochloric 
acid  of  the  gastric  juice  which  reduces  the  number  of  Bacteria  entering  the 
intestine,  and  partly  in  the  fact  that  the  foodstuffs  as  soon  as  they  are  suffi- 
ciently digested,  are  removed  by  absorption  from  the  sphere  of  influence  of 
the  Bacteria. 


298  DIGESTION 

A  very  intense  putrefactive  process  has  often  been  observed  in  animals  with 
a  biliary  fistula,  and  on  this  ground  it  has  been  assumed  that  the  bile  is  a  pow- 
erful antiseptic.  But  this  conclusion  is  not  correct ;  for  in  the  first  place  it  has 
been  shown  by  direct  experiments  that  bile  is  not  a  good  antiseptic  reagent, 
although  it  does  exert  an  adverse  influence  on  the  development  of  certain  Bac- 
teria for  a  short  time;  and  in  the  second  place,  animals  with  a  biliary  fistula 
which  receive  little  or  no  fat  but  plenty  of  other  food,  do  not,  in  spite  of  the 
diversion  of  the  bile,  experience  any  more  putrefaction  in  the  intestine  than  do 
normal  animals.  The  loss  of  bile  is  therefore  not  of  itself  the  cause  of  the  putre- 
faction, when  the  diet  is  not  exactly  regulated.  It  is  rather  to  be  explained  by 
the  scanty  absorption  of  fat;  for  when  fat  remains  in  the  intestine  as  a  foreign 
body,  it  affords  a  good  culture  medium  for  all  kinds  of  Bacteria,  which  multiply 
prodigiously  and  produce  an  intense  putrefaction,  and  through  this  a  severe 
intestinal  catarrh. 

The  same  thing  happens  with  new  born  children  when  they  are  fed  with 
starches.  The  starch  is  incompletely  digested  in  the  intestine,  it  remains  there 
as  a  foreign  body  and  an  offensive  diarrhea  develops,  notwithstanding  the  pres- 
ence of  bile. 

A  large  part  of  the  small  intestine  can  he  removed  from  man  as  well  as 
from  animals,  and  digestion  will  not  be  interfered  with  to  any  considerable 
extent.  After  the  removal  of  3.1  m.  of  the  intestine  of  a  man,  however,  the 
intestinal  evacuations  were  more  abundant  and  the  utilization  of  proteid  was 
less  than  normal  (Riva-Rocci).  In  the  dog  only  slight  permanent  changes 
made  their  appearance,  when  as  much  as  seventy  per  cent  of  the  intestine 
was  extirpated ;  although  the  diet  had  to  be  carefully  regulated  and  an  excess 
of  fat  especially  avoided  (Erlanger  and  Hewlett). 


§  4.    FORMATION   OF   FJECES   AND   DEFECATION 

Digestion  is  continued  in  the  large  intestine  by  enzymes  carried  in  with 
the  intestinal  contents.  In  the  dog,  digestion  in  this  part  of  the  alimentary 
canal  appears  to  be  of  little  importance,  since  complete  removal  of  the  large 
intestine  reduces  the  a])sorption  of  foodstuffs  but  slightly.  The  proteids  only 
are  less  perfectly  utilized  than  normally  (Harley). 

In  herbivorous  animals  the  large  intestine  must  play  a  more  important 
part,  for  in  the  horse,  for  example,  the  caecum  is  two  to  three  times  as  large 
as  the  stomach.  And  yet  rabl^its  from  which  the  caecum  is  removed  live  for 
months  without  showing  any  permanent  disorder  in  the  digestion  or  in  the 
general  health   (Hultgren  and  Bergman). 

The  cltief  function  of  the  large  intestine  is  to  provide  for  the  absorption 
of  foodstuffs  capable  of  being  absorbed  which  have  not  already  been  cared 
for  by  the  small  intestine,  and  by  withdrawal  of  water  to  reduce  the  residue 
to  a  firmer  consistency.  The  intestinal  contents  thus  transformed  are  then 
finally  voided  from  the  body  as  the  fseces. 

The  fceces  contain  some  undigested  constituents  of  the  food,  some  unab- 
sorbed  products  of  digestion,  putrefaction  and  fermentation  in  the  intestine, 
dead  intestinal  epithelium  and  residues  of  the  digestive  fluids,  and  finally 
substances  which  are  given  off  l)y  the  wall  of  the  alimentary  canal  as  excre- 


FORMATION   OF   FAECES   AND   DEFECATION  299 

tory  products  (cf.  pages  133,  308).  The  quantity  of  feces  evacuated  daily 
varies  somewhat  according  to  the  nature  and  quantity  of  the  food  eaten.  With 
an  ordinary  diet  it  is  estimated  for  the  adult  man  at  120-150  g.  with  30-37  g. 
dry  substance. 

The  hardened  masses  to  be  removed  collect  in  the  large  intestine  and  in 
the  rectum,  and  are  from  time  to  time  discharged  from  the  body.  The 
herbivorous  animals  (whose  food  is  itself  very  voluminous,  and  in  which  the 
work  of  digestion  goes  on  continuously)  have  frequent  evacuations,  notwith- 
standing the  great  diameter  of  the  intestine.  With  carnivorous  animals.  Avhose 
food  is  very  concentrated,  the  faeces  are  voided  less  frequently.  Man  ordina- 
rily has  one  stool  per  day. 

The  intestinal  contents  are  retained  in  the  rectum  by  the  tonic  contraction 
of  the  two  sphincters,  the  sphincter  ani  externus  and  interniis.  The  sigmoid 
tle.xure  of  the  descending  colon  has  the  effect  of  lessening  the  load  to  be  borne 
by  the  sphincters.  The  action  of  the  outer  sphincter  is  strengthened  by  the 
levator  ani,  this  muscle  being  thrown  round  the  rectum  like  a  loop. 

The  center  for  the  external  sphincter  in  the  rabbit  lies  within  the  spinal  cord 
in  the  re^rion  of  the  sixth  to  the  seventh  lumbar  vertebra,  in  the  dog  at  about  the 
lower  end  of  the  fifth  lumbar  vertebra.  Since  this  sphincter  can  be  strengthened 
voluntarily,  this  center  is  also  under  the  influence  of  the  higher  nerve  centers. 
Contractions  of  the  sphincters  are  obtained  by  stimulation  of  the  motor  zone 
of  the  cerebral  cortex  (dog).  On  the  other  hand,  the  tonus  of  the  sphincters  may 
be  abolished  by  strong*  psychic  excitation  (involuntary  defecation),  and  by  stimu- 
lation of  the  motor  zone  of  the  cortex  with  the  nervi  errigentes  cut  (Frankl- 
Hochwart  and  Frohlich). 

From  the  spinal  cord  the  nerves  to  the  sphincters  run  partly  in  the  hypo- 
gastric nerves  and  partly  in  the  nervi  errigentes,  and  in  the  dog  the  former  are 
said  to  be  inhibitory,  the  latter  motor.  Besides,  the  latter  mediate  contractions 
of  the  rectococcj'gealis  and  of  the  other  longitudinal  muscles  of  the  rectum. 

The  tonus  of  the  anal  sphincters  is  not  obliterated  even  by  destruction  of 
the  spinal  cord  (Goltz  and  Ewald),  a  fact  explicable  in  part  at  least  by  the  pres- 
ence of  a  center  for  the  sphincter  nerves  in  the  inferior  mesenteric  ganglion 
(Frankl-Hochwart  and  Frohlich). 

Defecation  is  mediated  by  a  reflex  process  not  yet  thoroughly  investigated, 
which  is  induced  from  the  rectum,  and  which  is  modified  by  influences  of  the 
will  upon  the  muscles  concerned.  The  sphincters  relax  and  the  hardened 
masses  are  discharged  by  contraction  of  the  rectal  musculature  with  the  assist- 
ance of  the  abdominal  pressure.  The  levator  ani  muscle  may  contribute  to 
the  general  effect.  By  its  contraction  it  presents  a  point  of  insertion  for  the 
longitudinal  muscles  of  the  rectum,  and  the  compression  of  the  rectum  pro- 
duced l)y  it,  coincident  with  the  relaxation  of  the  sphincters  and  the  power- 
ful effect  of  the  abdominal  pressure,  assists  in  discharging  the  contents 
(Henle). 

By  abdominal  pressure  we  mean  the  pressure  upon  the  al)dominal  viscera 
produced  by  simultaneous  contraction  of  the  diaphragm  and  of  the  abdominal 
muscles.  The  part  it  plays  in  defecation  depends  upon  the  consistency  of  the 
contents  of  the  rectum.     If  this  is  soft,  defecation  can  take  place  ^vithout 


300  DIGESTION 

any  assistance  from  the  abdominal  ])ressure;  but  witli  very  solid  excrement, 
the  power  of  the  intestinal  musculature  itself  is  not  sufficient  and  the  abdom- 
inal pressure  is  called  upon. 

References. — If.  Connstein,  "  Uber  fermentative  Fettspaltung,"  in  Die 
Ergebnisse  der  Physiologie,  III,  1,  1904. — D.  Gerhardt,  "  ttber  Darmfiiulnis," 
in  Die  Ergebnisse  der  Physiologie,  III,  1,  1904. — J.  P.  Pawlow,  "Die  Arbeit 
der  Vcrdauungsdriisen,"  Wiesbaden,  1898. — C.  Oppenheimer,  "  Die  Eermente  und 
ihre  Wirkungen,"  2d  edition,  Leipzic,  1903. 


CHAPTER    VIII 

ABSOIJPTIOX 

By  absorption  we  understand  all  those  processes  by  which  the  digested 
foodstuffs  are  taken  up  from  the  cavity  of  the  alimentary  canal  into  its  mucous 
membrane  and  are  forwarded  thence  to  the  general  circulating  fluids. 

§  1.    ABSORPTION   IN   GENERAL 

After  Dutrochet  had  discovered  tlie  osmotic  phenomena,  it  was  thought 
that  absorption  in  the  intestine  could  l^e  easily  explained  by  osmosis.  Diges- 
tion was  for  the  purpose  of  changing  the  foodstuffs  contained  in  the  food 
into  easily  diffusible  substances,  if  they  were  not  already  diffusible.  Hence 
absorption  took  place  according  to  the  well-kno^^Ti  physicochemical  laws  of 
osmosis. 

More  searching  investigation,  however,  of  matters  as  they  are,  have  made 
us  acquainted  with  facts  which  preclude  so  simple  a  process,  and  have  led 
us  for  the  present  to  the  view  that  the  activity  of  the  living  mucous  membrane 
plays  an  essential  part  in  absorption.  It  is  perfectly  evident  that  purely 
physicochemical  processes,  like  filtration,  osmosis,  imbibition,  etc.,  are  in- 
volved, and  this  requires  no  further  argument. 

Among  the  more  important  obsei'vations  for  the  theoretical  explanation  of 
absori)tion,  those  upon  the  behavior  of  weak  salt  solutions  and  of  blood  serum 
should  be  mentioned  first  (Voit,  Ileidenhain  and  others).  If  normal  or  slightly 
diluted  blood  serum  be  placed  in  an  intestinal  loop  of  a  dog,  notwithstanding 
that  the  conditions  of  the  experiment  exclude  the  cooperation  of  osmotic  pres- 
sure, water  and  salts  are  absorbed  in  almost  the  same  proportion  as  that  in  which 
they  exist  in  the  serum  introduced,  whereas  the  organic  substances  take  part  in 
absorption  in  far  less  proportion.  If  a  solution  of  common  salt  whose  osmotic 
tension  is  higher  than  that  of  the  blood  be  introduced,  according  to  the  laws  of 
osmosis  no  water  should  be  absorbed;  but  it  is  absorbed.  And,  vice  versa,  common 
salt  is  absorbed  from  a  solution  in  which  the  osmotic  tension  is  less  than  that 
of  the  blood.  The  absorption  of  water  from  a  weak  dextrose  solution  is  not 
changed,  if  the  osmotic  pressure  of  the  blood  be  raised  by  intravenous  injection 
of  common  salt  (Reid).  From  equimolecular  and  therefore  isosmotic  solutions 
of  different  kinds  of  sugar  which  are  stereoisomeric,  the  quantities  of  sugar 
absorbed  in  unit  time  are  not  equal  (RiJhmann  and  Negano). 

Moreover  it  has  been  shown  that  the  movement  of  salt  in  the  normal  intes- 
tine takes  place  in  the  direction  from  lumen  to  tissues,  much  more  easily  than 
in  the  opposite  direction  (O.  Colndieim)  ;  that  an  intestine  cut  out  of  an  animal 
in  full  digestion,  if  bathed  both  within  and  without  with  a  salt  solution  of  the 

301 


302  ABSORPTION 

same  strength,  transports  fluid  only  from  the  mucous  membrane  outward  and 
not  in  the  reverse  direction  (Reid) ;  that  if  the  cells  of  the  intestinal  epithelium 
be  injured  functionally,  but  not,  so  far  as  can  be  seen,  anatomically  by  poison- 
ing with  sodium  fluoride,  absorption  is  actually  altered  so  that  osmosis  now 
brings  about  only  an  exportation  of  fluid  from  the  intestine. 

Finally,  attention  should  be  called  to  the  discoveries  mentioned  at  page  34 
with  regard  to  the  permeability  of  animal  cells  for  different  substances.  Accord- 
ing to  those  results,  the  entrance  of  a  substance  into  a  cell  would  depend  upon 
its  solubility  in  the  lipoid  limiting  layer  of  the  cell,  carbohydrates  not  being 
soluble  therein.  To  surmount  the  difficulty  which  carbohydrates  present,  Hoeber 
supposes  that  the  absorption  of  these  and  other  compounds  which  do  not  pene- 
trate such  a  membrane  occurs  only  between  the  cells.  Something  of  the  kind 
might  be  true  of  substances  which  are  taken  up  in  verj'  small  quantities;  but 
carbohydrates  are  absorbed  by  the  mucosa  so  abundantly  that  this  explanation 
appears  to  have  little  probability  in  its  favor. 

The  power  of  absorption  is  very  different  in  different  divisions  of  the 
alimentary  canal.  In  the  stomach  pure  water  is  not  absorbed  at  all.  Sugar 
or  peptone  or  salts  (if  concentrated)  are  absorbed  from  their  water  solutions 
in  the  stomach  the  more  plentifully,  the  stronger  is  the  solution.  The  water 
is  absorbed  also  under  these  circumstances,  and,  as  it  seems,  most  actively 
from  solutions  of  peptone.  Absorption  of  water  from  peptone  solutions  in- 
creases with  the  concentration,  while  from  solutions  of  sugar  it  decreases 
with  the  concentration  (v.  Mering). 

In  the  upper  part  of  the  small  intestine  (Jejunum),  sugar  and  fat  are 
absorbed  more  rapidly  than  in  the  lower  part  (ileum).  On  the  other  hand 
the  water  of  sugar  solutions  is  said  to  be  taken  up  by  the  mucous  membrane 
more  slowly  in  the  jejunum  than  in  the  ileum  (Rohmann  and  Negano). 

Correspondingly,  under  a  pressure  of  10  cm.  of  water  for  1  cm.  of  length, 
about  0.7  c.c.  of  a  six-per-cent  salt  solution  was  absorbed  in  one  hour  by  the 
upper  part  of  the  small  intestine  of  the  dog,  and  1.3  c.c.  by  the  lower  part,  while 
in  the  large  intestine  under  the  same  circumstances  the  amount  was  2.1  c.c. 

The  large  intestine  appears  therefore  to  be  especially  well  adapted  for  the 
absorption  of  water.  Organic  foodstuffs  also  in  easily  absorbable  form  are 
taken  up  from  the  large  intestine,  as  has  been  shown  by  experiments  with 
nutrient  enemas,  in  which  a  supply  of  as  much  as  1,200  Cal.  per  day  has 
been  maintained.  It  is  to  be  observed,  though,  that  the  ileocaecal  valve  is  not 
an  absolute  barrier  to  the  passage  of  the  contents  back  into  the  small  intestine, 
and  that  a  part  of  the  nourishment  might  be  absorbed  there  instead  of  in 
the  large  intestine.  According  to  observations  on  men  and  dogs  with  fistulse 
into  the  large  intestine,  carbohydrates  are  absorbed  there  best  of  all  the  food- 
stuffs; fats  and  proteids  only  to  a  slight  extent.  The  salt  content  of  the 
enema  also  appears  to  have  a  certain  importance  in  promoting  absorption. 

All  kinds  of  locally  stimulating  substances  (e.  g.,  spices)  exert  a  remark- 
able influence  on  the  absorption  in  the  stomach  and  intestine.  In  the  former 
alcohol  is  absorbed  even  to  the  last  trace  in  two  hours,  and  besides,  it  accel- 
erates the  absorption  of  other  substances.  Common  salt,  oil  of  mustard,  pep- 
permint, pepper,  etc.,  have  the  same  effect.     The  condiments  therefore  not 


ABSORPTION   OF   CARBOHYDRATES  303 

only  favor  the  secretion  of  the  digestive  fluids,  they  further  the  absorption 
of  the  digested  foodstuffs.  Whether  this  action  is  due  to  a  stimulating  influ- 
ence of  these  substances  on  the  absorbing  elements  of  the  mucous  membrane, 
or  to  vasodilatation  caused  l)y  them,  must  for  the  present  be  regarded  as 
undecided,  although  in  the  opinion  of  the  author  the  former  supposition  is 
the  more  probable. 

Comparison  of  absorption  in  the  stomach  with  that  in  the  intestine  brings 
to  light  this  fact,  which  is  important  for  our  understanding  of  the  gastric 
functions :  that  the  stomach  tolerates  much  more  highly  concentrated  solutions 
of  the  foodstuffs  than  does  the  intestine.  The  stomach  acts  as  a  reservoir 
for  the  ingested  food,  in  order  that  the  gruelly  contents,  properly  diluted, 
may  be  discharged  into  the  intestine  gradually.  But  the  latter  plays  the 
chief  part  in  absorption. 

In  this  connection  we  may  mention  also  the  experiments  of  Ogata  in  which 
the  absorption  of  proteid  was  investigated  after  meat  feeding,  once  when  the 
meat  was  fed  by  the  mouth,  and  another  time  when  it  was  brought  directly  into 
the  duodenum  through  a  stomach  tistula.  The  nitrog'en  output  in  the  urine  was 
taken  as  an  expression  of  the  absorption.  It  was  shown  that  after  direct  intro- 
duction of  meat  into  the  duodenum  the  X-output  rose  much  more  rapidly  and 
exhibited  greater  variations  than  when  the  meat  had  first  to  undergo  digestion 
in  the  stomach.  The  absorption  of  proteid  therefore  takes  place  much  more 
rapidly  when  it  is  placed  directly  in  the  intestine,  than  when  it  must  pass  through 
the  stomach.  We  have  then  to  add  to  what  we  have  already  learned  about  the 
importance  of  the  stomach,  that  in  virtue  of  its  function  as  a  storehouse,  the 
absorption  of  ingested  proteid  is  distributed  more  uniformly  than  it  would  be 
otherwise. 

§  2.    ABSORPTION   OF   CARBOHYDRATES 

We  have  no  exact  information  as  to  how  the  carbohydrates  are  removed 
from  the  intestinal  cavity  (cf.  page  302). 

That  they  are  carried  off  chiefly  by  the  blood  vessels,  and  not  by  the 
lymphatics,  appears  to  be  shown  by  a  number  of  observations.  For  example, 
after  a  meal  rich  in  carbohydrates,  the  amount  of  sugar  in  the  chyle  is  no 
greater  than  after  one  poor  in  carbohydrates,  while  the  portal  blood  shows  a 
considerable  increase  in  the  former  case.  On  the  basis  of  these  results  and  of 
the  location  of  the  blood  vessels  in  the  villi.  Heidenhain  has  made  the  general 
statement  that  all  substances  soluble  in  water  pass  for  the  most  part  into  the 
roots  of  the  portal  vein.  Only  when  the  quantity  of  fluid  is  very  great  does 
any  sugar  enter  the  lacteals. 

This  conclusion  is  confirmed  in  its  entirety  by  observations  on  a  young 
girl  who  had  a  fistula  in  the  receptaculum  chyli,  from  which  all  the  chyle 
flowed  out  of  the  body.  In  this  patient  it  was  found  that  not  more  than 
five-tenths  per  cent  of  the  absorbed  sugar  was  taken  up  by  the  lymphatics 
(I.  Munk  and  Rosenstein). 


304  ABSORPTION 

I  3.    ABSORPTION   OF   FAT 

Because  of  the  ease  with  which  fat  can  be  demonstrated  bv  micro-chemical 
reactions,  much  attention  has  been  given  to  its  absorption. 

It  has  already  been  stated  (page  29(5)  that  fat  is  probably  not  absorbed 
as  an  emulsion,  but  in  the  form  of  a  solution  of  fatty  acids  effected  by  the 
bile  acids,  or  in  the  form  of  soaps. 

Since  the  chyle,  even  after  feeding  with  free  fatty  acids,  contains  neutral 
fat  almost  altogether,  and  free  fatty  acids  only  in  much  smaller  amount,  and 
after  feeding  ethylesters  of  the  higher  fatty  acids  contains  onlv  triglycerides 
and  not  a  trace  of  the  esters  fed  (Frank),  we  may  deem  it  fully  established 
that  the  free  fatty  acids  absorbed  from  the  intestinal  canal  are  synthesized 
again  to  neutral  fats  in  the  intestinal  wall.    This  is  confirmed  by  the  observa- 


Fig.  118. — Successive  stages  in  the  absorption  of  fat  in  the  epithelial  cells  of  the  frog's  intestine, 

after  Krehl. 

tion  that  the  intestinal  mucosa  at  the  height  of  digestion  contains  far  more 
neutral  fat  than  free  fatty  acids,  and  that  on  digestion  of  the  finely  divided 
mucous  membrane  with  a  mixture  of  soaps  and  glycerin  neutral  fat  is  formed. 

This  synthesis,  like  the  absorption  of  fats  from  the  intestinal  cavity,  is 
probably  carried  out  by  the  cellular  elements  of  the  mucosa — possibly  by  the 
numerous  leucocytes  occurring  therein,  but  more  probably  by  the  epithelium 
of  the  villi. 

If  the  intestinal  epithelium  of  the  frog  in  different  stages  of  fat  absorption 
be  studied  in  osmic  acid  preparations,  all  transitions  are  seen  from  small 
dustlike  gray  points  to  large,  black  fat  droplets  (Fig.  118.  A  to  C).  In  the 
Mammalia  the  fat  in  certain  early  stages  of  absorption  does  not  enter  in  the 
form  of  blackened  granules,  but  of  small  black  circles  with  a  clear  center. 
These  circles  increase  in  size  and  depth  of  color  in  the  further  course  of 
absorption — just  the  behavior  we  should  expect  if  the  fat  were  taken  up  as 
a  solution  of  fatty  acids  and  synthesized  in  the  intestinal  wall  to  neutral 
fat  again, 

"With  regard  to  the  further  fate  of  the  absorbed  fat.  it  is  supposed  that  it 
is  free  to  move  inside  the  parenchyma  of  the  villus  only  in  the  pericellular,  fluid- 


ABSORPTION   OF   PROTEID  305 

filled  spaces  incompletely  separated  from  one  another  by  the  connective-tissue 
trabeculse  of  the  stroma. 

It  has  long  been  known  that  fat,  for  the  most  part,  passes  into  the  lacteals 
and  is  conveyed  thence  to  the  thoracic  duct.  Eecent  experiments  have  shown, 
however,  that  no  small  part  of  it  passes  also  into  the  blood  vessels  of  the 
intestine.  In  the  case  of  the  above-mentioned  patient  with  a  fistula  in  the 
receptaculum  ehyli,  only  about  sixty  per  cent  of  the  absorbed  fat,  and  still 
less  when  free  fatty  acids  were  fed,  was  found  in  the  chyle.  Some  forty 
per  cent,  therefore,  had  taken  the  pathway  through  the  portal  vein. 

Besides  the  fatty  substances  absorbed  from  the  food,  other  fats  pass  into  the 
chyle,  which  have  their  origin  in  the  intestine  and  its  fluids.  In  this  way,  pos- 
sibly, we  may  explain  the  fact  that  after  feeding  a  fat  of  high  melting  point 
the  mixture  of  fat  in  the  chyle  melts  at  the  temperature  of  the  body — i.  e.,  that 
in  the  transition  from  intestine  to  chyle  a  lowering  of  the  melting  point  has 
taken  place. 

When  soaps  are  injected  directly  into  the  blood,  they  produce  symptoms  of 
weakened  heart  activity,  the  respiratory  exchange  of  gases  declines,  the  coagula- 
bility of  the  blood  is  abolished,  and,  with  a  dose  of  only  0.1  g.  oleic  acid  per 
kilogram  of  body  weight,  rabbits  are  killed  (I.  Munk).  The  cause  of  these  phe- 
nomena, according  to  Friedlander,  lies  in  the  fact  that  the  calcium  of  the  blood 
is  precipitated  by  the  fatty  acids. 

§  4.    ABSORPTION   OF    PROTEID 

If  the  digestive  enzymes  continue  to  act  long  enough,  the  proteids  are 
finally  decomposed  into  simple  crystallizable  end  products.  To  what  extent 
this  cleavage  takes  place  in  normal  digestion,  i.  e.,  whether  the  proteid  sub- 
stances are  taken  up  chiefly  as  albumoses  or  as  crystalline  end  products,  we 
cannot  say  definitely  at  present.  It  is  possible,  as  some  authors  assume,  mainly 
on  the  ground  of  the  action  of  erepsin,  that  the  cleavage  of  proteid,  either  in 
the  intestine  or  in  the  mucous  membrane,  extends  all  the  way  to  the  final  end 
products ;  but  it  is  conceivable  also  that  the  albumoses,  as  soon  as  they  are 
formed,  are  taken  up  from  the  intestinal  cavity,  and  are  not  further  decom- 
posed in  the  mucous  membrane. 

The  experiments  of  Voit  and  Bauer  have  shown  that  even  native  proteids  in 
solution  can  be  absorbed  from  the  intestine  without  previous  digestion.  As  much 
as  fifty-eight  per  cent  of  egg  albumin  placed  in  a  loop,  isolated  from  the  rest  of 
the  intestine,  disappeared  within  five  and  one-half  hours;  twenty-eight  per  cent 
of  blood  serum  in  the  course  of  one  hour;  etc.  This  however  constitutes  no 
proof  that  the  first  products  would  be  absorbed  in  the  course  of  normal  digestion. 

If  blood  be  pas.sed  through  the  vessels  of  a  surviving  intestine,  in  whose 
cavity  a  peptone  solution  is  contained,  the  peptone  is  absorbed  but  none  of  it 
can  be  demonstrated  in  the  blood.  From  this,  and  from  the  fact  that  after 
a  meal  rich  in  proteid,  the  blood  of  the  portal  vein  contained  no  more  albu- 
mose  than  the  blood  of  the  carotid,  it  was  concluded  that  the  absorbed  products 
of  proteid  digestion  were  changed  in  the  mucosa  to  proteids  of  the  same  kind 
as  those  occurring  in  the  blood. 


306  ABSORPTION 

But  these  experiments  are  not  conclusive.  If  peptones  are  not  to  be  found 
under  the  circumstances  named,  it  might  be  due  to  further  decomposition, 
and  the  discovery  of  erepsin  makes  such  a  view  not  improbable.  The  rapid 
rise  of  the  X-output  in  the  urine  after  feeding  proteid  shows  that  it  is  de- 
stroyed very  soon  after  absorption.  It  would  be  a  waste  of  energy  if  the  body 
were  to  construct  native  proteids  out  of  albumoses  and  peptones,  only  to 
destroy  them  immediately.  The  difficulty  of  obtaining  a  storage  of  proteid 
in  the  adult  body  also  can  be  easily  harmonized  viiih  its  ultimate  cleavage 
in  digestion. 

Direct  observations  thus  far  at  hand  are  not  by  any  means  sufficient  to 
establish  a  definite  view  of  the  matter.  On  the  one  hand,  Cobnheim  has  found 
that  one-third  of  a  cat's  intestine  surviving  was  able  to  split  0.6  g.  of  peptone 
into  its  end  products  in  two  hours ;  on  the  other  hand,  Glaessner  tinds  that  albu- 
moses are  changed  by  the  surviving  mucous  membrane  into  coagulable  com- 
pounds ;  whereas  Emden  and  Knoop  reach  the  conclusion  that  in  the  surviving 
intestine  taken  while  absorption  of  proteid  was  going  on,  there  is  neither  a 
reconstruction  of  coagulable  proteid  out  of  albumoses  and  peptones,  nor  a  cleav- 
age of  them  into  final  products.  They  as  well  as  Langstein  state  that  from  all 
appearances  albumoses  occur  plentifully  in  the  blood. 

So  far  as  the  question  can  be  judged  at  present,  we  might  say  that  a  part 
of  the  proteid  eaten  is  absorbed  as  end  products  of  digestion,  another  part  as 
albumoses  and  peptones.  How  and  where  the  latter  are  transformed  into 
native  proteids,  and  whether  a  synthesis  of  proteid  from  the  end  products 
can  take  place  under  an}^  circumstances,  cannot  yet  be  decided. 

Our  knowledge  is  still  unsatisfactory  also  with  regard  to  the  manner  of 
the  absorption  of  proteids.  Hofmeister  has  supposed  that  the  leucocytes  of 
the  mucous  membrane  are  especially  active  in  this,  and  the  following  facts 
among  others  appear  to  favor  such  an  hypothesis.  After  meat  feeding  the 
l}Tnph  system  in  the  small  intestine  of  rats  exhibits  a  larger  number  of  cellu- 
lar elements  than  after  feeding  lard  or  starch,  but  vrith  the  latter,  more  than 
in  fasting  (Asher).  An  hour  after  a  meal  rich  in  proteid.  the  number  of 
leucocytes  in  the  portal  blood  of  the  dog  is  considerably  increased,  and  reaches 
a  maximum  probably  during  the  third  hour  of  digestion.  This  increase  does 
not  occur  if  the  animal  receives  water,  meat  extract,  salt,  starch  or  fat,  but 
no  proteid.  In  proteid  absorption,  finally,  the  number  of  leucocytes  in  the 
venous  l^lood  of  the  intestine  is  greater  than  in  the  arterial  blood    (Pohl). 

Some  have  sought  to  demonstrate  an  increase  in  the  number  of  leucoc3^tes 
in  the  skin  capillaries  of  man  after  a  meal  rich  in  proteids ;  but  this  digestive 
leucocytosis  is  often  wanting  and  is  entirely  denied  by  some  authors.  The 
possibility  remains,  however,  that  the  leucocytes  may  take  part  in  the  absorp- 
tion of  proteids ;  for  it  is  easil}-  conceivable  that  the  transportation  of  proteids 
from  the  intestine  might  be  assisted  by  them,  without  their  entering  the 
general  circulation  in  larger  numbers. 

The  pathway  which  the  proteids  take  in  leaving  the  intestine  is  almost 
exclusivel}'  that  of  the  portal  vessels.  In  the  fistulous  patient  above-mentioned 
(page  303)  it  was  impossible  after  a  meal  rich  in  proteid  to  demonstrate  any 
increase  in  the  percentage  of  proteid  in  the  chyle. 


ABSORPTION   OF   MINERAL  SUBSTANCES  307 


§  5.    ABSORPTION   OF   MINERAL    SUBSTANCES 

Since  the  easily  diffusible  salts,  like  sodium  chloride,  are  absorbed  by  virtue 
of  the  activity  of  the  epithelial  cells  this  must  the  more  be  true  of  the  heavy 
salts  which  diffuse  slowly. 

With  regard  to  the  behavior  of  different  salts,  Iloeber  has  shown  that  solu- 
tions of  different  salts  isotonic  with  one  another  are  absorbed  at  different  rates. 
Since  in  these  experiments  solutions  so  dilute  that  the  salts  were  almost  wholly 
dissociated  were  used,  their  different  behavior  is  to  be  ascribed  to  the  properties 
of  individual  ions.  Of  the  cations  K,  Xa  and  Li  are  absorbed  with  approxi- 
mately the  same  rapidity,  XH,  and  urea  more  rapidly,  Ca  more  slowly  and  Mg 
slowest  of  all.  Of  the  anions  CI  is  absorbed  most  rapidly,  then  follow  in  order 
Br,  I,  XOj  and  SO^.     Xow  we  know  that  the  rate  of  diffusion  of  a  salt  in  any 


Fig.  119. — Duodenum  of  the  mouse,  after  Hochhaus  and  Quincke.  The  section  has  been  treated 
with  ammonium  sulphide.  The  black  granules  represent  absorbed  iron.  The  animal  had 
eaten  cheese  impregnated  with  '■  carniferrin  "  containing  three  per  cent  Fe.  (Carniferrin  is  a 
derivative  of  carnic  acid  obtained  from  meat  extract,  and  contains  botii  phosphoric  acid  and 
iron.) 

given  solution  depends,  first  upon  the  degree  of  dissociation  of  its  molecules,  and 
secondly  upon  the  velocity  of  migration  of  the  ions.  This  law  applies  also  in 
absori)tion ;  for  the  rates  of  absorption  of  salts  are  proportional  to  their  rates 
of  diffusion.  However,  parallelism  between  diffusion  and  absorption  is  subject 
to  some  limitations,  which  make  other  auxiliary  hypotheses  necessary  and  show 
once  more  that  the  i)hysical  factors  are  not  sufficient  to  explain  the  behavior  of 
the  salts  in  the  intestine. 

In  order  to  follow  the  absorption  of  water  and  of  substances  soluble  in 
water  more  closely,  a  solution  of  methylene  blue  has  been  introduced  into  an 
intestinal  loop  and  the  mucous  membrane  studied  microscopically.  The  pigment 
was  found  partly  in  the  epithelial  cells  and  partly  between  them,  which  means 
that  absorption  takes  place  here  both  between  the  cells  and  through  them 
(Ileidenhain). 

The  soluble  salts,  like  the  carbohydrates,  are  carried  away  from  the  intestine 
by  the  portal  vessels;  only  in  case  the  quantity  of  absorbed  fluid  is  great  does 
a  part  of  it  pass  out  by  way  of  the  lymph  vessels. 

The  absorption   of  iron   deserves  special  consideration.     After   it  had  been 


308  ABSORPTION 

observed  that  very  good  results  are  obtained  in  the  treatment  of  chlorosis  by 
administration  of  different  preparations  of  inorganic  iron,  and  observers  were 
pretty  well  convinced  that  these  preparations  were  actually  absorbed  in  the  intes- 
tine, Bunge  set  up  the  doctrine  that  all  the  iron  which  is  added  to  the  blood 
and  is  the  source  of  the  iron  contained  in  the  haemoglobin,  arises  exclusively 
from  complicated  proteidlike  compounds,  the  hcemaiogens,  which  are  formed  in 
the  life  processes  of  plants.  Such  compounds,  resembling  nucleo-albumins,  occur 
also  in  egg  yolk,  etc.  That  iron  preparations  are  certainly  of  great  use  in 
chlorosis,  Bunge  would  not  deny,  but  he  explained  the  facts  on  the  hypothesis 
that  inorganic  iron  compounds  in  s'ome  way  protect  the  organic  compounds  from 
decomposition  in  the  intestine,  and  thus  prevent  the  iron  in  them  from  being 
split  off.  Other  authors  have  advanced  other  hypotheses,  and  attempts  have  even 
been  made  to  explain  the  therapeutic  effects  of  iron  as  the  result  of  hypnotic 
suggestion. 

However,  it  appears  with  greater  definiteness  from  recent  researches  that 
the  so-called  inorganic  iron  compounds  are  absorbed  in  the  intestine  (Kunkel, 
MacCallum,  Hall,  Hochhaus.  and  Quincke  et  ah).  A  research  carried  out  a 
short  time  ago  by  Abderhalden  in  Bunge's  own  laboratory  shows  the  same  thing, 
namely,  that  iron  furnished  in  inorganic  compounds,  in  hiemoglobin  and  hsmatin 
is  absorbed  even  in  small  doses,  and  without  destroying  the  complicated  iron 
compounds.  The  absorption  takes  place  through  the  activity  of  the  epithelial 
cells  (cf.  Fig.  119).  These  cells  then  deliver  the  absorbed  iron  either  to  the 
leucocytes  or  directly  to  the  blood  stream. 

Some  of  the  absorbed  iron  passes  into  the  thoracic  duct  (Gaule).  According 
to  MacCallum  and  Hall,  if  the  amount  of  iron  given  be  small,  it  is  absorbed 
only  in  the  uppermost  part  of  the  duodenum;  with  larger  doses  its  absorption 
appears  to  take  place  in  the  lower  parts  of  the  small  intestine,  especially  in 
Beyer's  patches,  and,  according  to  Tartakowsky,  almost  throughout  the  entire 
extent  of  the  gastrointestinal  tract. 

We  have  the  following  data  with  regard  to  the  further  fate  of  iron  in  the 
body.  The  iron  contained  in  the  body  can  be  split  off  in  part  from  its  com- 
pounds by  certain  micro-chemical  reactions  (treatment  with  ammonium  sidphide 
and  ammonia,  or  with  potassium  ferrocyanide  and  hydrochloric  acid)  ;  another 
part  remains,  however,  in  very  stable  compounds  (e.  g.,  haemoglobin)  in  which 
it  can  be  demonstrated  only  by  their  decomposition.  The  iron  contained  in 
these  comiKiunds  represents  the  real  iron  stock  of  the  body,  other  iron  being  in 
a  state  of  transition  and  belonging  either  to  the  intake  or  the  output  of  the 
body  (Hall). 

A  part  of  the  absorbed  iron  is  used  to  renew  or  increase  the  supply  of  iron 
in  the  stable  compounds,  which  may  have  been  attacked  in  metabolism  (haemo- 
globin), a  part  is  stored  in  the  spleen,  the  liver  and  the  bone  marrow.  In  the 
spleen  iron  occurs  as  an  inclosure  within  the  pulp  cells  (Hall).  According  to 
Xesse,  the  iron  compounds  of  the  spleen  represent  products  which  have  arisen 
by  transformation  of  red  blood  corpuscles.  The  iron-containing  substances  of  the 
liver  are  either  nucleins  (hepatin,  Zoleski)  or  albuminates  (ferratin,  Schneide- 
berg),  or  saltlike  compounds  (Woltering). 

We  have  yet  much  to  learn  as  to  the  way  in  which  the  artificial  supply  of 
iron  affects  the  formation  of  haemoglobin.  It  is  conceivable  that  the  iron 
is  itself  used  in  this  formation,  but  it  is  also  possible  that  the  iron  salts  circu- 
lating in  the  blood  stimulate  powerfully  the  blood-forming  cells  of  the  bone 
marrow. 

Even  with  food  entirely  free  of  iron,  a  regular  elimination  of  this  element 
from  the  body  goes  on,  chiefly  through  the  bile  and  through  the  mucous  mem- 


ABSORPTION   OF   MINERAL  SUBSTANCES  309 

brane  of  the  stomach,  caecum,  colon  and  rectum— although  the  separate  portions 
of  the  intestine  appear  to  participate  to  a  different  degree  in  different  species. 
Elimination  into  the  intestine  appears  to  be  accomplished  by  emigration  of 
leucocytes  and  desquamation  of  epithelial  cells.  In  certain  animals  the  kidneys 
also  take  part  in  the  process  (Hall,  Hochhaus  and  Quincke). 

It  is  asserted  by  Raudnitz  that  the  absorption  of  calcium  and  strontium  takes 
place  chiefly  in  the  duodenum. 


CHAPTER    IX 


RESPIRATION 


The  function  of  respiration  is  to  provide  for  an  exchange  of  gases  be- 
tween the  tissues  and  the  external  air.  The  blood  in  its  circulation  through 
the  lungs  takes  up  oxygen  from  the  alveolar  air  and  gives  off  to  it  gaseous 
products  of  decomposition,  especially  carbon  dioxide.  In  order  to  renew  the 
supply  of  oxygen  and  to  free  the  alveolar  air  of  decomposition  products,  a 
constant  ventilation  of  the  lungs  is  kept  up  by  the  respiratory  movements. 
We  have  therefore  to  study  first  the  movements  of  respiration  and  then  the 
exchange  of  gases  in  the  lungs. 


FIEST    SECTION 

MOVEMENTS  OF   RESPIRATION 

§  1.    ELASTICITY   OF   THE   LUNGS   AND   INTRATHORACIC 

PRESSURE 

The  lungs  are  inclosed  in  an  air-tight  cavity — i.  e.,  between  them  and  the 
thoracic  wall  or  the  other  organs  contained  in  the  thorax  there  is  no  air. 
Since  the  lungs  are  hollow  sacs  with  elastic  and  easily  distensible  walls,  it  is 
obvious  that  they  must  dilate  every  time  the  thorax  is  expanded  and  must 
become  smaller  every  time  it  is  contracted.  Since,  further,  the  lungs  are  in 
open  communication  with  the  external  air  by  the  respiratory  passages,  it 
follows  that  in  the  former  event  air  must  be  sucked  into  the  lungs,  and  in  the 
latter  it  must  be  driven  out.  The  former  phase  of  respiration  is  called 
inspiration,  the  latter  expiration. 

In  the  static  position  of  the  thorax,  the  entire  atmospheric  pressure  takes 
effect  through  the  air  passages  upon  the  inner  surface  of  the  alveoli.  Indi- 
rectly through  the  alveoli  the  air  pressure  acts  upon  the  inner  wall  of  the 
thorax  and  upon  the  organs — heart,  oesophagus,  etc. — lying  between  it  and 
the  lungs.  Since  now  the  lungs  are  elastic,  a  part  of  the  air  pressure  is 
expended  in  unfolding  them,  and  the  pressure  taking  effect  upon  the  inner 
wall  of  the  thorax  must  be  less  than  the  atmospheric  pressure,  by  just  so 
much  as  is  necessary  to  expand  the  lungs.  The  intrathoracic  pressure  is 
therefore  negative.  Again,  the  more  the  thorax  is  dilated,  the  greater  is  the 
amount  of  the  air  pressure  consumed  in  expanding  the  lungs,  consequently 
the  greater  this  negative  pressure  becomes. 
310 


ELASTICITY  OF  THE   LUNGS   AND   INTRATHORACIC   PRESSURE      311 

The  following  methods  have  been  used  for  determining  intrathoracic  pres- 
sure. A  manometer  may  be  connected  terminally  with  the  trachea  of  a  corpse, 
and  the  thoracic  cavity  opened  without  injuring  the  lungs.  Since  the  pressure 
within  and  without  the  lungs  is  thereby  equalized,  the  lungs  contract  in  virtue 
of  their  elasticity,  the  force  of  the  contraction  being  measured  by  the  pressure 
which  the  air  column  exerts  on  the  mercury  of  the  manometer.     This  is  evi- 


Fio.  120. — A  simple  experiment  with  the  lungs  of  a  rabbit  to  illustrate  the  normal  expansion 
and  collapse  of  the  lungs  in  response  to  variations  of  the  intrathoracic  pressure.  When  the 
rubber  membrane  representing  the  diaphragm  is  drawn  down  (A)  a  negative  pressure  is 
produced  inside  the  bell  jar  and  the  air  enters  the  lungs  through  the  glass  tube  tied  into  the 
trachea.  When  the  membrane  is  released  (5)  the  pressure  inside  the  bell  jar  becomes  less 
negative  and  the  lungs  collapse  in  virtue  of  their  own  elasticity,  forcing  the  air  out.  The 
elastic  recoil  of  the  membrane,  which  tends  to  increase  the  pressure  inside  the  jar,  may  be 
taken  to  represent  the  elastic  recoil  of  the  abdominal  wall  (cf.  p.  317).  A  monometer  can 
be  connected  through  a  second  opening  in  the  rubber  stopper  and  the  actual  variations  o£ 
intrathoracic  pre-ssure  demonstrated  at  the  same  time. 


dently  equal  to  the  pressure  which  was  previously  necessary  to  expand  the  lungs 
to  their  original  volume.  If  the  thorax  were  dilated  more  or  less  before  being 
opened,  the  value  of  the  pressure  obtained  on  contraction  would  vary  accordingly 
(Donders). 

The  intrathoracic  pressure  can  be  determined  on  a  living  animal  also,  by 
introducing  a  flattened  cannula  through  a  slitlike  opening  into  the  pleural  cavity, 
care  being  taken  to  prevent  the  entrance  of  air  (Fredericq), 


312  RESPIRATION 

By  the  former  method  the  intratlioracic  pressure  in  man  has  been  found 
to  be:  for  the  normal  expiratory  position.  — 5  to  — 6  mm.  Hg. ;  for  ordinary 
ins])iration,  in  the  neighborhood  of  —8  to  —9  mm.  Hg. ;  for  deepest  inspira- 
tion. —  30  mm.  Hg.  Since  the  intrathoracic  pressure  rises  immediately  after 
death,  theses  figures  may  be  somewhat  too  low  (van  der  Brugh). 

With  the  glottis  open  the  pressure  in  the  pleural  space  is  never  positive. 
But  when  the  glottis  is  closed  and  expiratoi-y  efforts  are  made  so  that  the  air  in 
the  lungs  is  compressed,  the  intrathoracic  pressure  may  become  positive.  But 
in  this  case  also  the  pressure  within  the  lungs  is  greater  than  in  the  pleural 
spaces,  for  even  now  a  part  of  the  air  pressure  is  consumed  in  unfolding  the 
lungs. 

The  effect  of  suction  in  the  thorax  on  the  circulation  has  already  been 
mentioned  (pages  176  and  227).  It  plays  an  important  part  also  in  respira- 
tion. For  the  work  to  be  done  by  the  inspiratory  muscles  is  considerably 
increased  by  this  negative  pressure,  whereas  expiration  is  favored  by  it.  Thus 
since  the  air  pressure  acting  upon  the  inner  wall  of  the  thorax  is  lower  than 
the  atmospheric  pressure  exerted  upon  the  outer  wall,  every  dilatation  of  the 
thorax  is  counteracted  by  a  force  corresponding  to  the  difference  between  the 
outer  and  the  inner  pressure.  If  the  pressure  necessary  to  expand  the  lungs 
be  taken  as  8  mm.  Hg.,  with  an  atmospheric  pressure  of  760  mm.  the  internal 
pressure  would  be  only  752  mm.  Hg.  That  is,  the  inspiratory  effort  at  every 
movable  point  of  the  thoracic  wall  would  be  opposed  by  a  pressure  of  8  mm., 
and  this  resistance  increases  more  and  more  as  the  expansion  increases.  It 
is  obvious  without  further  discussion  that  the  expiratory  contraction  of  the 
thoracic  wall  is  favored  by  the  same  circumstances. 


§  2.    INSPIRATION 

The  expansion  of  the  thorax  is  accomplished  in  two  ways :  by  elevation 
of  the  ribs  and  by  contraction  of  the  diaphragm. 

A.    REGISTRATION   OF  RESPIRATORY   MOVEMENTS 

Some  of  the  methods  in  use  are  for  the  purpose  of  recording  movements  of 
the  thoracic  wall  or  of  the  diaphragm.  The  fonner  can  be  registered  either  for 
man  or  animal  by  fastening  a  receiving  tambour  to  the  chest  wall  by  means  of 
a  girth  of  suitable  form,  and  transmitting  the  pressure  variations  accompanying 
the  respiratory  movements  to  a  recording  tambour.  Fig.  121  represents  a  pneu- 
mographic  curve  obtained  in  this  way. 

Through  a  small  hole  in  the  upper  part  of  the  anterior  wall  of  the  abdomen 
a  spoon-shaped  instrument  may  be  introduced  between  the  diaphragm  and  the 
liver,  and  the  movements  of  the  diaphragm  recorded  by  the  movements  which 
the  instrument  makes  (phrenograph  of  Rosenthal). 

By  still  other  methods  the  volumes  of  inspired  and  expired  air  may  be 
recorded.  To  this  end  tracheotomy  is  performed  on  the  animal,  and  the 
trachea  is  connected  with  a  receiver  of  suitable  size  (Fig.  122,  B),  which  in  its 
turn  communicates  with  a  recording  tambour  of  Marey,  or,  better  still,  with  a 
small  spirometer  (Fig.  122,  A),  or  a  similarly  devised  box  known  as  an  aero- 


IXSPIRATIOX 


313 


Fig.  121. — Pneumographic  curve  of  a  man,  after  LangendorfF.     To  be  read  from  left  to  right. 

E,   expiration,  /,   inspiration. 

pie  thy  Sinograph  (Gad).    In  Fig.  123  is  reproduced  a  respiratory  curve  made  with 
the  apparatus  pictured  in  Fig.  122. 

The  variations  of  intrathoracic  pressure  also  are  used  for  registration  of 
the  respiratory  movements. 

Finally,  the  respiratory  movements  can  be  recorded  with  the  plethysmo- 
graph  by  placing  the  entire  animal  in  a  closed,  air-tight  box  and  allowing 


Fig.  122. — Apparatus  for  registering  the  volume  of  the  respired  air.      B,  receiver;  A,  spirometer; 
e,  writing  point.     The  trachea  of  tlie  animal  is  connected  with  a.     The  openings  at  b  and  c 
serve  to  ventilate  the  receiver. 
20 


314  RESPIRATION 

him  to  brcallio  tlirougli  a  tube  opening  to  the  exterior.  The  respiratory 
movements  are  represented  by  the  variations  in  the  volume  of  the  inclosed 
air  (Hering). 

B.    MOVEMENTS   OF  THE  RIBS 

The  twelve  ribs  (Fig-.  124)  are  thin,  partly  bony,  partly  cartilaginous  hoops 
projecting'  from  each  side  of  the  thoracic  vertebne,  and  bending  outward,  for- 
ward and  downward,  so  as  to  inclose  a  space  called  the  thoracic  cavity.     The 


Fig.  123. — Respiratory  curve  of  a  rabbit.      To  be  read  from  right  to  left.      The    downstroke 
represents  inspiration.      The  lower  tracing  is  a  time  record  in  seconds. 

upper  seven  pairs  are  fastened  in  front  directly  to  the  sternum  along  the  mid- 
line of  the  body,  while  of  the  lower  five  pairs,  two  or  three  unite  with  the  sternum 
indirectly  and  the  others  end  freely. 

Each  rib  is  joined  to  its  vertebra  by  two  articulations,  one  with  the  centrum, 
the  other  with  the  transverse  process.  Hence  the  axes  around  which  the  ribs 
rotate  in  their  movements  are  determined  by  the  relative  position  of  the  two 
articular  surfaces.  According  to  Landerer,  the  axes  of  the  ribs  from  the  first 
to  the  tenth  lie  in  horizontal  planes,  but  are  not  parallel,  the  angles  which  the 
axes  make  with  the  median  plane  being  of  unequal  size.  This  angle  for  the  first 
rib  is  about  80°,  and  decreases  nearly  uniformly  from  the  first  to  the  tenth 
where  it  is  44°.  From  this  follows  a  fact  very  important  for  the  study  of  the 
movements  of  the  ribs,  and  which  has  been  confirmed  also  by  direct  observation, 
namely,  that  the  individual  ribs  by  no  means  describe  identical  arcs.  The  axes 
of  rotation  of  the  last  two  ribs  are  inclined  at  angles  of  10°  and  20°  respectively 
from  the  horizontal,  while  their  intersecting  angles  with  the  median  plane  are 
50°  and  55°  respectively. 

When  the  ribs  are  raised  on  their  axes,  in  the  first  place  the  distance  of 
their  anterior  ends  from  the  backbone  is  increased,  and  in  the  second  place 
the  lateral  parts  of  the  ribs  are  carried  outward.  The  thoracic  cavity  is  en- 
larged therefore  in  both  the  dorso-ventral  and  the  transverse  diameters.  The 
extent  to  which  this  enlargement  takes  place  at  the  level  of  the  individual 
pairs  of  ribs  depends  upon  the  inclination  of  each  and  upon  the  intersecting 
angle  it  makes  with  the  median  plane.  The  greater  the  inclination,  the  greater, 
for  ribs  of  equal  length,  becomes  the  dorso-ventral  enlargement,  and  the  smaller 
the  intersecting  angle  of  the  axis  with  the  median  plane,  the  greater  is  the 
transverse  enlargement. 

In  this  elevation  and  projection  of  ribs  the  sternum  is  of  course  advanced, 
and  this  can  only  be  accomplished  by  its  rotation  about  a  horizontal  axis 
passing  through  the  upper  end  of  the  manubrium.     Since,  moreover,  the  dis- 


INSPIRATION 


315 


tances  of  the  sternal  ends  of  the  different  pairs  of  ribs  from  the  spinal  column 
are  unequal,  the  separate  segments  of  the  sternum  must  be  moved  unequally 
and  must  be  bent  on  each  other;  and,  what  is  more  important,  the  costal 
cartilages  are  thrown  into  a  twist.  Xaturally  this  occasions  some  resistance 
to  the  elevation  of  the  ribs,  which,  in  addition  to  the  resistance  of  their  weight 
and  of  the  negative  pressure  in  the  thoracic  cavity,  must  be  overcome  by  the 
muscles  of  inspiration. 

If  the  ribs  be  moved  out  of  their  natural  position  by  anv  force  and  this 
force  then  cease  to  act,  they  wUI  return  of  themselves  to  the  position  of  rest 
by  reason  of  the  above-mentioned  anatomical  circumstances. 

Since,  therefore,  the  elevation  of  the  ribs  causes  an  expansion  of  the  chest,  we 
shall  designate  as  inspiratory  all  those 
muscles  by  the  contraction-  of  which 
the  ribs  are  raised.  This  is  not  equiva- 
lent to  saying  that  these  muscles  al- 
ways act  in  inspiration.  Some  of  the 
rib-lifting  muscles,  be  it  expressly  ob- 
served, are  active  only  in  very  excep- 
tional cases,  while  in  natural,  quiet 
breathing  only  certain  of  the  muscles 
participate. 

The  most  widely  different  views 
have  been  expressed  from  time  to  time 
as  to  what  muscles  actually  lift  the  ribs. 
This  is  especially  true  of  the  intercostal 
muscles.  In  the  opinion  of  some,  both 
the  external  and  the  internal  intercostals 
are  inspirator^'  muscles,  in  the  opinion 
of  others  both  are  muscles  of  expiration; 
others  again  believe  that  the  external 
tend  to  raise,  the  internal  to  depress  the 
ribs;  and  finally,  the  view  has  been 
maintained  that  these  muscles  are  pres- 
ent only  for  the  purpose  of  regulating 
the  tension  in  the  intercostal  spaces 
and  of  rotating  the  thorax  in  its  long 
axis.  By  observations  on  living  animals 
in  which  all  the  muscles  of  respiration 
were  excluded  except  the  intercostals, 
it   has  now   been   made   clear   that    the 

outer  layer,  as  well  as  that  part  of  the  inner  included  between  the  costal  carti- 
lages, serves  to  elevate  the  ribs,  while  the  remainder  of  the  inner  layer  draws 
the  ribs  down  (Bergendal  and  Bergman,  E,.  Du  Bois-Reymond  and  ^lasoin,  R. 
Fick). 

In  the  rabbit  at  least  the  intercostal  muscles  are  the  most  important  so  far 
as  the  thoracic  breathing  is  concerned.  When  greater  demand  is  made  upon  the 
muscles  of  inspiration,  the  levatores  costanim  and  the  scaleni  are  added  first. 
The  levatores  alone  are  able  to  look  after  the  respiratory  movements  for  a  cer- 
tain time,  and  their  action  in  the  cat  is  very  important  (Koraen  and  B.  Moller). 
Since  these  muscles  are  inserted  quite  close  down  to  the  hinder  ends  of  the  ribs. 


Fig.   124. 


The  thorax  seen  from  the  right 
ide,  after  Spalteholtz. 


316 


RESPIRATION 


they  can,  with  very  slig'ht  contraction,  produce  verj-  marked  movements  of  the 
anterior  ends. 

In  the  rabbit  with  more  vigorous  respiration  the  serrati  postici  superiores, 
the  sternohyoidei  and  the  sternothyroidei  come  into  play.  In  man,  finally, 
Duchenne  has  found  that  in  the  greatest  respiratory  distress  the  following  mus- 
cles are  active:  the  sternocleido  mastoids  which  lift  the  sternum  when  the  head  is 
fixed;  the  pectorales  minores  which  lift  the  third  to  the  fifth  ribs  with  the  scapula 
fixed;  the  serrati  aiitici  magrii,  the  pectorales  majores  and  the  suhclavii. 

C.    MOVEMENTS   OF   THE   DIAPHRAGM 

The  diaphragm  springs  from  the  entire  inner  surface  of  the  lower  edge  of 
the  thoracic  skeleton;  its  fibers  converge  toward  the  axis  of  the  body,  and  attach 
themselves  to  the  flat  tendon  situated  in  the  center  of  the  muscle.     It  presents 


Fig.    125. — Schema,   after  Hasse,   showing  the  movements  of  the  diaphragm,  Hver,  stom.ach, 

and  spleen  in  respiration. 

a  convex  curvature  toward  the  thoracic  cavity,  being,  so  to  speak,  arched  over 
the  convex  upper  surface  of  the  liver. 

When  the  muscle  fibers  of  the  diaphragm  contract,  its  dome-shaped  upper 
part  is  flattened  and  moves  downward.  The  central  tendon  takes  part  in 
the  movement  and  becomes  flattened  because  of  the  pull  of  the  muscle  fibers 
on  all  sides  of  its  periphery.  However,  in  deep  respiration  the  dome  itself 
always  descends  further  than  does  the  center  (Hasse.  Fig.  125).  According 
to  observations  made  with  X  rays  (Cowl),  during  deep  respiration  the  sweep 
of  the  diaphragm  corresponds  to  the  distance  from  the  middle  of  the  tenth 
to  the  upper  edge  of  the  twelfth  thoracic  vertebra.  The  maximal  excursion 
of  the  central  tendon  is  about  -4  cm.  (Gronroos). 

At  the  same  time  by  elevation  of  the  ribs  and  of  the  sternum,  the  lower 
end  of  the  thorax  is  increased  in  diameter  (Duchenne).  This  is  possible 
because  the  abdominal  viscera,  although  depressed  as  an  entire  mass  by  the 
contraction  of  the  diaphragm,  present  their  upper  surface  as  a  fulcrum  on 
which  the  circumference  of  the  diaphragm  is  lifted.  If  the  abdominal  viscera 
be  removed,  when  the  diaphragm  contracts  the  lower  ribs  approach  each  other 
and  the  lower  end  of  the  thorax  is  narrowed. 

By  reason  of  these  changes  the  thoracic  activity  is  enlarged  from  above 
downward  and,  at  the  extreme  lower  end.  is  enlarged  also  from  side  to  side. 


EXPIRATION  317 

With  regard  to  the  relative  importance  of  the  diaphragm  and  the  rib-lifting 
muscles  in  inspiration,  we  find  among  civilized  people  that  in  the  man  the 
diaphragm  plays  a  more  significant  part  than  it  does  in  the  woman.  At- 
tempts have  been  made  to  relate  this  difference  to  the  state  of  pregnancy  and 
the  attendant  growth  of  the  uterus.  But  this  appears  to  l)e  true  only  to  a 
limited  extent,  for  Sewall  and  Pollak  have  found  that  the  respiration  of 
Indian  women  is  plainly  of  the  abdominal  t^'pe.  The  respiration  of  growing 
(European)  girls  is  characterized  by  Gregor  as  a  combination  of  the  abdom- 
inal and  the  thoracic  t}'pes,  with  the  diaphragmatic  part  predominant,  and 
with  weak  action  of  the  shoulder  girdle;  that  of  boys  as  predominantly  tho- 
racic with  strong  action  of  the  shoulder  muscles.  In  forced  respiration  of  boys 
the  chief  auxiliary  mechanism  called  into  play  is  the  shoulder  muscles,  in 
girls  it  is  the  diaphragm.  All  this  means  that  the  actual  cause  of  the  feminine 
type  of  respiration,  often  considered  as  normal,  is  to  be  sought  in  the  com- 
pression of  the  abdomen  by  clothes,  especially  the  corset;  and  this  has  been 
confirmed  directly  by  the  oljservations  of  Fitz.  As  a  consequence  of  this 
compression  a  woman  gradually  acquires  the  costal  type  of  respiration,  until 
finally  it  becomes  normal  for  her. 

We  have  at  present  but  a  single  measurement  of  the  absolute  value  of  the 
diaphragmatic  as  compared  with  the  costal  enlargement  of  the  thorax;  namely, 
out  of  490  c.c.  of  inspired  air  (in  a  man)  about  320  c.c.  devolved  upon  the  eleva- 
tion of  the  ribs  and  only  170  c.c.  on  the  descent  of  the  diaphragm  (Hultkrantz). 

§  3.    EXPIRATION 

In  ordinary  quiet  respiration  the  thorax  appears  to  pass  into  the  expira- 
tory position  principally  by  mere  cessation  of  the  inspiratory  phase.  When 
the  diaphragm  contracts  it  pushes  the  abdominal  viscera  downward  and  pro- 
duces an  increased  tension  of  the  abdominal  wall.  When  it  relaxes,  it  is 
brought  back  to  its  position  of  rest  by  the  elastic  recoil  due  to  this  tension. 
The  ribs  are  brought  back  from  the  inspiratory  position  to  their  position 
of  rest  by  the  force  of  gravity  and  by  the  elasticity  of  the  cartilaginous  con- 
nections between  the  ribs  and  the  sternum.  Both  in  the  abdominal  and  the 
thoracic  types  of  respiration,  the  return  to  the  expiratory  position  is  aided 
by  the  elastic  pull  of  the  hmgs  (cf.  page  311). 

Ordinary  expiration  appears,  therefore,  not  to  require  any  muscular 
effort.  The  fact  that  expiration  does  not  begin  suddenly,  but  gradually, 
can  be  explained  by  saying  that  the  contraction  of  the  inspiratory  muscles 
does  not  cease  all  at  once,  but  rather  slowly.  According  to  some  authors, 
however,  the  internal  intercostal  muscles,  which,  as  we  have  seen,  tend  to 
lower  the  ribs,  are  active  in  ordinary  expiration. 

Under  some  circumstances  expiration  takes  place  by  reason  of  muscular 
activity,  and  the  volume  of  the  thoracic  cavity  is  diminished  considerably 
more  than  is  ordinarily  the  case.  This  kind  of  expiration  is  described  as 
active  to  distinguish  it  from  the  ordinary  or  passive  expiration.  It  is  executed 
chiefly  by  the  abdominal  muscles. 

By  the  contraction  of  these  muscles  (primarily  the  recii  and  external 
oblique,  secondarily  the   internal  oblique,  and  least  of  all   the   tran^versi)   the 


318 


RESPIRATION 


ribs  are  drawn  downward  and  the  abdominal  cavity  is  compressed  so  that  the 
relaxed  diaphragm  is  forced  deeper  into  the  thoracic  cavity.  In  this  way  the 
thorax  is  narrowed  as  much  as  possible  in  all  directions. 

In  Fig.  126  are  represented  according  to  Hasse  two  extreme  types  of 
respiration :  in  A  a  purely  diaphragmatic  type,  and  in  B  a  purely  thoracic 
type.     In  A  no  movement  of  the  thoracic  wall  can  be  recognized,  and  the 


Fig.   126. — A,  a  purely  diaphragmatic  type  of  respiration.     B,  a  purely  thoracic  type,  after 
Hasse.     i,  i,  the  profile  of  the  body  in  inspiration;  e,  e,  the  same  in  expiration. 

anterior  contour  of  the  abdominal  wall  only  is  projected  in  inspiration  (i). 
In  B  the  strong  inspiratory  movement  of  the  thoracic  wall  forward  and 
upward  is  evident.  Because  of  the  passive  elevation  of  the  diaphragm  the 
anterior  wall  of  the  abdomen  is  at  the  same  time  drawn  in;  when  the  ribs 
fall  in  expiration  the  anterior  abdominal  wall  curves  forward  again.  The 
contour  i,  i,  is  the  position  of  inspiration,  the  contour  e,  e,  that  of  expiration. 


§  4.    THE   NUMBER   OF   RESPIRATORY   MOVEMENTS 

In  quiet  breathing  the  number  of  respiratory  movements  in  the  adult  man 
is,  on  the  average,  16  to  19  per  minute;  the  extremes  are  about  11  and  24 
(Quetelet).  With  younger  persons  the  respiratory  frequency  is  greater,  being, 
for  example,  during  the  first  year  on  the  average  44  ( maximum  70,  minimum 
23)  per  minute,  and  during  the  fifth  year  on  the  average  26  per  minute 
(cf.  Fig.  127). 

Various  circumstances,  however,  serve  to  alter  the  respiratory  frequency. 
It  is  increased,  for  example,  by  muscular  work  (see  below),  by  higher  external 
temperature,  or  by  an  elevated  body  temperature,  and  may  reach  a  very  high 
value. 


EXCHANGE  OF  AIR  IN  THE  LUNGS 


319 


§  5.    EXCHANGE    OF   AIR   IN   THE   LUNGS 

The  volume  of  air  taken  in  with  an  ordinary  inspiratory  effort  is  estimated 
for  the  adult  man  at  about  500  c.c.  With  a  frequency  of  16  per  minute  this 
would  give  a  ventilation  volume  (breath  volume,  Rosenthal)  of  8.000  c.c.  = 
S  liters,  per  minute. 

According  to  Gregor,  the  average  breath  volume  of  children  in  the  first 
month  amounts  to  1,300  c.c.  per  minute,  in  the  twelfth  month  3,000,  and  between 
the  second  and  thirteenth  years  it  varies  between  4,000  and  5,000  c.c. 

After  an  inhalation  of  the  average  volume,  a  considerable  quantity  of  air 
can  still  be  taken  into  the  lungs,  and  after  an  ordinary  expiration  a  consider- 
able quantity  can  still  be  expelled  from  the  lungs.  But  if  we  make  the  most 
extreme  expiratory  effort  with  the  assistance  of  all  the  expiratory  muscles, 
there  remains  in  the  lungs  a  certain  quantity  of  air  which,  so  long  as  the 
thorax  is  uninjured,  can  never  be  expelled. 

This  air  left  over  is  called  the  residual  air.     Attempts  have  been  made, 
by  various  methods  which  cannot  be  described  here,  to  determine  it<  amount, 


Fig.  127. — Tlie  number  of  respirations  per  minute  in  persons  of  different  ages,  after  Quetelet. 

and,  if  we  neglect  the  values  which  are  obviously  incorrect,  it  has  been  found 
to  vary  from  500  to  1,(500  c.c.  We  shall  probably  make  no  great  mistake  if 
we  estimate  it  for  the  healthy  adult  man  at  1,000  c.c.  in  round  numbers. 

The  reason  why  the  residual  air  cannot  be  expelled  from  the  lungs  is  simply 
that  when  entirely  collapsed  the  lungs  inclose  a  much  smaller  space  than  does 
the  thorax  contracted  to  its  smallest  capacity.  Since  the  lungs  are  pressed 
against  the  thoracic  wall  by  the  air  inclosed  within  them,  their  volume  cannot 
of  course  be  diminished  beyond  the  volume  of  the  chest  itself.  When,  however, 
the  thoracic  wall  is  opened,  and  the  air  pressure  inside  and  outside  the  lungs  is 
thereby  equalized,  they  collapse  in  virtue  of  their  own  elasticity  and  drive  out 
the  contained  air. 


320 


RESPIRATION 


Even  the  collapsed  lungs  are  not  wholly  empt}'  of  air;  indeed,  a  lung 
which  has  once  respired  can  never  he  entirely  freed  of  its  air  hy  mechanical 
means.  The  reason  of  this  is  that  in  their  collapsed  state  the  walls  of  the 
smallest  bronchioles  press  together  and  thus  prevent  further  exit  of  air  from 
the  alveoli.  This  last  quantity  of  air  is  spoken  of  as  the  minimal  air  (Her- 
numn).  That  volume  of  air  wdiich  can  be  expelled  after  an  ordinary  expira- 
tion amounts  to  about  l.fiOO  c.c.  and  is  called 
the  reserve  air.  If  after  the  usual  tidal  volume 
of  500  c.c.  has  been  inhaled,  inspiration  be  con- 
x,^       I  tinned  further,  one  can  with  the  greatest  pos- 

\/  y\  sible  effort  of  the  inspiratory  muscles  take  in 

some  1,G00  c.c.  more.  This  is  called  the  com- 
plemental  air.  The  sum  of  the  complemental, 
the  tidal  and  the  reserve  air  (1,600 -|- 500 + 
1.600  =  3,700  c.c.)  represents  the  maximal  ex- 
tent of  the  exchange  of  air  possible  with  a 
single  complete  respiration,  and  is  called  the 
vital  capacity  of  the  lungs. 

The  vital  capacity  is  measured  by  first  taking 
as  deep  an  inspiration  as  possible,  and  then  ex- 
haling with  the  help  of  all  the  expiratory  muscles 
into  a  spirometer  (Fig.  128). 

From  the  facts  thus  far  discussed  we  reach 
this  important  conclusion,  that  we  always  have 
the  power  of  increasing  consideratjly  the  quantity 
of  inspired  or  expired  air  without  exhausting  the 
capabilities  of  the  respiratoay  apparatus. 

To  be  able  to  judge  the  effective  result  of 
pulmonary  ventilation,  it  is  of  great  impor- 
tance to  know  whether  the  inspired  air  actually 
reaches  the  alveoli.  The  respiratory  exchange 
of  gases  takes  place  in  the  alveoli ;  but  the  air 
which  remains  in  the  air  passages,  including 
the  smallest  bronchioles,  can  only  contribute  to 
this  exchange  by  diffusion  with  the  alveolar  air, 
and,  in  view  of  the  small  diameter  of  the  small- 
est lironchioles  and  of  the  frequency  with  which 
air  in  the  passages  is  changed,  this  diffusion 
must  be  relatively  insignificant.  The  only  way 
to  determine  whether  air  goes  directly  to  the 
alveoli  is  to  estimate  the  total  capacity  of  the  respiratory  passages  from  the 
nasal  openings  to  the  smallest  bronchioles.  Knowing  already  the  volume  of 
tidal  air,  we  should  then  knoAv  whether  the  air  passages  alone  were  sufficient  to 
accommodate  the  tidal  volume.  Only  two  such  direct  determinations  have 
yet  been  made,  but  according  to  these  the  "  noxious  air  space,"  as  it  has  been 
called,  amounts  to  about  140  c.c.  (Zuntz).  By  an  indirect  method,  the  prin- 
ciples of  which  cannot  be  presented  here,  the  lower  limit  of  this  capacity  is 
said  to  be  about  100  c.c.  and  the  upper  150  c.c.   (Loewy).     Of  the  volume 


Fig.  128. — Spirometer,  after 
Hutchinson.  Tlie  expired  air  is 
blown  into  the  tank  B  through 
the  tube  E.  The  weight  C 
serves  to  offset  tlieweiglit  of  the 
tank. 


PRESSURE  CHANGES   IN  THE   RESPIRATORY   PASSAGES  321 

taken  in  at  each  inspiration  the  greatest  part  therefore  reaches  the  alveoli. 
It  is  evident  that  this  noxious  space  must  exercise  a  greater  influence,  the 
more  superficial  the  respiration. 


§  6.    CONCOMITANT   RESPIRATORY   MOVEMENTS 

Besides  the  muscles  already  considered  as  inflviencing  the  capacity  of  the 
chest,  still  others  are  active  at  the  same  time,  which  are  of  some  importance 
for  normal  respiration. 

Among  these  are  the  muscles  which  move  the  vocal  cords.  In  quiet  respi- 
ration the  glottis  is  rather  widely  open  and  makes  but  slight  movements 
(Czermak).  But  in  more  active  respiration  it  is  widened  by  contraction  of 
the  posterior  cricoarytenoid  muscles  at  each  inspiration.  When  the  muscles 
of  the  vocal  cords  are  paral3'zed,  the  cords  take  an  oblique  position  with  their 
upper  surfaces  directed  outward.  Their  inner  edges  are  thus  separated  but 
slightly  from  one  another  and,  being  relaxed,  are  drawn  toward  each  other 
by  the  current  of  air.  In  young  animals  complete  closure  of  the  glottis  may 
be  produced  in  this  way  and  suffocation  be  the  result  (Le  Gallois). 


§  7.    SPECIAL   FORMS   OF    RESPIRATORY   MOVEMENTS 

The  following'  are  to  be  mentioned  as  special  forms  of  respiratory  move- 
ments: (1)  Coughing,  a  powerful  expiration  produced  reflexly  and  begun  with 
a  closed  glottis,  which  is  then  opened  by  an  explosive  blast  of  air  under  high 
pressure,  whence  the  accompanying  sound ;  (2)  Sneezing,  a  powerful  reflex  expi- 
ration, with  open  glottis  and  the  mouth  cavity  closed  off  from  the  pharynx:  it 
is  often  introduced  by  a  deep  inspiration;  (3)  Laughing,  a  series  of  short  and 
weak  expiratory  blasts  with  lightly  closed  glottis;  (4)  Yawning,  a  deep  inspira- 
tion with  the  glottis  widely  open,  and  as  a  rule  with  the  mouth  open;  (5)  Sigh- 
ing, a  deep  inspiration  followed  by  a  prolonged  expiration  with  partially  closed 
glottis;  (6)  Sohhing  is  distinguished  from  sighing  only  by  the  velocity  of  the 
inspiratory  act;  it  is  usually  accompanied  by  a  spasmodic  ascent  of  the  larynx. 
All  these  forms  of  respiratory  movements  are  produced  reflexly,  or  are  the  accom- 
paniments of  psychical  states  and  are  even  then  to  a  certain  extent  reflex. 


§  8.    PRESSURE   CHANGES   IN   THE    RESPIRATORY   PASSAGES 

On  account  of  the  slight  force  necessary  to  expand  the  lungs,  when  the 
thorax  is  enlarged  they  begin  to  expand  immediately  at  the  beginning  of 
inspiration,  and  the  alveolar  air  naturally  is  at  first  somewhat  rarefied.  With 
the  glottis  open  new  air  flows  in  from  outside ;  but  in  view  of  the  relative 
narrowness  of  the  respiratory  passage  and  the  constrictions  occurring  at  dif- 
ferent places  along  it,  the  inflow  cannot  take  place  instantly,  and  as  a  conse- 
quence one  always  finds  a  negative  pressure  in  the  air  passages  during  the 
inspiratory  phase.  Vice  versa,  when  expiration  takes  place,  the  air  to  be 
exhaled  cannot  escape  immediately;  hence  we  always  find  a  positive  pressure 
in  the  passages  during  the  expiratory  phase. 

With  an  open  glottis  and  a  static  condition  of  the  thorax,  the  tension  of 


322  RESPIRATIOX 

tlie  pulmonary  air  very  quickly  strikes  a  Ijalanco  with  that  of  the  outer  air, 
so  that  we  meet  the  pressure  variations  just  described  only  when  the  capacity 
of  the  lungs  is  being  changed  by  inspiratory  or  expiratory  movements. 

In  order  to  determine  the  absolute  value  of  these  pressure  variations,  a 
T-shaped  cannula  is  introduced  into  the  trachea  of  a  dog,  the  animal  breathes 
as  usual  through  the  uninjured  glottis,  and  the  variations  of  pressure  are  meas- 
ured by  a  manometer  connected  with  the  unpaired  limb  of  the  cannula  (Kramer). 
This  method  has  been  used  also  on  patients  with  a  tracheal  fistula.  With  nor- 
mal persons  either  the  manometer  tube  is  placed  in  one  nostril  and  the  subject 
breathes  through  the  other  (Bonders),  or  he  is  allowed  to  breathe  from  a  wide 
bottle  connected  on  one  side  with  a  manometer  and  on  the  other  by  a  wide 
tubulure  with  the  outside  air  (Ewald). 

It  is  evident  that  the  values  obtained  in  these  experiments  must  be  smaller, 
the  nearer  the  manometer  is  brought  to  the  outer  openings  of  the  respiratory 
passages.  By  the  last-named  method  Ewald  found  a  pressure  of  —0.1  mm. 
Hg.  for  inspiration  and  +  0.13  mm.  for  expiration.  When  Bonders  placed  the 
manometer  tube  in  one  nostril,  he  obtained  for  inspiration  about  —0.7  and  for 
expiration  +  0.5  mm.  Hg.  In  experiments  on  men  with  a  tracheal  fistula,  Aron 
obtained  below  the  glottis  the  value  of  — 1.9  mm.  for  inspiration  and  -(-  0.7  for 
expiration. 

In  order  to  measure  the  force  of  the  different  phases  of  respiration,  a  Hg. 
manometer  is  placed  in  air-tight  connection  with  the  mouth  and  nose  by 
means  of  a  closely  fitting  mask,  and  the  subject  breathes  into  the  apparatus 
(Valentin,  Hutchinson).  Of  course  no  air  can  pass  into  or  out  of  the  lungs, 
but  instead  the  air  already  in  them  is  rarefied  or  compressed  according  as 
the  effort  is  made  to  inhale  or  exhale.  The  pressure  readings  given  by  the 
manometer  may  then  serve  as  relative  expressions  of  the  power  employed  in 
the  two  phases.  By  such  a  method  Hutchinson  found  in  ordinary  breathing 
a  pressure  of  —50  mm.  Hg.  for  inspiration  and  -|-  76  mm.  for  expiration. 
With  the  deepest  possible  inspiration  the  pressure  is  given  at  something  like 
—  110  to  —150  mm.  Hg. ;  for  the  most  intense  expiratory  effort  possible  the 
figures  vary  between  +  108  and  +  256  mm.  Hg. 

On  three  different  individuals  Mosso  determined  the  inspiratory  pressure 
for  pure  costal  and  pure  diaphragmatic  breathing  and  found  the  value  in  the 
former  to  be  from  —32  to  — -40  mm.,  in  the  latter  from  —10  to  —20  mm.  Hg. 
(cf.  page  317). 

§  9.    THE    RESPIRATORY   SOUNDS 

By  auscultation  of  the  lungs  and  of  the  air  passages,  two  different  sounds 
can  be  heard;  namely,  (1)  the  vesicular,  and  (2)  the  bronchial  sound. 

To  imitate  the  character  of  the  vesicular  sound  one  has  only  to  suck  in  air 
through  the  mouth  with  the  lips  pursed:  a  sipping  sound  is  produced  which  is 
almost  exactly  like  the  vesicular  sound.  It  is  said  to  be  produced  at  the  moment 
when  the  air  current  enters  the  alveoli. 

During  expiration  there  is  to  be  heard  in  the  normal  condition  of  the  thorax 
a  weak  and  soft,  indefinite  aspirating  sound  which  shows  no  trace  of  the  sipping, 
vesicular  sound  of  inspiration. 

Over  the  larjmx  one  can  hear  during  both  inspiration  and  expiration  a  very 


THE   EFFERENT   NERVES  323 

loud,  sharp,  aspirating  sound  in  which  h  or  ch  is  the  predominating  component. 
This  laryngeal  sound  is  propagated  along  the  trachea  and  the  two  main  bronchi, 
with  gradually  diminishing  intensity  (the  bronchial  sound). 

§  10.  MEANS  OF  PROTECTION  FOR  THE  LUNGS 

The  air  passages  leading  to  the  lungs  (nasal  cavities,  throat,  trachea  and 
hronchi)  serve  to  protect  the  pulmonary  alveoli  from  various  kinds  of  injuries. 

The  narrowness  of  the  nasal  passages  and  the  hend  which  the  air  passage 
makes  in  the  pharynx  serve  the  useful  purpose  of  freeing  the  inspired  air  very 
largely  of  its  dust  particles  since  the  latter  adhere  to  the  mucus-covered  walls 
of  one  cavity  or  the  other.  This  protection  is  largely  wanting  in  breathing 
by  the  mouth.  The  dust  particles  are  also  driven  outward  by  the  cilia  of  the 
epithelium  lining  the  air  passages.  This  movement,  especially  in  the  parts 
below  the  larynx,  is  of  great  service  in  keeping  the  alveoli  free  of  dust. 

Of  greater  importance  still  is  the  fact  that  the  parts  of  the  respiratory 
passages  below  the  glottis  under  ordinary  circumstances  do  not  permit  the 
development  of  Bacteria :  they  are  either  entirely  sterile  or  they  contain  an 
insignificantly  small  numl)cr  of  Bacteria  (Jundell).  Since  the  tracheal 
secretion  possesses  no  antiseptic  properties,  this  sterility  must  be  accounted 
for  in  some  other  way  as  yet  quite  unknown. 

Only  in  ver}-  exceptional  cases  does  the  inspired  air  have  the  temperature 
of  the  body;  but  the  expired  air  comes  out  warmed  to  the  temperature  of  the 
body  and  saturated  with  moisture.  These  changes  occur  chiefly  in  the  wider 
passageways  so  that  the  bronchi  and  especially  the  delicate  alveoli  are  protected 
from  the  harmful  effects  of  loss  of  heat  and  loss  of  water.  In  fact,  it  has  been 
found  that  when,  by  means  of  an  aspirator,  air  at  10°-12°  C.  is  taken  in  at  one 
nostril  and  passed  out  at  the  other,  entrance  to  the  pharjnix  being  closed,  it 
comes  out  warmed  to  31°  C  and  saturated  with  moisture.  If  the  outside  tem- 
perature be  0°-4°  C,  it  is  warmed  to  27.5°  C.  In  similar  experiments  with 
mouth  breathing,  the  air  reaching  the  pharynx  was  some  0.5°  C.  colder  than 
with  nose  breathing  (Aschenbrandt,  Kayser).  From  these  observations  we  are 
entirely  justified  in  concluding  that  the  air  in  the  middle-sized  bronchi  at  least 
has  acquired  the  temperature  of  the  body,  and  is  immediately  saturated  with 
moisture  at  that  temperature. 

The  closure  of  the  larynx  wliieli  takes  place  in  swallowing  (page  281) 
as  well  as  dilferent  expiratory  reflexes  which  are  to  be  discussed  in  the  fol- 
lowing section  are  essentially  for  the  protection  of  the  lungs. 


SECOND    SECTION 
INNERVATION    OF   RESPIRATION 

§  1.    THE   EFFERENT   NERVES 

Those  muscles  by  the  contraction  of  which  the  thoracic  cavity  is  enlarged 
or  diminished  in  size  (if  we  neglect  the  purely  accessory  muscles)  receive 
their  nerves  from  the  spinal  cord:  the  nerves  to  the  sraJeni  pass  by  way  of  the 


324  RESPIRATION 

second  to  the  seventh  cervical  roots;  those  to  the  levatores  costarum  and  the 
abdominal  muscles  by  the  thoracic  nerves;  those  to  the  diaphragm  chiefly  by 
the  third  and  fourth  cervical  roots  and  the  phrenic  nerve.  According  to 
Luschka  and  Cavalie,  the  edge  of  the  diaphragm  receives  some  fibers  also 
from  the  loAvermost  intercostal  nerves. 

If  the  spinal  cord  be  sectioned  below  the  exit  of  the  last  intercostal  nerves, 
the  operation  evidently  has  no  direct  influence  on  the  respiratory  movements. 
But  if  the  section  be  made  in  the  thoracic  cord,  those  muscles  whose  nerves 
emerge  from  the  spinal  cord  below  the  section  are  paralyzed.  After  section 
above  the  first  intercostal  nerves,  for  example,  the  movements  of  the 
ribs,  with  the  exception  of  those  provided  for  by  the  scaleni  muscles,  cease 
entirely  and  the  animal  now  breathes  only  with  the  diaphragm  and  the 
scaleni. 

With  still  higher  section  of  the  spinal  cord  all  the  muscles  above  named 
are  paralyzed  and  there  remain  only  the  movements  of  the  glottis,  the  mouth 
and  the  nose  (Galen.  Le  Gallois,  Flourens). 

When  the  diaphragm  is  paralyzed  by  bilateral  section  of  the  phrenics,  vari- 
ous disorders  in  respiration  appear,  especially  in  animals  which  breathe  mainly 
by  the  help  of  the  diaphragm.  These  may  be  accounted  for  partly  by  the  fact 
that  the  rib-lifting  muscles  now  have  all  the  work  to  do,  and  partly  by  the  fact 
that  since  the  diaphragm  is  now  relaxed,  the  abdominal  viscera  are  sucked  into 
the  thorax  with  each  inspiration.  However,  no  real  danger  to  life  is  occasioned, 
if  one  is  dealing  with  grown  animals,  which  have  a  rigid  chest  wall  and  strong 
muscles.  Young  animals  die  after  bilateral  section  of  the  phrenics,  because  the 
yielding  chest  wall  and  the  immature  muscles  make  it  impossible  to  dilate  the 
chest,  once  it  has  become  narrowed  by  paralysis  of  the  diaphragm. 

Observations  on  men  have  shown  that  when  all  the  muscles  except  the  dia- 
phragm are  paralyzed,  as  well  as  when  the  diaphragm  alone  is  paralyzed,  life 
may  be  still  maintained.  In  the  latter  case  the  respiratory  frequency  becomes 
greater  than  normal  and  breathing  goes  on,  without  any  participation,  of  the 
accessory  muscles,  under  the  cooperation  of  the  levatores,  the  intercostals  and 
the  scaleni.    Great  bodily  exertion,  however,  results  in  severe  respiratory  distress. 

The  motor  nerves  for  the  muscles  of  the  larynx  and  bronchi  run  in  the 
trunk  of  the  vagus.  Among  the  laryngeal  muscles  the  cricothyroid  is  inner- 
vated from  the  superior  laryngeal,  the  others  from  the  inferior  laryngeal. 

It  was  asserted  by  Longet  (18-42)  that  the  bronchial  muscles  also  are 
under  the  influence  of  the  vagus.  This  statement  was  often  disputed  by  later 
authors,  but  it  has  been  established  by  the  newer,  much  improved  technique 
that  the  vagi  do  in  fact  produce  contraction  of  the  bronchial  muscles,  and, 
especially  in  the  cat,  contain  inhibitory  fibers  also  for  these  muscles. 

The  bronchial  muscles  of  the  dog  are  under  weak  tonic  stimulation,  those 
of  the  horse  under  a  strong  tonus;  they  are  influenced,  feelfly  as  a  rule, 
by  various  afl'erent  nerves,  both  contraction  and  relaxation  appearing  as  the 
results  of  stimulation.  The  most  important  broncho-constrictor  reflexes  ap- 
pear to  be  started  from  the  mucous  membrane  of  the  respiratory  passages 
(nose,  lar\Tix),  and  may  possibly  be  regarded  as  protective  reflexes,  for  the 
narrower  the  bronchi  become  the  more  likely  is  the  dust  of  the  air  to  adhere 
to  their  walls. 


THE   RESPIRATORY  CENTER  325 

The  chief  service  of  the  bronchial  muscles  is  that  when  the  intrabronchial 
pressure  rises,  they  give  by  their  contraction  a  greater  degree  of  firmness  to 
the  bronchial  walls. 

The  mucous  glands  of  the  larynx  and  of  the  trachea  receive  their  nerve 
fibers  through  the  laryngei  nerves.  In  these  also  are  afferent  fibers  which  pro- 
duce a  reflex  secretion  of  mucus  in  the  larynx  and  trachea  (Kokin). 


§  2.    THE   RESPIRATORY   CENTER 

Since  in  the  movements  of  respiration  a  large  number  of  muscles  contract 
in  a  definite  sequence,  it  is  to  be  assumed  in  conformity  with  our  present 
views  of  innervation,  that  somewhere  in  the  central  nervous  system  is  a  center 
controlling  these  movements. 

From  the  fact  that  these  movements  do  not  cease  when  the  brain  is  cut 
through  as  high  up  as  the  pons,  it  follows  that  the  respiratory  center  must 
be  situated  below  that  point — i.  e.,  not  higher  than  the  medulla.  When  such 
a  section  is  made,  the  diaphragm  stops  for  a  moment,  but  begins  of  itself 
to  contract,  and  continues  quite  regularly  unless  some  unintentional  lesion 
has  occurred. 

When,  on  the  other  hand,  the  medulla  is  separated  from  the  spinal  cord, 
respiration  ceases.  Galen  knew  that  in  the  upper  part  of  the  spinal  cord  there 
is  a  place  the  destruction  of  which  at  once  stopped  respiration,  and  Le  Gallois 
(1812)  showed  that  this  spot  is  in  the  medulla.  For  a  long  time  it  was 
generally  agreed  that  the  respiratory  center  was  to  be  sought  only  in  the 
medulla.  Eecently,  however,  it  has  been  claimed  with  great  positiveness  that, 
although  there  is  a  regulatory  apparatus  in  the  medulla,  the  true  centers  for 
the  respiratory  movements  are  to  be  sought  in  the  spinal  cord,  and  the  advo- 
cates of  this  doctrine  go  so  far  as  to  say  that  the  nuclei  of  the  respiratory 
nerves  are  stimulated  simultaneously  by  the  blood,  thus  giving  the  impulse 
for  a  coordinated  respiratory  activity  (Brown-Sequard,  Langendorff,  Wert- 
heimer).  The  stoppage  of  respiration  after  section  of  the  cervical  cord  would, 
in  their  opinion,  be  due  not  to  separation  of  the  respiratory  nerves  from  their 
center,  but  to  the  shocklike,  inhibitory  effect  of  the  section. 

There  are  numerous  experiments  which  show  that  direct  stimulation  of  the 
spinal  cord  with  electricity  or  by  mechanical  means  may  stop  respiration,  and 
the  view  just  mentioned  is  well  supported  by  such  facts.  But  it  is  at  present 
impossible  to  decide  how  long  such  an  effect  of  shock  may  last.  If  an  animal 
whose  cord  has  been  sectioned  in  the  neck  be  maintained  by  artificial  respira- 
tion, it  can  be  kept  alive  for  hours.  But  if  the  animal  still  does  not  breathe 
spontaneously  one  cannot  refute  the  claim  that  shock  still  persists. 

In  cases  where  artificial  respiration  is  first  maintained  for  a  long  time, 
rhythmical  respiration  has  been  observed  on  animals  with  the  cord  severed  in 
the  neck.  Some  of  the  first  observations  of  this  kind  were  made  on  newly  born 
animals  and  some  on  animals  whose  reflex  irritability  had  been  artificially  in- 
creased with  strj-chnia  (Rokitansky,  Langendorff).  Later  Wertheimer  succeeded 
in  obtaining  spinal  respiration  in  grown  animals  which  had  not  been  poisoned. 
But  when  spinal  respiration  does  appear  it  is  never  of  the  same  extent  as  that 
controlled  from  the  medulla,  and  it  continues,  so  far  as  is  yet  known,  at  most 


326  RESPIRATION 

for  only  three-quarters  of  an  hour.  Often  it  cannot  be  induced  at  all.  The 
animal  reacts  unusually  well  to  all  kinds  of  sensory  stimuli  causing  reflex  mus- 
cular contractions,  and  the  spinal  vasomotor  centers  react  powerfully  to  the 
stimulus  of  asphyxiation.  The  eifect  of  shock  therefore  is  past ;  and  yet  as  a 
rule  one  observes  no  genuine  respiration.  To  maintain  the  doctrine  of  the  pre- 
ponderance of  spinal  respiratory  centers  under  such  circumstances,  one  must 
assume  that  these  centers  react  toward  shock  in  quite  another  way  from  the 
other  spinal  centers. 

The  fact  that  hemisection  of  the  spinal  cord  very  often  does  not  result  in 
cessation  of  the  respiratory  movements  of  the  same  side  (Brown-Sequard 
et  al.)  speaks  against  the  hypothesis  of  shock.  Moreover,  when  cessation  does 
occur,  it  is  immediately  nullified  if  the  phrenic  of  the  opposite  side  be  cut 
(Porter).  If  the  mechanical  injury  of  sectioning  were  to  produce  so  strong 
a  shock,  as  the  advocates  of  the  spinal  centers  assume,  hemisection  of  the 
spinal  cord  should  stop  the  respiratory  movements  on  the  side  of  the  section 
for  a  time  at  least. 

We  reach  the  conclusion  therefore  that  the  medulla  is  not  only  of  great 
importance  in  the  regulation  of  respiratory  movements,  but  that  it  controls 
also  the  codrdinated  activity  of  the  respiratory  muscles.  Only  in  rare  cases 
is  such  an  effect  carried  out  by  the  nuclei  of  the  spinal  cord,  and,  although 
we  can  speak  in  general  terms  of  spinal  respiratory  centers,  it  appears  that 
in  comparison  with  those  of  the  medulla  they  have  but  little  to  do  with 
producing  the  normal  stimuli. 

The  exact  location  of  the  respiratory  center  in  the  medulla  is  not  yet 
definitely  known.  This  much  appears  certain,  however,  that  it  is  not  a  small, 
circumscril^ed  spot,  but  is  a  region  of  relatively  large  extent.  This  is  what 
we  should  expect  in  view  of  the  very  large  number  of  nervous  connections 
which  it  has. 

After  median  section  of  the  medulla,  the  respiratory  movements  of  the  two 
halves  of  the  diaphragm  (Langendorif)  and  those  of  the  vocal  cords  and  the 
nose  (Kreidl)  continue  synchronously — which  shows  that  the  influences  origi- 
nating the  respiratory  movements  proceed  simultaneously  on  the  two  sides  of 
the  center.  But  this  synchronism  is  abolished  by  section  of  both  vagi,  and  each 
half  of  the  body  then  breathes  independently  of  the  other. 

That  section  of  the  vagus  on  one  side  does  not  always  stop  the  synchronism 
just  mentioned,  goes  to  show  that  the  two  centers  are  connected  by  commissural 
fibers.  The  presence  of  a  crossed  connection  between  the  respiratory  center  and 
the  nuclei  of  the  respiratory  muscles  follows  also  from  the  above-mentioned 
facts,  that  respiration  can  proceed  undisturbed  on  one  side  after  hemisection  of 
the  cord  on  that  side  and  section  of  the  phrenic  on  the  opposite  side. 

The  respiratory  movements  can  be  influenced  also  by  stimulation  of  parts 
of  the  brain  anterior  to  the  mednJJa.  Martin  and  Booker  obtained  inspiratory 
effects  by  stimulating  the  surface  of  a  section  between  the  anterior  and  posterior 
corpora  quadrigemina ;  Christiani  obtained  the  same  on  stimulation  of  the 
floor  of  the  third  ventricle,  and  expiratory  effects  on  stimulation  of  the 
entrance  of  the  aqueduct  of  Sylvius.  Finally,  the  cerel)ral  cortex  evidently 
exercises  control  over  the  respiratory  movements,  as  is  seen,  for  example, 
in  the  extremely  fine  gradations  of  these  movements  which  can  be  executed 


RESPIRATORY   REFLEXES  327 

by  a  good  singer.  Respiratory  movements  can  be  accelerated  or  retarded  1)Y 
electrical  stimulation  of  the  motor  cortex  of  the  dog  and  cat.  The  result, 
according  to  F.  Franck,  does  not  depend  upon  the  place  of  stimulus,  but  upon 
its  strength:  strong  stimulus  giving  a  retardation,  weak  stimulus  an  acceler- 
ation. The  depth  of  respiration  also  is  changed  in  one  direction  or  the  other. 
These  parts  of  the  brain  act  only  through  the  mediation  of  the  respiratory 
center  in  the  medulla;  the  fibers  running  from  them  to  the  center  are  there- 
fore to  1)6  regarded  as  afferent  pathways.  The  warrant  for  this  view  lies  in 
the  fact  already  mentioned,  that  the  respiratory  movements  continue  after 
section  above  the  medulla.  Moreover,  it  is  not  to  l)e  denied  that  some  of  the 
results  just  discussed  can  be  obtained  by  stimulation  of  the  conducting  path- 
ways. The  so-called  brain  centers  for  respiration  seem  therefore  to  represent 
only  pathways  to  the  center  in  the  medulla.  We  shall  see  immediately  that 
these  paths  and  certain  parts  of  the  brain  are,  under  certain  circumstances, 
of  great  service. 

§  3.    RESPIRATORY   REFLEXES 

Like  all  the  other  more  complicated  processes  of  the  body  the  respiratory 
movements  are  influenced  by  all  possible  kinds  of  afferent  nerves.  But  there 
are  two  of  these  paths  more  important  than  the  rest,  namely  (1)  the  vagus, 
and  (2)  the  fibers  which  connect  the  higher  parts  of  the  brain  with  the 
respiratory  center.     These  accordingly  we  must  consider  first. 

A.    REFLEXES  THROUGH   THE  VAGI 

Notnnthstanding  the  voluminous  literature  that  has  accumulated  on  the 
influence  of  the  afferent  vagus  fibers,  our  knowledge  of  their  action  on  respira- 
tion is  still  very  meager.  The  statements  of  authors  as  to  the  facts  l)earing 
on  even  the  most  important  points  differ  consideral)ly,  and  we  can  therefore 
present  the  action  of  the  vagus  on  respiration  only  in  the  broadest  outline. 

Generally  speaking,  in  the  investigation  of  the  influence  of  any  nerve  on 
the  processes  of  the  l)ody  one  ol)tains  the  best  results  by  direct  stimulation 
of  the  nerve.  Unfortunately  this  is  not  the  case  with  the  pulmonary  vagus, 
for  section  of  the  nerve  is  followed  hy  much  more  profound  effects  than  its 
stimulation. 

A  nerve  cannot  be  cut  with  a  pair  of  scissors  without  at  the  same  time 
stimulating  it.  Besides,  an  electric  current  (demarcation  current,  see  page  48) 
is  set  up  in  a  cut  nei-ve,  and  this  may  possibly  exercise  a  stimulating  influence. 
Gad  has  shown,  however,  that  the  pulmonarv  vagi  can  be  thrown  out  of  action 
without  stimulation  by  cooling  them  sufficiently.  For  this  purpose  the  vagi  are 
laid  upon  silver  tubes  which  are  filled  with  a  cold  mixture  (e.  g.,  a  solution  of 
ammonium  nitrate  in  water). 

Even  under  such  circumstances  different  authors  have  not  ol)tained  per- 
fectly harmonious  results,  although  all  are  agreed  that  after  bihtteral  blocking 
of  the  vagus  (1)  the  respiratory  frequency  falls,  (2)  that  the  inspirations 
become  deeper  and  (3)  that  the  summit  of  inspiration  shows  a  pause  of 
greater  or  less  length  (Fig.  129).    But  with  respect  to  expiration  after  double 


328 


RESPIRATION 


vagotomy,  views  are  very  divergent :  Gad  asserts  that  it  no  longer  reaches  its 
former  level,  whereas  Lindhagen  has  found  that  the  relaxation  of  the  in- 
spiratory muscles  is  diminished  little  or  none  at  all,  and  Boruttau  remarks 
that  sooner  or  later  expiration  reaches  the  same  height  as  before  freezing  the 
vagi.  According  to  Gad  and  Lindhagen,  the  expiratory  pause  is  nearly  always 
shortened,  according  to  Boruttau  it  is  the  same  as  before  or  even  a  little 
longer.  These  statements  all  apply  to  the  rabbit.  In  the  dog,  after  freezing 
of  the  vagi,  the  expirator}^  muscles  fall  into  a  state  of  almost  regular  activity 
(Boruttau).  The  breath  volume  also,  according  to  Gad,  becomes  smaller  after 
freezing  the  vagi ;  according  to  Lindhagen,  it  remains  on  the  whole  unchanged. 


u  y 


i^nrunj" 


rrrinnnrw 


Fig.  129. — The  respirator}'  curve  of  a  rabbit  recorded  witli  the  apparatus  showTi  in  Fig.  122, 
after  Lindhagen.  To  be  read  from  left  to  right.  The  downstroke  representing  inspiration. 
The  lower  tracing  is  a  time  record  in  seconds.  At  the  vertical  hne  the  two  vagi  were 
"  blocked  "  by  freezing. 

These  discrepancies  depend  in  part  at  least  upon  the  species  of  animal 
used  in  the  experiment,  in  part  upon  the  depth  of  narcosis  and  upon  other 
circumstances  not  yet  fully  understood.  We  shall  soon  see,  however,  that 
they  can  be  explained  without  great  difficulty  (cf.  page  330). 

This  much,  at  all  events,  is  well  established  by  the  experiment  of  discon- 
necting the  vagi  by  rendering  them  nonirritable,  that  the  control  exercised  by 
those  nerves  is  such  as  to  induce  respiratory  acts  of  greater  frequency  and  of 
less  depth  than  otherwise,  and  that  the  inspiratory  pause  is  thereby  prevented. 
Since  this  inspiratory  pause  is  not  of  the  least  service  in  the  ventilation  of 
the  lungs,  and  the  contraction  of  the  muscles  of  inspiration  maintaining  it 
is  therefore  of  no  use  whatever,  it  is  evident  that  even  when  the  breath  volume 
before  and  after  disconnection  of  the  vagi  is  the  same,  respiration  afterwards 
is  carried  on  with  greater  effort  than  normally.  The  result  achieved  by  the 
vagus  reflex,  therefore,  is  that  respiration  takes  place  with  less  expenditure 
of  energy. 

The  investigations  of  Hering  and  Breuer  have  yielded  some  very  valuable 
results  as  to  the  way  in  which  that  regulation  is  accomplished.  Artificial 
inflation  of  the  lungs  inhibits  the  inspiratory  muscles  and  induces  an  act  of 
expiration ;  collapse  of  the  lungs  calls  out  an  act  of  inspiration.  Self-regula- 
tion of  the  respiratory  movements  would  thus  seem  to  l)e  afforded  by  the  vagi 
— i.  e.,  when  the  lungs  have  expanded  to  a  certain  extent  inspiration  is  re- 
flexly  interrupted,  and  when  they  are  afterwards  emptied  to  a  certain  extent, 
expiration  is  interrupted  and  an  act  of  inspiration  is  reflexly  induced.  Both 
phases  of  the  regulation  are  lost  when  the  vagi  are  sectioned. 


RESPIRATORY  REFLEXES  329 

We  may  conceive,  therefore,  that  the  peripheral  endings  of  the  afferent  pul- 
monary fibers  of  the  vagi  are  excited  by  the  variations  in  the  volume  of  the 
lungs,  and  this  is  confirmed  by  the  fact  that  if  the  vagus  be  cut  on  the  one  side 
and  the  lung  on  the  other  side  be  caused  to  collapse  by  puncture  of  the  pleural 
cavity,  we  get  the  same  result  as  after  section  of  both  vagi  (Loewy). 

Any  more  precise  explanation  of  these  facts  is  very  difficult  to  give.  It  has 
been  supposed  that  there  are  two  kinds  of  fibers  in  the  vagiis,  one  of  which 
serves  to  mediate  an  inspiratory  effort,  the  other  an  expiratory  effort.  But  it 
is  also  possible  to  suppose  that  there  is  but  a  single  kind  of  fibers  and  that  the 
effect  produced  depends  upon  the  momentary  condition  of  the  respiratory  center. 
Thus,  if  the  center  already  roused  to  inspiratory  action  were  affected  by  a 
stimulus  arriving  over  the  vagus,  it  might  be  inhibited,  and  the  result  of  stop- 
ping the  inspiratory  movements  might  be  to  inaugurate  the  relatively  passive 
movements  of  expiration.  Then  after  expiration  proceeds  to  a  certain  stage, 
the  collapsing  lungs  might  send  up  a  stimulus  by  the  vagus  and  the  inspiratory 
phase  would  be  started  because  the  respiratory  center  at  that  particular  instant 
was  in  a  condition  to  discharge  such  an  impulse.  We  have  as  a  matter  of  fact 
some  data  which  can  be  harmonized  very  well  with  this  conception  of  the  way 
in  which  the  respiratory  center  works  (cf.  Chapter  XXII).  But  there  is  still 
another  explanation  possible,  namely,  that  the  respiratory  center  constantly  tends 
to  discharge  inspiratory  impulses,  but  this  tendency  is  inhibited  by  an  impulse 
resulting  from  the  inflation  of  the  lungs;  that  after  the  lungs  have  collapsed  to 
a  certain  extent,  the  inhibition  is  then  removed  and  the  tendency  to  inspiration 
once  more  asserts  itself.  This  explanation  is  strongly  supported  by  the  observa- 
tion made  by  Lewandowsky,  that  inflation  of  the  lungs  is  accompanied  by  an 
action  current  in  the  vagus,  but  that  collapse  is  not. 

Artificial  stimulation  of  the  central  cut  end  of  the  vagus  ought,  one  would 
think,  to  give  a  definite  answer  to  this  question  as  to  the  mode  of  action  of  the 
nerve.  But  it  does  not.  For  in  the  many  experiments  of  this  kind  which  have 
been  made,  both  inspiratory  and  expiratory  effects  of  stimulation  have  been 
observed,  and  the  statements  of  authoi-s  differ  so  much  that  it  is  impossible  as 
yet  to  draw  any  definite  conclusion  from  them.  Still  less  is  it  possible  to  decide 
from  these  experiments  whether  one  or  two  kinds  of  nerve  fibers  are  concerned. 

B.    FIBERS  FROM  ANTERIOR  PARTS  OF  THE   BRAIN  TO   THE  MEDULLA 

We  have  already  seen  that  the  brain  can  be  sectioned  above  the  medulla 
without  affecting  respiration  to  any  considerable  extent.  If.  however,  the 
vagi  be  sectioned  in  such  an  animal,  or  if  the  brain  be  sectioned  above  the 
medulla  in  an  animal  whose  vagi  have  already  been  cut,  noteworthy  alterations 
of  the  respiratory  movements  ensue.  Respiration  is  greatly  diminished  in 
frequency,  since  the  inspiratory  pauses  are  now  very  much  prolonged.  In- 
spiration becomes  spasmodic,  expiration  begins  very  suddenly  and  not  infre- 
quently is  aided  by  contraction  of  the  abdominal  muscles.  The  expiratory 
pause  is  of  short  duration,  being  soon  interrupted  by  a  new,  long-drawn  in- 
spiration. The  breath  volume  is  very  much  diminished  and  the  animal  dies 
for  want  of  sufficient  respiratory  exchange  in  the  lungs  (Marckwald).  These 
phenomena  may  appear  in  varying  degree,  and  it  is  even  stated  that  the 
inspiratory  spasms  may  be  at  times  entirely  wanting  after  this  operation. 

The  respiratory  center  isolated  from  the  higher  parts  of  the  brain  may  there- 
fore maintain  respiration  in  an  essentially  normal  fashion  even   after  section 


330  RESPIRATION 

of  both  vagi,  although  it  is  very  often  unable  to  do  so.  At  any  rate,  it  appears 
from  these  facts  that  the  paths  coming  from  the  brain  are,  under  certain  cir- 
cumstances, of  very  great  importance  for  respiration,  and,  what  is  more,  that 
they  act  in  the  same  way  as  the  vagi  nerves — i.  e.,  to  inhibit  inspiration.  Expla- 
nation of  these  phenomena  is  rendered  more  difficult  because  we  cannot  tell  yet 
to  what  extent  they  depend  upon  the  stimulus  given  at  the  time  the  section  is 
made,  and  to  what  extent  upon  the  mere  disconnection  of  the  pathways. 

In  view  of  the  profound  infiuence  of  these  brain  pathways  over  the  move- 
ments of  respiration,  it  is  not  difficult  to  understand  why  the  severance  of  the 
vagi  is  not  always  accompanied  by  the  same  results;  for  the  effect  must  depend 
largely  upon  the  state  of  excitability  of  these  brain  paths  at  the  time.  For 
example,  it  is  possible  that  the  shortening  of  expiration  and  the  tonic  contrac- 
tion of  the  inspiratory  muscles  mentioned  by  Gad  (but  not  observed  by  others), 
was  due  to  a  stronger  narcosis,  on  account  of  which  the  influence  of  the  pathways 
in  the  brain  was  somewhat  weaker  than  in  the  investigations  of  the  other  authors. 


C.    OTHER   RESPIRATORY   REFLEXES 

The  respiratory  movements  are  influenced  in  one  way  or  another  by  other 
afferent  nerves.  Among  these  the  nerves  of  the  respiratory  passages  are  of 
the  greatest  interest,  because  through  them  certain  reflexes  are  discharged 
which  are  of  great  service  as  a  means  of  protection  to  the  lungs. 

The  nasal  openings  and  the  mucous  membrane  of  the  nasal  passages  re- 
ceive their  sensory  fibers  from  the  trigeminal  nerve.  Stimulation  of  this 
nerve  retards  respiration.  When  the  raucous  nieml)rane  of  the  nose  is  stimu- 
lated at  the  external  openings  or  on  the  anterior  or  posterior  end  of  the  middle 
and  lower  turbinated  bones,  or  on  the  corresponding  parts  of  the  septum, 
retardation  or  expiratory  standstill,  or  even  sneezing,  results,  according  to  the 
strength  and  the  kind  of  stimulus  employed.  Sneezing  may  also  be  abortive 
— i.  e.,  only  the  first  phase  of  it.  the  deep  inspiration,  may  occur.  Expiratory 
standstill  may  also  be  induced  by  stimulation  of  the  skin  of  the  face  under 
certain  circumstances,  as  when  an  animal's  head  is  submerged  in  water 
(Fratschmer). 

Inasmuch  as  these  reflexes  prevent  the  entrance  of  foreign  l)odies  or  of 
noxious  vapors  into  the  wider  respiratory  passages,  the  afferent  nerves  of  the 
larynx,  particularly  the  superior  lar^-ngeal,  serve  to  protect  the  deeper  respir- 
atory passages  from  foreign  bodies.  With  feeble  stimulation  of  the  superior 
laryngeal  slowing  of  respiration  and  prolongation  of  the  expiratory  pause  are 
obtained ;  on  this  account  the  individual  respirations  become  deeper  and  longer. 
With  stronger  stimulation  one  may  obtain  expiratory  standstill  or  active  ex- 
piratory movements.  Inspiratory  spasms  can  be  stopped  by  stimulation  of  the 
superior  laryngeal. 

The  coughing  reflex  is  discharged  principally  by  the  same  nerve.  The 
statements  of  authors  do  not  agree  entirely  as  to  the  places  in  the  larynx 
and  trachea  from  which  the  reflex  is  produced. 

We  have  the  following  statements  concerning  the  effect  of  other  afferent 
nerves.  Stimulation  of  the  olfactory  by  an  actual  odor  either  slows  or  quickens 
respiration  or  gives  an  expiratory  pause.  Stimulation  of  the  optic  by  electricity 
or  by  light  has  an  accelerating  effect  on  inspiration.     The  auditory  nerve  has 


NORMAL  STIMULATION   OF   THE   RESPIRATORY  CENTER  331 

the  same  effect.  After  destruction  of  the  semicircular  canals  respiration  becomes 
slower  and  deeper.  According  to  Marckwald,  the  glossopharyngeal  produces 
respiratory  standstill  in  whichever  phase  the  respiratory  center  happens  to  be 
overtaken  by  the  stimulus,  but  according  to  others  it  behaves  just  like  the  other 
cutaneous  nerves.  The  last  named  have  an  inspiratory  effect  with  weak  stimu- 
lation, and  an  expiratory  effect  with  strong  stimulation.  The  phrenic  also  eon- 
tains  afferent  fibers  which  appear  to  act  like  the  cutaneous  nerves,  and  other 
afferent  muscular  nerves  behave  on  the  whole  like  these.  With  regard  to  the 
sympathetic  nerves  it  is  stated  that  the  splanchnic  causes  only  an  expiratory 
contraction  and  that  the  cervdcal  sympathetic  influences  both  phases  of  respira- 
tion. Finally,  by  stimulation  of  the  heart  and  of  the  aorta,  reflex  respiratory 
movements  and  contractions  in  the  air  passages  have  been  obtained. 


§  4.    NORMAL   STIMULATION   OF   THE    RESPIRATORY   CENTER 

Seeing  then  that  the  respiratory  center  is  reflexly  influenced  by  the  most 
widely  different  afferent  nerves,  it  would  be  natural  to  suppose  that  it  is 
roused  to  action  only  in  the  reflex  manner.  But  this  conclusion  is  not 
warranted.  We  have  already  seen  indeed  that  the  respiratory  center  isolated 
from  the  brain  pathways  on  a  vagotomized  animal  is  still  very  powerfully 
active.  This  might  be  due  partly  to  the  stimulating  effect  of  the  section  and 
partly  to  the  afferent  impulses  still  reaching  the  center.  But  respiratory 
movements  continue  when  the  cerebrum  is  extirpated,  the  vagi  cut  and  the 
spinal  cord  sectioned  below  the  exit  of  the  respiratory  nerves  (Rosenthal). 
It  can  scarcely  be  assumed  that  the  respiratory  movements  are  called  out  by 
the  few  afferent  impulses  remaining  after  all  these  operations.  Besides  there 
are  still  other  facts  which  tend  to  prove  that  the  excitation  of  the  respiratory 
center  is  attrihutahh  mainly  to  the  properties  of  the  hlood. 

The  foetus  in  the  uterus  does  not  breathe:  respiration  begins  only  after 
birth.  What  is  the  cause  of  the  very  first  act  of  respiration  ?  The  blood  of  the 
foetus  is  arterialized,  so  long  as  the  placental  circulation  is  maintained,  at  the 
expense  of  the  mother's  blood.  The  temperature  of  the  amniotic  fluid  in  which 
the  foetus  is  submerged  is  exactly  the  same  as  that  of  the  foetus  itself,  so  that 
it  is  not  subjected  to  any  temperature  stimuli  nor  to  any  other  cutaneous 
stimuli.  At  birth  the  circumstances  of  life  change  suddenly:  the  placental  cir- 
culation ceases  and  the  skin  is  subjected  to  different  sensory  stimuli.  The  cause 
of  the  first  act  of  respiration  is  to  be  sought  therefore  either  in  the  cessation  of 
the  placental  circulation  or  in  the  sensory  stimulation  of  the  skin. 

Both  these  possibilities  have  their  advocates.  But  from  the  present  infor- 
mation it  would  seem  that  the  discontinuance  of  the  placental  circulation  is 
the  real  determining  factor.  It  is  true  that  one  can  produce  various  motor 
reflexes,  and  respiratory  movements  among  them,  by  means  of  cutaneous  stimuli 
applied  while  the  placental  circulation  is  still  continuous.  But  such  responses 
are  both  infrequent  and  temporary'  in  character.  Besides,  cutaneous  stimulation 
may  be  kept  up  for  a  long  time  without  ever  a  sign  of  a  respiratory  movement. 
Contrast  with  this  the  result  of  destroying  the  placental  circulation.  However 
the  experiment  be  performed,  whether  by  clamping  or  bleeding  the  umbilical 
cord,  or,  the  uterus  being  undisturbed,  by  poisoning  the  mother  with  carbon 
dioxide  or,  finally,  by  bleeding  the  mother,  respiratory  movements  of  the  foetus 
are  always  obtained. 


332  RESPIRATION 

If  then  the  first  act  of  respiration  be  induced  by  some  property  of  the 
blood,  it  follows  with  a  high  degree  of  prol^ability  that  the  respiratorij  renter 
is  roused  to  activity  in  the  same  way  throughout  life.  This  is  confirmed  also 
by  a  large  number  of  experimental  facts.  Thus  it  has  been  shown  that  every- 
thing that  tends  to  heighten  the  combustion  in  the  body  or  to  render  more 
difficult  the  elimination  of  the  gaseous  products  of  decomposition  or  the 
absorption  of  oxygen,  produces  an  augmented  respiration.  This  condition  of 
things  is  described  as  dyspncea,  if  it  involves  the  cooperation  of  the  accessory 
muscles  of  respiration. 

One  might  conceive  that  the  products  of  combustion  present  in  the  blood 
in  increased  quantity  stimulate  the  end  arborizations  of  the  afferent  nerves, 
and  that  the  augmented  respiration  now  under  consideration  is  therefore 
reflex  in  nature.  Even  if  this  were  true,  experiment  has  shown  in  the  clearest 
possible  manner  that,  in  muscular  work,  for  example,  the  increased  respiration 
is  not  due  to  this  cause  alone;  for  it  appears  when  the  hinder  parts  of  the 
body,  cut  off  from  every  possible  nervous  communication  with  the  fore  parts, 
are  stimulated  to  active  contractions,  but  is  entirely  wanting  if  the  return 
flow  of  blood  from  the  hinder  parts  is  prevented.  The  blood  returning  from 
the  posterior  active  parts  has  therefore  a  direct  stimulating  effect  upon  the 
respiratory  center  (Zuntz  and  Geppert). 

Finally  it  has  been  shown  that  the  respiratory  movements  react  very  deli- 
cately to  any  change  in  the  carbon-dioxide  content  of  the  blood,  since,  the 
respiratory  frequency  remaining  almost  unchanged,  the  breath  volume  of 
the  individual  respirations  increases  with  an  increasing  quantity  of  CO,  in 
the  inspired  air  (Miescher).  On  the  other  hand,  considerable  changes  in  the 
oxygen  content  of  the  surrounding  air  (12.5  to  60  volumes  per  cent)  influence 
the  respiration  relatively  little. 

We  conclude,  therefore,  that  the  respiratory  center  is  excited  by  the  direct 
effect  of  the  blood  or  the  lymph,  but  that  its  action  is  regulated  by  all  kinds 
of  afferent  nerves,  especially  by  the  vagi  and  the  brain  pathways. 

The  condition  of  apncea,  or  respiratory  standstill,  which  is  induced  by  ex- 
cessive inflation  of  the  lungs,  or  in  man  by  one  or  more  very  deep  inhalations, 
has  often  been  regarded  as  a  very  important  fact  in  support  of  the  conception 
here  presented.  Apnoea  might  have  its  justification  in  the  unusual  opportunity 
which  the  blood  has,  in  consequence  of  unusually  ample  ventilation,  of  becom- 
ing saturated  with  oxygen  and  of  freeing  itself  of  carbon  dioxide,  so  that  the 
next  respiration  would  be  less  necessary.  But  the  matter  is  not  so  simple.  It 
has  been  made  clear,  for  example,  that  in  the  rabbit  apnoea  is  much  more  diffi- 
cult to  obtain  if  the  vagi  are  cut.  These  nerves  must  have  something  to  do, 
therefore,  with  bringing  about  this  condition.  Moreover,  apnoea  appears  as  the 
result  of  inflation  with  hydrogen  and  can  be  induced  by  forcing  the  same  air 
into  the  lungs  over  and  over  (Gad).  Finally,  it  ceases  only  after  the  other 
organs  have  shown  signs  of  asphyxiation.  We  may  say,  therefore,  that  apnoea 
depends  at  least  in  part  upon  an  inhibitory  action  of  the  vagus  upon  the  respira- 
tory center.  But  the  condition  of  the  blood  is  not  without  its  importance  also, 
as  the  following  experiment  shows.  Two  dogs  were  operated  upon  in  such  a 
way  that  the  carotid  blood  of  the  first  was  led  into  the  head  of  the  second.  A 
condition  of  apncea  was  then  induced  in  the  second  dog  by  artificial  respiration 
applied   to  the  first    (Fredericq).     We  might  distinguish  this  form  of  apnoea 


THE   BLOOD   GASES  333 

which  is  evoked  mainly  by  a  diminished  quantity  of  COj  in  the  blood  as  true 
apnoea,  and  that  mediated  by  the  vagus  as  false  apnoea  (Miescher). 

In  asphyxiation  and  severe  hemorrhage  we  meet  with  inhibitory  effects  upon 
the  respiratory  mechanism  which  are  of  central  origin.  Both  conditions  agree 
in  that  the  supply  of  oxygen  to  the  organs  of  the  central  nervous  system  and 
the  CO,  removed  from  them  are  diminished.  The  consequence  is,  first  a  well- 
marked  dyspnoea,  upon  which  follows,  after  a  time,  a  period  of  apnoea  of  greater 
or  less  duration.  This  in  its  turn  is  interrupted  by  a  series  of  new  respiratory 
movements  (gaspings).  Closer  analysis  of  the  apnoea  seen  here  shows  that  it 
probably  owes  its  origin  to  the  action  of  some  inhibitory  mechanism  upon  the 
respiratory  center  (Landergren). 

In  certain  diseases,  in  chloral  narcosis  and  certain  other  forms  of  poison- 
ing, and  with  pressure  upon  the  medulla,  etc.,  a  special  form  of  respiration  is 
observed,  known  after  two  English  physicians  as  the  Cheyne-Stokes  respiration. 
It  consists  of  a  regular  rise  and  fall  in  the  depth  of  the  respiratory  acts.  No 
positive  explanation  of  the  phenomena  has  yet  been  given. 

We  have  spoken  so  far  of  the  respiratory  center  as  a  whole.  Closer  in- 
vestigation, however,  reveals  that  here,  Just  as  in  the  mechanism  of  degluti- 
tion, we  have  to  do  with  several  functional  centers  hound  together,  the  anatom- 
ical relations  of  which  are  at  present  unkno^Ti  to  us,  but  the  individuality 
of  which  can  be  demonstrated  by  physiological  experiments  (Mosso). 

It  is  a  fact  by  this  time  familiar  to  us  that  expansion  of  the  thorax  can 
be  accomplished  either  by  the  diaphragm  or  by  the  rib-lifting  muscles.  But 
experiment  has  shown  that  in  the  same  individual  these  two  groups  of  muscles 
do  not  always  contribute  toward  the  expansion  of  the  thorax  in  the  same  ratio. 
This  appears  most  plainly  in  sleep,  when  respiration  in  man  is  essentially 
of  a  costal  type,  whereas  the  diaphragm  exhibits  a  certain  paresis,  in  some 
persons  behaving  like  an  inert  membrane.  In  deep  distress  just  the  opposite 
occurs:  the  diaphragm  moves  after  the  rib  movements  have  ceased.  These 
and  other  observations  to  the  same  effect  bear  witness  that  the  centers  for 
the  rib-lifting  muscles  and  for  the  diaphragm  are  to  a  certain  extent  inde- 
pendent. Again,  the  centers  which  preside  over  the  expiratory  muscles  are 
independent;  and  finally,  it  has  been  shown  that  the  respiratory  movements 
of  the  mouth  and  nose,  as  a  rule,  begin  before  those  of  the  thorax,  which  is 
evidence  of  the  relative  independence  of  the  centers  for  those  parts. 


THIRD    SECTION" 

THE   BLOOD   GASES 

As  long  ago  as  the  middle  of  the  seventeenth  century,  Robert  Boyle 
pumped  a  gas  from  the  blood,  and  Mayow  (1674)  claimed  that  this  gas 
contained  a  substance  called  by  him  spiritus  nitrocBveus  (oxygen).  Likewise 
Priestley  demonstrated  the  presence  of  oxygen  in  the  blood,  and  H.  Davy 
found  carbon  dioxide  in  it.  These  statements,  however,  were  disputed  by 
others  and  only  after  Magnus  (1838)  had  demonstrated  beyond  a  doubt  the 
presence  of  oxygen,  carbon  dioxide  and  nitrogen  in  the  blood,  were  the  facts 
generally  accepted. 
21 


334 


RESPIRATION 


A  very  important  advance  in  our  knowledge  of  the  blood  gases  was  made 
by  the  introduction  of  the  Torricelli  vacuum  for  the  purpose  of  extracting 

them.     This  method  was   first  used  by 
Ludwig   (1859),  after  Collard,  de  Mar- 
tigny,    and    Hoppe-Seyler   had    tried   it 
^  for  other  purposes.     Since  that  time  it 

has   been    improved    in   many    ways    by 
many  different  authors   (Fig.  130). 


1.    ABSORPTION   OF   GASES  IN 
LIQUIDS 


When  a  liquid  stands  in  contact  with 
a  space  filled  with  gas,  the  gas  passes 
from  the  space  into  the  liquid  until  the 
latter  has  taken  up  as  much  gas  as  the 
conditions  will  permit.  We  must  distin- 
guish clearly  between  two  of  these  con- 
ditions. 


A.  The   liquid   exercises   no    chemical 

attraction  upon  the  gas.    In  this  case  the 

amount    of    gas    absorbed    depends    upon 

three  factors:  (1)  the  nature  of  the  liquid 

\^^  and  the  g'as,  (2)  the  temperature,  and  (3) 

the  pressure  to  which  the  gas  is  subjected. 
We  may  formulate  the  facts  in  the  follow- 
ing law:  The  volume  of  a  gas  absorbed 
under  different  pressures  by  a  given  liquid, 
when  reduced  to  the  same  pressure  and 
temperature,  is  proportional  to  the  pres- 
sures  (Law  of  Henry). 

The  coefficient  of  absorption  is  the  vol- 
ume of  the  gas  (reduced  to  0°  and  760 
mm.  LIg.)  which  is  absorbed  by  a  unit 
volume  of  the  liquid  under  a  pressure  of 
760  mm. 

When  several  gases  within  the  same 
space  are  brought  in  contact  with  a  liquid, 
the  absorption  of  each  is  quite  independ- 
ent of  the  others,  and  depends  only  upon 
that  pressure  which  the  gas  itself  exerts 
(Law  of  Dalton). 

This  partial  pressure  of  each  gas  can 
be  calculated,  if  the  total  pressure  exerted 
by  the  mixture  and  the  composition  of  the 
mixture  are  known.  It  is  always  that 
percentage  of  the  total  pressure,  repre- 
sented by  its  volume  percentage  of  the 
mixture.  For  example:  Water  is  in  contact  with  air  under  a  pressure  of 
760  mm.  Hg.    Air  consists  of  21  vols,  per  cent  of  oxygen,  and  79  vols,  per  cent 


Fig.  130. — Schema  of  Ludwig's  pump  for 
extraction  of  the  blood  gases.  The 
pump  consists  of  two  bulbs  C  and  D  con- 
nected by  rubber  tubing  with  the  mer- 
cury bulbs  A  and  B.  When  the  stop- 
cocks a,  b,  c,  d  are  opened  and  the  bulb 
B  is  raised,  the  bulbs  C  and  D  are  filled 
with  mercury.  Then  if  the  stopcock  c 
is  closed  and  the  bulb  B  lowered  until 
the  difference  in  level  between  B  and  C 
is  greater  than  barometric  presssure,  a 
Torricelli  vacuum  is  created  in  C.  When 
C  is  empty  of  mercury  a  is  closed.  Then 
if  a  vessel  containing  blood,  which  has 
not  been  exposed  to  the  air,  but  has  been 
drawn  directly  from  an  artery  or  vein, 
is  connected  with  b,  the  contained  gases 
will  bubble  off  into  C.  By  suitable 
manipulations,  which  may  be  readily 
understood  from  the  figure,  the  gases 
are  transferred  to  D  and  finally  to  the 
graduated  burette  E,  where  they  are 
measured. 


THE   BLOOD   GASES  335 

of  nitrogen.  The  partial  pressure  of  the  oxygen  therefore  is  .21  X  T60  =  159.6 
mm.  Hg.,  and  that  of  nitrogen  is  .79  X  760  =  600.4  mm.  Hg.  The  absorption 
of  oxygen  into  water  takes  place  then  under  a  pressure  of  159.6  and  that  of 
nitrogen  under  a  pressure  of  600.4  mm.  Hg. 

B.  When  the  liquid  exercises  a  chemical  attraction  for  the  gas,  it  is  not 
only  absorbed  physically,  but  is  combined  chemically.  We  have,  however,  to 
distinguish  two  cases,  according  as  the  chemical  combination  does  or  does  not 
depend  upon  the  partial  pressure  of  the  gas.  If  it  does  not,  the  whole  quantity 
of  gas  will  be  absorbed  whatever  the  pressure.  If  it  does,  that  is,  if  the  com- 
bination between  the  liquid  and  the  gas  is  a  function  of  the  gas  pressure,  the 
combination  will  gradually  become  less  and  less  as  the  partial  pressure  dimin- 
ishes, and  with  a  partial  pressure  of  zero  will  cease  entirely  on  account  of  dis- 
sociation. In  the  latter  case,  therefore,  just  as  when  the  absorption  is  purely 
physical,  the  quantity  of  gas  entering  a  liquid  is  a  function  of  the  pressure, 
but  with  the  important  difference  that  there  is  here  no  direct  proportion  between 
the  volume  absorbed  and  the  pressure. 

When  a  liquid  has  stood  for  a  long  time  in  contact  with  a  certain  volume 
of  mixed  gases  until  it  has  become  saturated  with  the  different  gases  in  the 
mixture,  the  tension  of  each  gas  in  the  liquid  is  equal  to  its  partial  pressure  in 
the  surrounding  space.  If  the  partial  pressure  of  any  one  gas  becomes  less,  the 
liquid  gives  off  just  enough  of  this  gas  to  establish  equilibrium  once  more,  and 
vice  versa. 

In  order  to  determine  the  tension  of  gases  in  a  liquid,  the  liquid  is  placed 
under  a  definite  pressure  in  contact  with  a  mixture  of  gases  previously  analyzed, 
and,  after  a  certain  time,  the  mixture  is  again  analyzed.  The  tension  of  any 
gas  in  the  liquid  is  equal  to  the  partial  pressure  of  this  gas  in  the  surrounding 
space,  if  at  the  end  of  the  experiment  its  partial  pressure  is  the  same  as  it  was 
before.  In  order  to  hasten  the  equalization  of  tensions,  the  liquid  can  be  shaken 
up  with  the  mixture  of  gases,  or  may  be  allowed  to  flow  through  them  in  a 
fine  stream. 

§  2.    THE    BLOOD    GASES 

A.    NITROGEN   AND   ARGON 

These  gases  are  only  absorbed  physically  in  the  blood.  The  coefficient  of 
absorption  for  nitrogen  at  the  temperature  of  the  body  is  about  0.013-0.02 
and  the  content  of  nitrogen  and  argon  together  is  in  the  neighborhood  of 
2  vols,  per  cent ;  according  to  Regnard  and  Schloessing  the  blood  contains  some 
0.04  vols,  per  cent  of  argon. 

When  the  air  pressure  is  very  much  increased,  as  in  diving  and  in  caisson 
work,  the  quantity  of  nitrogen  taken  up  by  the  blood  must  be  considerable.  If 
the  pressure  is  removed  rapidly,  the  nitrogen  (the  other  gases  of  the  blood  in 
part  also)  passes  suddenly  over  into  the  form  of  a  gas  and  air  emboli  are  formed 
in  the  vascular  system,  which  may  cause  more  or  less  serious  disorders  or  even 
death  (Hoppe-Seyler,  Bert).  The  gas  collected  from  the  heart  in  such  cases 
consists  of  about  eighty  per  cent  nitrogen. 


B.    OXYGEN 

After  Lothar  Meyer  had  demonstrated   that  the  oxygen  content   of  the 
blood  presents  but  slight  variations  with  diiferent  partial  pressures,  whence 


336 


RESPIRATION 


it  is  known  to  be  chemically  combined,  Hoppe-Seyler  showed  that  oxygen  is 
found  exclusively  in  the  red  hlood  corpuscles  combined  with  the  haemoglobin. 
Many  investigations,  some  of  them  with  ha?raoglobin  solutions,  some  with 
blood,  were  then  made  looking  to  a  closer  determination  of  the  dependence 
of  oxygen  absorption  upon  its  partial  pressure.  It  was  not  to  be  expected 
a  priori  that  the  haemoglobin  solutions  would  conduct  themselves  in  exactly 
the  same  way  as  the  blood,  for  ha?moglobin  does  not  occur  in  the  blood  cor- 
puscles as  such,  but  in  combination  probabh'  with  lecithin.  It  appears  from 
these  experiments  that  equal  quantities  of  blood  and  hagmoglobin  combine 
the  same  maximum  quantities  of  oxygen,  but  at  lower  partial  pressures  the 
two  behave  very  differently. 

It  is  impossible  to  discuss  here  the  facts  bearing"  on  the  absorption  of  oxygen 
by  hfemoglobin  solutions  of  different  concentrations  and  the  theoretical  conclu- 
sions appertaining  thereto.  I  shall  limit  myself  therefore  to  the  summarized 
results  obtained  by  Bohr  with  dog's  blood,  by  Krogh  with  horse's  blood  (Fig. 
131),  and  by  Loewy  with  human  blood,  all  at  a  temperature  of  SS'^. 

Oxygen  Absorption  in  Percentage  of  Saturation 


Partial  Pressure  of 

Dog's  Blood 

Horse's  Blood 

Human  Blood 

Oxygen;  mm.  Hg. 

(Bohr). 

(Krogh). 

(Loewy). 

10 

33 

24 

36 

20 

67 

68 

53 

30 

81 

82 

67 

40 

91 

75 

50 

93 

95 

81 

80 

97 

98 

•• 

Oxygen  in  small  quantities  is  present  also  in  the  plasma.  If  all  the  oxygen 
were  to  be  removed  from  the  plasma  at  once,  dissociation  of  the  oxyhsemoglobin 
would  of  course  take  place  immediately,  and  continue  until  equilibrium  was 
once  more  established  between  the  oxygen  tension  in  the  plasma  and  in  the  blood 
corpuscles.  The  coefficient  of  absorption  of  oxygen  in  the  blood  at  body  tem- 
perature is  approximately  0.025. 

Since  the  partial  pressure  of  oxygen  in  the  atmospheric  air  may  be  esti- 
mated at  about  160  mm.  Hg.,  and  in  the  alveoli,  as  we  shall  see  later,  at 
120-130  mm.  Hg.,  it  follows  that  under  normal  circumstances  the  blood  can 
be  saturated  with  oxygen  up  to  ninety-eight  per  cent  at  least  (Fig.  131).  At 
a  partial  pressure  of  50  mm.  Hg.  the  absorption  of  oxygen  in  man  falls  to 
nineteen  per  cent  of  saturation,  and  in  the  dog  to  seven  per  cent.  On  the 
other  hand,  the  absorption  is  not  noticeably  greater  in  an  atmosphere  of 
pure  oxygen. 

These  conclusions  are  confirmed  by  observations  on  respiration  under  dif- 
ferent oxygen  pressures.  So  far  as  absorption  of  oxygen  is  concerned,  respira- 
tion runs  a  perfectly  even  course  when  the  partial  pressure  of  oxygen  is 
raised  from  twenty-one  to  sixty,  seventy-five,  and  ninety  per  cent.  There  is 
an  increase  in  the  absorption  only  during  the  first  three  minutes  of  respira- 
tion in  air  rich  in  oxygen,  and  this  is  due  to  the  physical  effect  of  a  higher 


THE   BLOOD  GASES 


337 


partial  pressure  in  the  alveoli.     A  storage  of  oxygen  in  the  tissues  does  not 
take  place  under  such  circumstances  (Falloise,  Durig). 

Neither  does  the  absorption  of  oxygen  suffer  any  change  in  consequence 
of  a  fall  in  the  partial  pressure  to  86  mm.  or  lower.  Only  when  the  atmos- 
pheric pressure  sinks  to  380  mm.  (partial  pressure  of  oxygen,  80  mm.)  does 
a  decline  in  the  oxygen  content  of  the  blood  become  evident;  at  a  partial 
pressure  of  55  mm.  the  decline  is  marked  (Loewy). 

The  absorption  of  oxygen  becomes  less  as  the  carbon-dioxide  tension  in  the 
blood  increases.  At  an  oxygen  tension  of  50  mm.  Hg.  and  a  carbon-dioxide 
tension  of  5  nun.,  the  absorption  of  oxygen  was  ninety-three  per  cent ;  with  the 


Fig.  131. 


-The  absorption  of  oxygen  by  horse's  blood,  after  Krogh.      The  abscissa-  represent  the 
partial  pressures  of  oxygen  and  the  ordinates  percentages  of  saturation. 


same  oxygen  tension  and  a  carbon-dioxide  tension  of  40  mm.  it  was  seventy- 
eight  per  cent.  As  the  blood  flows  through  the  capillaries  the  oxygen  is  gradu- 
ally used  up  and  at  the  same  time  the  carbon-dioxide  tension  increases ;  the  lat- 
ter has  the  effect  of  conferring  a  greater  tension  on  the  oxygen  present,  as  a 
consequence  of  which  a  larger  quantity  of  oxygen  can  be  placed  at  the  disposal 
of  the  tissues.  The  influence  of  this  factor  is  especially  great  in  asphyxiation 
(Bohr,  Hasselbach  and  Krogh). 

C.    CARBON   DIOXIDE 

Where  carbon  dioxide  occurs  in  the  blood  and  how  it  is  combined  are 
much  more  complicated  questions  than  in  the  case  of  oxygen,  and  notwith- 
standing many  investigations  directed  to  this  end,  the  matter  is  not  to  be 


338  RESPIRATION 

considered  as  by  any  means  settled.  The  difficulty  lies  just  here,  that  whereas 
oxygen  is  evidently  present  only  in  haemoglobin,  carbon  dioxide  is  united  with 
several  different  substances. 

The  researches  of  Paul  Bert,  Zuntz,  Setchenow,  and  others  have  made  it 
perfectly  evident  that  carbon  dioxide  is  present  for  the  most  part  in  dissociable 
compounds,  the  existence  of  which  depends  upon  the  prevailing  partial  pres- 
sure of  CO2.  In  accordance  with  what  was  said  regarding  the  combination 
of  oxygen  with  haemoglobin,  it  is  evident  also  that  a  certain  quantity  of  free 
CO,  in  the  blood  must  be  present  in  physical  combination  (cf.  page  336). 
The  coefficient  of  absorption  of  carbon  dioxide  in  water  at  37°  is  0.569.  The 
dissociable  compounds  are  found  both  in  the  plasma  and  in  the  corpuscles. 

Of  the  substances  in  the  blood  with  which  carbon  dioxide  can  be  combined, 
sodium  bicarbonate  NaHCOs  is  likely  to  be  thought  of  first.  The  phenomena 
of  dissociation  in  solutions  of  this  salt  show  however  that  it  cannot  play  any 
great  part  in  this  connection;  for  according  to  Bohr  a  0.15-per-cent  solution 
of  sodium  bicarbonate  under  a  pressure  of  0.6  mm.  Hg.  takes  up  eighty  per 
cent  of  the  total  quantity  of  carbon  dioxide  which  can  be  taken  up  under  a 
pressure  of  120  mm.,  and  at  a  pressure  of  only  10  mm.  it  is  almost  com- 
pletely saturated. 

Again  great  importance  has  been  ascribed  to  the  phosphates  in  the  com- 
bination of  COo,  since  it  was  supposed  from  analyses  of  the  blood  that  the 
plasma  contained  large  quantities  of  these  salts.  But  it  has  been  shown  that 
the  phosphorus  found  in  the  ash  is  primarily  a  constituent  of  lecithin  and 
nucleoalbumin,  and  occurs  only  in  traces  as  Na2HP04. 

The  globulin-alkali  compounds,  on  the  other  hand,  appear  to  be  of  far 
greater  importance  for  the  combination  of  COj  in  the  blood.  The  globulins 
play  the  part  of  weak  acids  and  enter  into  saltlike  combinations  with  the 
alkalies  of  the  blood.  They  can  be  replaced  from  these  compounds  by  carbon 
dioxide  and  can  themselves  in  turn  replace  the  carbon  dioxide. 

The  significance  of  this  fact  will  be  more  apparent  from  the  following: 

If  two  acids  of  different  avidity  represented  respectively  by  a  and  h  be  pres- 
ent in  a  solution  of  a  basic  substance,  they  divide  the  basic  substance  between 
them  in  the  ratio  of  a/b.    Under  the  influence  of  equal  mass  equivalents  of  the 

two  acids  and  of  the  base,  ■ — —7  equivalents  of  the  one  acid,  and  — —7  of  the 

a  -i-  0  a  -\-  0 

other  will  unite  with  the  base.  But  if  the  substances  are  not  present  in  equal 
mass,  the  distribution  of  the  base  between  the  two  acids  will  depend  upon  the" 
relative  masses  of  the  two,  so  that  the  acid  present  in  the  greater  quantity  rela- 
tively, even  if  its  avidity  is  weaker,  will  get  the  greater  quantity  of  the  base. 

Applied  to  the  problem  before  us,  this  would  mean  that,  if  the  mass  of  car- 
bon dioxide,  or  more  properly  its  tension  in  the  plasma,  is  high,  the  globulin 
will  be  forced  out  of  its  alkali  compound.  If,  however,  the  blood  comes  into 
such  relations  that  the  car])on  dioxide  tension  falls,  the  globulins  again  suc- 
ceed to  their  rights  and  the  carbon  dioxide  leaves  the  alkali  (Torup). 

As  already  observed,  carbon  dioxide  occurs  also  in  the  blood  corpuscles 
in  the  form  of  dissociable  compounds.  It  is  very  probable  that  the  globulin- 
alkali  compounds  of  the  blood  corpuscles  act  in  the  same  way  as  those  of  the 


THE   BLOOD   GASES  339 

serum.  It  should  be  added,  however,  that  the  curve  of  CO,  absorption  for 
the  corpuscles  exhibits  a  much  greater  dependence  upon  the  partial  pressure 
of  CO2  than  that  for  the  serum  (Bohr).  The  constituent  most  actively 
concerned  here  again  is  the  haemoglobin  (Fig.  133). 

Hcemoglobin  therefore  can  combine  carbon  dioxide  as  well  as  oxygen.  We 
are  not  yet  clear  just  how  this  takes  place.  Bohr  has  shown  that  the  absorp- 
tion of  carbon  dioxide  by  haemoglobin  free  of  alkalies  is  influenced  little 


Fig.  132. — The  absorption  of  carbon  dioxide  in  a  solution  of  hsemoglobin,  after  Bohr, 

1.76  per  cent  solution; 3.8  per  cent  solution.  The  abscissa-  represent  the  pres- 
sure to  which  the  gas  was  subjected,  the  ordinates  the  amount  of  carbon  dioxide  in  c.c. 
absorbed  by  1  g.  of  haemoglobin. 

or  not  at  all  by  oxygen.  For  this  reason  he  assumes  that  the  two  gases  are 
combined  with  different  parts  of  the  haemoglobin  molecule — the  oxygen  with 
the  pigment  nucleus,  and  the  carbon  dioxide  with  the  proteid  component. 


D.  THE  QUANTITY  OF  BLOOD  GASES 

The  content  of  gases  is  very  different  in  arterial  and  venous  blood.  Anal- 
yses of  the  gases  in  dog's  blood,  carried  out  under  the  direction  of  Ludwig  and 
Pfliiger,  give  us,  according  to  the  summary  of  Zuntz,  the  following  average 
percentages:  arterial  blood,  18.3  vols,  per  cent  oxygen  and  38.3  vols,  per  cent 
£ar])on  dioxide.  By  very  rapid  extraction  of  the  gases  Pfliiger  obtained  for 
arterial  blood  22.6  vols,  per  cent  oxygen  and  34.3  vols,  per  cent  carbon  dioxide. 
Merely  by  standing,  therefore,  the  ])lood  uses  up  oxygen  and  forms  carbon 
dioxide.  From  arterial  human  blood  Setchenow  obtained  21.6  vols,  per  cent 
oxygen  and  40.3  vols,  per  cent  carbon  dioxide.  The  percentage  of  oxygen  and 
carbon  dioxide  in  arterial  blood  moreover  exhibits  considerable  variations. 

The  content  of  gases  in  venous  blood  depends  naturally  upon  the  velocity 
of  blood  floiv  and  upon  the  activity  of  metaholism.  That  the  blood  gases 
exhibit  great  variations  in  the  different  vascular  regions,  according  as  the 
organs  are  more  or  less  active,  is  quite  beyond  question.  But  at  present  we  have 
analyses  of  only  the  mixed  blood  from  the  right  heart  and  from  the  central 
veins.     These  give  us,  according  to  the  summary  of  Zuntz,  as  compared  with 


340  RESPIRATION 

arterial  blood,  a  mean  increase  of  9.3  vols,  per  cent  carbon  dioxide,  and  a 
deficit  of  8.15  vols,  per  cent  oxygen,  or,  after  correcting  for  the  venous  stasis 
caused  by  the  catheter,  -|-  8.2  CO2  and  —  7.15  vols,  per  cent  O2  respectively. 

E.    THE   DISTRIBUTION    OF  THE   BLOOD  GASES  BETWEEN   CORPUSCLES 

AND   PLASMA 

The  distribution  of  the  blood  gases  between  corpuscles  and  plasma  has 
been  studied  by  Fredericq  on  the  venous  blood  of  the  horse,  and  in  this  case 
only  the  carbon  dioxide  was  determined;  71.4  vols,  per  cent  were  found  in  the 
plasma,  49.6  vols,  per  cent  in  the  corpuscles. 

All  other  determinations  along  this  line  relate  to  defibrinated  blood.  The 
following  noteworthy  facts  have  been  recorded.  Only  traces  of  oxygen  (0.1-0.3 
vols,  per  cent)  occur  in  the  serum;  almost  the  entire  quantity  belongs  to  the 
blood  corpuscles.  We  have  already  remarked  that  these  traces  can  never  be 
entirelv  absent  from  the  serum  so  long  as  the  blood  corpuscles  contain  oxvgen 
at  all." 

The  serum,  on  the  other  hand,  contains  most  of  the  carhon  dioxide.  Ac- 
cording to  the  investigations  of  Fredericq,  Zuntz,  and  A.  Schmidt,  the  carbon 
dioxide  of  the  serum  amounts  to  about  eighty-six  per  cent  of  the  total  quantity 
in  the  blood.  However,  it  is  not  impossible  that  by  changes  taking  place  in 
the  process  of  defibrination  carbon  dioxide  might  wander  from  the  serum  to 
the  blood  corpuscles  or  from  these  to  the  serum.  The  observations  of  Ham- 
burger indicate  that  in  changing  the  quantity  of  gases  in  the  blood,  sub- 
stances pass  from  the  serum  to  the  corpuscles  and  vice  versa,  and  it  is  possible 
that  such  migrations  might  occur  in  coagulation,  as  the  result  of  which  the 
carbon  dioxide  carriers  of  the  blood  would  probably  become  differently  dis- 
tributed between  the  corpuscles  and  the  serum. 

When  the  whole  blood  is  exposed  to  a  vacuum,  the  entire  quantity  of 
carhon  dioxide  escapes.  Not  so  with  the  serum :  it  loses  in  a  vacuum  only  a 
part  of  its  carbon  dioxide,  while  a  part  can  be  driven  out  only  by  the  addition 
of  acids.  According  to  Pfliiger,  the  carbon  dioxide  firmly  combined  in  the 
serum  amounts  to  five  to  nine  vols,  per  cent.  Since  this  portion  firmly  com- 
bined is  expelled  in  the  presence  of  the  blood  corpuscles  without  the  addition 
of  acids,  there  must  be  present  in  the  corpuscles  certain  constituents  which 
act  as  an  acid. 

FOURTH    SECTION 

THE   RESPIRATORY   EXCHANGE  OF  GASES 

§  1.    MECHANISM   OF   EXCHANGE   BETWEEN   BLOOD   AND 
ALVEOLAR   AIR 

Knowing  that  the  carbon  dioxide  exists  in  the  blood  in  the  form  of  a 
dissociable  compound  independent  of  the  partial  pressure,  it  is  reasonable  to 
suppose  that  the  transfer  of  carbon  dioxide  from  the  blood  to  the  alveoli  of 
the  lungs  takes  place  by  the  equalization  of  the  existing  difference  in  tension. 


EXCHANGE   BETWEEN   BLOOD  AND   ALVEOLAR  AIR 


341 


Fig.  133. — The  lung  catheter,  Ludwig's  construction. 


It  is  likewi.se  to  be  assumed  that  the  absorption  of  oxygen  into  the  blood  is  the 
result  of  a  difference  in  ox^-gen  tension  between  alveolar  air  and  venous  blood. 

The  method  of  determining  the  tension  of  a  gas  in  a  liquid  has  been  given 
above  (page  335).  For  the  measurement  of  gas  tension  in  the  blood,  Pfliiger 
let  the  blood  flow  in  a  fine  jet  directly  from  the  open  vessel  through  a  tube 
charged  with  a  mixture  of  gases  of  known  composition,  and  afterwards  analyzed 
the  gas.  By  this  method  the  blood  is  but  a  short  time  in  exchange  with  the 
mixture  of  gases,  and  on  this  account  a  complete  equalization  of  tension  differ- 
ences is  not  insured. 

For  the  purjjose  of  obtaining  pure  alveolar  air  for  analysis,  Pfliiger  con- 
structed a  special  instrument,  the  lung  catheter  (Fig.  133).  This  consists  of  two 
tubes,  one  inclosed  within  the 
other.  The  outer  tube,  made 
of  hard  rubber,  communi- 
cates with  a  soft  rubber  bulb 
(a),  the  thin-walled  end  of 
which  can  be  inflated  by 
means  of  the  air  pump  (h) 
after  it  is  introduced  into 
the  bronchus,  so  as  to  close 
hermetically  the  bronchial 
opening.  The  inner  tube  (d), 
an  ordinary  elastic  catheter, 
places  the  confined  lung  space 
in  connection  with  a  suitable 
tube  (c)  filled  with  mercury. 

After  the  air  has  been  confined  for  the  desired  length  of  time,  it  can  be  drawn 
into  this  tube  c  by  allowing  the  mercury  to  run  out. 

From  determination.'^  carried  out  bv  this  method,  chiefly  in  Pfliiger's 
laborator}^,  the  tension  of  carl)on  dioxide  in  the  arterial  blood  has  been  found 
to  be  2.8  atmospheres,  and  in  the  venous  blood  3.8  to  5.4  atmospheres;  that 
of  oxygen  in  the  arterial  blood  at  most  fifteen  per  cent  of  one  atmosphere. 
Since  the  partial  pressure  of  car])on  dioxide  in  the  alveolar  air  proved  to  be 
less,  and  that  of  oxygen  greater,  than  the  tensions  of  these  gases  in  the  arterial 
blood,  evidence  was  found  for  the  conception  that  the  respiratory  exchange 
takes  place  by  a  simple  equalization  of  tensions. 

Bohr  has  entered  the  lists  decidedly  opposed  to  this  view.  By  a  special 
method  he  determined  the  tension  of  the  gases  in  flowing  blood,  and  analyzed 
the  expired  air  at  the  same  time.  He  found  that  the  tension  of  carbon  dioxide 
in  the  arterial  blood  may  be  lower  than  the  partial  pressure  of  carbon  diox- 
ide in  the  air  which  passes  the  bifurcation  of  the  trachea;  also  that  the  tension 
of  oxygen  in  the  arterial  blood  may  be  greater  than  the  partial  pressure  of 
oxygen  in  the  same  air.  Other  factors  than  the  tension  differences  therefore 
must  be  concerned  in  the  respiratory  exchange.  Bohr  lays  special  stress  upon 
the  activity  of  the  alveolar  wall,  which  is  said  to  secrete  carbon  dioxide  and 
actively  absorb  oxygen. 

In  general  it  may  be  assumed  that  the  total  amount  of  carbon  dioxide  given 
off  in  the  lungs  comes  to  the  lesser  circulation  from  the  veins  of  the  greater 
circulation.     However,  the  opinion  was  long  ago  expressed  by  Lavoisier  in  his 


342  RESPIRATION 

studies  on  the  respiration,  that  carbon  dioxide  is  formed  in  the  lung^;  and 
recently  Bohr  and  Henrique  have  published  experiments  which  purport  to  show 
that  a  considerable  part  (two  to  sixty-six  per  cent)  of  the  carbon  dioxide  given 
oflF  is  formed  there.  If  these  results  should  be  confirmed,  it  would  be  necessary 
to  suppose  that  in  the  combustions  going  on  in  the  body  in  addition  to  carbon 
dioxide,  a  number  of  intermediary  products  of  decomposition  are  formed,  given 
off  to  the  blood,  and  there  further  oxidized  (cf.  page  339) ;  also,  possibly,  that 
some  final  oxidation  takes  place  in  the  lungs. 


§  2.    EXCHANGE   OF   GASES   BETWEEN   BLOOD   AND   LYMPH 

During  its  passage  through  the  capillaries  the  blood  gives  off  oxygen  to 
the  tissues  and  receives  carbon  dioxide  from  them.  We  know  very  little  at 
present  about  the  manner  of  this  exchange  in  the  tissues.  But,  since  the 
tension  of  oxygen  in  the  tissues  is  extremely  small,  while  according  to  Stras- 
burg  the  tension  of  carbon  dioxide  there  exceeds  that  of  the  venous  blood 
(COo  tension  in  venous  blood  43  mm.  Hg.,  in  the  intestine  59,  in  the  bile  51, 
in  acid  urine  67),  the  exchange  might  be  looked  upon  as  a  simple  matter  of 
equalizing  the  tension.  In  view  of  the  facts  with  which  we  have  just  become 
acquainted  under  respiratory  exchange  in  the  lungs,  and  since  the  consumption 
of  oxygen  (cf.  page  37)  does  not  depend  upon  the  oxygen  tension  but  upon 
the  activity  of  the  tissues,  it  is  possible  that  the  vital  activity  of  the  vascular 
wall  should  exercise  some  influence — but  we  have  no  positive  information  on 
this  at  present. 


§  3.    CHANGES   PRODUCED   IN  THE   RESPIRED   AIR 

The  excretory  products  eliminated  in  the  breath  are  carbon  dioxide,  water 
vapor  and  possibly  some  other  gaseous  substances  as  yet  imperfectly  known. 

Inspired  air  contains  in  round  numbers  twenty-one  vols,  per  cent  oxygen 
and  seventy-nine  vols,  per  cent  nitrogen,  if  we  disregard  argon,  etc.  To  these 
are  to  be  added  some  carlwn  dioxide,  which  amounts  to  only  0.03  per  cent  in 
atmospheric  air,  but  sometimes  to  considerably  more  in  room  air,  and  water 
vapor,  the  quantity  of  which  varies  within  wide  limits. 

The  expired  air  is  saturated  with  water  vapor,  which  for  the  most  part 
has  its  source  in  the  respiratory  passages  (cf.  page  333).  To  what  extent  this 
water  vapor  represents  a  product  of  metabolism  cannot  yet  be  decided. 

In  different  animals  and  in  different  individuals,  as  well  as  in  the  same 
individual  under  different  circumstances,  the  amount  of  carbon  dioxide  in  the 
expired  air  exhibits  wide  variations  according  to  the  depth  and  frequency  of 
the  respiratory  movements,  etc.  The  figure  generally  given  for  the  normal 
percentage  of  CO,  in  the  expired  air  of  man  is  4.1  vols,  per  cent  (Vierordt). 
With  quicker  and  deeper  respirations  the  lungs  are  better  ventilated  and  the 
amount  of  CO,  sinks  to  about  3.5-3.78  vols,  per  cent.  Along  with  this  the 
quantity  of  CO,  given  off  per  minute  becomes  greater,  which  in  itself  how- 
ever serves  only  as  an  expression  of  the  improved  ventilation  and  signifies 
nothing  concerning  the  wav  in  which  the  formation  and  elimination  of  CO, 


CHANGES  PRODUCED   IN   THE   RESPIRED  AIR 


343 


are  influenced  by  the  altered  frequency  and  extent  of  the  respiratory  move- 
ments. As  far  as  this  latter  question  is  concerned,  numerous  observations 
teach  us  that  augmented  respiration  increases  the  absolute  output  of  CO, — 
not  in  consequence  of  the  greater  exchange  of  air,  but  on  account  of  the 
increased  work  of  the  respiratory  muscles. 

The  j)ercentage  of  oxygen  in  the  expired  air  is  of  course  less  than  that 
of  the  inspired  air,  and  in  fact  it  decreases  more  as  a  rule  than  the  percentage 
of  CO2  increases.  Wlien  carbon  burns  in  oxygen,  the  volume  of  the  gas  does 
not  change.  Since  in  respiration,  however,  the  amount  of  oxygen  which  has 
disappeared  is  greater  than  that  of  the  carbon  dioxide  formed,  it  follows  that 
the  oxygen  is  used  in  the  body  for  other  oxidations  than  that  of  carbon.     The 

ratio  between  carbon  dioxide  formed  and  oxygen  used  -^  is  called  the  respir- 
atory quotient.  " 

The  value  of  the  respiratory  quotient  is  very  different  under  different 
circumstances,  and  depends  upon  the  kind  of  foodstuffs  which  at  the  time  are 


12    2 

p.m.  p.  m.  p.m. 

Fig.  134. — The  amount  of  carbon  dioxide  measured  in  two-hour  periods,  expired  by  a  woman 
who  slept  during  the  entire  time,  and  who  for  five  days  previously  had  eaten  scarcely  any- 
thing. 

being  burned  in  the  body.  The  carbohydrates  contain  in  their  molecule  just 
as  much  oxygen  as  is  necessary  to  completely  utilize  their  hydrogen.  The 
total  quantity  of  the  inspired  oxygen  therefore  can  be  u.sed  for  the  oxidation 
of  their  carbon.  Hence,  if  carbohydrates  exclusively  are  being  burned,  the 
value  of  the  respiratory  quotient  will  be  1. 

Fat  and  proteid  require  more  oxygen  than  carbohydrates  for  their  com- 
plete oxidation  because  the  oxygen  contained  in  their  molecule  is  not  sufficient 
for  the  complete  saturation  of  their  hydrogen.  Consequently  when  these 
substances  are  being  burned  the  respiratory  quotient  will  be  less  than  1 — for 
fats  0.71  and  for  proteid  0.78.  (Fat  contains  on  the  average  76.5  per  cent  C, 
12  per  cent  H,  11.5  per  cent  0;  proteid  (dry  muscle)  50.5  per  cent  C,  7.6 
per  cent  H,  15.4  per  cent  N  and  20.97  per  cent  0,  of  which  11.3  per  cent  C, 
2.8  per  cent  H,  15.4  per  cent  N,  and  11.44  per  cent  0  are  eliminated  in  the 
urine  and  faeces,  leaving -39.2  per  cent  C,  4.8  per  cent  H,  and  9.53  per  cent  0 
to  be  eliminated  in  the  breath.)  Since  it  only  rarely  happens  that  carbohy- 
drates alone  are  burned  in  the  body,  the  respiratory  quotient  as  a  rule  is 


344 


RESPIRATION 


less  than  1,  and  with  ordinary  food  may  be  estimated  at  about  0.8.  When 
fat  is  being  formed  from  carbohydrates  and  being  stored  the  respiratory 
quotient  may  exceed  1. 

Keduced  to  dryness  and  to  0°  the  expired  air,  therefore,  has  a  smaller 


10      12      2       4 
a.m.        p.m. 


Fig.  135. — The  elimination  of   carbon   dioxide: 


on  ordinary  diet   (mean  for  three 


davs) ;  and while  fasting  (mean  for  five  days).      All  the  determinations  were 

made  on  the  same  individual,  a  man  twenty-five  years  old.  On  the  food  days  he  slept 
between  12  o'clock  midnight  and  6  a.m.  On  the  fasting  days  he  slept  between  10  p.m. 
and  6  a.m. 


volume  than  the  inspired  air.    Measured  directly  its  volume  is  greater  because 
of  its  water  vapor  and  higher  temperature. 

For  example,  let  us  suppose  that  the  inspired  air  (500  c.c.)  has  a  tempera- 
ture of  20°  C,  and  that  it  is  saturated  with  water  vapor  at  this  temperature 
(tension  17.4  mm.  Hg.).  Expired  air,  we  will  suppose,  has  a  temperature  of 
37.5°  C,  is  saturated  with  water  vapor  (tension  at  this  temperature  47  mm.  Hg.) 
has  lost  4.783  per  cent  oxygen  and  has  gained  4.380  per  cent  carbon  dioxide. 
Measured  directly  then  the  expired  air  would  have  a  volume  of  554.89  c.c. — i.  e., 
approximately  one-ninth  greater  than  inspired  air.  The  difference  would  evi- 
dently be  greater  the  colder  the  inspired  air  (J.  R.  Ewald). 

During  recent  years  the  question  whether  the  expired  air  contains  poison- 
ous gaseous  constituents  has  been  very  actively  discussed.     Brown-Sequard 


THE  ABSOLUTE  AMOUNT  OF  RESPIRATORY  EXCHANGE 


345 


and  D'Arsonval  on  the  basis  of  numerous  experiments  had  answered  the 
question  in  the  affirmative.  Their  statements  were  put  to  the  test  by  several 
other  authors,  but  by  most  of  them  without  results.  Formanek,  however, 
proved  by  exact  methods  that  the  poisonous  effects  observed  by  the  above- 
named  authors  on  confined  animals  came  in  fact  only  from  ammonia  set  free 
from  the  solid  and  fluid  excretions  of  the  animal  employed. 

Since  the  carbon  dioxide  in  the  air  may  rise  to  four  or  five  per  cent  and 
higher  without  exercising  any  harmful  effects,  we  may  conclude  that  the  indis- 
position which  results  from  long  confinement  in  badly  ventilated  or  overcrowded 
rooms  is  due,  not  to  the  influence  of  any  poisonous  constituents  of  the  expired 
air,  but  to  other  circumstances — e.g.,  higher  temperature,  higher  humidity, 
gaseous  substances  coming  from  the  intestine  or  from  an  unclean  skin,  etc.  It 
is  assumed  of  course  that  the  ventilation  is  not  so  bad  that  carbon  dioxide  accu- 
mulates in  too  large  quantities. 

§  4.    THE   ABSOLUTE   AMOUNT   OF   RESPIRATORY   EXCHANGE 

In  the  section  on  the  nutrition  of  man  (page  13T)  will  be  found  fuller 
information  bearing  on  this  subject.     Here  we  must  limit  the  discussion  to 


nnpiiM 


Fig.  136. — The  elimination  of  carbon  dioxide,  in  two-hour  periods,  by  an  eleven-year-old  boy. 
He  slept  between  10:30  p.m.  and  8  .v..m. 

some  facts  concerning  the  variations  in  the  normal  output  of  carbon  dioxide 
(Figs.  134,  135,  and  13fi)  estimated  for  two-hour  periods. 

In  view  of  the  many  circumstances  which  affect  the  amount  of  metabolism 
and  therefore  the  output  of  CO.,,  it  is  impossible  to  specify  in  a  few  figures 


346  RESPIRATION 

the  quantities  excreted  daily.  In  a  man  not  at  work  it  can  be  estimated  on 
the  basis  of  direct  observations  for  twenty-four-hour  periods  at  0.5  g.  per  hour 
per  kilogram  of  body  weight,  which  for  a  person  of  the  average  weight  of 
70  kg.  would  amount  to  35  g.  per  hour  and  840  g.,  or  427  1.  per  twenty-four 
hours.  At  heavy  physical  labor  the  hourly  output  of  COo  may  rise  to  169  g. 
and  higher;  in  complete  bodily  rest  it  falls  to  about  30  g.  per  hour  (Fig.  134). 
The  intake  of  oxygen,  like  the  output  of  carbon  dioxide  depends  upon  the 
food,  work,  temperature,  age,  etc.  With  a  respiratory  quotient  of  0.80  the 
oxygen  consumption  corresponding  to  a  carbon  dioxide  output  of  427  1.  per 
day  would  be  534  1.,  or  764  g.  According  to  the  indirect  determinations  of 
Pettenkofer  and  Voit,  in  the  grown  man  fasting  and  at  rest  it  amounts  to 
740-780  g.,  fasting  and  at  work  1,070  g.,  on  a  moderate  diet  and  at  rest 
700-900  g.,  on  a  moderate  diet  and  at  work  1,000  g.,  etc.  By  direct  deter- 
minations with  the  respiration  apparatus  of  Hoppe-Seyler  the  oxygen  absorp- 
tion in  a  grown  man  on  a  mixed  diet  and  not  at  work  amounted  to  559-586  g. 
per  twenty- four  hours  (Laves).  In  experiments  of  shorter  duration  Magnus- 
Levy  found  the  oxygen  absorption  in  a  fasting  individual  at  complete  rest 
to  be  17.5-19  g.  per  hour,  which  corresponds  to  a  daily  absorption  of  438 
to  456  g. 


CHAPTER    X 

THE    LYMPH    AND    ITS    MOVEMENTS 

The  lymph  or  "tissue  fluid"  is  the  medium  in  which  the  cells  of  the 
body  live.  In  part  it  is  imbibed  into  the  living  substance  itself,  and  in  part 
is  collected  in  otherwase  empty  spaces  about  and  between  the  cells.  The 
entire  body  is  permeated  throughout  with  such  spaces  which  are  of  the  greatest 
variety  of  forms:  clefts,  minute  canals,  sheaths,  sacs,  etc.,  and  exhibit  the 
greatest  possible  difference  in  size.  Some,  such  as  the  so-called  serous  sacs, 
like  the  peritoneum,  the  pleura,  the  pericardium,  the  serous  sacs  surrounding 
the  organs  of  the  central  nervous  system,  etc.,  are  enormously  large,  while 
others  can  only  be  detected  with  high  magnification.  All  these  fluid-filled 
spaces,  of  whatever  kind,  communicate  ^  with  the  lymph  vessels,  and  through 
them  with  the  blood  system. 

The  lymph  comes  from  the  blood  and  is  conveyed  again  by  the  lymph 
vessels  to  the  blood.  Besides,  certain  constituents  of  the  lymph  are  taken  up 
directly  into  the  blood  vessels  through  the  permeable  walls  of  the  capillaries. 

From  the  blood  the  lymph  receives  all  the  substances  necessary  for  the 
life  of  the  cells;  from  the  cells  it  receives  the  products  formed  in  their  own 
life  processes,  both  those  which  arise  as  a  result  of  the  dissimilatory  activities 
and  those  which  are  formed  by  synthetic  processes  in  one  organ  or  another 
for  use  in  still  other  organs.  It  follows  that  the  lymph  in  the  different 
organs  must  he  of  different  composition,  since  on  the  one  hand  the  require- 
ments of  the  different  organs  are  different  both  qualitatively  and  quantita- 
tively, and  on  the  other  the  products  of  assimilation  and  dissimilation  are 
different. 

However,  we  have  at  present  no  complete  analyses  of  the  lymph  in  the 
different  organs,  nor  of  the  lymph  flowing  from  the  different  organs;  our 
knowledge  is  limited  almost  entirely  to  the  composition  of  the  mixed  IjTnph 
to  be  obtained  from  the  thoracic  duct. 

§  1.  THE  CHEMICAL  PROPERTIES  OF  THE  LYMPH 

The  lymph,  as  one  of  the  discoverers  of  the  lymph  system  (Olaus  Rud- 
beck,  1673)  remarked,  is  a  water-clear  liquid  of  salty  taste,  which  coagulates 
spontaneously.     Our  knowledge  is  at  this  time  but  little  more  extensive. 

The  lymph  contains  scattered  leucocytes.  Its  chemical  composition  agrees 
qualitatively  with  that  of  the  blood  plasma  but  quantitatively  differs  from  it 

'According  to  the  recent  researches  of  McCallum  and  Sabin,  the  lymph  vessels  are 
closed  tubes  like  the  capillaries.  If  so,  we  must  think  of  the  tissue-spaces  and  serous 
cavities  as  separated  by  thin  walls  from  the  real  lymph  channels. — Ed. 

347 


348  THE  LYMPH  AND  ITS  MOVEMENTS 

chiefly  in  that  the  lymph  is  poorer  in  proteid.  In  comparison  with  the  total 
proteid  of  the  plasma,  the  lymph  is  said  to  contain  less  globulin. 

In  the  dog's  h-mph  Hammersten  found  almost  no  oxygen,  but  found 
thirty-seven  to  fift\"-three  vols,  per  cent  of  carbon  dioxide.  It  is  stated  that 
the  carbon  dioxide  tension  in  the  lAinph  is  greater  than  in  the  arterial  blood, 
but  less  than  in  the  venous  blood. 

According  to  analyses  at  present  available,  the  lymph  of  man  contains: 
93.5-95.9  per  cent  water,  4.2-6.4  per  cent  solids,  0.04-0.05  per  cent  fibrin, 
3.5—4.3  per  cent  proteid,  0.7-0.8  per  cent  ash,  0.4-0.9  per  cent  fat,  cholesterin 
and  lecithin. 

There  are  found  in  Ivmph  also  substances  which  have  a  marked  influence 
on  certain  parts  of  the  central  nervous  system.  If  lymph  from  the  cervical 
lymph  trunks  of  the  dog  be  injected  into  the  internal  carotid  of  the  same  animal, 
changes  in  the  circulation  are  noted.  Certain  nervous  mechanisms  are  stimu- 
lated, others  are  paralyzed,  and  the  form  of  the  blood-pressure  curve  is  altered. 
Similar  injections  of  blood  have  no  such  effect  (Asher  and  Barbera).  The 
chemical  nature  of  these  substances  is  not  yet  perfectly  known,  but  in  all  proba- 
bility they  are  products  of  combustion  in  the  organs. 

The  quantity  of  lympli.  inclusive  of  the  chyle,  which  flows  through  the 
thoracic  duct  into  the  blood  stream  in  twenty-four  hours  may  be  estimated 
for  man  at  one  to  two  liters.  In  view  of  the  passage  of  certain  constituents 
into  the  blood  by  way  of  the  capillaries,  an  exact  determination  of  the  quantity 
of  fluid  flowing  through  the  thoracic  duct  possesses  no  great  interest. 


§2.    MOVEMENTS   OF   THE   LYMPH 

To  determine  the  flow  of  lymph  quantitatively,  a  fistula  is  made  in  the 
thoracic  duct  or  in  one  of  the  larger  lymphatics.  The  quantity  which  flows 
from  the  thoracic  duct  immediately  after  the  operation  is  fairly  large  owing 
to  the  stoppage  incident  to  tying-in  the  cannula,  but  it  declines  rapidly.  In 
the  further  course  of  an  experiment  of  this  kind  the  quantity  may  either 
remain  constant  for  a  time,  or  may  continue  to  fall ;  the  latter  appears  to  be 
the  rule. 

Xo  hTnph  at  all  is  to  be  obtained  from  the  main  lymph  vessel  of  an 
extremit}',  unless  its  flow  is  aided  by  active  or  passive  movements  of  the  part. 
From  this  we  may  conclude  that  by  far  the  greater  part  of  the  l3anph  flowing 
from  the  thoracic  duct,  when  the  animal  is  perfectly  quiet,  comes  from  the 
viscera. 

The  lymph  vessels  are  always  full;  the  pressure  of  lymph  in  the  cervical 
trunk  of  the  dog  and  horse  is  from  10  to  20  mm.  soda  solution.  The  velocity 
of  lymph  flow  is  much  less  than  the  velocity  of  blood  flow  in  vessels  of 
similar  size. 

Among  the  forces  which  maintain  the  flow  of  honph,  the  tension  which 
is  exerted  by  the  elasticity  of  the  tissues  should  be  ranked  first;  every  increase 
of  tissue  fluid  must  naturally  heighten  this  tension  and  thus  accelerate  the 
flow  of  lymph.  The  movements  of  the  individual  parts  of  the  body  whether 
they  be  passive  or  active,  occasion  elevations  of  pressure  on  the  honph  spaces 


THE  FORMATION   OF  LYMPH  349 

and  lymph  vessels,  which  act  in  the  same  way  as  the  tension  of  the  tissues 
to  favor  the  flow.  Besides,  throughout  such  passive  tissues  as  tendons  and 
fascia  stresses  occur,  in  some  cases  regularly  and  rhythmically  as  the  result 
of  voluntary  movements,  but  more  often  quite  accidentally,  which  favor  the 
movements  of  the  hnnph. 

In  certain  animals  (rats  and  guinea  pigs),  the  walls  of  the  lymph  vessels 
execute  rhythmical  contractions,  and  in  the  Amphibia  the  flow  of  lymph  is 
aided  materially  by  the  so-called  lymph  hearts — small  contractile  structures  situ- 
ated on  both  sides  of  the  coccyx  and  beneath  the  scapula.  The  lymph  is  forced 
by  their  contractions  into  the  iliac  and  jugular  veins  respectively. 

The  liquid  flowing  from  the  villi  of  the  intestine  through  the  lacteals  is 
forced  along  by  contraction  of  the  smooth  muscle  fibers  of  the  villi.  Finally, 
the  suction  of  the  thorax  must  be  taken  into  account,  inasmuch  as  it  affects  the 
flow  of  the  lymph  just  as  it  does  the  flow  of  blood  in  the  central  veins.  It  is 
evident  at  once  that  the  valves  of  the  lymph  vessels  are  of  great  importance  for 
all  of  the  above-named  factors. 

The  smooth  muscles  of  the  receptacidum  chyli  and  of  the  thoracic  duct 
at  least  are  under  the  influence  of  the  central  nervous  system.  The  left 
splanchnic  contains  dilating  fibers,  and.  though  in  smaller  numbers,  con- 
strictors also,  for  the  receptaculum.  The  motor  nerves  for  the  thoracic  duct 
are  in  the  thoracic  sympathetic.  Here  also  the  dilator  fibers  are  superior 
to  the  constrictors  in  their  control  over  the  wall  of  the  duct.  The  dilating 
nerves  can  be  excited  reiiexly  by  various  afferent  nerves  (Gley  and  Camus). 


§3.    THE   FORMATION   OF   LYMPH 

Since  the  blood  pressure  in  the  capillaries  is  higher  than  the  tension  of 
lymph  in  the  surrounding  tissues,  it  was  for  a  long  time  supposed  that  the 
lymph  is  pressed  out  of  the  capillaries  by  this  difference  in  pressure  (filtra- 
tion), and  that  the  osmotic  processes  between  the  blood  and  lymph  exercise 
a  more  or  less  considerable  influence  on  both  the  quantity  and  composition 
of  the  latter. 

The  most  im]X)rtant  experimental  support  of  this  view  was  the  easily 
confirmed  fact  that  the  lymph  streams  become  swollen  considerably  after 
tying  off  a  vein,  as  a  consequence  of  which  the  pressure  in  the  capillaries  is 
increased  (venous  hyperemia).  On  the  other  hand  it  was  shown  that  an 
increase  in  capillary  pressure  produced  by  dilatation  of  an  artery  (arterial 
hyperemia)  often  does  not  increase  the  formation  of  lymph  in  the  least. 

If  the  cervical  and  brachial  nerves  of  an  animal  be  cut  so  that  the  vessels 
of  the  arm  are  removed  from  the  influence  of  the  nervous  system,  and  the  cer- 
vical spinal  cord  be  then  stimulated,  the  blood  vessels  all  over  the  body,  with  the 
exception  only  of  the  arm,  contract,  wherefore  the  blood  flow  to  the  arm,  and 
consequently  the  blood  pressure  in  its  capillaries  are  greatly  increased.  Not- 
withstanding this,  the  quantity  of  lymph  flowing  from  the  l;sTnph  vessels  of  the 
arm  by  the  aid  of  passive  movements  is  not  increased  in  the  least,  but  continues 
to  fall  gradually  as  before  (Ludwig  and  Paschutin).  The  same  is  true  of  the 
submaxillary  gland,  when  after  section  of  the  cervical  sympathetic  of  an  animal 
23 


350  THE  LYMPH  AND  ITS  MOVEMENTS 

poisoned  with  atropine,  the  spinal  cord  and  the  chorda  tympani  are  stimulated: 
the  greatlj-  augmented  supply  of  blood  to  the  gland  produces  not  a  trace  of 
a'dema  (Heidenhain). 

The  difference  in  pressure  between  the  blood  and  lympli,  therefore,  is  at 
least  not  the  only  cause  of  the  formation  of  lymph. 

After  the  insufficiency  of  the  filtration  hypothesis  had  been  established, 
there  still  remained  a  possibility  of  explaining  the  formation  of  lymph  by 
reference  to  osmotic  processes.  In  the  numerous  investigations  which  have 
been  carried  on  in  the  last  few  years  many  facts  have  been  observed  which 
present  no  special  difficulty  for  this  hypothesis.  But  there  are  other  phenom- 
ena which  cannot  be  explained  so  simply,  and  which  have  led  therefore  to  the 
hypothesis  that  not  only  the  difference  in  pressure  and  the  osmotic  processes, 
but  some  specific  secretory  process  in  the  capillary  wall  also  is  concerned  in 
the  formation  of  lymph  (Heidenhain). 

Of  the  facts  which  led  Heidenhain  to  adopt  this  view,  some  have  lost  much 
of  their  force,  in  view  of  more  recent  work ;  others,  however,  are  not  yet  satis- 
factorily explained  from  the  physical  point  of  view.  We  shall  discuss  briefly 
and  in  order  the  most  important  of  these  phenomena. 

1.  If  a  hypertonic  solution  of  common  salt  or  of  sugar  be  injected  into  the 
blood  vessels,  within  a  short  time  a  large  quantity  of  water  passes  from  the 
lymph  into  the  blood,  while  simultaneously  the  salt  or  sugar  rapidly  disappears 
from  the  blood,  and  the  lymph  stream  becomes  greatly  augmented  for  a  long  time. 

This  phenomenon  might  be  explained  by  saying  that  the  vascular  wall  is 
less  permeable  for  sugar  (or  salt)  than  for  water;  consequently  water  passes 
into  the  blood  vessels  by  osmosis  until  the  sugar  can  pass  out.  Once  out  of  the 
vessels  the  sugar  in  its  turn  draws  water  from  the  tissues  and  thus  occasions 
the  increase  of  lymph.  Among  the  difficulties  which  such  an  explanation  en- 
counters is  this,  that,  according  to  Heidenhain,  the  content  of  sugar  in  the 
lymph  surpasses  that  found  at  the  same  time  in  the  whole  blood  or  in  the  serum : 
the  escape  of  sugar  from  the  blood,  therefore,  cannot  be  explained  by  any  process 
of  osmosis,  but  may  be  due  to  the  activity  of  the  capillary  wall. 

Cohnstein,  in  opposition  to  this  view,  remarks  that  it  is  not  fair,  because 
of  the  slow  movement  of  IjTnph,  to  compare  the  composition  of  blood  and  lymph 
drawn  at  the  same  time,  but  in  order  to  obtain  harmonious  results  one  must 
compare  only  the  maximum  concentrations  of  the  two.  If  this  rule  be  observed, 
the  maximum  concentration  of  serum  is  generally  higher  than  that  of  the  lymph. 
But  sometimes  the  opposite  relationship  obtains,  and  this  Cohnstein  thinks  may 
be  because  the  blood  test  is  not  made  immediately  after  injection  of  the  fluid. 
But,  again,  it  mig-ht  be  said  that  the  injected  fluid  had  not  had  time  to  mix 
thoroughly  with  the  blood.  Be  that  as  it  may,  the  phenomena  now  under  dis- 
cussion can  undoubtedly  be  explained  on  a  purely  physico-chemical  basis,  and 
constitute  therefore  no  conclusive  proof  for  the  secretion  hypothesis. 

2.  Likewise,  the  fact  emphasized  by  Hamburger  that  the  osmotic  tension  of 
the  lymph  flowing  from  the  lymphatics  of  the  extremities  under  perfectly  normal 
circumstances  is  greater  than  that  of  the  blood  from  the  corresponding  arteries, 
is  not  a  conclusive  proof,  for  it  is  conceivable  that  the  lymph  owes  its  high  ten- 
sion to  the  contained  products  of  decomposition  from  the  tissues  (Koranyi). 

3.  The  following  facts  appear  to  be  of  greater  weight.  There  is  a  large  num- 
ber of  noncrystalloid  substances,  which  when  injected  into  the  blood  produce  a 
considerable  increase  in  the  formation  of  lymph  (Heidenhain).    To  these  belong 


THE  FOR^L\TION  OF  LYMPH  351 

curare,  extracts  of  crab's  muscle,  leech  extract,  dilute  solutions  of  egg  albumin 
and  peptone,  nuclein  and  metabolic  products  of  Bacteria,  water  extract  of  straw- 
berries, etc.  The  seat  of  this  increased  formation  is  almost  exclusively  in  the 
liver  and  the  pressure  in  the  liver  capillaries  shows  only  a  temporary  rise.  The 
cause  in  this  case  cannot  be  sought  in  any  sort  of  filtration,  and  the  osmotic 
processes  cannot  play  any  part,  since  the  quantity  of  injected  substance  was 
always  very  small.  It  is  most  natural  therefore  to  conceive  of  the  process  as 
secretoiy  in  nature,  unless  one  supposes  with  Starling  that  the  liver  capillaries 
are  injured  by  the  substances  used  and  thus  permit  a  freer  passage  of  fluid — 
which  however  is  not  yet  proved. 

The  flow  of  lymph  from  the  glandular  organs  at  least  always  increases  when 
the  glands  are  active.  Stimulation  of  the  salivary  glands  through  their  secretory 
nerves  for  example  raises  the  quantity  of  lymph  in  the  vessels  of  the  neck. 
Injection  of  sodium  taurocholate  produces  a  copious  secretion  of  bile  and  the 
lymph  stream  in  the  lymphatics  of  the  liver  swells  in  size.  The  same  is  true 
when  the  formation  of  urea  in  the  liver  is  intensified  by  the  injection  of  am- 
monium tartrate;  and  we  should  probably  include  here  also  the  increase  in  the 
quantity  of  lymph  flowing  through  the  thoracic  duct  during  digestion  of  proteid. 

According  to  Asher  and  Barbera,  the  activity  of  the  gland  cells  is  the  pri- 
mary phenomenon  in  these  processes  and  the  increased  production  of  lymph  is 
only  secondary.  It  is  clear  of  course  that  a  secreting  gland  must  receive  more 
water,  the  more  active  is  its  production.  It  can  be  easily  understood  also  that 
a  certain  part  of  this  water  should  be  carried  away  by  the  lymphatics ;  the  only 
question  is.  What  are  the  forces  which  cause  the  increased  output  of  IjTnph? 

Here,  again,  one  may  conceive  of  an  active  participation  of  the  capillary 
endothelium,  and  yet  the  possibility  of  a  change  in  the  osmotic  tension  of  the 
lymi)h  by  the  process  of  secretion  of  such  a  nature  that  new  quantities  of  l.ATnph 
would  pass  out  of  the  capillaries  by  pure  osmosis  is  not  excluded.  A  definite 
decision  between  these  two  explanations  is  not  possible  at  present,  because  exact 
quantitative  determinations  of  the  osmotic  pressure  of  the  lymph  and  of  its 
changes  during  secretion  are  wanting. 

4.  Not  only  water,  however,  but  salts  and  organic  foodstuffs  also  pass  from 
the  blood  into  the  lymph.  Here  again  theoretical  explanation  of  the  phenomena 
meets  with  certain  difficulties.  The  metabolism  of  the  different  organs  of  the 
body  differs  greatly  with  respect  both  to  quantity  and  kind;  they  require  dif- 
ferent substances  in  verv^  different  quantities.  A  milking  cow,  for  example, 
secretes  daily  from  the  milk  glands  25  1.  of  milk  containing  42.5  g.  of  calcium; 
which  means  that  from  the  capillaries  of  the  milk  glands  there  passes  a  much 
larger  quantity  of  calcium  than  from  all  the  other  capillary  regions  of  the  body 
put  together. 

This  holds  true  with  regard  to  combinations  of  iodine  by  the  thyroid  gland. 
The  thyroid  takes  up  the  iodine  occurring  only  in  excessively  small  quantities 
throughout  the  body  (the  blood  of  the  dog  contains  according  to  Gley  and  Bour- 
cet  0.01-0.11  mg.  of  iodine  per  liter)  and  stores  it  up  in  a  compound  very  rich 
in  iodine  (Baumann). 

The  different  organs,  therefore,  must  possess  a  specific  power  of  selection, 
in  virtue  of  which  each  levies  upon  the  blood  for  the  constituents  necessary  to 
its  activity.  Since  however  the  gland  cells  are  not  attaohed  to  the  capillary  cells, 
but  are  separated  from  them  by  lymph  spaces,  they  cannot  themselves  exercise 
this  power  of  choice  but  must  delegate  it  to  the  capillary  cells. 

Cohnstein  rejoins  with  the  supposition  that  after  the  parenchyma  cells  of 
the  glands,  etc.,  have  removed  a  certain  constituent  from  the  lymph,  the  latter 
receives  its  replenishment  from  the  blood  by  a  process  of  diffusion,  so  that  no 


352  THE  LYMPH  AND  ITS  MOVEMENTS 

delegation  of  the  selective  power  is  necessary.  But  to  make  this  supposition 
valid,  it  must  first  be  shown  that  the  distribution  of  the  individual  substances  in 
the  lymph  of  the  different  organs  is  the  same,  that,  for  example,  iodine  occurs  in 
the  lymph  of  all  the  organs  as  plentifully  as  it  does  in  that  of  the  thyroid  gland. 
Only  when  such  proof  has  been  furnished  can  we  regard  the  assumption  of  an 
active  participation  of  the  capillary  wall  in  the  delivery  of  these  substances  as 
finally  refuted. 

5.  We  can  say  nothing  definite  at  present  concerning  the  entrance  of  proteid 
and  fat  into  the  IjTuph.  What  we  know  of  filtration  elsewhere,  in  the  opinion 
of  the  author,  speaks  very  decisively  against  the  assumption  often  made,  that 
we  are  here  dealing  with  a  simple  physical  process  of  this  kind. 

To  sum  up  the  foregoing  discussion  we  may  say,  tliat  purely  physical  forces 
such  as  difference  of  pressure  and  of  osmotic  tension  are  not  of  themselves 
sufficient  to  explain  all  the  phenomena  incident  to  the  formation  of  lymph. 
At  present  we  are  forced  to  suppose  that  the  living  capillary  wall  participates 
in  the  formation  by  some  sort  of  a  secretory  process.  This  does  not  exclude 
the  purely  physical  factors,  although  we  cannot  as  yet  distinguish  what  part 
should  be  ascribed  to  them,  and  what  to  the  vital  activity  of  the  capillary  wall. 

If  this  view  be  correct,  it  follows  that  the  capillary  wall  ^  can  be  thrown  into 
action  by  the  most  different  substances,  including  such  as  are  present  in  the 
normal  composition  of  the  blood ;  also  that  the  capillaries  in  the  different  organs 
are  different  in  certain  respects.  In  general  they  offer  a  certain  resistance  to 
the  passage  of  water  and  other  substances,  but  after  death  or  under  certain 
abnormal  conditions — e.  g.,  venous  stasis,  poisoning  with  chloroform,  chloral,  and 
ether  (Magnus) — this  resistance  is  more  or  less  reduced.  Hamburger  seems 
even  to  assume  that  the  increased  outflow  of  liquid  in  venous  stasis  is  caused  by 
the  stimulating  action  of  lymphagogic  substances  collected  in  larger  quantity. 
The  following  phenomenon  observed  by  Hamburger  may  be  mentioned  in  this 
connection.  If  a  horse  with  his  head  perfectly  quiet  moves  his  legs,  the  flow 
of  lymph  in  the  cervical  lymphatic  trunk  increases.  We  probably  have  to  do 
here  with  an  excitation  of  the  vascular  wall  induced  by  some  product  formed  in 
the  working  muscles  and  given  off  to  the  blood. 

Against  the  general  view  which  is  given  most  prominence  here  it  might  be 
objected  that  the  capillary  wall  is  so  thin  that  it  is  bound  to  permit  a  plentiful 
filtration,  and  that  this  physical  process  must  therefore  play  a  much  greater 
part  than  has  here  been  assumed.  It  appears,  however,  that  other  living  animal 
membranes,  if  they  are  uninjured,  do  not  permit  any  filtration.  This  is  the 
case,  for  example,  with  the  lung  of  the  frog,  and  with  the  membrane  of  Descemet 
(Leber)  in  the  eye.  When  they  have  been  killed  they  filter  very  well;  but  in  the 
living  state  they  do  not  let  a  single  drop  of  an  indifferent  liquid  pass  throvigh. 
The  thinness  of  the  capillary  cells  signifies  nothing  against  the  assumption  that 
they  can  develop  a  powerful  secretory  activity.  They  are  thin  because  they  live 
immediately  in  the  blood  and  hence  need  not  maintain  a  reserve  store  of  material 
within  their  own  borders. 

§  4.    THE   LYMPH   GLANDS 

Our  information  as  to  the  functions  of  the  lymph  glands  is  at  present 
very  meager.     From  what  we  know  of  the  leucocytes  on  other  grounds  it  is 

^  And  possibly  the  wall  of  the  lymphatic  vessels ;  see  note  page  347. — Ed. 


ABSORPTION  FROM  SEROUS  CAVITIES  353 

conceivable  that  the  ghmds  change  the  substances  in  the  liquid  flowing  through 
them  in  some  way.  From  the  fact  that  they  swell  up  under  various  patholog- 
ical conditions  we  may  also  conclude  that  they  retain  injurious  substances  to 
some  extent  and  thus  prevent  their  entrance  into  the  blood  stream. 

If  the  afferent  and  efferent  vessels  of  a  lymph  gland  be  tied,  but  the  blood 
vessels  be  left  open,  the  leucocytes  in  the  gland  disappear  (Koeppe).  From 
this  it  would  seem  to  follow  that  the  lymph  constitutes  a  stimulus  for  the  lymph 
gland,  to  which  the  latter  responds  by  the  formation  of  leucocytes  (Asher  and 
Barbera). 

§  5.    ABSORPTION   FROM    SEROUS   CAVITIES 

Dissolved  substances  as  well  as  water  can  pass  from  the  lymph  into  the 
blood  vessels.  This  we  know  because  solutions  injected  subcutaneously  or  in- 
jected without  injury  into  the  blood  vessels  of  a  limb  which  is  connected  with 
the  rest  of  the  body  only  by  means  of  the  blood  vessels,  are  completely  absorbed 
(Magendie). 

Substances  can  also  be  absorbed  from  the  serous  cavities  of  the  body,  such 
as  the  peritoneal  space,  the  pericardial  cavity,  pleural  cavity,  etc.  A  fluid, 
whether  serous  in  character  or  not,  and  whatever  its  origin,  when  injected  into 
such  a  cavity  is  always  first  rendered  isotonic  with  the  blood  plasma.  If  it  be 
hypertonic — as  e.  g.  a  two-per-cent  solution  of  XaCl — to  begin  with,  it  is  diluted 
by  the  addition  of  water  until  it  has  exactly  the  osmotic  pressure  of  the  blood 
plasma ;  if  it  be  hypotonic — e.  g.,  a  0.5-per-cent  solution  of  XaCl — it  loses  water 
until  it  has  the  osmotic  tension  of  a  0.92-per-cent  XaCl  solution,  and  then  in 
either  case  remains  at  this  concentration  until  absorption  is  complete. 

These  alterations  of  the  osmotic  pressure  are  unquestionably  to  be  referred 
to  osmotic  processes  going  on  between  the  injected  fluid  and  the  blood  plasma. 

It  might  be  very  naturally  supposed  that  absorption  from  these  cavities  takes 
place  through  the  lymph  spaces  which  open  into  them,  and  in  the  case  of  the 
pleural  cavities  and  the  peritoneal  space  this  seems  to  be  quite  readily  demon- 
strable. But  absorption  from  the  abdomen  and  the  thorax  can  take  place  also 
through  the  blood  vessels,  and  in  fact  the  latter  seem  to  play  the  chief  role  here. 

Xow,  since  the  blood  vessels  can,  as  may  be  assumed  without  definite  proof, 
absorb  fluids  isotonic  with  their  contents,  one  would  be  inclined  at  once  to  ascribe 
the  action  to  some  specific  vital  activity  of  the  endothelial  cells.  But  the  sur- 
prising thing  is  that  absorption  from  these  cavities  can  take  place  to  about  the 
same  degree  in  dead  animals  as  in  live  ones.  Active  cells  therefore  are  not 
essential  to  the  process. 

There  remains  to  be  mentioned,  besides  the  processes  of  diffusion  and  the 
attractive  power  of  proteid  for  water  (cf.  page  154),  the  process  of  imbibition. 
All  tissues,  living  as  well  as  dead,  have  the  power  of  taking  up  fluids  either  by 
molecular  imbibition — i.  e.,  of  absorbing  fluids  through  homogeneous  substance 
— or  by  capillar?'  imbibition — i.  e.,  through  discrete  pores.  Hamburger  supposes 
that  by  imbibition  of  the  first  kind  fluids  are  absorbed  by  the  homogeneous 
cement  substance  between  the  endothelial  cells  lining  the  peritoneum,  and  that 
by  the  same  process  the  fluid  is  passed  on  into  the  subei)ithelial  connective  tissue. 
Also,  that  the  cement  substance  between  the  endothelial  cells  of  the  capillaries 
acts  in  the  same  way,  and  by  means  of  the  minute  lumina  of  the  capillaries  an 
imbibition  by  capillarity  assists  in  draining  the  abdominal  cavity. 

This  power  of  imbibition,  however,  is  limited  and  would  soon  come  to  a  stop, 
since  a  given  volume  of  tissue  could  only  take  up  a  certain  quantity  of  fluid. 


354  THE   LYMPH   AND  ITS  MOVEMENTS 

After  a  time  a  plethoric  state  would  be  reached  which  would  cause  stagnation 
unless  the  fluid  entering  the  capillaries  were  rapidly  drained  off  in  the  blood 
stream.  In  fact  it  is  found  that  perfusion  of  fresh  serum  through  the  blood 
vessels  of  a  dead  animal  accelerates  the  process  of  absorption  very  materially. 

Besides  we  are  not  to  suppose  that  the  mechanisms  here  spoken  of  are  every- 
where the  means  of  absorption  of  fluids  by  membranes,  for  it  is  fairly  certain 
that  in  the  absorption  of  substances  by  the  frog"'s  skin  the  epidermal  cells  take 
up  the  substance  from  the  outside  and  pass  it  over  into  the  inside.  A  surviving 
frog's  skin  placed  between  solutions  of  NaCl  of  equal  strength  will  take  up  salt 
from  the  outside  surface  and  pass  it  through  to  the  inside  surface — a  thing  which 
does  not  occur  in  the  dead  skin.  Similar  phenomena  have  also  been  mentioned 
in  connection  with  the  absorption  from  the  intestine  of  mammals  (page  301). 

Solid  particles  also  like  milk  droplets,  carmine  granules,  etc.,  can  be  absorbed 
from  the  serous  cavities  probably  by  way  of  the  lymph  space*.  They  can  also 
be  ingested  and  carried  away  by  leucocytes. 

Our  conclusion  must  be  that,  aside  from  the  passage  of  fluids  into  the  open 
channels  [if  such  there  be;  cf.  note  page  347]  communicating  with  the  serous 
cavities,  the  purely  physicochemical  processes  of  diffusion,  chemical  attraction, 
molecular  and  capillary  imbibition  go  far  toward  explaining  the  absorption  of 
liquids  from  those  cavities. 

References. — Alexander  Ellinger,  "Die  Bildung  der  Lymph"  in  "Die 
Ergebnisse  der  Physiologic,"  I,  1,  1902. 


CHAPTER    XI 

THE    INFLUEXCE    OF    THE    ORGANS    OX    ONE    ANOTHER 

Although  the  individual  organs,  and  indeed  the  individual  cells  of  the 
Metazoa,  carry  on  their  life  to  a  certain  extent  independently,  they  are  in 
many  ways  dependent  on  one  another.  In  truth  it  is  only  by  this  mutual 
relationship  that  the  activity  of  the  numberless  minute  parts  can  result  in 
tlie  life  of  the  whole  body. 

Tliis  interdependence  of  the  individual  parts  of  the  body  is  made  effective 
primarily  through  the  nervous  system.  There  occur,  however,  between  the 
separate  organs  many  reciprocal  influences  more  or  less  independent  of  the 
nervous  system,  which  are  of  very  great  importance  for  the  functions  of  the 
body  and  which  participate  largely  in  the  regulation  of  its  mechanisms.  Here 
belong  osmotic  processes  brought  about  by  alterations  in  the  cells  or  in  the 
lymph,  and  the  influence  which  different  organs  exercise  on  one  another  by 
means  of  products  formed  in  them  and  delivered  to  the  liquids  of  the  body. 

§  1.    THE    OSMOTIC    PHENOMENA 

All  the  colls  of  the  body  are  permeable  to  water,  although  some  of  them 
are  permeable  only  in  one  direction.  If  salts  were  neither  added  to  nor  lost 
from  the  body,  in  time,  by  the  absorption  and  elimination  of  water,  the  same 
osmotic  pressure  would  come  to  prevail  not  only  in  all  the  cells,  but  throughout 
all  free  liquids  of  the  body.  After  the  exchange  between  water  and  the  ultimate 
particles  of  salts  had  ended,  an  equilibrium  would  everywhere  be  established 
between  the  contents  of  the  cells  and  the  liquid  bathing  the  cell. 

This  condition  of  absolute  equilibrium  of  osmotic  pressure  within  the  whole 
organism  would  cease  however,  and  in  fact  would  cease  all  at  once  for  the  entire 
system,  the  instant  the  osmotic  pressure  at  any  one  place  were  changed  by  the 
solution  or  by  the  deposition  of  new  molecules.  If  the  osmotic  pressure  in  a 
cell  be  raisetl  by  an  increase  in  the  number  of  molecules  dissolved  in  it,  the 
following  phenomena  may  ensue:  (1)  if  the  cell  walls  are  perfectly  permeable  to 
salt  molecules,  the  latter  in  their  endeavor  to  diffuse  uniformly  will  wander 
out  of  the  cell — i.  e.,  will  betake  themselves  from  a  place  of  higher  concentration 
to  a  place  of  lower  until  equilibrium  again  prevails  cverj^vhere;  (2)  if  the  cell 
wall  is  impermeable  to  these  molecules,  then  in  their  endeavor  to  diffuse  they 
will  exert  a  pressure  upon  the  wall,  and  water  will  pass  from  the  surrounding 
medium  into  the  cell.  In  this  way  the  liquid  in  the  immediate  neighborhood 
of  the  cell  becomes  more  concentrated  and  now  acts  in  turn  to  draw  water  toward 
the  periphery  of  the  cell.  The  movement  of  water  thus  set  up  continues  until 
the  difference  of  pressure  becomes  too  small  to  be  effective.  A  third  case  still 
is  conceivable,  namely  that  the  cell  wall  is  not  absolutely  permeable  to  the  salt 

355 


356  THE  INFLUENCE  OF   THE  ORGANS  ON   ONE  ANOTHER 

molecules,  but  only  imperfectly  so.     Then  an  emigration  of  salt  molecules  and 
immigration  of  water  molecules  will  take  place  simultaneously. 

According  to  the  forgoing,  the  least  change  in  the  osmotic  pressure  of  a 
single  cell  will  result  in  a  movement  of  substance  of  some  kind.  For  a  com- 
plex of  cells  the  currents  of  the  individual  cells  will  be  added  together  if  they 
proceed  in  the  same  direction ;  they  will  weaken  or  entirely  neutralize  each  other 
if  they  proceed  in  opposite  directions.  We  must  think  of  the  entire  organism 
therefore  as  permeated  by  numberless  currents  and  counter  currents.  Never 
during  life  can  there  be  a  moment  of  complete  equilibrium,  and  yet  there  is  a 
constant  endeavor  to  reach  this  condition.  Thus  we  might  expect  a  priori  what 
is  abundantly  confirmed  by  experience,  that  the  osmotic  pressures  of  the  different 
fluids  of  the  body  are  approximately  the  same  though  never  exactly  so.  In  the 
same  way  the  osmotic  pressure  of  the  same  fluid  will  not  always  be  uniform, 
but  will  vary  within  narrow  limits  (Koeppe). 

§  2.    INTERNAL    SECRETIONS 

A.    GENERAL 

The  organs  affect  one  another  in  many  ways  by  means  of  their  metabolic 
products.  Carried  by  the  blood  to  all  parts  of  the  body,  these  products  act  either 
to  heighten  or  to  reduce  the  activities  of  the  other  organs. 

The  so-called  automatic  excitation  (cf.  page  52)  by  the  action  of  decompo- 
sition products  of  the  organs  on  different  parts  of  the  central  nervous  system  is 
of  vast  importance  in  the  regulation  of  the  physiological  activities  of  the  body, 
and  is  to  be  mentioned  first  in  this  connection  (cf.  also  Chapter  XXII).  For 
example,  when  by  the  activity  of  the  digestive  apparatus  proteid  in  increased 
quantity  is  thrown  into  the  blood,  and  the  proteid  destruction  in  the  body  rises 
as  a  consequence,  the  effect  in  all  probability  is  due  to  the  direct  influence  of 
the  proteid  and  its  digestive  products  on  the  organs — i.  e.,  the  activity  of  the 
digestive  apparatus  has  brought  about  an  increase  in  the  decompositions  of 
the  body  without  the  cooperation  of  the  nervous  system  (cf.  page  99). 

Various  products  of  the  decomposition  of  proteid  formed  in  the  different 
parts  of  the  body  are  carried  by  the  blood  to  the  liver  and  there  are  transformed 
into  urea  (cf.  Chapter  XII).  With  more  active  destruction  of  proteid  urea  is 
formed  in  larger  amount  and  this  according  to  our  present  information  stimu- 
lates the  kidneys  to  increased  activity  (cf.  Chapter  XIII). 

The  organs  act  upon  one  another  not  only  by  their  katabolic  products,  but 
also  by  substances  formed  synthetically  in  some  organs,  which,  entering  the 
blood,  profoundly  influence  the  general  bodily  functions.  Such  substances, 
the  chemical  nature  of  which  is  for  the  most  part  entirely  unknown  to  us, 
are  formed  by  the  testes,  ovaries,  thyroid  gland,  pancreas,  and  adrenal  bodies, 
probably  also  by  the  pituitary  body  and  the  kidneys.  It  is  very  likely  that 
such  internal  secretions  (Brown-Sequard)  are  formed  by  other  and  perhaps 
by  all  organs. 

Strictly  speaking,  the  enzymes  formed  in  the  different  organs  belong  here. 
Since  their  importance  for  the  general  processes  of  the  body  has  not  been  estab- 
lished, we  shall  not  consider  them  here,  but  shall  merely  refer  to  the  facts  already 
cited  at  page  38. 

In  the  investigation  of  these  internal  secretions,  workers  have  often  been 
content  to  test  the  action  of  organ  extracts  upon  the  body.     This  method  of 


INTERNAL  SECRETIONS  357 

experiment  of  itself,  however,  does  not  preclude  the  possibility  that  the  active 
constituents  of  the  extract  are  products  of  post-mortem  changes  and  have 
therefore  no  real  significance  normally.  In  order  to  establish  the  presence 
of  an  internal  secretion,  one  must  demonstrate  that  the  venous  blood  flowing 
from  the  organ  exercises  a  specific  influence  upon  the  bodily  functions,  also 
that  the  extirpation  of  the  organ  produces  disturbances  which  are  not  due 
to  accidental  lesions,  and  which  eventually  disappear  on  transplantation  of 
the  organ  or  upon  administration  of  its  extract. 

B.    THE  TESTES 

It  has  long  been  known  that  castration  produces  a  series  of  profound 
changes  in  both  men  and  animals.  A  steer  which  has  been  castrated  loses 
the  vehement  strength  of  the  bull  and  becomes  a  relatively  tractable  and 
quiet  animal.  If  a  boy  be  castrated,  his  voice  does  not  change  as  it  otherwise 
would  at  puberty,  but  retains  more  of  the  high  register  of  the  childish  voice. 
The  power  and  endurance  of  the  eunuch's  muscles  are  not  those  of  a  fully 
grown  man,  but  are  as  a  rule  soft  and  flabby.  His  body  frequently  has  a 
bloated  appearance  and  becomes  very  corpulent.  The  amount  of  oxygen  ab- 
sorbed also  declines  after  castration.  Aside  from  their  sexual  functions,  which 
call  forth  profound  physical  and  psychical  phenomena  at  the  time  of  sexual 
heat,  the  testes,  therefore,  exercise  a  very  marked  influence  over  the  entire 
body. 

It  might  be  supposed  that  this  influence  is  mediated  in  some  way  by  the 
afferent  nerves  of  the  testes.  But  even  if  this  were  true — and  we  do  not  know 
that  it  is — still  other  circumstances  would  have  to  be  considered.  If  both  testes 
be  removed  from^  a  very  young  cock,  and  pieces  of  them  be  grafted  into  the 
abdominal  cavity,  the  secondary  sexual  characters  which  are  othenvise  wanting 
after  castration  make  their  appearance  much  as  usual.  Since  the  testes  were 
in  this  case  entirely  separated  from  their  nei-vous  connections,  their  influence 
can  only  be  explained  from  the  viewpoint  of  an  internal  secretion  (Foges). 

The  compounds  given  off  to  the  body  are  probably  the  same  as  the  active 
constituents  of  a  glycerin  extract  of  the  testis,  the  subcutaneous  injection  of 
which,  according  to  Brown-Sequard,  raises  the  tonus  and  power  of  the  neuro- 
muscular mechanisms  and  acts  favorably  upon  the  bodily  conditions  in  general. 

On  the  basis  of  Brown-Sequard's  recommendation,  testicular  extract  has 
found  a  very  extensive  use  in  the  treatment  of  various  forms  of  weakness.  It 
was  often  assumed  that  the  unquestionably  favorable  effects  were  psychical,  for 
it  is  well  known  that  very  often  a  medicine,  of  itself  absolutely  without  effect, 
produces  a  very  marked  improvement  or  even  cures  all  sorts  of  neiwous  dis- 
orders if  only  the  patient  is  convinced  beforehand  that  he  will  be  cured.  It  has 
been  shown,  however,  by  means  of  experiments,  which  appear  to  be  entirely 
trustworthy,  that  the  extract  really  favors  the  action  of  muscular  exercise  either 
by  raising  the  power  of  the  neuromuscular  apparatus,  by  diminishing  its  exhaus- 
tibility  or  by  improving  its  ability  to  recover.  This  effect  lasts  for  a  long  time 
after  the  conclusion  of  exercise  and  after  the  injections  have  ceased,  and  dis- 
appears very  gradually  (Pregl  and  Zoth).  Even  on  the  isolated  heart  perfused 
with  blood  testicular  extract  exerts  a  distinct  and  powerful  effect  (Iledbom). 

The  active  substance  of  the  extract  has  not  yet  been  isolated  and  is  known 
only  in  solution.  The  seat  of  its  action  in  favoring  muscular  exercise  is  not 
definitely  known,  but  is  probably  central. 


358     THE  INFLUENCE  OF  THE  ORGANS  ON  ONE  ANOTHER 

C.  THE  OVARIES 

Just  as  removal  of  the  testes  produces  deep-seated  changes  in  the  male 
organism,  the  failure  of  the  ovarial  function,  whether  by  reaching  the  climac- 
teric or  by  artificial  removal  of  the  ovaries,  is  signalized  by  a  series  of  dis- 
turbances— cardiac  palpitations,  sweatings,  vertigo,  and  the  like — which  can- 
not be  due  to  the  cessation  of  the  sexual  activity  alone.  Since  an  ovary 
completely  isolated  from  its  nervous  connections,  and  engrafted  into  some 
other  part  of  the  body,  prevents  the  atrophy  of  the  other  sexual  organs, 
including  the  mammary  glands,  and  prevents  the  failure  of  menstruation 
(Halban),  it  is  evident  that  the  influence  here  spoken  of  cannot  be  due 
exclusively  to  the  nervous  relationships  of  the  organ,  but  that  we  have  to  do 
again  with  an  internal  secretion,  the  removal  of  which  causes  the  disturbances 
alluded  to. 

It  is  often  stated  by  gynecologists  that  castration  of  the  woman,  exactly  as 
in  man,  is  in  many  cases  followed  by  pronounced  corpulency,  which  indicates 
that  metabolism  declines  after  the  operation.  This  conclusion  is  confirmed  by 
a  series  of  experiments  on  fasting  dogs  by  Loewy  and  Richter.  After  removal 
of  the  ovary  the  consumption  of  oxygen  fell  on  the  average  twelve  per  cent, 
whereas  feeding  the  castrated  females  with  ovarial  substance  raised  the  metabo- 
lism again,  in  some  cases  above  the  original  level.  The  ovarial  substance  has 
no  influence  on  the  metabolism  of  normal,  noncastrated  male  or  female  animals ; 
but  on  castrated  male  animals  its  action  is  intense. 

How  this  substance  raises  metabolism,  whether  because  of  an  increased 
muscular  tonus,  or  muscular  activity,  or  in  some  other  way,  nothing  can  be 
said  at  present.  We  only  know  that  the  destruction  of  proteid  appears  to 
suffer  no  change  under  its  influence. 

D.    THE  THYROID   GLAND 

Exact  knowledge  of  the  physiological  purpose  of  the  thyroid  gland  dates 
properly  from  1882,  when  J.  L.  Reverdin  drew  attention  to  the  profound 
disturbances  which  follow  total  extirpation  of  the  gland  for  goiter.  Shortly 
afterwards  Kocher  and  Reverdin  pointed  out  the  great  similarity  of  these 
changes  with  the  complex  of  symptoms  which  was  first  described  by  Gull 
(1873)  and  named  by  Ord  myxccdema. 

The  contribution  of  Reverdin  induced  Schiff  to  take  up  again  certain 
experiments  on  the  extirpation  of  the  thyroid  in  dogs  which  he  had  carried 
out  as  far  back  as  1856,  but  which  had  remained  unnoticed.  Out  of  60  dogs 
operated  on  by  Schiff,  59  died  within  four  weeks.  From  this  time  on  spirited 
efforts  were  made  to  throw  light  on  the  function  of  the  thyroid  gland,  and 
all  observers  reached  the  same  result:  that  its  removal  from  the  dog  led  to 
a  fatal  end  within  a  few  days  or  weeks;  that  in  man  its  removal  caused  very 
considerable  disturbances  in  the  nutrition  of  the  body;  also  that  younger 
individuals  succumbed  to  the  operation  more  quickly  than  older  ones. 

It  has  sometimes  been  assumed  that  the  resulting  symptoms,  which  will 
be  discussed  more  fully  presently,  are  caused  by  the  incidental  effects  of  the 
operation.  But  this  is  certainly  not  correct.  The  whole  operation  can  be 
carried  on  in  the  roughest  possible  manner,  and  the  animal  will  show  none 


INTERNAL  SECRETIONS 


359 


of  the  characteristic  symptoms  if  one  fails  to  remove  the  glands  (Fano). 
If  only  a  part  of  the  gland  is  left  the  symptoms  do  not  appear,  but  hypertrophy 
of  the  part  remaining  takes  place.  The  disease  of  m3'xoedema  in  man  also 
speaks  against  such  a  view.  And,  finally,  it  is  controverted  absolutely  by  the 
fact  that  intraperitoneal  grafting  protects  the  patient  from  the  consequences 
of  thyroidectomy  so  long  as  the  transplanted  gland  continues  to  be  functional 
(v.  Eiselberg)  ;  if  it  atrophies,  the  usual  symptoms  appear. 

Likewise  by  subcutaneous  injection  of  thyroid  extract,  as  well  as  by  ad- 
ministration of  thyroid  preparations  l)y  the  stomach  (Howitz).  the  same  favor- 


FiG.  1.37. 


-A  myxcedematous  woman,  after  J.  A.  Andersson.     A,  before  treatment, 
seven  months'  treatment  with  thyroid  extract. 


B,  after 


able  effect  is  obtained — i.  e.,  the  harmful  effects  of  the  removal  of  the  thyroid 
can  be  prevented  ])y  artificially  introducing  thyroid  substance  into  the  body. 

It  happens  exceptionally  that  a  dog,  after  extirpation  of  the  thyroid,  is  not 
attacked  by  the  usual  symptoms.  In  this  case  there  are  probably  accessory 
thyroids  which  have  taken  up  the  function  of  the  main  gland. 

The  disturbances  appearing  after  extirpation  of  the  thyroid  affect  the  most 
widely  different  organ  systems  of  the  body.  We  shall  now  summarize  them 
briefly  with  special  reference  to  their  appearance  in  man. 

The  skin,  especially  of  the  head  and  face,  becomes  greatly  swollen  (Fig. 
137,  A)  because  of  an  accumulation  of  mucin  in  the  subcutaneous  connective 
tissue.  In  later  stages  of  the  disease  the  mucin  decreases,  and  atrophic  changes 
of  the  connective-tissue  fibers  appear  along  with  general  emaciation.  The  skin 
becomes  hard,  rough  and  dry;  its  secretion  ceases;  the  hairs  change  and  fall  out; 
the  visible  mucous  membranes  become  swollen;  and  the  voice  becomes  harsh 
and   monotonous.     The   internal   organs  exhibit  marked   pathological  changes; 


360 


THE  INFLUENCE  OF  THE  ORGANS  ON  ONE  ANOTHER 


the  kidneys  and  the  liver  undergo  fatty  and  colloidal  degeneration,  and  the 
arterial  walls  a  hyaline  degeneration. 

Metabolism  is  abnormally  low;  in  one  of  the  patients  investigated  by  J.  A. 
Andersson  it  amounted  on  the  average  to  only  about  1,200  Cal.  per  day — i.  e., 
18.8  Cal.  per  kilogram  of  body  weight.  The  appetite  is  poor  and  the  utilization 
of  foodstuft's  is  below  the  normal.  On  the  other  hand  no  noteworthy  change  is 
observed  in  the  rate  of  the  pulse. 

The  disturbances  of  the  nervous  and  muscular  systems  are  very  marked. 
In  the  monkey  the  individual  contractions  of  the  muscles  succeed  each  other 
after  the  usual  manner  of  clonic  convulsions ;  then  comes  a  summation  of  con- 


FiG.  138. — A  cretinous  child,  after  Holt.     A,  twenty-three  months  old,   previous  to  treatment. 
B,  after  six  months'  treatment  with  thyroid  extract. 


tractions  and  after  this  tetanuslike  spasms,  ending  finally  in  complete  rigidity 
and  contracture.  Besides  these,  indications  of  reduced  nervous  activity  occur 
in  the  form  of  paralysis  and  anaesthesia.  Thyroidectomy  not  infrequently 
brings  on  functional  neuroses,  such  as  epilepsy,  etc.  These  disorders  are  not  of 
peripheral  origin,  for  they  are  wanting  after  section  of  the  motor  nerves;  on 
the  other  hand  they  are  not  abolished  by  scraping  off  the  motor  zone  of  the 
cerebral  cortex.  The  point  of  discharge  of  impulses  for  the  muscular  convul- 
sions appears  therefore  to  lie  in  the  lower  parts  of  the  central  nervous  system, 
although  the  higher  nerve  centers  are  not  in  a  perfectly  normal  condition,  as 
judged  by  histological  appearances  after  extirpation  of  the  thyroid.    This  appears 


INTERNAL  SECRETIONS  361 

also  from  the  fact  that  the  motor  cortical  fields  soon  become  fatigued  by  elec- 
trical stimulation,  until  in  the  later  stages  of  the  disease,  when  the  voluntary- 
movements  become  extremely  slow  and  imperfect,  stimulation  produces  no  vis- 
ible effect  at  all.  The  same  is  true  also  with  stimulation  of  the  corona  radiata 
and  of  the  spinal  cord.  At  the  height  of  the  convulsions,  on  the  contrary,  the 
excitability  of  the  entire  nervous  system  is  plainly  increased. 

Again,  all  those  parts  of  the  brain  which  are  active  in  the  psychical  func- 
tions become  functionally  reduced  by  extirpation  of  the  thyroid.  In  myxoedema- 
tous  patients  we  meet  with  weak  memory,  extreme  irritability,  stupidity,  etc., 
which  in  turn  find  expression  in  a  decline  of  muscular  tone  and  in  the  vigor  of 
the  bodily  movements  generally. 

Finally,  disturbances  in  the  temperature  and  the  heat  regulation  of  the 
body  are  seen.  A  considerable  rise  in  temperature  has  very  often  been  observed 
during  the  height  of  the  muscular  convulsion;  but  when  this  stage  has  passed 
a  decided  fall  ensues — in  the  monkey  to  33°.  In  man  also  the  subnormal  tem- 
perature is  one  of  the  most  constant  symptoms,  and  the  patient  feels  cold. 

In  the  growing  organism  after  suppression  of  the  thyroid,  the  bones  fall 
considerably  behind  in  their  development  and  the  ossification  of  the  epiphysial 
cartilages  and  synchondroses  is  delayed  materially.  The  psychical  disturbances 
are  probably  more  pronounced  also  than  in  grown  persons  (Fig.  138). 

Most  of  these  disorders  gradually  disappear  after  treatment  with  prepara- 
tions of  thyroid.  The  skin  acquires  again  a  normal  appearance  (Fig.  137,  B)  ; 
metabolism  increases — in  the  above-mentioned  case,  reported  by  Andersson,  after 
nine  months'  treatment  it  had  returned  to  the  normal  value  of  2,099  Cal.  =  32.3 
Cal.  per  kilogram  of  body  weight ;  the  utilization  of  foodstuffs  is  more  complete ; 
the  muscular  and  nervous  disorders  are  reduced,  and  in  young  individuals  one 
can  often  obsei-^'e  with  this  treatment  absolutely  brilliant  results  (Fig.  138,  B). 

From  all  this  it  follows  that  the  thyroid  gland  must  be  regarded  as  an 
organ  which,  by  internal  secretion  of  certain  substances,  performs  a  vitally 
important  function.  These  substances  represent  either  important  constituents 
of  the  liquids  of  the  body,  or  are  used  for  the  neutralization  of  poisons  which 
may  be  present.  We  cannot  say  definitely  whether  the  thyroid  has  still  other 
functions  or  not. 

From  histological  investigations  of  the  process  of  secretion  in  the  thyroid, 
we  appear  to  be  justified  in  the  assumption  that  the  follicular  contents  are 
elaborated  by  the  epithelium  surrounding  the  follicle ;  and  that  it  passes  through 
openings  in  the  wall  of  the  follicle — formed  by  simple  atrophy  (colloidal  fusion) 
of  the  epithelial  cells — from  the  cavity  of  the  follicle  into  the  lymph  spaces  of 
the  gland.  In  the  lymph  spaces  the  contents  are  gradually  diluted  with  lymph ; 
the  secretion  soon  loses  its  characteristic  consistency  and  ability  to  take  stains, 
and  is  added  to  the  general  circulation  through  the  lymph  vessels  (Hiirthle). 

Our  knowledge  of  the  innervation  of  the  thyroid  is  still  very  imperfect. 
According  to  Exner,  Jr.,  after  section  of  the  thyroid  nerves  of  the  cat  on 
one  side,  when  the  opposite  half  of  the  gland  has  been  removed,  various  dis- 
turbances (hypersesthesia,  apathy,  convulsive  twitchings,  etc.)  appear  during  the 
first  few  days,  but  disappear  completely  within  a  few  weeks.  How  far  these 
disturbances  are  the  direct  result  of  the  loss  of  nervous  control,  or  whether  they 
are  due  to  other  circumstances,  can  scarcely  be  decided  at  present.  Hiirthle 
and  Katzenstcin  were  unable  to  produce  any  histological  changes  by  stimulation 
of  the  thyroid  nerves.  The  latter  succeeded,  however,  in  demonstrating  distinct 
signs  of  degeneration  in  the  thyroid  of  the  dog  after  section  of  its  nerves. 


362  THE  INFLUENCE  OF  THE  ORGANS  ON  ONE  ANOTHER 

Eecently  attempts  have  been  made  in  many  ways  to  isolate  the  active  sub- 
stance of  the  thyroid,  and  the  iodotliyrin  produced  by  Baumaun  has  been  tlie 
special  object  of  numerous  investigations. 

lodothyrin  is  a  brown-colored,  amorphous  substance  which  on  heating  swells 
up  enormously  and  is  decomposed,  yielding  an  odor  suggestive  of  the  pyridin 
bases.  It  is  almost  insoluble  in  water,  and  is  soluble  with  difficulty  in  alcohol. 
It  dissolves  readily  in  dilute  alkalies  and  is  precipitated  again  on  addition  of 
acids.  Concentrated  caustic  soda  with  heat  decomposes  it  slowly.  The  gland 
can  be  boiled  for  days  in  a  ten-per-cent  sulphuric  acid  without  dcstroj'ing  its 
lodothyrin. 

This  substance  gives  none  of  the  proteid  reactions,  but  always  contains  phos- 
phorus in  organic  combination  (0.56  per  cent  P)  and,  what  is  most  important, 
at  least  9.3  per  cent  iodine.  Notwithstanding  that  it  occurs  in  the  thyroid  gland 
to  the  extent  of  only  0.3  per  cent,  lodothyrin  has  a  marked  effect  on  the  symp- 
toms following  the  suppression  of  the  thyroid,  even  when  administered  in  very 
minute  quantities. 

According  to  Baumann,  iodotliyrin  occurs  in  the  gland  in  combination  with 
proteid;  and  Ostwald  has  reached  the  conclusion  that  the  so-called  colloid  of 
the  thyroid  gland  consists  of  two  proteid  bodies,  only  one  of  which,  the  thyreo- 
globulin, contains  iodine;  the  other  is  a  nucleoproteid  containing  a  carbohydrate 
group.  By  boiling  the  former  with  ten  per  cent  H.SO^,  Ostwald  isolated  a 
product  containing  14.3  per  cent  I,  which  he  regards  as  an  extremely  pure 
lodothyrin. 

The  entire  yield  of  this  substance  calculated  on  the  basis  of  iodine  is,  how- 
ever, only  about  one-tenth  of  the  iodine  in  the  gland,  and  it  is  therefore  doubtful, 
as  Blum  and  Tambach  have  remarked,  whether  lodothyrin  occurs  as  a  conjugant 
with  proteid  in  the  gland,  or  whether  it  is  not  first  split  off  by  destruction  of 
the  proteid  molecule. 

A  fuller  presentation  of  the  views  expressed  by  different  authors  concerning 
the  nature  and  the  mode  of  action  of  the  thyroid  substance  is  impossible  here. 
We  may  mention  only  the  fact  that  S.  Frankel,  as  well  as  Drechsel  and  Kocher, 
Jr.,  have  isolated  two  other  substances  of  a  basic  nature  which  exert  a  well- 
marked,  though  not  very  strong,  favorable  action  on  animals  whose  thyroid  has 
been  removed. 

If  a  healthy  animal  be  fed  with  a  great  quantity  of  thyroid,  various  symp- 
toms of  poisoning  make  their  appearance,  such  as  tachycardia,  polydipsia,  poly- 
phagia, polyuria ;  the  quantity  of  urea  increases,  sugar  appears  after  some  time 
in  the  urine,  and  the  animal  falls  off  in  weight.  Likewise  in  men  when  thyroid 
is  administered  as  a  medicine,  in  too  large  doses,  excitement,  abnormal  sensa- 
tion of  heat,  increased  destruction  of  proteid,  jaundice,  albuminuria,  cardiac 
pali)itation  and  cardiac  weakness  make  their  appearance. 

E.    THE   PANCREAS 

When  the  pancreas  of  a  mammal  (dog,  cat,  pig)  is  totally  removed  with- 
out any  accidental  lesions,  a  severe  diabetes  (according  to  some  authors  in- 
variably, according  to  others  generally)  ensues  (v.  Mering,  Minkowski,  de 
Dominicis,  1889). 

The  appearance  of  svgar  in  the  urine  does  not  always  show  immediately 
after  the  operation.  It  appears  sometimes  sooner,  sometimes  later,  but  in- 
variably increases  in  intensity  within  the  next  twenty-four  hours,  and  as  a  rule 


INTERNAL  SECRETIONS  363 

also  on  succeeding  days.  In  most  cases  on  the  first  day  there  are  found  only 
traces,  up  to  one  per  cent;  on  the  following  day  from  four  to  six  per  cent; 
and  only  on  the  third  day  does  the  sugar  elimination  reach  its  maximum  of 
eight  to  ten  per  cent  and  over.  If  now  food  be  not  given,  the  quantity  of  sugar 
in  the  urine  begins  gradually  to  fall  off;  but  it  does  not  disappear  altogether 
after  seven  days  of  fasting.  With  a  plentiful  supply  of  food  the  sugar  in  the 
urine  may  amount  to  ten  or  twelve  per  cent,  and  the  daily  quantity  of  sugar 
eliminated  by  a  dog  of  15  kilos  on  a  pure  meat  diet  may  reach  103  g.,  and 
on  addition  of  carbohydrates  may  reach  a  still  higher  value. 

From  these  observations  it  is  clear  that  the  pancreas  is  extremely  im- 
portant for  the  normal  decomposition  of  the  carbohydrates  of  the  body.  But 
it  is  conceivable  that  the  effects  described  are  due  to  some  accidental  lesion 
attending  the  operation.  This  is  opposed  by  the  following  experimental  facts. 
If  a  relatively  small  piece  of  the  gland  be  left  in  the  abdominal  cavity,  diabetes 
does  not  occur,  notwithstanding  that  the  operative  procedure  is  the  same. 
Further,  if  in  the  operation  a  piece  of  the  gland  be  grafted  under  the  abdom- 
inal skin  in  such  a  way  that  it  remains  in  vascular  connection  with  the 
abdominal  cavity,  and  after  it  has  become  healed  in,  the  rest  of  the  gland 
left  in  the  normal  position  be  removed,  the  animal  does  not  ])ocome  diabetic, 
nor  does  diabetes  result  from  section  of  the  vascular  stalk  to  the  subcutaneous 
graft.  But  sugar  appears  in  the  urine  immediately  and  in  large  quantities, 
and  the  sugar  content  in  the  l)lood  rises  consideral)ly,  as  soon  as  the  subcu- 
taneous graft  is  removed,  although  the  operation  for  its  removal  is  quite  an 
insignificant  one.  We  must  conclude  that  neither  the  operative  lesions  nor 
the  absence  of  the  pancreatic  secretion  from  the  intestine  can  be  the  cause 
of  the  sugar  elimination.  The  pancreas  therefore  exercises  a  specific  influ- 
ence on  the  transformation  of  sugar  in  the  body. 

The  pancreas  may  bo  made  to  waste  away  by  gradual  injection  of  fat  or  of 
acids  into  the  duct  of  Wirsung.  When  this  is  done  in  the  dog,  in  many  cases 
no  sugar  appears  in  the  urine  (Hedon,  Rosenberg).  To  explain  these  remark- 
able facts,  we  are  almost  compelled  to  assume  that  some  other  organ  has  taken 
over  the  function  of  the  pancreas  in  the  metabolism  of  sugar,  and  that  this  can 
only  happen  in  case  the  function  of  the  pancreas  is  abolished  very  gradually. 
The  most  natural  explanation,  namely  that  portions  of  the  pancreas  remain 
intact,  is  excluded  by  the  express  statements  to  the  contraiy  of  the  authors 
themselves  who  report  these  experiments. 

How  are  the  phenomena  which  follow  extirpation  of  the  pancreas  to  he 
explained?  Even  under  normal  circumstances  with  a  very  large  amount  of 
sugar  in  the  food,  a  part  of  it  passes  out  in  the  urine  (alimentary  gh'co- 
suria).  Different  kinds  of  sugar  behave  differently  in  this  respect.  Levulose 
is  ahnost  all  burned,  while  cane  sugar,  grape  sugar  and  especially  milk  sugar 
pass  over  in  relatively  large  quantities  into  the  urine.  After  extirpation  of 
the  pancreas,  much  larger  quantities  of  sugar  than  usual  are  found  circulating 
in  the  blood ;  it  is  evident,  therefore,  that  sugar  must  also  appear  in  the  urine. 

The  different  carbohydrates  fed  to  an  animal  whose  pancreas  has  been 
removed  behave  very  differently.  On  feeding  grai>e  sugar  the  entire  quantity 
fed  appears  in  the  urine.     Maltose  is  transformed  into  dextrose  and  as  such  is 


364     THE  INFLUENCE  OF  THE  ORGANS  ON  ONE  ANOTHER 

eliminated.  On  the  other  hand  the  laevorotatory  carbohydrates  (levulose,  inosit) 
are  used  by  the  body,  although  they  are  in  part  transformed  into  grape  sugar 
and  are  excreted  as  such.  After  feeding  with  cane  sugar,  neither  cane  sugar 
itself  nor  levulose  are  to  be  found  in  the  urine;  instead  there  always  appears  a 
considerable  increase  of  the  dextrose  output.  Presumably  therefore  the  cane 
sugar  is  inverted,  and  besides  the  usual  dextrose  arising  from  it,  a  part  of  the 
levulose  also  leaves  the  body  as  dextrose.  Milk  sugar  also  appears  to  be  trans- 
formed into  grape  sugar  and  to  be  eliminated  as  such. 

The  gh/cogen  disappears  from  the  liver  of  animals  made  diabetic  in  this 
way,  down  to  the  last  traces.  But  in  animals  in  which  parts  of  the  pancreas 
have  been  left  in  the  abdominal  cavity,  fairly  large  quantities  of  glycogen 
are  still  found.  Finally,  after  feeding  levulose,  there  occurs  under  certain 
circumstances  a  considerable  deposit  of  glycogen  in  the  liver,  and,  what  is 
especially  noteworthy,  this  glycogen  is  dextrorotatory  as  usual. 

After  suppression  of  the  pancreas,  therefore,  the  power  of  the  body  to 
form  glycogen  or  fat  from  dextrose  is  destroyed.  Such  animals  show  an 
increased  destruction  of  tissue  proteid,  which  is  most  clearly  attested  l)y  the 
fact  that  in  spite  of  an  excessive  supply  of  food,  they  very  rapidly  become 
emaciated,  losing  in  two  weeks  as  much  as  one-third  or  more  of  the  body 
weight.  That  is,  they  live  principally  at  the  expense  of  their  own  ])odies. 
Since,  in  spite  of  this,  sugar  is  eliminated  in  large  quantities  in  the  urine, 
the  organism  must  have  lost  the  ability  to  burn  sugar  to  the  usual  extent. 

The  consequences  of  removing  the  pancreas  make  it  evident,  therefore, 
that  this  organ  plays  an  essential  part  for  the  storage  of  carbohydrates  in  the 
body,  for  their  transformation  into  fats,  and  for  the  comlnistion  of  sugar. 

In  explanation  of  these  effects  of  the  pancreas  on  the  transformation  of 
sugar,  one  might  conceive  either  that  a  substance  is  formed  in  the  gland  which 
is  necessary  for  the  normal  metabolism  of  sugar,  or  that  the  gland  destroys  some 
substance  formed  elsewhere,  the  retention  of  which  in  the  organism  would  pro- 
duce the  effects  described.  The  former  of  these  suppositions  appears  the  more 
probable,  although  there  is  scarcely  yet  to  be  found  any  binding  proof  of  it,  and 
nobody  has  so  far  succeeded  in  obtaining  the  active  substance  from  the  pancreas. 
It  appears  from  some  facts  not  presented  here  that  the  discharge  of  this  sub- 
stance into  the  blood  is  under  partial  control  of  the  central  nervous  system. 


F.    THE  ADRENAL   BODIES 

In  1855  Brown-Sequard  announced  that  bilateral  extirpation  of  the  ad- 
renal bodies  resulted  fatally  within  a  short  time  after  the  operation.  Later 
experiments  have  on  the  whole  confirmed  this  statement.  Death  follows  within 
a  few  hours  or  days  at  most.  If  the  organs  are  removed  in  several  operations, 
portion  at  a  time,  the  animals  (cats)  die  somewhat  later.  If  some  time  be 
allowed  to  elapse  between  the  operations  for  the  two  sides,  the  animal  (rab- 
bit) may  exhibit  no  abnormal  symptoms  within  a  month. 

After  extirpation  of  one  adrenal  body  and  a  part  of  the  other,  animals 
may  continue  to  live,  though  in  a  reduced  state  of  health,  for  some  time  after 
the  operation.  They  are  more  sluggish  than  usual,  they  quickly  become 
fatigued  by  muscular  efforts,   and  the  body  rapidly   falls   away  in  weight. 


INTERNAL  SECRETIONS  365 

These  conditions  gradually  pass  away  and  the  animals  recover.  When  only 
a  part  of  one  adrenal  l)ody  is  left  in  position,  regeneration  of  its  substance 
takes  place.  Just  as,  after  unilateral  extirpation,  a  compensatory  hypertrophy 
of  the  one  remaining  appears.  In  both  man  and  animals  accessory  adrenals 
are  found  which  are  sufficient  to  maintain  life  after  total  extirpation  of  the 
main  bodies. 

Hultgren  and  0.  Andersson  describe  the  abnormal  phenomena  appearing 
after  the  removal  of  the  adrenals  as  follows:  The  animal  recovers  from  the 
operation  within  a  few  hours,  and  aside  from  a  poor  appetite  or  none  at  all, 
shows  no  unfavorable  symptoms  within  the  next  few  days.  During  the  last 
twenty-four  hours  before  death,  or  still  earlier  when  the  symptoms  run  a 
slower  course,  the  animal  becomes  dull  and  stupid,  most  of  the  time  sits 
perfectly  quiet  and,  what  is  particularly  striking,  in  cats,  exhibits  weakness 
and  uncertainty  in  the  movements  of  its  hinder  extremities.  At  the  same 
time  the  temperature  begins  to  fall,  and  as  this  continues  the  general  list- 
lessness  and  weakness  of  the  animal  increases.  Cats  lie  most  of  the  time 
with  the  nose  on  the  floor,  and  with  eyes  half-closed  follow  what  is  going 
on  about  them,  but  not  with  the  usual  interest.  They  react  to  stimuli  more 
feebly  and  more  slowly  than  before.  They  walk  unsteadily  and  with  a  pecul- 
iar stiffness  of  the  hinder  legs.  In  leaping  down  from  a  chair  they  are  likely 
to  fall  in  a  heap.  They  become  fatigued  with  very  slight  movements,  and  lie 
for  a  long  time  deeply  exhausted.  This  loss  of  strength  continues  more  and 
more  and  finally  dyspnoea  sets  in;  respiration  becomes  deep  and  slower;  the 
heart  l^ecomes  less  frequent  and  irregular,  and  death  ensues.  Convulsions 
rarely  occur  in  cats  and  dogs,  but  in  rabbits  they  are  fairly  common. 

Among  other  conditions  observed  on  such  anim^als  the  following  may  be 
mentioned.  Xeither  digestion,  nor  the  combustion  of  proteid,  nor  the  content 
of  haemoglobin  in  the  blood,  nor  the  number  of  red  blood  cells  is  influenced  by 
the  operation.  Xo  paralyses  are  to  be  observed  and  the  electrical  excitability  of 
the  nerves  remains  unchanged  to  the  time  of  death. 

The  blood  pressure  falls  immediately  after  the  operation  and  in  the  last  few 
hours  reaches  a  very  low  level. 

The  blood  of  the  operated  animals  is  said  to  have  a  pronounced  toxic  action. 
Thus  if  blood  from  one  operated  animal  be  injected  into  another  whose  adrenals 
have  also  been  removed,  the  symptoms  which  would  otherwise  not  appear  for 
several  hours  come  on  within  a  short  time. 

The  profound  effects  of  the  removal  of  the  adrenals  cannot  be  caused  by 
the  operation  alone  nor  by  accidental  lesions.  This  we  know  from  the  obser- 
vation that  portions  of  the  adrenals  which  have  been  left  unintentionally 
suffice  to  keep  the  animal  alive;  also  from  the  fact  that  no  disturbance  occurs 
if  the  adrenals  be  separated  from  all  their  connections  except  those  with  the 
vascular  system. 

The  evil  effects  of  the  extirpation  of  the  adrenals  are  therefore  due  to  the 
loss  of  some  function  which  is  important  for  the  whole  body.  This  function 
may  be  one  of  two  kinds :  either  they  destroy  some  product  or  products  formed 
in  metal)olism  which,  when  present  in  larger  quantity  than  the  normal,  poison 
the  organism,  or  they  form  substances  which  are  necessary  for  the  normal 
activities  of  the  body.  The  results  of  extirpation,  and  especially  the  influence 
23 


366  THE  INFLUENCE  OF  THE  ORGANS  ON  ONE  ANOTHER 

set  up  by  the  injection  of  the  blood  of  one  animal  deprived  of  its  adrenals 
into  another  animal  operated  on  in  the  same  way,  appear  to  speak  rather 
definitely  for  the  former  supposition.  Even  if  this  were  correct,  however, 
the  physiological  purpose  of  the  adrenals  would  not  be  wholly  explained  there- 
by, for  injection  of  adrenal  extract  or  of  blood  from  the  adrenal  vein  (Cy- 
bulski)  into  animals  which  have  lost  their  adrenal  bodies  produces  a  marked 
improvement  in  the  symptoms  for  some  time,  and  has  an  unmistakable  effect 
on  perfectly  normal  animals.  The  conclusion  which  seems  to  be  inevitable 
is  that  the  adrenals  give  off  to  the  Mood  one  or  more  specifically  active 
substances. 

These  substances  are  dialyzable;  soluble  in  water,  dilute  alcohol  and  in 
glycerin,  but  insoluble  in  absolute  alcohol  and  ether ;  withstand  drying  at  110°  C. 
and  boiling,  if  not  too  prolonged.  They  are  destroyed  by  alkalies,  but  not  by 
acids.  Xumerous  attempts  have  been  made  to  isolate  and  identify  this  sub- 
stance. According  to  v.  Fiirth,  it  is  related  to  the  pyridin  series  and  contains 
a  ring  nucleus  with  two  hydroxyl  groups  in  the  ortho  position  (adrenalin).  It 
has  an  alkaline  reaction  and  forms  salts  with  the  acids.  Its  empirical  formula, 
according  to  Takamine,  is  CioHi^XOa,  according  to  Abel  0101113^03.  -f  i  H„0. 
The  percentage  of  this  substance  in  the  adrenals  is  said  to  be  about  0.1-0.17 
per  cent. 

If  the  extract  be  injected  directly  into  a  vein,  it  acts  powerfully  in  very 
small  quantities.  Thus  Takamine  obtained  a  distinct  rise  of  pressure  by  inject- 
ing 0.0000013  g.  of  adrenalin.  The  chief  effect  of  such  an  injection  of  this 
extract  is  a  sudden  rise  of  blood  pressure.  This  is  due  in  part  to  an  augmented 
heart  action  which  can  be  demonstrated  alsoon  an  excised  heart  or  heart  muscle, 
and  in  part  to  a  powerful  contraction  of  the  smaller  arteries  caused  by  a  direct 
action  of  the  extract  on  the  musculature  of  the  vessels.  According  to  Cyon,  the 
vasomotor  center  in  the  medulla  and  the  cardiac  inhibitor^'  center  are  excited. 
The  slowing  of  the  heart  beats  observed  by  many  authors,  which  do  not  appear 
after  section  of  the  vagi  (according  to  most  authors),  is  said  to  be  a  direct  effect 
of  the  injection  and  the  result  of  a  sudden  increase  of  intracranial  pressure. 

Most  of  the  effects  of  injection  of  adrenalin  last  only  a  few  minutes,  and 
then  gradually  disappear.  This  temporary'  character  might  be  due  either  to  a 
transformation  of  the  adrenalin  taking  place  in  the  blood  stream,  or  to  its 
removal  from  the  vessels.  Adrenalin  is  eliminated  in  the  urine  only  in  very 
small  quantities. 

When  injection  is  made  subcutaneously  in  animals  from  which  the  adrenals 
have  been  removed,  it  produces  a  rise  during  the  premortal  fall  of  temperature, 
and  improves  the  general  bodily  condition  of  the  animals.  They  become  more 
active,  the  weakness  and  uncertainty  of  their  movements  are  diminished  and 
they  leap  with  much  more  vigor  than  before.  After  repeated  injections,  how- 
ever, the  effect  fails,  and  it  is  possible  to  prolong  the  life  of  the  animal  in  this 
way  for  only  about  twenty-four  hours  (Ilultgren  and  O.  Andersson).  On  ad- 
ministration of  very  large  quantities  of  adrenalin  to  normal  animals,  especially 
after  intravenous  injection,  profound  toxic  effects  ensue  which  result  fatally. 

With  regard  to  the  inflnence  of  the  nervous  system  on  the  formation  and 
secretion  of  the  active  substance  of  the  adrenals,  Biedel  and  Dreyer  state  that 
stimulation  of  the  splanchnic  below  the  diaphragm  produces,  quite  independ- 
ently of  the  alterations  in  the  blood  flow,  a  copious  secretion  of  it  into  the 
blood. 


INTERNAL  SECRETIONS  367 


G.    THE   PITUITARY   BODY 

On  the  basis  of  anatomical  and  embrj'ological  facts  most  authors  assume  a 
close  physiological  relationship  between  the  hypophysis  cerebri — i.  e.,  anterior 
part  of  the  pituitary  body — and  the  thyroid  gland.  This  supposition  is  supported 
by  the  facts,  to  this  extent  at  least,  that  hypertrophy  of  this  structure  has  been 
obsei^ed  in  animals  after  extirpation  of  the  thyroid,  and  in  men  suffering  from 
myxa?dema.  A  satisfactory  explanation  of  this  relationship  has  not  yet  been 
found. 

Recently  many  experiments  have  been  made  on  the  effect  of  injecting  extract 
of  the  hypophysis  into  the  circulation,  and  a  distinct  action  upon  the  heart  and 
blood  vessels  has  been  obtained.  According  to  Schafer  and  Vincent,  we  have 
to  do  here  with  two  different  substances,  which  are  distinguished  chemically  by 
their  solubility  in  alcohol  and  ether,  one  being  soluble,  the  other  not. 

The  former  brings  about  a  very  temporary  fall  in  the  arterial  blood  pressure. 
The  other  increases  the  blood  pressure,  slows  and  strengthens  the  heart  beat 
and  produces  a  marked  diuresis.  The  effect  is  tolerably  permanent,  although  it 
becomes  less  and  less  with  successive  injections.  From  experiments  on  the  iso- 
lated heart  or  heart  muscle  it  appears  that  this  influence  extends  to  the  peripheral 
end  apparatus  of  the  cardiac  nerves.  Other  observations  indicate  that  the  extra- 
cardial  center  also  is  stimulated  (Cyon).  The  vasomotor  nerves  behave  in  the 
same  way :  on  the  one  hand  the  vessels  contract  after  destruction  of  the  medulla 
(Oliver  and  Schafer)  ;  on  the  other,  the  vasoconstriction  occurs  if  the  extract 
is  injected  into  the  brain  vessels  only  (Cyon).  In  Cyon's  opinion  the  effects  of 
an  extract  on  the  heart  and  on  the  vessels  depends  upon  two  different  substances. 

Curiously  enough  the  substances  Avhich  produce  this  effect  \ipon  the  circu- 
lation, according  to  Howell,  Schafer,  and  Vincent,  are,  for  the  most  part  at 
least,  not  contained  in  the  anterior  glandular  part  of  the  pituitary  body,  but  in 
the  posterior  infundibular  part.  However,  this  section  of  the  pituitary  body 
also  contains  glandular  epithelial  cells,  which  surround  cavities  filled  with  a 
colloidal  substance  (Berkley). 

From  results  thus  far  before  us  no  positive  conclusion  can  be  drawn  as  to 
the  normal  working  of  the  hypophysis.'  It  is  conceivable  that  the  substances 
obtained  by  different  methods  from  the  gland  are  normally  formed  there  and 
are  given  off  to  the  blood.  But  it  is  also  possible  that  they  represent  products  of 
decomposition  which  are  formed  post  mortem  only,  in  the  methods  of  extraction. 

A  definite  choice  between  these  two  possibilities  is  not  yet  possible,  since 
from  the  many  conflicting  statements  as  to  the  results  of  extirpation,  we  cannot 
tell  certainly  whether  any  disturbances  follow  loss  of  the  hypophysis  alone. 

H.    THE   KIDNEYS 

Certain  observed  facts  indicate  that  the  kidneys  not  only  remove  different 
products  of  decomposition  from  the  body,  but  give  off  to  the  blood  one  or  more 
substances  which  are  of  service  in  the  body.  When  the  kidneys  are  removed 
from^  an  animal,  or  are  rendered  functionless  in  man,  within  a  few  days  symp- 
toms of  severe  uraemic  poisoning  make  their  appearance.  The  most  natural 
assumption  is  that  the  symptoms  are  caused  by  the  retention  of  the  products 

'  Fischera  has  reported  quite  recently  that  castration  of  cocks,  guinea  pigs  and  rab- 
bits produces  a  marked  hyperplasia  of  the  hj^pophysis.  The  change  in  the  capon  is  very 
sudden  and  can  readily  be  recognized  in  microscopical  sections  of  the  part.  Injection  of 
testicular  extract  just  as  quickly  abolishes  the  hyperplasia  or  prevents  it  altogether. — Ed. 


368  THE  INFLUENCE  OF  THE  ORGANS  ON  ONE  ANOTHER 

otherwise  eliminated.  ■  But  it  has  been  observed  that  patients  who  suffer  with 
anuria  for  weeks  may  not  show  any  signs  of  uraemia.  Brown-Sequard  explains 
this  failure  of  abnonnal  results  by  supposing  that  only  the  excretion  of  urine, 
but  not  the  production  of  the  "  internal  secretion  "  of  the  kidneys,  has  ceased. 
In  support  of  this  view  he  carried  out  experiments,  in  which  animals  whose 
kidneys  were  removed  and  which  showed  the  urajmic  symptoms  were  very  much 
benefited  by  injection  of  an  aqueous  extract  of  kidney.  Moreover  E.  Meyer  has 
shown  that  nephrectomized  animals  which  exhibited  the  periodic  respiration 
resulting  from  uraemia,  again  began  to  breathe  normally  after  intraperitoneal 
injection  of  a  kidney  extract  or  intravenous  injection  of  blood  of  a  normal  ani- 
mal. Other  authors  have  reached  entirely  negative  results  with  similar  experi- 
ments. The  view  of  Brown-Sequard  therefore  cannot  be  regarded  as  by  any 
means  established  in  fact. 

I.    THE    SPLEEN 

Extirpation  of  the  spleen  produces  no  serious  effects;  it  is  therefore  not  a 
vitally  important  organ.  According  to  Schiff  and  Herzen,  the  spleen  is  in  some 
way  concerned  in  the  formation  of  trypsin  from  the  zymogen  formed  in  the 
pancreas,  and  this  has  recently  been  confirmed  by  Gachet  and  Pachon  (cf.  page 
252).  The  quantity  of  bile  pigments  formed  in  the  liver  is  also  said  to  fall 
considerably  after  extirpation  of  the  spleen  (Pugliese).  This  is  in  line  with  the 
view  arrived  at  by  many  authors,  and  latterly  by  Jawein,  that  the  spleen  removes 
from  the  blood  and  transforms  the  worn-out  red  blood  corpuscles. 

An  intravenous  injection  of  splenic  extract  at  first  lowers  the  blood  pressure 
and  later  raises  it  slightly;  it  also  appears  to  be  able  to  regulate  the  rhythm  of 
the  excised  heart.  Again,  it  is  said  to  have  the  same  effect  as  an  infusion  of 
red  bone  marrow  in  raising  the  number  of  red  blood  corpuscles  and  the  content 
of  hemoglobin  in  the  blood  (Danilewsky). 

Since  we  have  no  data  as  to  the  effect  of  the  venous  blood  from  the  spleen, 
these  results  furnish  no  definite  point  of  vantage  for  the  explanation  of  the 
physiological  purpose  of  this  still  very  enigmatical  organ. 


CHAPTER    XII 

THE    FINAL    DECOMPOSITIOX    OF    FOODSTUFFS    IN    THE    BODY 

As  already  mentioned  at  page  27,  the  foodstuffs  in  their  combustion  do 
not  pass  over  immediately  into  their  end  products,  but  are  gradually  split 
up  into  simpler  and  simpler  substances,  oxidation  and  reduction  processes 
probably  succeeding  each  other  in  rapid  succession.  In  order  to  secure  more 
light  on  these  processes,  investigators  have  studied  the  transformations  which 
organic  substances,  more  or  less  closely  related  to  the  foodstuffs,  undergo  in 
the  bod3\  Important  as  these  investigations  are,  and  significant  as  are  the 
results  which  we  expect  from  this  field  in  the  future,  we  must  limit  ourselves 
here,  for  want  of  space,  to  the  transformations  of  the  true  foodstuffs.  Un- 
fortunately our  knowledge  of  these  subjects  is  still  very  imperfect  and  the 
views  of  authors  are  considerably  at  variance  with  one  another  on  many  of 
the  most  important  points. 

§  1.    THE   FINAL   DESTRUCTION   OF   PROTEID 

In  its  digestion  in  the  alimentary  canal,  proteid  is  for  the  most  part  split 
up  into  relatively  simple  products.  To  what  extent  it  is  absorbed  in  the 
form  of  albumoses  and  peptones  we  cannot  say  definitely.  Xor  is  anything 
known  concerning  the  extent  to  which  synthesis  of  proteid  from  the  end 
products  just  named  eventually  takes  place  in  the  body.  If  the  proteid  is 
not  stored,  both  the  primary  and  the  final  digestive  products  are  still  further 
decomposed  until  the  elements  of  proteid  are  ready  to  be  eliminated  as  carbon 
dioxide,  water  and  urea. 

Formerly  it  was  supposed  tliat  proteid  in  its  decomposition  is  split  up 
into  a  nitrogenous  and  a  nonnitrogenous  portion.  This  view  however  is  no 
longer  tenable,  for  from  the  fact  that  numerous  nitrogenous  compounds  appear 
successively  in  the  hydrolytic  cleavage  of  proteid,  it  follows  that  the  final 
separation  of  the  carbon  from  the  nitrogen  takes  place  at  a  very  late  stage 
of  the  process. 

In  the  body  proteid  and  its  digestive  products  do  not  undergo  a  continuous, 
progressive  cleavage  by  oxidation.  There  undoubtedly  occur  a  number  of 
synthetic  processes  by  which  the  groups  contained  in  the  proteid  molecule 
undergo  many  changes  of  position  of  one  kind  and  another.  Hence,  the 
problem  of  the  decomposition  of  proteid  in  the  body  is  extremely  complicated 
and  cannot  be  regarded  as  by  any  means  solved. 

In  the  destruction  of  proteid  by  chemical  reagents  outside  the  body  a 
certain  quantity  of  urea  is  formed,  which  comes  from  arginin,  not  by  oxida- 

369 


370        THE  FINAL  DECOMPOSITIOX  OF   FOODSTUFFS  IX  THE  BODY 

tion,  but  b}'  cleavage  of  the  arginin  with  absorption  of  water  into  urea  and 
diamino-valerianic  acid  (Drechsel). 

Drechsel  estimated  that  100  parts  of  proteid  undergoing  cleavage  in  the 
body  would  be  able  to  yield  in  this  way  3.8  parts  of  urea  without  suffering  any 
oxidation.  Since,  further,  100  parts  of  proteid  yield  altogether  34.3  parts  urea, 
it  follows  that  about  one-ninth  of  the  total  urea  eliminated  may  issue  from  the 
proteid  by  a  simple  process  of  cleavage.  In  fact  we  always  find  in  all  animals, 
even  in  those  in  which  the  greatest  part  of  the  nitrogen  of  the  urine  appears  as 
uric  acid,  a  certain  quantity  of  urea  (cf.  pages  TO  and  75  for  the  arginin  con- 
tent of  the  different  proteids). 

But  by  far  the  greatest  part  of  the  urea  eliminated  arises  from  proteid 
by  processes  of  oxidation.  When  amino  acids  (glycocoll.  leucin,  aspartic  acid) 
are  digested  with  finely  ground,  fresh  organs,  ammonia  is  split  off  from  them 
(Lang).  In  the  mammals  these  compounds  as  well  as  ammonia  are  trans- 
formed into  urea  and  as  such  are  given  off  through  the  kidneys  (Xencki, 
Salkowski  et  ah).  It  is  conceivable,  therefore,  that  ammonia  represents  an 
intermediate  stage  in  the  formation  of  urea.  Since,  however,  both  ammonia 
and  the  above-mentioned  amino  acids  contain  only  one  atom  of  X  in  the 
molecule,  and  urea  contains  two.  the  latter  can  only  be  formed  from  the 
former  by  a  process  of  synthesis.  This  might  take  place  by  the  combination 
of  ammonia  with  carbon  dioxide  into  carbamic  acid  or  ammonium  carljamate, 
and  the  formation  of  urea  from  these  by  the  loss  of  water.  In  fact,  Drechsel 
succeeded  in  preparing  urea  by  subjecting  an  aqueous  solution  of  ammonium 
carbamate  to  electrolysis  with  an  automatic  commutator  in  the  circuit,  so  that 
the  salt  was  alternately  exposed  in  rapid  succession  to  oxidation  by  nascent 
oxygen  and  reduction  by  nascent  hydrogen.  The  processes  taking  place  are 
illustrated  by  the  following  scheme: 

I.  XH,.CO.O.XH,  -{-0  =  XH,.CO.O.XHo  -f  H,0 

ammonium  carbamate 

II.  XH,.C0.0.XH2  +  H,  =  XH..CO.XH,  -f  H,0 

urea. 

The  fact  that  carbamic  acid  can  be  demonstrated  in  the  blood  and  in  the 
urine  constitutes  a  strong  argument  for  this  view. 

The  formation  of  urea  might  also  take  place  by  the  union  of  an  amido 
residue,  COXH.,  at  the  instant  of  its  formation,  with  the  amidogen,  XH,,  aris- 
ing by  oxidation  of  ammonia  (Hofmeister). 

A  definite  decision  between  these  two  possible  explanations  is  not  to  be  had 
at  present;  besides,  it  is  not  at  all  certain  that  the  formation  of  urea  takes  place 
by  one  method  only. 

Concerning  the  seat  of  urea  formation,  we  can  think  of  two  possibilities: 
either  it  is  formed  in  all  parts  of  the  body  wherever  proteid  is  broken  down, 
or  certain  organs  have  the  function  of  transforming  the  intermediary  prod- 
ucts of  metabolism  into  urea.  After  removal  of  the  kidneys  urea  collects  in 
the  body  in  consideral)le  quantities ;  these  organs  cannot  therefore  play  an 
all-important  part  in  its  production.  Meissner  found  in  the  liver  of  the  dog 
larger  quantities  of  urea  than  in  the  blood,  and  so  designated  this  organ  as 
the  one  in  which  the  major  part  of  the  urea  of  mammals  originates. 


THE  FINAL  DESTRUCTION  OF  PROTEID  371 

This  view  received  substantial  support  in  the  experiments  of  v.  Schroeder, 
in  which  by  artificial  perfusion  of  an  excised  dog's  liver  with  ammonium 
carbonate  or  formate,  the  production  of  urea  from  these  salts  was  demon- 
strated directly.  Experiments  carried  out  in  the  same  way  on  the  kidneys 
and  muscles  gave  onh^  negative  results.  Likewise  by  digestion  of  glycocoll 
with  crushed  liver  tissue  or  liver  extract,  urea,  or,  to  be  more  exact,  a  closely 
related  compound  is  formed  (Eichet,  Loewi  et  al.). 

Indirectly  the  importance  of  the  liver  in  this  connection  is  shown  by  the 
experiments  of  Nencki  and  Pawlow  on  dogs  with  an  Eck  fistula  between  the  por- 
tal vein  and  the  inferior  vena  cava  (of.  page  274)  in  which  the  liver  therefore 
received  its  blood  by  the  hepatic  artery  only.  In  these  animals  the  elimination 
of  ammonia  in  the  urine  increased  and  the  power  of  the  organism  to  form  urea 
from  carbamic  acid  introduced  into  the  stomach  was  lost.  After  a  time  char- 
acteristic abnormal  symptoms  made  their  appearance  (namely,  somnolence, 
ataxia,  excitation,  loss  of  vision,  epilepsy,  anaesthesia,  tetanus)  and  these  could 
be  produced  at  will  by  an  abundant  supply  of  nitrogenous  food,  ammonium  salts, 
or  glycocoll. 

In  birds  and  reptiles  the  nitrogen  of  the  decomposed  proteid  leaves  the 
body  chiefly  as  uric  acid.  Any  information  Ave  can  get  as  to  the  seat  of  uric 
acid  production  in  birds  ought  therefore  to  be  strongly  suggestive  of  the  seat 
of  urea  production  in  mammals.  Birds  are  especially  well  adapted  to  experi- 
mental investigation  of  this  subject  because  extirpation  of  the  liver  is  rela- 
tively easy  on  account  of  the  peculiar  relations  of  the  circulation.  The  ani- 
mals live  for  as  much  as  twenty  hours  after  the  operation.  Their  urine, 
however,  is  very  poor  in  uric  acid,  since  only  about  three  to  four  per  cent 
of  the  total  nitrogen  is  now  eliminated  in  this  form,  whereas  the  percentage 
of  ammonium  salts  (lactate)  is  considerably  increased.  Amino  acids,  which 
normally  are  transformed  into  uric  acid  in  birds,  when  fed  to  geese  deprived 
of  the  liver,  are  eliminated  as  ammonium  lactate.  Urea  passes  out  unchanged 
(Minkowski).  The  quantity  of  uric  acid  eliminated  also  has  been  increased 
by  electrical  stimulation  of  the  liver  (Milroy).  Hence  the  liver  must  be 
regarded  as  the  seat  of  uric  acid  production  in  birds. 

We  may  conclude  also  that  urea  is  formed  from  ammonia  to  a  very  large 
extent  in  the  liver,  and  that  the  other  organs  probably  have  at  most  only 
a  small  share  in  this  function.  The  digestive  tract  is  indicated  as  the  chief 
source  of  the  ammonia ;  for,  according  to  the  investigations  of  Xencki,  Salas- 
kin  and  others,  the  percentage  of  ammonia  in  the  intestinal  and  gastric 
mucosa  is  considerably  greater  than  that  of  the  other  organs;  the  portal  blood 
also  is  considerably  richer  in  ammonia  than  the  blood  of  the  hepatic  arteries 
and  veins.  The  ammonia  split  off  in  the  liver  from  the  amino  acids  must 
be  taken  into  account  also. 

There  is  in  all  this  however  no  proof  that  all  of  the  urea,  exclusive  of  that 
split  off  directly  from  the  proteid  (cf.  page  369).  comes  from  ammonia  and 
is  formed  in  the  liver.  Observation  shows  rather  that  in  the  dog  large  quan- 
tities of  urea  are  eliminated  even  after  complete  extirpation  of  the  liver. 
Similarly  it  has  been  found  that  in  diseases  of  the  human  liver  where  the 
entire  organ,  to  judge  from  examination  of  sections,  had  become  completely 
inefficient,  more  than  sixty  per  cent  of  the  total  nitrogen  in  the  urine  has 


372       THE  FINAL  DECOMPOSITION  OF  FOODSTUFFS  IN  THE  BODY 

been  excreted  as  urea.  Now  if  it  be  true  tbat  only  the  liver  can  transform 
ammonia  into  urea,  it  follows  that  only  a  part  of  the  nitrogen  contained  in 
proteid  passes  over  into  ammonia,  while  another  part  runs  through  other 
stages  until  finally  it  also  is  given  off  from  the  body  as  urea. 

Under  normal  circumstances  ammonia  in  certain  quantities  is  always  present 
in  the  urine.  This  ammonia  is  necessary  in  order  to  help  saturate  the  acids 
excreted  in  the  urine,  for  the  fixed  bases  are  not  sufficient  for  this  purpose.  If 
the  acid  production  in  the  body  is  larg-e,  or  if  free  acids  are  taken  into  the  body, 
the  quantity  of  ammonia  is  larger  and  the  quantity  of  urea  correspondingly 
decreases.  With  increased  supply  of  fixed  alkalies  the  quantity  of  ammonia  falls, 
and  the  quantity  of  urea  rises.  The  formation  of  urea  from  ammonia  varies 
therefore  according  as  a  greater  or  less  amount  of  ammonia  finds  employment 
as  such.  It  appears  to  follow  from  what  has  already  been  said  that  the  regula- 
tion of  this  function  is  committed  to  the  liver. 

The  uric  acid  which  is  eliminated  from  mammals  in  general  does  not 
represent  a  product  of  proteid  decomposition,  but  appears  to  come  mainly 
from  the  nucleins  (Horbaczewski).  The  nucleins  are  split  up  in  the  body 
into  proteid,  phosphoric  acid  and  purin  bases  (cf.  page  76).  The  latter 
pass  by  oxidation  over  into  uric  acid:  however,  some  purin  bases  besides  uric 
acid  occur  in  the  urine,  though  the  quantity  of  these  is  rather  small. 

Recent  observations  (Burian  and  Schur,  Siven)  have  proved  that  uric  acid 
is  derived  in  part  from  ptirin  bases  which  are  introduced  into  the  body  with 
the  food  (exogenous),  and  in  part  from  those  present  in  the  body  itself 
(endogenous). 

The  amount  of  the  latter  is  constant  for  the  same  individual — for  an  adult 
man  in  health  amounting  to  0.3-0.6  g.  (^0.1-0.2  g.  X)  per  day.  It  can  be 
determined  directly  if  a  diet  containing  no  nucleins  (purin  bases) — consisting 
for  example  of  milk,  cheese,  eggs,  potatoes,  rice,  white  bread,  etc. — be  given. 
The  amount  of  purin  bases  and  of  uric  acid  in  the  urine  is  then  relatively  con- 
stant, notwithstanding  that  very  great  variations  in  the  quantity  of  proteid 
may  be  supplied  in  such  foods.  We  have  no  positive  information  yet  as  to  the 
processes  upon  which  the  so-called  endogenous  acid  depends. 

If,  however,  the  diet  consist  of  foods  which  contain  purin  bases  (meat,  liver, 
thymus,  etc.)  the  quantity  of  uric  acid  eliminated  increases  in  proportion  to  the 
amount  of  purin  eaten.  The  amount  of  any  purin  base  that  will  appear  in  the 
urine  as  such,  or  as  the  closely  related  uric  acid,  depends  upon  its  chemical 
nature.  Thus  with  hypoxanthin  (meat,  liver,  spleen)  one-half,  and  with  adenin 
(thymus)  one-fourth  of  the  purin  nitrogen  fed  appears  again  in  essentially  the 
same  form  in  the  urine  (Burian  and  Schur). 

According  to  the  investigations  of  Wieners,  uric  acid  is  formed  at  least  in 
the  liver,  the  thymus  and  spleen,  and  it  is  not  unlikely  that  all  the  organs  par- 
ticipate in  its  production  according  to  the  quantity'  of  nucleins  contained  in  them. 

At  any  rate,  the  purin  derivatives  given  off  in  the  urine  of  mammals  is  only 
a  fractional  part  of  that  taken  up  in  the  food,  or  of  that  formed  in  the  body 
itself.  A  considerable  part  of  both  must  be  further  oxidized  and  be  transformed 
into  urea.  Probably  the  best  proof  of  this  is  the  fact  that  after  extirpation  of 
the  kidneys,  uric  acid  does  not  accumulate  in  the  blood.  Hence  the  normal 
elimination  of  uric  acid  might  be  due  to  the  circumstance  that  the  transforma- 
tion of  urea  is  not  quite  complete,  but  the  blood  takes  the  opportunity  presented 


THE  FINAL  DESTRUCTION  OF  PROTEID  373 

during  its  passage  through  the  kidneys  of  partially  ridding  itself  of  waste  in 
the  form  of  uric  acid. 

Allantoin  appears  in  the  urine  of  the  dog  after  ingestion  of  uric  acid 
( Salkowski ) .  It  has  been  demonstrated  also  in  the  urine  of  man — e.  g.,  in 
hepatic  cirrhosis.  This  compound  might,  therefore,  represent  an  intermediary 
step  in  the  destruction  of  uric  acid.  The  genetic  relationship  between  the 
substances  considered  here  will  be  evident  from  the  following  formulae: 

HN— CO  HX— CO  NH, 

HC     C-NH  OC     C_XH  CO^  CO-NH  CO(^IJ' 

D       II  CH  I       II  CO  \  I  CO  ^^11, 

N—C—  N  ^  HN— C— XH^  XH— CII— NH^ 

Hypoxanthin  Uric  acid  AUantoin  Urea 

(6-Oxypurin)  (2,  6,  8-Trioxypurin)  (Glyoxyl-diureid)  (Carbamide) 

It  appears  from  several  observations  that  the  liver  is  the  seat  of  the  destruc- 
tion of  uric  acid.  By  artificial  perfusion  of  this  organ  with  blood,  or  by  digestion 
of  uric  acid  with  ground  liver  substance,  uric  acid  disappears.  Moreover, 
according  to  Burian  and  Schur,  it  immediately  appears  in  the  blood  of  nephrec- 
tomized  dog's  when  the  liver  also  is  thrown  out  of  the  circulation.  And  yet 
.there  are  other  observations  which  go  to  show  that  other  organs  also  are  capable 
of  decomposing  uric  acid. 

Uric  acid  therefore  represents  an  intermediary  product  of  metabolism  in 
Mammalia.  In  birds  it  is  the  chief  nitrogenous  end  product  of  proteid,  and  is 
formed  for  the  most  part  by  a  synthetic  process  carried  to  completion  in  the 
liver.  A  residue  of  urea  and  sarcolactic  acid  are  probably  to  be  regarded  as  the 
basal  material  of  this  synthesis. 

The  sulphur  contained  in  proteid  is  eliminated  in  the  urine  mainly  as 
sulphates  and  ethereal  sulphates  ("acid  sulphur"'),  but  in  part  also  as  "neu- 
tral sulphur"  (sulplio-cyanic  acid,  derivatives  of  taurin.  cystein,  oxyproteic 
acid,  and  other  organic  compounds).  A  part  of  the  sulphur  moreover  is 
given  off  as  taurocholic  acid  in  the  bile  (cf.  page  353).  It  is  likely  that  this 
sulphur  comes  mainly  from  the  cystein  group. 

As  mentioned  at  page  127,  it  is  very  probable  that  under  certain  circum- 
stances at  least,  carbohydrates  are  formed  in  the  body  from  proteid.  and, 
indeed,  that  this  may  take  place  without  the  participation  of  the  carbohydrate 
group  contained  in  most  proteids.  From  all  that  we  know  of  the  manner 
of  cleavage  of  proteids,  this  formation  of  carbohydrates  must  be  regarded 
as  a  synthetic  process,  in  which  sugar  is  constructed  by  splitting  off  of  the 
amido  groups,  and  by  synthesis  and  partial  oxidation  of  the  X-free  fraction 
remaining  (F.  Miiller). 

According  to  a  summary  of  Langstein,  the  following  possibilities  are  to  be 
considered.  Lactic  acid  can  be  obtained  very  easily  from  alanin  by  the  action 
of  nitrous  acid.  This  is  an  isomer  of  glycerin  aldehj'de  which  easily  condenses 
to  dextrose. 

CH,  CH,  CH,.OH         CH^.OH 

CH.NH,       CH.OH        CH.OH  (CH.OH), 

COOH         COOH         CHO     '       CHO 

Alanin  Lactic  acid  Glycerin  aldehyde  Dextrose 


374       THE  FINAL  DECOMPOSITION  OF  FOODSTUFFS  IN  THE  BODY 

111  fact  after  fcediiijr  with  alaiiiii  lactic  acid  is  observed  in  the  urine,  some- 
times also  an  increase  of  the  liver  glycogen.  Whether  we  have  here  a  direct  or 
an  indirect  formation  of  glycogen  (cf.  page  126)  cannot  be  decided. 

Moreover  sugar  might  be  formed  from  leucin  by  passing  through  the  stage 
of  tetra-oxyamino-caproic  acid  (actually  demonstrated  in  the  body)  to  dextrose. 

CH,.OH 
CO.OH  CH,.OH  CH,.OH  CH.OH 

CH.NH,  a  CH.NH,  CH.OH  CH.OH 

CH,  ^  CH.OH  CH.OH  CH.OH 

CH  y  CH.OH  COH  CH.OH 

CH^  CH3  CH3  COOH  Ch'^  \^00H  CHO 

Leucin  Tetra-oxyamino-  Saccharinic  acid  Dextrose 

caproic  acid 

It  would  be  possible  also  for  leucin,  by  breaking  down  the  carbon  chain 
between  the  ^  and  y  atoms,  to  pass  into  sugar  by  way  of  alanin  and  lactic  acid.^ 
Observations  on  diabetic  patients  likewise  favor  this  idea  of  a  production  of 
sugar  from  leucin ;  for  by  feeding  leucin,  a  distinct  increase  of  the  sugar  elimi- 
nation is  obtained. 

Finally,  a  production  of  sugar  from  diamine  acids  by  way  of  oxyamino  acids 
is  possible. 

§2.    THE   DECOMPOSITION   OF   CARBOHYDRATES 

The  carbohydrates  absorbed  from  the  intestine  reach  the  blood  for  the  most 
part  as  dextrose.  If  the  percentage  of  sugar  in  the  blood  by  reason  of  an 
extra  large  quantity  in  the  food,  exceeds  a  certain  low  limit  (from  0.3  to 
0.3  per  cent),  a  part  of  the  sugar  is  eliminated  through  the  kidneys  in  the 
urine  (alimentary  glycosuria,  cf.  page  127)  ;  otherwise  the  urine  contains  only 
traces  of  sugar.  The  kind  of  sugar  appearing  in  the  urine  under  these  con- 
ditions is  always  the  same  as  that  fed  in  excess.  Starch  does  not  produce 
alimentary  glycosuria,  probably  because  a  sudden  flooding  of  the  blood  with 
sugar  is  prevented  by  its  relatively  slow  rate  of  digestion. 

Sugar  which  is  not  immediately  oxidized  is  stored  in  the  body  either  as 
fat  or  as  glycogen,  and  is  then  drawn  upon  as  required.  The  greatest  part 
of  the  glycogen  is  deposited  in  the  liver,  but  it  is  not  burned  there.  It  passes 
in  some  way  into  the  general  circulation  and  is  oxidized  in  the  tissues  of 
the  body,  especially  in  the  muscles.  It  is  possible  that  this  transportation 
is  accomplished  in  part  by  the  help  of  the  leucocytes.     Another  and  in  all 

*  This  pos.sibility  is  strengthened  by  the  observation  of  Embden,  Salomon  and  Schmidt 
that  acetone  is  obtained  by  perfusion  of  leucin  through  a  glycogen-free  liver.  Quite  re- 
cently also  Lusk  and  A.  R.  Mandel  have  shown  that  in  phloridzin  diabetes  sarcolactic 
acid,  injected  subcutaneously,  can  be  synthesized  into  dextrose ;  and  Almagia  and 
Embden  have  obtained  a  production  of  lactic  acid  by  perfusing  blood  containing  glyco- 
gen or  dextrose  through  a  liver  containing  no  glycogen,  as  well  as  by  perfusing  a  blood 
poor  in  sugar  through  a  liver  rich  in  glycogen.  Lusk  has  suggested,  therefore,  that  the 
history  in  tlie  body  of  carbohydrates  derived  from  proteid  may  include  the  following 
events  :  (1)  lactic  acid,  (2)  dextrose,  (3)  glycogen,  (4)  dextrose,  (5)  lactic  acid. — Ed. 


THE   DECOMPOSITION   OF  CARBOHYDRATES  375 

probability  a  much  more  important  part  takes  place  by  the  transformation 
of  glycogen  into  dextrose,  which  is  then  carried  in  solution  by  the  blood 
plasma. 

The  physiological  production  of  sugar  in  the  liver  which  was  discovered  by 
CI.  Bernard  (1853),  has  since  that  time  often  been  denied  on  the  assumption 
that  the  increase  of  sugar  easily  demonstrated  in  an  excised  liver,  is  due  to 
post-mortem  processes.  This  explanation,  however,  is  not  borne  out  by  well- 
authenticated  facts  obtained  from  many  experiments;  hence  the  formation  of 
sugar  in  the  liver  must  be  regarded  as  a  physiological  process. 

For  example,  if  a  puncture  in  the  middle  of  the  floor  of  the  third  ventricle 
between  the  points  of  origin  of  the  auditory  nerve  and  the  vagus,  be  made  with 
a  blunt  needle,  sugar  immediately  appears  in  the  urine  (puncture  diabetes  of 
CI.  Bernard),  and  the  liver  glycogen  rapidly  disappears.  If,  however,  the 
puncture  experiment  be  performed  on  a  fasting'  animal  whose  liver  glycogen  is 
already  used  up,  no  sugar  appears  in  the  urine. 

After  a  time  the  liver  recovers  its  ability  to  store  up  carbohj^drates  as  glyco- 
gen. On  this  ground  the  formation  of  sugar  might  be  regarded  as  the  result 
of  a  stimulus,  and  not  as  the  result  of  decomposition.  The  stimulus  is  conveyed 
to  the  liver  by  the  splanchnics,  for  after  section  of  these  nerves  the  puncture 
is  ineffective. 

Sugar  in  the  urine  can  be  caused  also  by  stimulation  of  numerous  afferent 
nerves,  as  well  as  by  various  traumatic  and  operative  effects  widely  different  in 
character  (e.  g.,  concussion  or  hemorrhage  of  the  brain,  inflammation  of  the 
brain  membranes,  neuralgia,  etc.).  Reflexes  are  involved  here,  which,  with  the 
cooperation  of  the  medulla,  lead  to  an  increased  formation  of  sugar  in  the  liver. 
By  means  of  these  reflexes  the  w^orking  organs,  especially  the  muscles,  remove 
from  the  liver  the  carbohydrate  fuel  required  in  the  performance  of  their  func- 
tions. They  constitute,  therefore,  as  Pfliiger  has  pointed  out,  an  important 
regulatory  mechanism  for  the  consumption  of  the  available  material  in  the 
body. 

The  transformation  of  glycogen  to  sugar  is  regarded  by  some  authors  as  an 
expression  of  the  vital  activity  of  the  liver  cells ;  others  explain  it  as  the  effect 
of  a  special  enzyme  which  is  formed  in  the  cells. 

After  extirpation  of  the  pancreas  (cf.  page  362),  after  poisoning  with  the 
glucoside  phloridzin,  in  diabetes  mellitus,  and  under  certain  other  circum- 
stances, the  metabolism  of  the  carbohydrates  undergoes  a  chronic  change,  so 
that  sugar  in  aljnormally  large  quantities  is  given  off  in  the  urine.  In 
phloridzin  poisoning  this  is  caused  primarily  by  an  increased  permeability 
of  the  kidneys  to  sugar,  whereas  the  other  forms  of  morbid  glycosuria  arise 
because  the  body  has  lost  to  a  greater  or  less  extent  the  power  either  to  burn 
sugar  or  to  store  it  up  as  glycogen  or  fat. 

In  the  so-called  light  form  of  diabetes,  sugar  is  given  off  through  the 
kidneys  only  in  case  the  food  contains  carbohydrates;  if  carbohydrates  are 
prohibited,  the  loss  of  sugar  ceases.  In  the  severe  form  of  the  disease  to 
whicli  pancreatic  diabetes  belongs,  sugar  appears  in  the  urine  even  if  no 
carbohydrates  be  given  in  the  food.  The  body  then  oxidizes  little  or  no  sugar, 
although  its  power  to  oxidize  is  not  at  all  reduced.  Since,  as  was  above 
remarked,  at  page  128.  sugar  is  prol)ably  not  formed  from  fat  in  the  bod}', 
the  sugar  in  this  case  must  come  from  the  proteid. 


376       THE  FINAL  DECOMPOSITION  OF  FOODSTUFFS  IN  THE  BODY 

In  diabetes  there  appear  in  the  urine  besides  sugar  the  so-called  acetone 
bodies:  /3-oxybutyric  acid,  aceto-acetic  acid  and  acetone,  the  relations  of  which 
to  each  other  are  evident  from  the  following  formulae: 

CH3  CH3  CH3 

CH.OH  CO  CO 

CH,  CH,  CH3 

COOH  COOH  ,^.     Acetone 

(di-methyl-ketone) 
/J-Oxybutyric  acid  Aceto-acetic  acid 

With  the  exception  of  acetone,  which  is  eliminated  in  small  quantities  under 
physiological  conditions  also,  these  compounds  never,  so  far  as  known,  appear 
in  the  normal  urine;  from  which  it  follows  that  diabetes  must  be  intimately 
connected  with  deep-seated  changes  in  the  general  metabolism. 

Most  of  the  carbohydrates  pass  through  the  stage  of  hexoses  before  they 
are  further  decomposed  in  the  body.  Like  the  other  foodstuffs  they  are  not 
immediately  oxidized  to  their  end  products,  but  pass  through  more  or  less 
complex  groups  ])efore  being  eliminated  as  carlion  dioxide  and  water.  To 
these  intermediary  products  belong:  glycuronic  acid  CHO.(CHOH)^.COOH, 
which  in  its  turn  can  be  transformed  into  oxalic  acid  in  the  body;  sarcolactic 
acid  (  ?)  ;  and  ethyl  alcohol.  It  cannot  be  decided  yet  from  the  observations 
thus  far  reported  whether  sugar  always  breaks  up  in  the  same  way,  or  whether 
under  different  circumstances  and  in  different  organs  it  runs  through  different 
cleavage  products. 

§  3.    THE   DECOMPOSITION   OF   FAT 

Fat  eaten  in  excess  is  directly  deposited  as  such  in  the  fat  cells.  How  it 
is  transported  and  how  deposited  is  not  yet  entirely  clear.  Metzner  in  his 
investigations  of  this  question  was  unable  to  find  anywhere  a  depository 
where  fat  was  entering  cells  in  corpuscular  form ;  he  never  found  in  the 
immediate  neighborhood  of  cells  any  fatty  granules  similar  to  those  found 
inside  of  the  cells.  Moreover,  in  the  very  early  stages  of  deposition,  fat  is  not 
laid  down  in  the  form  of  granules,  but  in  the  form  of  minute  vacuoles  which 
expand  and  enlarge  from  day  to  day  (cf.  page  304).  Tliese  facts  are  inter- 
preted by  Metzner  and  Altmann  to  mean  that  fat  is  added  to  the  cells  only 
in  the  form  of  soluble  cleavage  products  (fatty  acids),  which  are  synthesized 
again  into  neutral  fats  in  the  cell.  It  is  not  unlikely  that  fat  is  again  split 
up  when  it  leaves  the  fat  cells  and  is  carried  to  the  different  organs  in 
soluble  form. 

For  the  purpose  of  obtaining  some  light  on  the  oxidation  of  fats  in  the 
animal  organism,  Pohl  has  studied  the  behavior  in  the  body  of  those  inter- 
mediary cleavage  products  which  theoretically  may  be  expected  to  appear  in  the 
normal  course  of  fat  destruction.  Thus,  if  the  series  of  substances  which  can 
be  formed  in  the  oxidation  of  highly  complex  fatty  bodies — i.  e.,  fatty  acids  and 
carbohydrates — be  arranged  in  order,  it  is  seen  that  relatively  simple  inter- 
mediary compounds  precede  the  formation  of  CO,,,  alike  for  the  most  widely 
different  bodies.    If  now  it  can  be  shown  by  experiments  on  animals  that  some 


THE  DECOMPOSITION  OF  FAT  377 

of  the  theoretically  possible  predecessors  of  carbon  dioxide,  when  injected  directly 
into  the  animal  body,  are  destructible  but  others  are  not,  some  idea  can  be 
formed  whether  or  not  such  intermediary  compounds  appear  in  the  physiological 
oxidation  of  complex  fat  bodies.  Pohl's  investigation  has  shown,  for  example, 
that  oxalic  acid  is  indestructible  in  the  animal  body;  that  the  acids  presumably 
occurring  in  the  oxidation  of  the  ethane  derivatives,  glycolic  acid,  CH,.OH. 
COOH,  and  glyoxylic  acid,  CH(nO),.COOH,  can  be  destroyed  in  relatively 
large  quantities  without  fonning  any  oxalic  acid,  as  occurs  when  they  are  oxi- 
dized outside  the  body.  Therefore,  the  most  highly  oxidized  acid  of  the  series, 
which  is  combustible  in  the  body,  namely  glyoxylic  acid,  may  be  considered  as 
the  stage  immediately  preceding  the  carbon  dioxide  excreted.  Glycol,  CHjOH. 
CH.,OH,  is  only  partly  combustible  in  the  body  without  forming  oxalic  acid. 
Malonic  acid,  CH,(CdOH)„,  tartronic  acid,  CH.OH(COOH),,  mesoxalic  acid, 
(HO),. C.  (COOH),,  glyceric  acid,  CH,.  (OH)  .CH(OH)  .COOH,  are  combus- 
tible and  thus  their  production  as  intermediary  stages  in  animal  combustion  is 
rendered  possible.  On  the  other  hand,  the  body  has  the  power  to  burn  tartaric 
acid,  C^HoOa,  only  to  a  slight  extent. 


CHAPTER    XIII 

THE    EXCRETIONS    OF    THE    BODY 

Several  organs,  the  skin,  the  intestine  and  liver,  the  lungs  and  the 
kidneys,  in  addition  to  their  other  functions  have  the  function  of  eliminating 
various  substances  which  are  useless  or  harmful  to  the  body.  We  place  first 
among  these  substances  the  products  formed  in  the  decomposition  of  the 
foodstuffs.  Substances  also  which  enter  the  body  in  one  way  or  another, 
and  themselves  exert  a  harmful  influence  are  thro\\Ti  out  either  unchanged 
or  more  or  less  transformed  by  the  activity  of  some  organ.  These  trans- 
formations in  many  cases  are  for  the  purpose  of  changing  harmful  suhstaiices, 
which  cannot  be  eliminated  at  once,  into  relatively  harmless  ones.  We  have 
already  become  acquainted  with  an  example  of  this  in  the  formation  of  urea 
out  of  ammonium  salts  (cf.  page  370).  Here  belong  also  the  following 
phenomena : 

In  the  putrefaction  of  proteid  in  the  intestine  there  arise  among  other  prod- 
ucts indol,  skatol,  paracresol,  phenol,  phenyl-propionic  acid,  phenyl-acetic  acid, 
paroxy-phenyl-acetic  acid,  paroxy-phenyl-propionic  acid,  etc.,  all  belonging  to 
the  aromatic  series — which  in  part  pass  into  the  circulation.  Of  these  the  last 
two  named  (the  so-called  aromatic  oxyacids),  paroxy-phenyl-propionic  acid, 
CeHi(OH)  .C2H4.COOH,  derived  from  tyrosin  by  the  splitting  off  of  ammonia, 
and  the  oxidation  product  of  this  acid,  paroxy-phenyl-acetic  acid,  CcH^COH). 
CH2.COOH — these  two  pass  out  in  the  urine  mostly  unchanged.  The  others 
are  not  burned  in  the  body,  but  before  they  come  out  in  the  urine,  they  undergo 
a  synthetic  transformation  by  which  they  are  rendered  innocuous. 

The  earliest  known  example  of  such  transformations  is  the  demonstration 
by  Wohler  (1824)  that  benzoic  acid,  when  ingested  into  the  animal  body,  passes 
over  into  an  acid  rich  in  carbon,  but  poor  in  nitrogen,  namely  hippuric  acid,  and 
is  excreted  as  such  through  the  kidneys.     Hippuric  acid,  CeHs.CO 

I 
HKCH,.COOH, 

is  a  compound  of  glycocoll  (amino-acetie  acid,  NH^.CHo.COOH)  with  benzoic 
acid,  which  is  an  oxidation  product  of  phenyl-propionic  acid  (CcH5.CH,.CH,. 
COOH)  formed  in  intestinal  putrefaction. 

The  synthesis  of  hippuric  acid  takes  place  in  the  dog  exclusively  in  the  kid- 
neys (Schmiedeberg  and  Bunge),  but  in  the  rabbit  in  other  organs  also  such  as 
the  liver  and  muscles.  If  salicylic  acid,  oxybenzoic  acid,  paroxy-benzoic  acid, 
etc.,  instead  of  benzoic  acid,  be  fed  to  mammals  they  all  undergo  transformations 
analogous  to  that  of  benzoic  acid  into  hippuric  acid,  since  like  it  they  unite 
to  a  greater  or  less  extent  with  glycocoll.  The  acids  thus  formed  have  been 
designated  as  salicyluric,  oxybenzuric,  paroxybenzuric,  etc. 
378 


THE  URIXE  379 

The  following  syntheses  appear  to  take  place  in  different  organs  of  the 
body,  especially  in  the  liver: 

CH  C.OH 

Indol,    CJI^     CH    passes    after  absorption    into    indoxyl,    C,H^        CH, 

and  this  body  then  unites  with  sulphuric  acid  into  indoxyl-sulphuric  acid,  urine 
/C.O.SO,(COH) 

indican,  C.H^CH 

In    an    exactly   similar    way   there    arise   from   skatol   or   methyl-indol, 
C.CH,  C.CH, 

C,H^      CH,    first    skatoxyl,    C^H^      C.OH,    and    then,    skatoxyl  -  sulphuric 

NH     C.CH,  NH 

acid,  CgH^     C.O.SO,(OH)  ;   from  phenol,  C.H^.OH,  phenol-sulphuric  acid, 

NH  Qjj 

C,Hj.O.SO,(OH) ;    from    paracresol,    C.H^^pxT     paracresol-sulphuric      acid, 

/O.SO,(OH) 
^.^«xCH, 

If  the  sulphuric  acid  available  is  not  sufficient  for  the  combination  of  the 
phenols,  they  are  paired  with  glycuronic  acid  (page  376).  This  acid  is  an  inter- 
mediary product  of  metabolism  and  is  further  decomposed  except  when  it  is 
protected  from  combustion  by  pairing  with  other  substances. 

Wo  have  already  studied  the  processes  of  excretion  in  the  intestine,  in  the 
liver  and  in  the  lungs.  There  remains  for  us  to  discuss  excretion  through  the 
kidneys  and  the  skin. 

FIRST    SECTION" 

THE   URINE   AND   ITS   EXCRETION 

§  1.    THE   URINE 

The  urine  is  formed  by  the  action  of  the  kidneys.  It  contains  the  most 
of  the  nitrogenous  and  sulphur-containing  products  of  metabolism  as  well 
as  a  large  number  of  other  substances  to  be  eliminated  from  the  body. 

A.    THE   GENERAL   PROPERTIES   OF   THE   URINE 

The  reaction  of  a  sample  of  urine  differs  according  to  the  indicator  used. 
With  pbcnolphthalein  it  is  acid,  with  litmus  acid,  neutral  or  alkaline,  with 
methyl  orange,  alkaline.  This  difference  is  referable  to  the  properties  of  the 
(Hffcrout  iiidicators,  wliich,  according  to  the  theory  worked  out  by  Ostwald,  rep- 
resent weak  acids  or  bases  whose  radicals  as  free  ions  possess  other  colors  than 
those  which  the  electrically  neutral  molecules  possess.     Thus  phenolphthaleni  in 


380  THE  EXCRETIONS  OF  THE  BODY 

the  nondissociable  condition  is  colorless;  as  soon  however  as  the  solution  is  ren- 
dered alkaline  a  salt  of  high  dissociability  is  formed,  and  the  intensely  red 
color  of  its  negative  ion  comes  to  the  fore.  But  in  order  that  the  reaction  may 
appear  with  a  very  slight  excess  of  hydroxyl  or  hydrogen  ions  the  acid  or  base 
used  as  the  indicator  must  be  very  weak  in  comparison  to  the  acid  or  base  to  be 
tested.  The  acidity  of  weak  acids  obviously  can  only  be  determined  by  the  help 
of  an  indicator  which  itself  is  still  weaker  than  the  weakest  of  the  acids  to  be 
tested :  in  the  presence  of  weak  bases  the  alkalinity  can  only  be  ascertained  with 
the  help  of  a  somewhat  stronger  acid  as  indicator — e.  g.,  methyl  orange. 

Xow  the  urine  contains  weak  acids  such  as  CO,  and  HaPO^  in  considerable 
quantities  and  a  rather  weak  base,  ammonium  in  very  small  quantities.  In 
order  to  obtain  the  true  reaction  of  urine,  one  must,  therefore,  use  a  verj-  weak 
acid  as  indicator.  Xeither  methyl  orange  nor  litmus  is  weak  enough  to  be 
liberated  by  carbon  dioxide  or  to  detect  phosphoric  acid  as  a  dibasic,  much  less 
as  a  tribasic  acid.  Phenolphthalei'n,  however,  is  sensitive  to  both,  although  the 
third  hydrogen  atom  of  phosphoric  acid  escapes  it. 

With  phenolphthalein  the  reaction  of  the  urine  is  always  neutral  or  weakly 
acid.  A  plainly  alkaline  reaction  is  never  met  with  except  in  urine  which 
has  suffered  bacterial  decomposition  (Auerbach  and  Friedenthal ) . 

By  titration  one  may  ascertain  the  true  chemical  acidity  of  the  iirine 
measured  as  the  quantity  of  alkali  which  must  be  added  to  displace  all  the 
acid  hydrogen  with  a  metal.  From  the  physico-chemical  standpoint,  how- 
ever, acidity  means  the  concentration  of  hijdrogen  ions  present  in  the  liquid. 
According  to  v.  Rhorer  and  Hoeber,  1  1.  of  urine  contains  on  the  average 
about  0.003-0.005  (minimum  0.0004,  maximum  0.01)  mg.  of  ionized  hydro- 
gen as  compared  with  0.0001  mg.  in  distilled  water.  This  acidity  corresponds 
to  an  acid  which  in  -jV  solution  is  dissociated  to  y^o  P^r  cent,  and  is  some  ten 
thousand  times  less  than  that  determined  by  titravion. 

In  view  of  the  very  complicated  physico-chemical  relations  of  the  urine,  it 
is  scarcely  possible  to  determine  the  share  of  the  diiferent  constituents  in  its 
total  acidity. 

FresJi  urine  as  a  rule  is  perfectly  clear;  but  on  standing  it  sometimes 
becomes  turbid  owing  to  the  separation  of  urates.  There  also  appears  in  it  a 
weak,  floeeulent  precipitate  (nubecula),  which,  according  to  K.  A.  H.  Morner, 
contains  a  special  mucous  substance  (urine  mucoid),  probably  formed  in  the 
mucous  membrane  of  the  urinary  passages  and  mixed  with  the  urine  as  a  weak 
gelatinous  solution. 

The  color  of  the  urine  depends  to  a  certain  extent  upon  its  concentration, 
and  varies  with  increasing  concentration  from  straw  yellow  to  dark  reddish 
yellow  and  reddish  brown.     Its  taste  is  salty,  its  odor  peculiarly  aromatic. 

The  quantity  of  urine  depends  upon  many  circumstances,  and  therefore 
varies  considerably.  The  average  quantity  for  an  adult  man  may  be  estimated 
at  about  1,500  c.c.  per  day. 

The  specific  gravity  of  the  urine  also  varies  in  man  from  1.017  to  1.020; 
but  it  may  fall  as  low  as  1.002  and  rise  as  high  as  1.047. 

The  molecular  concentration  (  A)  of  the  urine,  measured  by  the  lowering 
of  the  freezing  point,  stands  in  a  certain  relation  to  the  specific  gravity  (s),  and 


THE   URINE 


381 


can  be  estimated  approximately  by  the  formula:  A  =75  (s — 1).  The  relation 
between  the  molecular  concentration  of  organic  (Co)  and  inorganic  (Ci)  mole- 
Co 


cules, 


Ci 


is  commonly  0.75   (Burgarsky). 


Urine  injected  intravenously  into  an  animal  produces  an  acute  poisoning 
which  results  fatally.  The  toxicity  of  different  urines  appears  to  be  some- 
what different,  and  Bouchard  designates  as  the  toxic  unit  (urotoxy),  the 
quantity  (cubic  centimeters  per  kilogram)  of  urine  sufficient  to  kill  a  rabbit: 
this  quantity  varies  from  30-(jO  c.c.  According  to  Beck,  the  toxicity  of  normal 
urine  depends  upon  the  presence  of  potassium  salts;  however,  there  are  alka- 
loidal  substances  in  the  urine  which  are  present  only  in  small  quantities  nor- 
mally, but  under  abnormal  conditions  are  probably  eliminated  in  larger  quan- 
tities, and  these  mic^ht  therefore  increase  its  toxicity. 


B.    COMPOSITION   OF   URINE 

1.  Urea,  or  carljamide  (cf.  page  370;  also  Fig.  139),  is  the  most  important 
and  most  abundant  constituent  of  urine.  The  daily  excretion  depends  upon 
the  supply  of  proteid  in  the  food.  On  Voit's  normal  ration  for  a  moderate 
worker,  the  quantity  is  about  30  g.  per  day.  Usually  two  to  three  per  cent 
of  the  urine  is  urea.  Al)out  ninety  per  cent  of  the  total  quantity  of  nitrogen 
in  the  urine  of  man  appears  in  the  form  of  urea. 

Urea  was  first  separated  from  urine  by  Rouelle  (1773).  In  1828  "Wohler 
succeeded  in  preparing  it  synthetically  by  heating  a  solution  of  ammonium 
isocyanate : 

NH, 

Urea 


C  =  N-NH,  =  CO: 

Ammonium 
isocyanate 


This  synthesis  was  the  first  instance  of  the  production  by  artificial  means 
of  a  substance  occurring  in  the  animal  body,  and  led  the  way  for  all  the  organic 
syntheses  possible  to  modern  science.  For  this  reason  Berzelius  proposed  that 
the  radical  of  urea  be  named  proin  (signifying  "  dawn  "). 

The  origin  of  urea  in  the  animal  body  has  already  been  considered  in  Chap- 
ter XII.  Here  we  may  add  the  following  data  from  Schondorff  with  regard 
to  the  percentage  of  urea  in  the  different  organs.  These  relate  to  a  dog  of 
32  kg.  weight  after  abundant  meat  feeding.  The  organs  investigated  amounted 
altogether  to  fifty-three  per  cent  of  the  entire  body. 


Organ. 

Per  cent  of  urea. 

Absolute  quantity  in  gms. 

Blood 

O.llG 
0.080 
0.112 
0.670 
0.173 
0.122 
0.119 
0.128 

1.36 

Muscle 

12.15 

Liver 

0.94 

Kidneys. 

1.04 

Heart . 

0.29 

Spleen 

0.12 

Pancreas.             ...            .            

0.06 

Brain.           ,    

0.92 

Total . . 

16.88 

382 


THE  EXCRETIONS  OF  THE   BODY 


The  percentage  of  urea  in  the  individual  organs,  with  the  exception  of  the 
muscles,  the  heart  and  the  kidneys,  is  thus  about  the  same  as  that  of  the 
blood — i.  e.,  on  the  average  0.12  per  cent.  The  high  percentage  in  the  kid- 
neys is  to  be  explained  by  the  presence  there  of  urea  formed  in  other  organs, 
and  which  is  necessarily  included  in  making  the  analysis. 

2.  O.vi/protc'ic  acid  was  discovered  by  Bondzynski  and  Gottliel)  (1897). 
Its  barium  salt,  according  to  the  analyses  of  various  authors,  has  the  follow- 


FiG.  139. 


Fig.  140. 


Fig.  139. — Crystals  of  urea,  obtained  from  liuman  urine  after  long-continued  evaporation,  after 

Funke. 
Fig.  140. — Crystals  of  uric  acid,  after  Funke.     Some  of  the  forms  represented  were  obtained  by 

solution  and  recrystallization   of  chemically  pure  uric  acid;  some  by  treatment  of  urinary 

sediments  containing  urates  with  mineral  acids;  some  by  spontaneous  crj'stallization  from 

urine.     Most  of  the  crystals  are  tinged  with  urea. 

ing  composition:  C  27.5-30.0,  H  3.9-4.1,  X  7.0-10.6,  S  1.6-1.8.  Ba  28.7-29.8, 
0  26.5-31.6.  The  quantity  of  this  acid  (calculated  as  the  Ba  salt)  excreted 
in  twenty-four  hours  amounts  to  not  less  than  3-4  g. 


NH- 


-CO 


3.  Creatinin,    Methvl-glvco-cyanamid,    NH:C^  ,      occurs  to  the 

^       ^  N(CHJ.CH 

extent  of  about  0.25  per  cent  in  the  urine.     The  daily  output  in  the  urine 
amounts  to  0.6-2.1  g.  and  may  be  estimated  at  1  g.  as  a  mean  value. 

4.  Ammonia,  NH3.  The  daily  quantity  amounts  to  0.5-0.9  g.  =  two  to 
four  per  cent  of  the  nitrogen  in  the  urine.  The  ratio  of  ammonia  to  urea 
is  approximately  1:40  (cf.  page  371). 

5.  Uric  acid  (Figs.  140  and  141)  2,  6,  8-tri-oxypurin  (page  373)  occurs 
in  the  urine  of  man  and  the  mammals  only  in  small  quantities  (about  0.7  g. 
per  day).  This  is  a  dibasic  acid.  Of  the  alkaline  urates,  the  neutral  potas- 
sium and  lithium  salts  are  the  most  soluble,  the  acid  ammonium  salt  least  so; 
the  urates  of  the  alkaline  earths  are  also  very  difficultly  soluble.  In  the  urine, 
uric  acid  probably  occurs  as  monosodinm  urate  which  is  held  in  solution 
mainly  by  di sodium  phosphate. 

6.  Uric  acid  is  derived  from  the  purin  bases  and  is  in  its  turn  oxidized 
to  allanto'in  (cf.  page  373).  These  substances  also  occur  in  the  urine:  the 
purin  bases  to  the  extent  of  0.08-0.13  g.  (mean). 


THE  URINE 


383 


Of  the  total  organic  substance  in  the  urine,  urea,  creatinin,  ammonia, 
uric  acid  and  purin  bases  together  constitute  seventy-five  per  cent,  but  they 
contain  ninety-three  per  cent  of  the  total  nitrogen  of  the  urine  (Donze  and 
Lambling). 

7.  Oxalic  acid  occurs  in  very  slight  traces. 

8.  Hippuric  acid  (Fig.  142),  benzoyl-glycocoll  (page  378)  occurs  in  con- 
siderable quantity  in  the  urine  of  herbivorous  animals  and  in  smaller  quan- 
tity in  the  urine  of  man.  In  the  latter  on  ordinary  diet  it  amounts  to  only 
about  0.7  g.  per  day;  after  a  plentiful  quantity  of  vegetable  foods  it  may 
reach  2  g.  or  more  per  day. 

9.  The  ethereal  sulphates  and  the  aromatic  oxyacids  already  mentioned 
at  page  379.  The  quantity  of  the  former  per  day  in  the  urine  of  man  is  only 
about  0.09-0.62  g. ;  the  oxyacids  amount  to  about  0.03  per  day. 

10.  Among  the  pigments  of  the  urine  the  iron-free,  nitrogenous  urochrome, 
carefully  studied  by  Garrod,  is  the  most  important.  Besides,  there  are  present 
in  normal  urine:  the  red  pigment  uroerytlirin,  hcematoporphyrin  (in  very 
small  quantities),  and  urobilin,  first  described  by  Jaffe.  The  latter  has  a 
red  or  reddish-yellow  color,  and  in  the  opinion  of  many  authors  is  identical 
with  hydrobilirubin  (CgoH^oX^O^)  ;  but  this  is  contested  by  others  on  the 
ground   that   hydrobilirubin   contains   twice   as   much  nitrogen   as  urobilin. 


Fig.  141.  Fig.  142. 

Fig.  141. — Still  other  forms  of  uric-acid  crystals,  after  Funke.  The  "wheat  stone"  and 
"sheaf"  crystals  especially  are  shown.  Some  of  them  were  found  ready  formed  in 
urinary  sediments;  others  were  obtained  by  treatment  of  ordinary  sediments  containing 
sodium  urate  with  acids. 

Fig.  142. — Hippuric-acid  crystals,  obtained  from  human  urine  by  recrystallization  from  a  water 
solution,  after  Funkc. 

Stcrl-ohilin  (cf.  page  295),  on  the  other  hand,  has  exactly  the  same  composition 
as  urobilin.  At  all  events  urobilin,  as  well  as  other  pigments,  probably  stands 
in  a  close  relationship  l)oth  to  the  1)ilo  pigments  and  to  the  blood  pigments. 

11.  The  urine  contains  also  under  perfectly  normal  circumstances  reducing 
substances  and  proteids,  though  in  very  small  quantities. 

Besides  uric  acid  and  croatinin,  the  reducins'  substances  are  dextrose,  iso- 
maltose(?),  animal  gum,  and  conjugated  compounds  of  glj'curonic  acid  (page 
24 


384  THE  EXCRETIONS  OF  THE  BODY 

37G.     The  reducing  power  of  normal  urine  corresponds  to  a  0.15-O.G-per-cent 
solution  of  dextrose. 

Heller's  test  (cf.  page  69)  is  commonly  used  to  demonstrate  proteid  in  the 
urine.  A  urine  which  does  not  give  this  reaction  is  generally  regarded  as  free 
of  proteid.    And  yet  there  is  proteid,  chiefly  serum  albumin,  even  in  such  urine. 

12.  The  inorganic  constituents  of  the  urine  on  a  normal  diet  amount  to 
about  25  g.  per  day.  For  the  most  part  they  come  from  the  ingested  food, 
and  consequently  decrease  in  fasting.  Naturally  their  percentages  vary 
greatly :  hence  the  following  table  is  only  for  the  purpose  of  giving  a  general 
idea  of  the  average  quantities: 

Sodium  chloride,  XaCl 15.0  g.  per  day 

Sulphuric  acid,  H^SO,  2.5  g 

Phosphoric  acid,  P^O, 2.5  g 

Potassium,  KO   3.3  g 

Magnesium,  MgO 0.5  g 

Calcium,  CaO 0.3  g 

Other  inorganic  substances 0.2  g 

Besides  these  the  urine  contains  4-5  vols,  per  cent  of  CO^  which  for  the 
most  part  is  physically  absorbed,  but  occurs  also  in  the  form  of  acid  car- 
bonates. 

13.  Accidental  constituents.  The  urine  may  contain  either  in  solution  or 
suspension  a  large  number  of  different  bodies  coming  from  substances  ingested 
for  one  reason  or  another,  or  originating  from  abnormal  processes  in  the  body. 
I  shall  merely  enumerate  the  most  important  of  these : 

(a)  Blood,  blood  pigments  and  their  derivatives;  blood  corpuscles,  haemo- 
globin, methsemoglobin,  haematin,  melanin,  etc. 

(h)  Bile  acids,  bile  pigments,  and  their  transformed  products. 

(c)  Leucin,  tyrosin,  and  diosy-phenyl-acetic  acid,  C8H3(OH),.CH2. COOH. 

(d)  Proteid. 

(e)  Sugar. 

(f)  Acetic  acid,  ^-oxybutyric  acid  and  acetone. 

(g)  Drugs,  either  as  such  or  as  transformed  products. 

§  2.    THE   EXCRETION   OF   URINE 

In  no  other  secreting  organ  are  the  peculiarities  of  structure  so  significant 
for  a  conception  of  its  function  as  in  the  kidney.  It  is  therefore  necessary 
to  discuss  the  microscopic  structure  of  the  kidney  here  somewhat  in  detail. 

A.    STRUCTURE    OF   THE   KIDNEYS 

The  larger  branches  of  the  renal  artery  (Fig.  143)  run  along  the  outer  sur- 
face of  the  pyramids  to  their  base  and  there  form  an  anastomosing  network. 
From  this  network  branches  pass  toward  the  surface  of  the  kidney  (radial 
arteries),  and  others  pass  off  in  tufts  toward  the  pelvis  of  the  kidney.  The 
individual  branches  of  the  latter  run  between  bundles  of  urinarj-  tubules  in  the 
pyramids. 

The  radial  arteries  send  out  small  branches,  vosa  afferentia,  which  soon  break 
up   in   the    so-called  glomeruli    of  the   Malpighian   corpuscles   presently   to   be 


THE  EXCRETION  OF  URIXE 


385 


described.  From  these,  a  new  vessel,  the  vas  efferens,  arises  and  this  in  its  turn 
breaks  up  into  a  capillary  network  which  embraces  the  kidney  tubules.  Those 
vasa  efferentia  which  belong  to  the  deeper  layers  of  the  cortex  push  down  into 

the  outer  layer  of  the  medulla,  and  from  here  run 
between  the  renal  tubules  and  break  up  into  tufts 
of  vessels,  whence  again  proceed  capillaries  to  the 
tubules. 

From  the  capillaries  of  the  renal  cortex  the 
blood  collects  in  venous  trunks  which  run  parallel 
with  the  radial  arteries  to  the  outer  layer  of  the 
medulla,  and  like  them  foi*m  an  anastomosing 
netwoi'k    at    the   base  of   the    pyramids.     Into   this 


o  ;'0 
o  ' 


o 


^rp 


O 


,7i« 


\'-'  n\ 


Fig.  143. — Schema  rcpre.sent- 
ing  the  distribution  of  the 
blood  vessels  of  the  kidney, 
after  Ludwig.  Arteries  red, 
veins  blue. 


Fig.  144. — Schematic  representations  of  the  secreting 
and  conducting  elements  of  the  kidney,  after  I.udwig. 
7,  Bowman's  capsule;  //,  first  convoluted  tubule; 
HI,  IV,  Henle's  loop;  F,  second  convoluted  tubule; 
y/,' collecting  tubule;  r,  cortex;  g,  medulla;  p,  papilla. 


network  empty  the  veins  from  the  medullaiy  substance,  which,  like  the 
arteries,  run  in  the  interstices  between  the  renal  tubules  and  converge  forming 
tufted  groups. 

The  qlomeruhis  interpolated  between  the  vas  afferens  and  the  vas  efferens 
has    the    following    structure.      The    afferent    arteriole   breaks    up    into    several 


386  THE  EXCRETIONS  OF  THE  BODY 

branches,  each  of  which  by  repeated  divisiim  forms  a  lobule  composed  of  sev- 
eral collateral  vessels.  These  vessels  do  not  anastomose,  but  unite  finally  to 
form  a  simple  vas  efferens,  the  beginning  of  which  lies  in  the  middle  of  the 
glomerulus.  They  have  a  simple  wall  and  hence  are  to  be  regarded  as  capillaries. 
In  the  kidney  therefore  the  blood  passes  through  two  sets  of  capillaries,  one  in 
the  glomeruli  and  the  other  between  the  secreting  elements. 

The  secreting  and  conducting  elements  of  the  kidney  are  numerous,  much- 
convoluted  tubules,  which  begin  at  the  glomeruli  and  end  on  the  free  surface 
of  the  papillae.  The  glomerulus  is  surrounded  by  a  thin  capsule  (the  capsule  of 
Bowman),  the  whole  constituting  a  Malpighian  corpuscle  (Fig.  144,  I).  The 
capsule  is  a  vesicle  composed  of  thin  epithelial  cells  of  0.13  to  0.22  mm.  diameter, 
and,  like  the  serous  sacs,  consists  of  two  layers,  a  visceral  and  a  parietal.  The 
former  layer  is  closely  applied  to  the  surface  of  the  glomerulus  and  is  reflected 
at  the  place  where  the  vessels  enter  the  glomerulus  to  form  the  latter  layer. 
From  the  point  opposite  the  entrance  of  the  vessels  the  .capsule  is  continued  into 
the  renal  tnhule.  In  the  transition  to  this  there  comes  first  a  short,  narrow 
neck;  then  follows  a  much  convoluted  portion  (II)  0.045  mm.  in  diameter  which 
reaches  down  to  and  enters  the  outer  layer  of  the  medullary  substance.  Here 
the  tubule  suddenly  diminishes  in  size  very  considerably  (the  diameter  is  only 
0.014  mm.)  and  passes  into  the  medullary  substance,  then  turns  back,  forming 
a  loop  (loop  of  Henle,  III  and  IV)  and  runs  toward  the  cortex.  Sooner  or 
later  it  becomes  enlarged  (0.026  mm.)  and  soon  thereafter  becomes  convoluted 
again  (V).  Then  it  unites  hj  means  of  a  narrow  connecting  portion  with  a 
collecting  tubule  (VI). 

Up  to  this  point  each  tubule  is  independent  of  every  other,  forming  no 
anastomoses.  The  collecting  tubes,  however,  in  their  course  through  the  medul- 
lary substance,  unite  repeatedly  with  others,  so  that  finally  the  number  of  tubes 
opening  on  the  surface  of  a  papilla  is  only  about  fourteen  to  twenty,  whereas 
there  are  from  4,000  to  6,000  collecting  tubules  tributary  to  them. 

The  epithelium  of  the  urinary  tubule  and  of  the  collecting  tubule  is  dif- 
ferent in  different  divisions.  In  the  human  foetus  Bowman's  capsule  is  com- 
posed of  cubical  cells;  in  the  newborn  child  the  cells  are  flatter,  and  later  they 
become  very  thin.  The  convoluted  tubules,  the  thicker  portion  of  Henle's  loop, 
and  the  collecting  tubule  are  lined  with  fairly  tall  epithelial  cells,  which  pre- 
sent minor  differences  in  the  different  divisions  named.  In  the  narrower  por- 
tion of  Henle's  loop  the  epithelium  consists  of  clear,  flat,  spindle-shaped  cells. 

B.    MECHANISM    OF   THE   EXCRETION   OF   URINE 

Any  attempt  to  explain  theoretically  the  process  of  secretion  in  the  kidneys 
must  take  into  account  the  remarkable  arrangement  of  its  blood  vessels  and 
the  renal  tubules. 

In  the  glomeruli  the  blood  flowing  in  is  suddenly  divided  into  a  consid- 
erable number  of  tiny  streams,  which  of  course  must  favor  the  passage  of 
constituents  into  the  capsule.  Moreover,  the  vas  efferens  has  a  smaller  diam- 
eter than  the  vas  afferens,  and  it  is.  divided  up  within  a  short  space  into 
another  true  capillary  network.  The  resistance  distal  to  the  glomeruli  must 
therefore  be  much  greater  than  the  resistance  proximal  to  them,  which  means 
that  the  blood  must  flow  through  the  glomeruli  under  a  relatively  high  pres- 
sure. If  now  the  further  fact  that  the  renal  tubules  begin  with  the  Bowman's 
capsule  surrounding  the  glomeruli  be  considered,  it  cannot  readily  be  denied 
that,  seen  merely  from  the  anatomical  point  of  view,  the  glomerulus  and  the 


THE  EXCRETION  OF  URINE  387 

capsule  must  play  an  extremely  important  part  in  the  secretion  of  urine.  A 
theoretical  account  of  the  kidney  function  must  assign  some  purpose  also  for 
the  tortuous  course  of  the  tubules  up  to  the  point  where  they  enter  the  col- 
lecting tubules. 

This  has  been  done  in  the  view  advanced  by  Ludwig  and  supported  by 
many  experiments,  namely  that  a  process  of  filtration  takes  place  from  the 
glomerulus  into  the  capsule,  and  that  the  filtrate  represents  a  very  dilute 
urine,  Avhich  during  its  passage  through  the  tubules  becomes  gradually  con- 
centrated by  transfusion  of  water  into  the  lymph  bathing  their  outer  surface. 

To  test  this  view  we  have  first  of  all  to  form  some  conception  of  the  physico- 
chemical  processes  necessary  for  the  filtration  of  liquid  through  the  capsular 
epithelium.  As  Tammann  was  the  first  to  show,  the  latter  cannot  be  regarded 
as  a  semipermeable  membrane,  for,  if  it  were,  a  blood  pressure  sufficient  to  over- 
come the  osmotic  pressure  of  the  plasma — several  atmospheres — would  be  required 
to  force  the  filtrate  through.  On  this  account  Tammann  considers  the  epithelium 
completely  permeable  to  all  the  crystalloids  dissolved  in  the  urine,  and  imper- 
meable only  to  the  colloids.  In  order  to  separate  a  proteid-free  filtrate  of  the 
composition  of  the  crystalloids  found  in  the  plasma,  the  blood  pressure  need 
only  be  high  enough  to  overcome  the  osmotic  pressure  of  the  colloids  occurring 
there.     The  latter  according  to  Starling  amounts  to  about  25-30  mm.  Hg. 

However,  the  osmotic  pressure  of  the  sugar  in  the  blood  (more  than  100 
mm.  Hg.)  is  not  taken  into  account  in  this  calculation;  whereas  it  may  be 
considered  that  the  capsular  epithelium  is  permeable  to  sugar  just  as  to  the 
other  crystalloids.  It  is  possible  too  that  the  sugar  is  not  free,  but  occurs  in 
the  blood  in  chemical  composition  with  other  substances  such  as  lecithin  or 
proteid.  If  this  were  true  the  osmotic  pressure  occasioned  by  the  sugar  would 
of  course  be  considerably  lower  than  if  it  were  dissolved  as  such  in  the  plasma. 

The  lowest  pressure  in  the  glomeruli  at  which  a  production  of  urine  could 
take  place  would  thus  be  about  25-30  mm.  Hg.  And  yet  Gottlieb  and  Magnus 
have  shown  that  under  the  influence  of  diuretic  substances,  separation  of  urine 
can  take  place  with  a  carotid  pressure  of  only  6-9  mm.  Hg. 

Besides  this  difficulty  we  have  another  just  as  little  to  be  explained  from 
the  standpoint  of  the  filtration  hypothesis,  and  that  is  this :  if  the  supply  of  the 
blood  to  the  kidney  be  completely  interrupted  by  clamping  the  renal  artery 
for  a  short  time,  say  one  and  one-half  minutes,  the  formation  of  urine  stops 
and  is  resumed  again  only  after  a  considerable  time  (as  much  as  forty-five 
minutes).  The  properties  of  a  perfectly  inert  filter  could  scarcely  be  changed 
to  such  an  extent  by  anaemia  of  so  short  a  duration. 

The  second  part  of  Ludwig's  theory  likewise  meets  with  several  difficulties. 
If  the  glomerular  filtrate  as  above  assumed  has  the  same  composition  and  there- 
fore the  same  osmotic  pressure  as  the  blood  plasma  (with  the  exception  of  the 
colloids)  then  only  the  osmotic  pressure  occasioned  by  the  colloids  can  have 
anything  to  do  with  the  concentration  of  the  filtrate.  Whether  or  not  this  force 
is  sufficient  to  produce  the  necessary  transfusion  of  water  back  into  the  lymph 
has  not  yet  been  decided.  Moreover,  the  proportion  of  cr>-stalloids  in  the  urine 
is  quite  different  from  that  in  the  blood.  It  requires  more  than  the  mere  absorp- 
tion of  water  to  get  a  fluid  with  the  properties  of  the  urine  out  of  such  a  filtrate 
as  we  are  able  to  suppose  this  to  be;  we  must  assume  an  unequal  absorption  of 
different  constituents.  Finally,  it  would  be  impossible  for  this  fluid  to  be  ab- 
sorbed back  into  the  lymph  by  purely  osmotic  processes,  for  the  osmotic  pressure 
of  the  urine  as  a  rule  is  higher  than  that  of  the  blood  plasma. 


388  THE  EXCRETIONS  OF  THE  BODY 

For  these  and  other  reasons  those  authors  who  regard  the  process  in  the 
glomeruli  as  a  pure  filtration  are  themselves  inclined  to  explain  the  reabsorp- 
tion  from  the  urinary  tubules  postulated  by  this  theory,  as  an  active  process 
carried  on  in  virtue  of  the  vital  properties  of  the  parenchyma  cells.  By  so 
doing,  however,  the  fundamental  position  of  Ludwig's  theory  is  surrendered, 
for  that  theory  set  out  to  give  a  purely  physico-chemical  explanation  of  the 
secretion  of  urine,  without  reference  to  vital  processes. 

But  can  it  l)e  regarded  as  proved  that  a  reabsorption  of  fluid  passed  through 
the  capsule  actually  takes  place  in  the  urinary  tubules?  Is  it  not  possible 
that  we  have  here  not  an  absorptive  but  a  secretory  process? 

In  order  to  answer  this  question  Heidonhain  carried  out  some  experiments 
on  the  elimination  of  sodium  indigosulphate,  which  is  easily  recognized  in 
microscopical  preparations,  and  reached  the  conclusion  that  this  salt  is  thrown 
out  by  the  epithelium  of  the  urinary  tubules.  From  analogy  he  concluded 
that  the  same  is  true  of  urea  and  other  specific  constituents  of  the  urine,  and 
that  therefore  the  tubules  have  the  function  of  enriching  the  fluid  coming 
from  the  capsule  with  solid  constituents. 

Direct  observations  on  the  elimination  of  urea  are  not  feasible  because 
there  are  no  micro-chemical  reactions  by  which  urea  can  be  recognized.  But 
in  birds  and  reptiles  it  is  not  a  difficult  matter  to  demonstrate  uric  acid 
microscopically.  And  yet  investigators  of  the  subject  have  not  succeeded  in 
satisfactorily  demonstrating  uric  acid  within  the  epithelial  cells.  Hence,  the 
mode  of  separation  of  sodium  indigosulphate  cannot  be  regarded  as  deter- 
minative for  the  elimination  of  the  normal  constituents  of  the  urine.  More- 
over, the  microscopical  findings  after  injection  of  dyes  are  not  harmonious, 
for  the  pictures  obtained  have  been  regarded  by  other  authors,  like  v.  Soljier- 
anski,  as  the  indication  of  an  absorptive  process  going  on  in  the  urinary 
tubules. 

The  following  experimental  fact  speaks  strongly  for  secretion  by  the  epi- 
thelium of  the  urinary  tubules.  The  frog's  kidney  receives  its  blood  vessels 
partly  from  the  renal  artery,  partly  from  the  renal-portal  vein.  The  former 
provides  the  glomerulus,  the  latter  the  tubules.  As  was  remarked  by  Xuss- 
baum,  and  later  verified  by  Beddard,  the  glomeruli  or  the  urinary  tubules  can 
be  thrown  out  by  tying  off  the  one  or  the  other  of  these  vessels.  After  tying 
the  renal  artery  the  flow  of  urine  ceases  entirely.  If  the  fluid  coming  through 
the  capsule  of  Bowman  during  its  passage  along  the  tubule  were  to  become 
thicker  b}^  absorption  of  water,  then  tying  the  renal  portal  ought  to  produce 
an  increased  flow  of  urine.  But  according  to  Gurewitsch  this  is  not  true; 
instead,  the  quantity  of  urine  is  reduced  by  the  operation. 

If  this  observation  proves  to  be  absolutely  correct,  it  constitutes  a  conclu- 
sive argument  against  the  doctrine  of  absorption  in  the  renal  tubules.  Accord- 
ingly, the  epithelium  would  have  the  function  of  taking  up  the  specific  con- 
stituents of  the  urine  from  the  blood  and  of  delivering  them  to  the  urinary 
tubules. 

We  come  therefore  for  the  present  to  the  following  view,  first  expressed 
by  Bowman  and  further  elaborated  by  Heidenhain,  concerning  the  activity 
of  the  kidneys.  The  cells  covering  the  glomerulus  give  out  water  and  salts 
hy   a    true   process   of   secretion,    those    of    the    convoluted    tubules   and    of 


THE  EXCRETION  OF  URINE  389 

the  wide  part  of  Henle's  loop  secrete  the  specific  constituents  of  the  urine 
and  water. 

As  an  indirect  support  of  this  theory,  the  following  consequence  of  the 
filtration  hypothesis,  emphasized  by  Heidenhain,  is  to  be  considered.  If  the 
outflow  of  fluid  from  the  glomeruli  takes  place  by  filtration,  the  filtrate  cannot 
be  richer  in  urea  than  the  blood ;  it  would  contain  therefore  about  0.05  per  cent 
urea.  Since  however  the  urine  as  voided  contains  two  per  cent  of  urea,  the 
filtrate  must  be  concentrated  forty  times.  With  a  daily  excretion  of  1,500  g. 
urine  containing  30  g.  urea  the  total  quantity  of  filtrate  would  thus  amount  to 
60,000  g.  of  which  58,500  g.  would  have  to  be  absorbed  again  into  the  urinary 
tubules. 

Various  other  circumstances  favor  the  idea  of  a  secretory  process  in  the  kid- 
neys. (1)  The  excretion  of  urine  occasions  a  measurable  rise  of  temperature  (the 
temijerature  of  the  urine  may  be  0.4°  C.  higher  than  that  of  the  blood)  (Grijns). 
(2)  Atropin  which  is  poisonous  for  all  glands  reduces  the  excretion  of  urine  to  a 
considerable  extent  (Thompson),  although  pilocarpine  which  is  stimulating  for 
glands  in  general  has  no  effect  on  the  activity  of  the  kidneys  (Loewi).  (3)  When 
by  feeding  benzoic  acid  and  glycocoll  the  kidneys  are  called  upon  to  synthesize 
hippuric  acid  (cf.  page  378),  the  output  of  NaCl  in  the  urine  is  considerably 
increased,  notwithstanding  that  the  flow  of  blood  and  the  percentage  composi- 
tion of  NaCl  in  it  remain  constant  (Asher). 

The  amount  of  work  done  by  the  kidneys  depends  essentially  on  two 
factors,  namely,  the  volume  of  the  Mood  flowing  through  them,  and  the 
percentage  of  diuretic  substances  in  the  blood. 

The  influence  of  the  blood  flow  was  first  established  by  Ludwig  and  his 
pupils  on  the  basis  of  a  great  many  experimental  observations.  Ever^iihing 
which  increases  the  blood  flow,  such  as  great  but  not  excessive  distention  of 
the  vascular  system,  extensive  vasoconstriction  with  the  renal  nerves  cut,  etc., 
intensifies  the  secretion  of  urine.  Conversely  it  falls  pari  passu  with  the 
blood  flow,  whether  that  fall  be  occasioned  by  diminution  of  the  general  blood 
pressure  due  to  stimulation  of  the  vagus,  to  bleeding,  to  section  of  the  spinal 
cord,  or  be  caused  by  a  local  constriction  or  compression  of  the  renal  vessels. 

Since  every  change  of  the  arterial  blood  supply  alters  the  pressure  in  the 
capillaries  in  the  same  direction,  the  above-mentioned  facts  were  adduced  as 
the  most  important  support  for  the  filtration  hypothesis;  for  it  is  evident 
that  filtration  through  the  glomeruli  should  be  more  abundant,  the  higher  the 
pressure  brought  to  bear  on  them.  Likewise  if  the  excretion  of  urine  be  the 
result  of  a  secretory  process,  the  variations  of  the  blood  floiu  are  of  vast  im- 
portance, for  by  this  means  the  activity  of  the  kidney  cells  can  be  influenced 
in  one  way  or  the  other. 

The  action  of  diuretic  substances  is  shown  most  clearly  by  experiments 
on  the  secretion  of  urine  with  the  renal  veins  compressed.  It  is  well  known 
also  that  the  kidney  is  surrounded  by  a  tolerably  firm  capsule,  and  that  its 
mass  is  incompressible.  Here,  as  in  the  brain  (cf.  page  241),  venous  stasis 
must,  therefore,  cause  an  arterial  anfemia.  Consequently  when  the  renal  vein 
or  inferior  vena  cava  is  constricted,  the  secretion  of  urine  declines  or  stops 
altogether.  If.  however,  a  solution  of  sodium  nitrate,  for  example,  be  then 
injected  into  the  blood,  the  urine  gushes  out  in  a  strong  stream,  even  if  the 


390  THE  EXCRETIONS  OF  THE  BODY 

general  blooa  pressure  be  low   (I'aneth).     It  is  evident  that  the  same  effect 
can  be  produced  with  the  reual  circulation  unobstructed. 

To  the  diuretic  substances  belong:  urea,  common  salt,  sodium  nitrate,  caf- 
fein,  grape  sugar,  peptone,  albumoses,  etc.  Their  effect  undoubtedly  depends 
in  part  upon  the  accompanying  dilatation  of  the  renal  vessels;  but  it  is  con- 
nected also  with  a  rise  in  the  osmotic  pressure  of  the  blood  occasioned  by  these 
substances,  and  the  consequent  abstraction  of  water  from  the  tissue  spaces  into 
the  blood  vessels.  In  this  way  the  blood  is  diluted,  and  the  vessels  are  more 
tensely  filled,  the  result  being  a  more  copious  flow  of  blood  through  the  kidnej's. 
Here  we  have  almost  the  same  process  as  when  water  is  slowly  transfused  into  a 
vein  after  a  certain  quantity  has  been  injected;  the  excretion  of  urine  increases 
up  to  a  certain  point,  beyond  which  the  transfusion  and  excretion  keep  pace 
with  each  other. 

The  effects  of  diuretic  substances  cannot,  however,  be  explained  from  this 
point  of  view  alone.  For  there  are  various  experimental  facts  which  indicate 
that  the  ingested  substance  stimulates  the  kidneys  to  increased  activity,  quite 
independently  of  changes  in  the  diameter  of  the  blood  vessels,  etc.,  and  that, 
therefore,  tliese  substances  are  specific  stimuli  for  the  kidney  cells. 

Finally,  the  general  condition  of  the  body  plays  a  part  in  the  secretion  of 
the  urine  which  is  not  to  be  neglected.  When  certain  diuretics  are  given  to 
a  body  poor  in  sodium  chloride,  there  is  no  increase  in  the  excretion  of  NaCl. 
Xotwithstanding  the  diuresis,  the  body  holds  on  to  its  NaCl  very  energetically, 
giving  it  up  only  in  the  smallest  possible  quantities.  But  in  cases  where  the 
body  has  plenty  of  XaCl.  whenever  there  is  a  strong  secretion  of  urine,  there 
is  also  an  abundant  output  of  this  salt. 

It  has  long  been  known  that  one  kidney  is  sufficient  for  all  purposes  of  metab- 
olism. One  can  even  remove  as  much  as  two-thirds  of  the  kidney  substance  and 
still  leave  an  efficient  excretory  apparatus.  Here  moreover  we  meet  the  remark- 
able fact  that  the  renal  secretion  increases  considerably  and  permanently.  At 
the  same  time  the  elimination  of  urea  is  increased  and  animals  die  within  two 
to  six  weeks  in  spite  of  a  fairly  good  appetite  (Bradford).  How  this  phenomenon 
is  to  be  explained  or  what  theoretical  weight  it  has,  we  are  not  able  to  say  at 
present. 

Nothing  is  known  which  would  indicate  the  presence  of  secretory  nerves 
to  the  kidneys.  It  is  true  that  by  various  operations  on  the  central  nervous 
system  or  on  peripheral  nerves,  changes  in  the  secretion  of  urine  may  be 
obtained;  but  all  these  admit  of  an  explanation  as  vasomotor  effects.  The 
secretion  continues  also,  though  somewhat  diminished,  after  division  of  the 
nerves  running  along  the  renal  vessels.  So  far,  then,  as  we  are  able  to  judge 
at  present,  the  secretion  of  urine  is  accomplished  by  the  influence  of  the  urine- 
producing  substance  in  the  blood,  and  is  regulated  by  variations  in  the  quan- 
tity and  the  quality  of  these  substances,  as  well  as  by  alterations  in  the  blood 
supply  to  the  kidney. 

§  3.  MICTURITION 

From  the  pelvis  of  the  kidney  the  urine  flows  through  the  ureters  into  the 
bladder,  remains  there  for  a  time,  and  is  finally  expelled  at  varying  intervals. 


MICTURITION  391 


A.    THE   URETERS 

Contractions  of  the  ureters  begin  always  at  the  upper  end  and  pass  pro- 
gressively downward  to  the  bladder,  but  do  not  involve  the  musculature  of 
the  latter.  They  appear  to  be  started  by  the  entrance  of  the  urine  into  the 
ureters  themselves.  After  one  contraction  the  lumen  gradually  fills  again  at 
its  upper  end,  until  the  next  one  follows. 

In  the  ureters  of  man  subjected  to  direct  observation  it  has  been  found  that 
as  a  rule  the  bladder  ends  of  the  two  do  not  conti'act  at  the  same  time,  that  in 
the  same  ureter  the  contractions  do  not  succeed  each  other  at  regular  intervals, 
and  that  the  total  quantity  of  urine  conveyed  in  a  unit  of  time  varies  greatly. 
The  maximum  quantity  delivered  to  the  bladder  by  a  single  contraction  is  placed 
at  4  c.c.  On  the  contrary,  Bardier  and  Frankel  have  found  that  the  flow  of  urine 
from  the  ureters  of  dogs  is  generally  pretty  uniform  whether  one  or  both  be 
considered. 

Fagge  states  that  stimulation  of  the  hypogastric  nei-ve  produces  a  series  of 
contractions  of  the  ureter.  Furthermore,  the  ureter  when  entirely  cut  out  of 
the  body  contracts  rhythmically.  Whether  these  contractions  are  due  to  ganglion 
cells  present  in  the  wall  of  the  ureter,  concerning  whose  occurrence  authors  still 
differ,  or  whether  they  are  due  essentially  to  the  automatic  activity  of  the  mus- 
culature of  the  wall  (Engelmann),  is  not  yet  decided. 

B.    THE   URINARY   BLADDER 

The  ureters  pierce  the  bladder  wall  obliquely.  The  greater  the  pressure  inside 
the  bladder  becomes,  the  more  securely  are  the  mouths  of  the  ureters  closed;  the 
consequence  of  wdiich  is  that  the  return  of  urine  from  the  bladder  to  the  ureters 
is  prevented.  However,  this  closure  is  not  absolutely  secure;  for  although  no 
return  flow  is  possible  so  long  as  the  bladder  wall  is  passively  stretched,  it  may 
happen  when  the  wall  contracts,  as  it  will,  for  the  purpose  of  preventing  excess- 
ive distention.  Entrance  to  the  ureter  is  possible  even  then  only  at  the  end  of 
a  contraction  of  the  ureter  itself,  when  its  mouth  is  open.  In  the  dog,  each 
mouth  is  guarded  by  a  strong  muscular  band.  If  this  band  be  cut,  regurgitation 
is  comparatively  easy.  From  the  ureter  the  urine  may  pass  on  into  the  pelvis 
of  the  kidney  and  be  pressed  into  the  lymphatics  and  the  renal  tubules,  thence 
in  some  way  or  other  into  the  renal  vessels.  Even  solid  matters  from  the  urinary 
bladder  can  in  some  such  way  reach  the  g'eneral  circulation  (L.  Lewin). 

The  closure  of  the  external  opening  of  the  bladder  appears  to  be  accom- 
plished mainh'  bv  its  anatomical  position,  for  after  death  when  the  voluntary- 
sphincters  are  relaxed,  the  urine  does  not  escape.  However,  the  bladder  will 
stand  a  stronger  internal  pressure,  without  being  emptied,  during  life  than 
it  will  after  death.  Tlie  difference  is  due  to  the  external  sphincter  and  the 
so-called  internal  sphincter — i.  e..  the  strong  band  of  muscle  fibers  beginning 
on  the  neck  of  the  bladder  and  reaching  to  the  prostate  (Eehfisch). 

The  desire  to  urinate  is  in  all  likelihood  roused  primarily  by  the  sense 
of  fullness  of  the  bladder.  This  is  preceded  by  a  greater  degree  of  ten- 
sion of  the  bladder  wall.  Cold  and  warm  fluids  in  the  bladder  also  cause 
the  sensation  named  and  the  consequent  desire  to  urinate,  but  indifferent 
fluids  at  the  temperature  of  the  body,  especially  urine,  are  not  felt  at  all. 
Stimulation  of  the  prostatic  part  of  the  urethra  is  felt,  but  does  not  pro- 


392 


THE  EXCRETIONS  OF  THE   BODY 


duce  the  desire  to  empty  the  bladder;  hence  the  doctrine  that  this  desire 
is  due  to  the  escape  of  the  urine  into  the  urethra  is  not  correct  (Guyon). 
The  flow  of  urine  can  be  suppressed  by  voluntary  contraction  of  the  outer 
sphincter  (probably  also  of  the  inner). 

Micturition  results  from  a  voluntary  relaxation  of  the  external  sphincter, 
whereupon  the  reflex  contraction  of  the  whole  musculature  of  the  bladder, 


Nerves  to 
cceliac  Sympathetic 

axis  nerves 


Superior 

mesenteric 

ganglion 


Connecting 
strands 

Superior 
mesenteric  nerve 


5Ied.  mes.  nerve 

Inf.  mes.  nerve 

Nerve  to  mes. 

artery 

Inf.  mes.  gang. 


in.  Lumbar 
vertebra 


Ramus 
communicans 


IV.  Lumb.  vert. 


V.  Lumb.  vert. 


., Rami 

communicantes 


"  VI.  Lumb.  vert. 


Hypogastric 
nerves 


VII.  Lumb.  vert. 


_  Vesical  plexus 


Hypogastric 

plexus 


Sciatic  nerve 
-■^-\-—  Sacral  nerves 


—\\ — 1-^ Coccyx 

Fig.  145. — The  nerves  of  the  bladder,  after  NawTocki  and  Skabitschewsky. 

including  that  of  the  internal  sphincter,  follows.  A  large  part  of  the  longi- 
tudinal fibers  pass  over  without  interruption  into  the  fibers  of  the  sphincter — 
an  arrangement  which  insures  the  dilatation  of  the  opening.  (Rehfisch  advo- 
cates the  view  that  the  internal  sphincter  also  relaxes  when  the  passage  is 
opened.)  Micturition  is  aided  by  the  bulbo-cavernosus  muscle,  in  that  it 
compresses  the  bulbous  urethrae,  thus  expelling  the  contents  of  the  latter.     Ab- 


MICTURITION  393 

dominal  pressure  plays  no  essential  part  in  micturition,  and  unaided  is  not 
suiiicient  to  empty  the  bladder. 

The  bladder  receives  its  motor  nerves  in  part  from  the  lumbar,  in  part 
from  the  sacral  nerves  (Fig.  145).  The  former  in  the  dog  emerge  in  the 
second  to  fourth  lumbar  roots  and  run  through  the  lumbar  part  of  the  sym- 
pathetic, the  mesenteric  nerves,  the  inferior  mesenteric  ganglion,  the  hypo- 
gastric nerves  and  the  hypogastric  plexus  to  the  vesical  plexus.  The  sacral 
nerves  arise  from  the  second  to  fourth  sacral  roots,  and  pass  in  the  iiervi  erri- 
gentes,  through  the  hypogastric  plexus  to  the  plexus  of  the  bladder. 

Both  the  circular  and  the  longitudinal  muscle  fibers  are  supplied  through 
these  nerves ;  action  extends  in  part  also  to  the  opposite  side,  so  that  the 
function  of  the  bladder  is  not  impaired  if  the  nerves  of  one  side  only  are 
uninjured. 

According  to  v.  Zeissl,  Eehtiseh,  and  others,  the  sphincter  of  the  bladder  is 
relaxed  by  stimulation  of  the  nervus  errigens;  C.  Stewart  has  observed  also  a 
relaxation  of  the  contracted  bladder  under  the  influence  of  these  nerves.  Such 
an  inhibiting  effect,  however,  is  positively  denied  by  other  authors. 

A  hilateral  center  for  the  control  of  the  bladder  is  located  in  the  lumbar 
cord  (Goltz).  Each  half  of  this  center  has  control  of  the  entire  bladder. 
Besides,  the  higher  parts  of  the  central  nervous  system  exert  an  influence  on 
the  bladder.  Contractions  (in  the  cat)  are  obtained  by  stimulation  of  the 
anterior  portion  of  the  sigmoid  gyrus  of  the  cerebrum.  The  conducting  path- 
way is  said  to  pass  through  the  thalamus,  the  crura  cerebri,  the  pons  and 
the  medulla  to  the  spinal  cord.  In  the  cord  the  paths  traverse  the  posterior 
section  of  the  lateral  columns,  and  are  direct  as  far  as  the  lumbar  cord  (and 
the  inferior  mesenteric  ganglion)  where  they  undergo  a  partial  crossing  (C. 
Stewart ) . 

These  centers  are  roused  hy  various  reflex  influences,  contractions  of  the 
bladder  having  been  observed  as  the  result  of  stimulation  of  all  kinds  of 
afferent  nerves  except  the  vagus.  Of  still  greater  interest  are  the  true  afferent 
nerves  from  the  bladder  which  reach  the  cord  mainly  by  the  second  and  third 
posterior  sacral  roots.  The  reflex  center  lies  between  the  third  and  fifth 
lumbar  roots,  and  the  sacral  nerves  to  the  bladder  only  contain  the  efferent 
fibers.  Contractions  are  reflexly  produced  also  by  stimulation  of  the  central 
end  of  the  hypogastric  nerves,  the  inferior  mesenteric  ganglion  in  this  case 
assuming  the  role  of  a  reflex  center  ( Xawrocki  and  Skabitschewsky ;  cf ., 
however,  "axon  reflex"  in  Chapter  XXII). 

The  bladder  is  not  absolutely  dependent  on  the  cooperation  of  the  central 
nervous  system  in  carrying  out  its  movements.  Dogs,  whose  spinal  cord  was 
extirpated  below  the  tlioracic  portion,  showed  at  first  a  greater  or  less  dis- 
turbance of  the  bladder  function,  but  the  condition  gradually  improved,  the 
urine  was  expelled  spontaneously  and  in  larger  quantities  at  a  time,  and 
after  some  months  micturition  was  performed  in  a  manner  perfectly  adequate 
for  the  continuance  of  health  (Goltz  and  Ewald). 

IJnder  normal  circumstances  the  urine  in  the  bladder  does  not  undergo  any 
visible  changes,  either  by  diffusion  or  absorption.  Even  with  forced  retention 
of  the  urine  diffusion  is  too  slight  to  be  held  responsible  for  anj'  of  the  symptoms 
accompanying  that  condition. 


39-4  THE  EXCRETIONS  OF  THE  BODY 


SECOND    SECTION 


EXCRETION   THROUGH   THE   SKIN 

Various  substances  are  eliminated  by  the  skin  through  tlie  sebaceous  and 
sweat  glands,  as  well  as  through  the  so-called  insensible  perspiration.  And 
vet  secretion  through  the  skin  has  an  essentially  different  purpose  from  the 
e.xcretion  of  urine  and  f^ces.  for  its  object  is  partly  to  protect  the  skin  from 
various  sorts  of  injuries,  partly  to  play  a  leading  part  in  the  regulation  of 
the  body  temperature. 

§  1.    THE    SEBACEOUS   GLANDS 

With  the  exception  of  the  palm  of  the  hand  and  the  sole  of  the  foot,  the 
skin  everywhere  contains  sebaceous  glands,  which  secrete  the  so-called  sebum. 
Freshl}^  secreted,  this  is  an  oih',  semifluid  mass,  which  hardens  into  a  shining 


Fig.  146. — Portion  of  the  preputial  gland  of  the  mouse,  after  treatment  with  osmic  acid,  after 

Altmann. 

greas}^  coat  on  the  surface  of  the  skin,  and  consists  of  proteid  substances,  fat 
and  eholesterin.  By  means  of  this  secretion  the  skin  is  oiled  and  is  thereby 
rendered  soft,  pliant  and  almost  impervious  to  water.  Even  after  a  warm 
l)ath.  only  those  parts  of  the  skin  which  contain  no  sebaceous  glands  exhibit 
distinct  traces  of  the  effect  of  water.  The  skin  in  a  bath  at  32.5°  C.  takes 
up  about  0.0006  g.  of  water  per  square  centimeter  of  surface,  and  in  a  bath  at 
39.5°  C,  0.0048  g.  For  the  entire  skin  (2  sq.  m.)  this  would  amount  to  12 
and  96  g.  respectively  (Spitta).    The  hair  also  owes  its  pliancy  to  the  sebum. 

Fig.  146,  which  represents  a  portion  of  the  preputial  gland  of  a  mouse,  will 
give  some  idea  of  the  formation  of  the  sebum.  The  vesicular  end  of  the  fundus 
is  filled  with  spherical  granules,  the  periphery  of  which  is  formed  by  a  fatty 
membrane  of  greater  or  less  thickness.  Xuclei  and  cell  boundaries  are  not  visible, 
being  obscured  by  the  granular  structures.  In  the  middle  portion  of  the  fundus 
we  see  the  ring-shaped  granules  more  and  more  fused  together,  until  in  the 
mouth  a  compact  black  mass  is  formed.  "We  find  the  same  black-colored  secre- 
tion throughout  the  duets  of  the  gland  (Altmann). 

Certain  experimental  facts  appear  to  indicate  that  the  secretion  of  sebum 
is  under  the  influence  of  the  sympathetic  nerves  (Arloing). 


EXCRETION  OF  SWEAT  395 

§2.    EXCRETION   OF    SWEAT 

A.    COMPOSITION   AND  PROPERTIES 

Sweat  is  the  thinnest  of  all  the  body  fluids,  and,  when  filtered,  is  clear 
and  colorless,  and  has  a  specific  gravity  of  1.003-1.008.  Its  reaction  to  litmus 
may  be  acid,  neutral  or  alkaline;  its  taste  is  salty;  its  odor  is  unpleasant  and 
differs  for  the  different  portions  of  the  body.  The  odor  is  destroyed  by 
heating  it  up  to  110°  C. 

In  the  following  table  two  analyses  of  sweat  are  given.  The  one  by  Harnack 
is  taken  from  the  sweat  of  a  rheumatic  patient,  secreted  in  one  to  two  hours  in 
a  vapor  bath;  the  other  by  Camerer,  Jr.,  was  taken  from  sweat  secreted  in  an 
electric-light  bath  in  the  course  of  seventy-five  to  ninety  minutes. 


Harnack. 


Water I  99.09-99.16  per  cent. 

Solids 0.91-0.85        " 

Organic  matter 0.24-0.20        " 

Inorganic  matter 0.67-  0.65        " 

NaCl 0.52 

Phosphates  of  the  alkaline  earths 1  0.03 


H,S04 
KHO  . . . 

Urea 

Nitrogen 


0.05-  0.06 
0.05-  0.04 
0.12 


Camerer,  Jr. 


97.9    per  cent. 
2.1 
1.06 
1.04 
0.66 


0.05  per  cent. 
0.19-  0.15 


Human  sweat  is  said  to  contain  also  about  0.045  per  cent  proteid  matter  and 
two  enzymes,  one  diastatic  and  the  other  proteolytic,  as  well  as  ethereal  sul- 
phates, aromatic  oxyacids,  skatol  and  creatinin  in  small  quantities. 

According  to  Arloing,  the  sweat  of  a  healthy  man  possesses  toxic  proper- 
ties; by  intravenous  injection  of  a  dose  of  10-15  c.c.  per  kg.  of  body  weight,  it 
kills  a  dog  in  fifteen  to  eighty-four  hours.  The  sweat  produced  in  work  is  more 
poisonous  than  that  given  off  during  a  vapor  bath.  Vomiting  and  congestion 
of  the  alimentary  canal  are  mentioned  as  the  most  prominent  symptoms.  Par- 
ticipation of  Bacteria  in  these  phenomena  appears  to  be  excluded,  because  sweat 
is  said  to  lose  only  a  little  of  its  toxicity  by  sterilization  in  the  autoclave. 

It  has  long  been  known  that  animals,  in  which  the  cutaneous  secretions 
are  stopped  by  means  of  varnishes,  die  within  a  short  time;  and  attempts 
were  made  to  explain  this  effect  by  the  retention  of  products  normally  given 
off  in  the  sweat.  Then  came  the  "conviction  that  the  sweat  does  not  remove 
any  to.xic  .substances  from  the  body,  and  the  influence  of  the  varnish  was 
sought  in  the  great  radiation  of  heat  caused  by  it.  It  is  altogether  possible 
that  the  increased  loss  of  heat  has  a  certain,  probably  even  a  great,  signifl- 
cance.  But  if  the  above-mentioned  experimental  facts  with  reference  to  the 
toxicity  of  sweat  are  confirmed,  we  must  again  ascribe  the  most  important 
role  to  the  retention  of  decomposition  products.  This  view  is  supported  more- 
over by  the  fact  that  varnished  animals  take  only  a  little  food,  notwithstand- 
ing great  loss  of  heat  and  the  increased  heat  production  thereby  demanded— 


396  THE  EXCRETIONS  OF  THE  BODY 

which  has  induced  Loulanie  to  describe  the  death  of  these  animals  as  death 
by  inanition. 

The  quantity  of  sweat  excreted  daily  is  variable.  It  depends  chiefly  upon 
the  requirements  of  heat  regulation.  The  greater  the  quantity  of  sweat  se- 
creted, the  greater  is  the  absolute  quantity  of  solid  constituents,  among 
which  urea  is  of  special  importance.  Ordinarily  the  output  of  urea  in 
the  sweat  is  negligibly  small,  and  yet  as  already  observed  (page  89),  under 
certain  circumstances  it  may  become  considerable. 

B.    THE   EXCRETORY   PROCESS 

In  view  of  the  importance  of  sweat  in  regulating  the  temperature  of  the 
body,  it  is  but  natural  to  assume  that  the  action  of  the  sweat  glands  is  under 
the  control  of  the  central  nervous  system.     This  is  confirmed  by  experiment. 

Stimulation  of  the  cut  sciatic  nerve  or  of  the  brachial  plexus  in  a  cat  pro- 
duces in  a  short  time  large  drops  of  sweat  on  the  balls  of  the  foot  (Goltz).  This 
production  of  sweat  is  an  actual  secretion  and  not  a  filtration  from  the  blood, 
for:  (1)  a  powerful  secretion  can  be  evoked  by  stimulation  as  much  as  twenty 
minutes  after  amputation  of  a  leg  (Kendall  and  Luchsinger) ;  (2)  secretion 
occurs  when  the  pressure  of  the  surrounding  air  is  higher  than  that  of  the  aortic 
blood  (Lev5'-Dorn) ;  (3)  it  does  not  occur  without  stimulation  when  a  paw  is 
subjected  to  a  low  air  pressure;  and  (4)  it  is  prevented  by  very  small  doses  of 
atropine,  despite  the  strongest  nerve  stimulus. 

The  siveat  filers  for  the  fore  paw  of  the  cat  have  been  found  in  the  median 
and  ulnar  nerves,  for  the  hind  paw  in  the  sciatic.  It  appears  however  that 
most  of  them  do  not  come  directly  from  the  spinal  roots  of  these  nerves,  but 
that  they  first  traverse  the  sympathetic  paths  (thoracic  or  abdominal  trunk) 
before  they  join  the  nerves  to  the  extremities.  The  sources  of  the  sweat  fibers 
in  the  abdominal  sympathetic  are  the  three  lower  thoracic  and  the  four  upper 
lumbar  roots;  those  of  the  fore  paw  spring  from  the  fourth  thoracic  root. 

Sweat  colters  are  present  in  the  spinal  cord;  for  if  the  cord  of  a  young 
cat  be  cut  at  the  level  of  the  fourth  thoracic  root,  secretion  can  be  obtained 
on  the  hind  paws  by  the  influence  either  of  heat  or  of  dyspnoea.  Considering 
the  importance  of  sweat  in  heat  regulation,  it  is  very  probable  that  a  general 
sweat  center  is  present  in  the  medulla,  although  we  know  nothing  definite 
about  it  at  this  time. 

Secretion  of  siveat  is  induced  by  psychical  stimuli  (fear,  etc.),  by  heat, 
asphyxiation,  and  reflex  effects,  as  well  as  by  various  poisons.  Among  the 
latter,  pilocarpine  is  especially  worthy  of  mention,  for  it  has  the  power  to 
produce  sweat  even  when  the  secretory  nerves  are  cut. 

The  effectiveness  of  a  stimulus  applied  to  the  secretory  nerves  depends 
mainly  upon  the  temperature  of  the  glands.  When  very  cold,  no  effect  at  all 
is  produced,  although  at  a  body  temperature  of  22°-28°  C.  the  glands  of  a  cat's 
foot  can  be  made  to  secrete  by  psychic  excitation,  by  reflex  action  or  by  asphyxia- 
tion. On  the  other  hand  heat  produces  secretion  of  sweat  even  in  case  the  spinal 
cord  is  severed  at  the  ninth  thoracic  root  and  all  the  posterior  roots  of  the  sev- 
ered cord  are  cut — i.  e.,  heat,  like  asphyxiation,  has  a  direct  stimulating  effect 
upon  the  sweat  centers. 


THE  SO-CALLED  INSENSIBLE  PERSPIRATION  397 

Various  experimental  facts  favor  the  view  that  sweat  glands  are  under  the 
influence  of  inhibitory  nerves,  which,  like  the  secretory  fibers,  traverse  sympa- 
thetic paths. 

Many  animals  do  not  sweat  at  all ;  others,  like  the  cat,  sweat  only  in  certain 
places,  as  the  balls  of  the  feet.  In  man  the  ability  to  sweat  is  very  highly 
developed:  in  varying  degrees  it  is  a  function  of  the  entire  skin — principal 
places  being  the  brow,  palms  of  the  hands  and  the  soles  of  the  feet. 


§  3.    THE    SO-CALLED   INSENSIBLE    PERSPIRATION 

We  include  under  this  head  the  excretion  of  carbon  dioxide  through  the 
skin,  and  the  exhalation  of  water  independently  of  the  sweat  glands. 

The  elimination  of  carbon  dioxide  through  the  skin  is  very  small  in  com- 
parison with  the  elimination  through  the  lungs.  Both  this  and  the  exhalation 
of  water  vapor  have  repeatedly  been  studied  on  limited  areas  of  the  skin ;  but 
such  investigations,  although  they  may  yield  valuable  results  as  to  the  influ- 
ence of  different  factors,  give  no  certain  criteria  for  the  estimation  of  the 
total  output  of  CO2  and  water  vapor  for  the  whole  surface  of  the  liody.  In 
order  to  make  such  a  determination,  an  individual  is  inclosed,  all  but  his 
head,  in  a  cabinet  suitably  ventilated,  so  that  the  elimination  may  go  on 
continuously. 

According  to  Schierbeck  and  v.  Willebrand,  the  output'  of  CO,  at  a  tem- 
perature of  20°-33°  C.  is  fairly  constant,  and  amounts  to  0.35  g.  per  hour — 
i.  e.,  7.2-8.4  g.  per  day.  If  the  surrounding  temperature  be  raised  above 
33°  C.  the  output  of  CO,  suddenly  increases,  so  that  at  33.5°-34°  C.  it  reaches 
the  relatively  high  value  of  0.87-1.35  g.  per  hour  (=  20.9-32.4  g.  per  day). 

This  sudden  rise  is  coincident  with  the  appearance  of  "  sensible  perspira- 
tion " ;  it  is  possible,  therefore,  that  it  may  be  due  to  the  increased  work  of 
the  sweat  glands. 

Excretion  of  water  vapor  goes  on  also  below  this  critical  temperature. 
Other  conditions  being  equal,  it  is  greater  the  higher  is  the  surrounding  tem- 
perature, and  from  12°-31°  C.  the  output  from  the  naked  body,  according  to 
v.  Willebrand,  is  proportional  to  the  atmospheric  temperature  (e.  g.,  at  12°, 
10.5  g.  per  hour;  at  18.2°,  18.4  g. ;  at  24°,  22.7  g. ;  and  at  28°,  27.3  g.),  but 
with  the  appearance  of  visible  sweat  it  rises  suddenly. 

We  can  think  of  two  possibilities  as  to  the  source  of  the  water  given  off 
from  the  skin  before  the  appearance  of  sweat :  either  it  is  a  product  of  the 
sweat  glands,  or  it  is  derived  by  a  purely  physical  process  of  diffusion  from 
the  gland  cells  and  the  epidermis.  Considering  the  proportional  increase 
parallel  with  the  temperature  up  to  the  point  where  water  is  poured  out  as 
visible  sweat,  the  latter  possibility  seems  the  more  likely. 


CHAPTER  XIV 

ANIMAL  HEAT  AND  ITS  REGULATION 

§  1.    THE   TEMPERATURE    OF   THE   HUMAN   BODY 

Birds  and  Mammals  differ  from  all  other  living  creatures  in  that  their 
body  temperature  remains  constant  in  spite  of  all  variations  in  the  tempera- 
ture of  the  surrounding  medium.  For  this  reason  they  are  called  homoiother- 
mous,  or,  since  the  temperature  of  the  medium  in  which  they  live  is  generally 
lower  than  their  body  temperature,  warm-blooded  animals. 

Among  different  species  of  warm-blooded  animals  the  body  temperature 
exhibits  considerable  differences.  In  general  it  is  higher  in  birds  (39.4°-4:3.9° 
C.)  than  in  mammals  (35.5°-40.5°  C),  and  among  the  latter  many  genera 
have  a  higher  temperature  than  that  of  man,  37.5°  C.  With  a  temperature 
as  high  as  the  nonnal  in  birds,  or  even  as  high  as  the  normal  in  some  other 
mammals,  a  man  would  be  very  ill. 

The  temperature  of  an  animal  is  usually  taken  in  the  rectum,  that  of 
man  either  in  the  rectum  or  in  the  mouth  or  in  the  axilla.  It  is  evident  that 
the  thermometer  must  always  remain  in  place  for  a  certain  length  of  time 
if  it  is  to  register  the  temperature  exactly;  also  that  the  temperature  cannot 
be  the  same  in  these  different  places  owing  to  loss  of  heat  from  the  superficial 
parts  of  the  body;  and  further  that  of  the  places  named  the  temperature  is 
highest  in  the  rectum,  lowest  in  the  axilla.  If  the  person  is  doing  physical 
work  the  temperature  in  the  mouth  may  fall,  whereas  the  temperature  in 
the  rectum  rises.  This  circumstance,  which  shows  that  the  registration  of 
temperature  in  the  mouth  does  not  always  give  trustworthy  results,  is  prob- 
ably due  to  the  cooling  of  the  skin  of  the  face  through  the  agency  of  sweat, 
to  the  augmented  respiration  by  which  the  lining  of  the  mouth  is  cooled,  etc. 
(Pembrey  and  Nicol). 

In  taking  the  rectal  temperature  it  is  necessary  that  the  thermometer  be 
inserted  to  a  sufficient  depth  to  register  the  actual  temperature  of  the  interior 
of  the  body.  In  the  mouth  the  thermometer  bulb  is  placed  under  the  tongue 
and  the  mouth  is  closed.  The  posterior  opening  of  the  mouth  cavity  (see  page 
279)  normally  is  always  closed.  The  axilla  never  forms  a  completely  closed 
cavity,  but  for  the  purpose  of  taking  the  temperature,  can  be  approximately 
closed  by  pressing  the  arm  firmly  against  the  chest  wall.  It  requires,  however, 
some  time  for  the  temperature  in  such  a  cavity  to  reach  its  maximum,  and 
hence  the  thermometer  must  remain  longer  in  the  axilla  than  in  the  mouth  or 
in  the  rectum. 

The  temperature  of  the  surface,  especially  of  the  parts  habitually  exposed, 
varies   greatly,  but   for   the   clothed   parts   can   be   estimated   in  general    at 
398 


THE  TEMPERATURE  OF  THE  HUMAN   BODY  399 

33°-35°  C. ;  the  naked  skin  in  a  bath  of  5°  C.  still  has  a  temperature  of 
17°,  and  in  a  bath  of  18°  and  25°  has  a  temperature  of  22°  and  26.5°  re- 
spectively. The  temperature  2  mm.  below  the  surface — i.  e.,  in  the  subcu- 
taneous tissues — under  the  same  circumstances  is  24°,  24.8°,  and  27.5°  re- 
spectively, and  in  the  muscles  12  mm.  below  the  surface  is  36.3°,  35.9°,  and 
36.9°  C.  (Lefe\Te).  The  organs  in  the  upper  part  of  the  abdominal  cavity 
are  still  warmer  than  the  muscles  and  the  rectum.  According  to  Quincke, 
the  temperature  in  the  interior  of  the  stomach  (man)  is  0.12°  C.  higher 
than  the  rectal  temperature,  and  according  to  Ito,  that  of  the  duodenum 
(rabbit)   is  0.7°  C.  higher.     These  higher  temperatures  may  be  due,  in  part 


Fig.  147. — The  normal  diurnal  variation  of  temperature  in  man,  after  Jiirgensen. 

at  least,  to  the  proximity  of  the  liver,  for,  according  to  Lefevre,  the  tem- 
perature of  the  liver  (of  the  dog)  may  be  more  than  1°  C.  higher  than  the 
rectal  temperature. 

Numerous  determinations  of  the  normal  body  temperature  of  man  have 
shown  that  it  presents  individual  variations  of  some  tenths  of  a  degree.  As 
a  mean  value  37.5°  C.  is  given  as  the  temperature  in  the  rectum,  37.2°  C. 
in  the  mouth,  and  37°  C.  in  the  axilla.  Moreover  it  is  not  entirely  correct 
to  say  that  man  has  a  constant  temperature.  Even  if  we  neglect  the  varia- 
tions due  to  diseases  or  the  diminutions  due  to  excessive  cooling  of  the  body, 
it  has  been  shown  that  the  temperature  of  man  in  the  course  of  a  day  under- 
goes certain  normal  variations.  The  difference  between  minimum  and  maxi- 
mum in  a  thoroughly  healthy  individual  may  amount  to  1°-1.5°  or  more. 
These  variations  run  a  very  regular  course  which,  according  to  Jiirgensen, 
shows  a  minimum  early  in  the  morning  from  three  to  six  o'clock,  increases 
gradually  from  that  time,  and  after  some  fluctuations,  reaches  a  maximum 
about  six  to  seven  o'clock  in  the  evening  (Fig.  147). 

The  cause  of  these  variations  is  primarily  the  variations  in  the  intensity 
of  metabolism.  If  the  CO.  elimination,  which  to  a  certain  extent  may  be 
looked  upon  as  an  expression  of  the  relative  amount  of  metabolism,  be  deter- 
mined at  different  times  of  the  day,  a  surprising  agreement  is  found  between 
its  course  and  that  of  the  body  temperature  (cf.  Fig.  148).  It  should  be 
noticed  that  the  temperature  curve  in  the  figure  was  not  taken  from  the  same 


400 


ANIMAL  HEAT  AND  ITS  REGULATION 


subject  as  the  CO,  curve.     The  discrepancies  between  the  two  are  no  more 
than  can  be  satisfactorily  explained  by  this  circumstance  alone. 

If  the  CO2  output  at  different  hours  of  the  day  be  obtained  on  the  fasting 
body  in  purposely  enforced  physical  rest,  it  shows,  as  Magnus-Levy  and  espe- 
cially Johansson  have  pointed  out,  but  very  slight  variations ;  and  in  the  course 
of  any  given  period,  the  body  temperature  decreases  because  of  the  relatively 
small  metabolism.  From  which  it  follows  that  the  above-mentioned  varia- 
tions in  the  intensity  of  metabolism  are  called  forth  primarily  by  the  variations 
in  the  movements  and  tension  of  the  muscles  occurring  for  one  reason  or 

another  in  the  course  of  the 
day.  A  cooperating  factor, 
though  not  of  itself  l)y  any 
means  so  potent  as  the  mus- 
cular work,  is  the  increase  of 
n\otabolism  due  to  taking 
food. 

One  inference  from  this 
view  is  that  with  a  reversal 
of  the  daily  habits,  the  tem- 
perature variations  ought  to 
be  reversed.  According  to 
some  authors  this  actually 
takes  place.  But  Benedict 
and  Snell  were  unable  to  ob- 
serve any  perceptible  tend- 
ency to  a  reversal  of  the  tem- 
perature curve  in  the  case  of  a  man  who,  for  ten  successive  days,  worked  at 
night  and  slept  by  day,  although  the  curve  did  vary  decidedly  from  the  normal. 


Fig.  148. — The  elimination   of  carbon  dioxide  in  man, 

determined  every  two  hours.      CO^,   in 

grams. diurnal  variation  of  temperature 

from  the  curve  by  Jiirgensen  in  Fig.  147. 


In  my  opinion  one  cannot  conclude  from  these  observations  that  other  fac- 
tors than  those  mentioned  above  are  concerned  in  production  of  the  daily  varia- 
tions of  temperature.  In  this  research  the  subject  slept,  as  the  authors  remark, 
a  much  shorter  time  than  he  was  accustomed  to,  and  it  is  in  fact  a  fairly  com- 
mon experience  that  a  man  cannot  accustom  himself  to  a  reversed  mode  of  life 
to  the  extent  of  completely  converting  day  into  night  and  night  into  day.  On 
this  account  the  muscular  activity  cannot  be  exactly  adjusted  to  the  changed 
order  of  life.  Moreover,  we  possess  observations  on  monkeys  which  show  that 
the  reversed  order  does  produce  a  complete  reversal  of  the  temperature  varia- 
tions. When  these  animals  were  kept  for  days  either  in  complete  darkness  or 
constantly  in  the  light,  the  normal  variations  ceased  and  were  replaced  by  quite 
irregular  ones  (Galbraith  and  Simpson). 


Temporary  changes  of  the  body  temperature  in  one  direction  or  the  other 
may  be  produced  by  various  voluntary  acts  which  tend  to  increase  either 
the  heat  production  or  the  heat  loss.  Thus  the  temperature  falls  as  the  result 
of  sitting  perfectly  still,  of  drinking  cold  water,  etc. ;  it  rises  as  the  result  of 
muscular  work,  etc. 

However,  all  these  changes  in  the  body  temperature  are  as  a  rule  very 
insignificant,  and  this  very  remarkable  fact  has  been  established — that  the 


THE  TEMPERATURE  OF  THE  HUMAN  BODY 


401 


mean  value  of  the  body  temperature  obtained  from  a  large  number  of  deter- 
minations extending  over  periods  of  twenty-four  to  forty-eight  hours,  remains 
the  same  in  spite  of  all  such  disturbances.  This  maintenance  of  the  mean 
body  temperature  unquestionably  is  closely  related  to  the  fact  that,  with  a 
free  choice  of  food,  and  within  periods  of  some  days,  the  body  automatically 
measures  out  its  supply  of  energy  with  unerring  regularity. 

Variations  of  the  temperature  between  persons  of  different  age  are  but 
slight.  Since  the,  foetus  has  a  certain  small  metabolism  of  its  own,  its  body 
temperature  must  be  somewhat  higher  than  that  of  its  mother,  which  direct 
observations  tend  to  prove.  The  difference  amounts  however  to  only  0.3°  C. 
After  birth  the  temperature  of  the  child  sinks  from  0.5°  to  0.8°  C,  a  fact 
dependent  in  part  only  on  the  first  bath ;  it  returns  during  the  first  week, 
as  it  appears,  with  some  fluctuations,  and  then  is  maintained  at  the  value 
given  above  until  old  age,  when  the  temperature  is  said  to  become  some  tenths 
of  a  degree  higher. 

Wlien  the  body  is  subjected  to  excessive  loss  of  heat,  it  is  no  longer  able 
to  maintain  its  temperature  at  a  constant  level.  The  lower  the  temperature 
of  the  body  falls,  the  greater  are  the  disturbances  thereby  produced.  The 
highest  nerve  centers  are  the 
first  to  suffer  from  this  cool- 
ing, but  the  centers  of  the 
medulla  which  are  important 
for  the  maintenance  of  life,  are 
not  paralyzed  until  the  reduc- 
tion has  been  carried  much  fur- 
ther. Theoretically  it  may  be 
assumed  that  in  man  restora- 
tion is  possible  from  a  very 
considerable  reduction  of  the 
body  temperature,  so  long  as 
the  centers  of  the  medulla  have 
not  lost  their  vitality.  Cases 
have  been  observed  in  fact 
where  patients  recovered  from 
a  fall  of  the  body  temperature 
to  24°  C.  due  to  great  exposure. 
Indeed,  a  case  has  been  re- 
ported of  a  man  who  retained 
consciousness  with  a  tempera- 
ture of  only  26.7°  C. 

In  like  manner,  an  increase 
of  the  temperature,  if  it  passes  a  certain  limit,  which  is  different  for  dif- 
ferent individuals,  involves  first  disturbances  to  the  general  health,  and 
later  loss  of  consciousness,  while  the  centers  of  the  medulla  remain  func- 
tional. In  general  it  may  be  said  that  the  body  stands  a  fall  better  than 
a  rise  in  its  temperature.  A  rise  of  only  2°  or  3°  C.  causes  very  severe 
disorders,  and  experience  has  showm  that  a  temperature  of  41°-42°  C.  con- 
stitutes a  very  dangerous  symptom.     And  3'et  a  man  can  endure  still  higher 


Fig.  149. — The  temperature  of  the  body  after  death 

(Niederkorn).      ,    typhoid    fever   (the 

temperature    in    degrees    centigrade    is    given    at 

the  left).     ,  pulmonary  consumption 

(temperature  at  the  right).     The  abscissae  repre- 
sent hours  after  death. 


402  ANIMAL  HEAT  AND  ITS  REGULATION 

temperatures  provided  they  do  not  last  too  long.  The  highest  authenticated 
temperatures  of  patients  who  afterwards  recovered  are:  43.6°  C,  sunstroke; 
44°  C,  scarlatina,  malaria;  46°  C,  malaria  (  ?). 

After  death  the  body  of  course  cools  down,  but  not  always  immediately. 
Thus  it  has  been  shown  that  the  temperature  of  a  body  which  has  died  from 
infectious  fevers  or  injuries  to  the  brain  or  medulla  rises  for  a  time.  This  is 
an  indication  that  the  metabolism  and  consequent  heat  production  do  not 
cease  everywhere  in  the  body  the  moment  the  patient  draws  his  last  breath.  Also 
after  death  from  chronic,  long-continued  diseases,  where  no  such  post-mortal 
rise  of  temperature  is  observed,  the  manner  in  which  the  fall  of  temperature 
occurs  is  evidence  that  combustion  in  some  organs  does  not  cease  the  moment 
of  death.  We  find  in  such  cases  that  the  temperature  remains  unchanged  for 
a  time,  or  falls  very  slightly,  and  then  declines  rapidly.  The  first  stage  can 
only  be  explained  by  supposing  that  heat  production  is  still  going  on  after  death 
(Fig.  149). 

§  2.    THE   SOURCE   OF   ANIMAL   HEAT 

The  source  of  animal  heat  is  the  combustion  going  on  in  the  body  (cf. 
page  46).  Inasmuch  as  combustion  takes  place  in  all  parts  of  the  body,  all 
the  different  organs  participate  in  the  production  of  heat.  And  yet  the  share 
of  the  different  organs  in  this  process  is  very  different,  since  in  certain  organs 
metabolism  is  more  active  than  in  others. 

The  cross-striated  muscles  are  the  most  important  in  this  connection.  They 
constitute  al)out  forty  per  cent  of  the  total  weight  of  the  body,  and,  if  we 
neglect  the  skeleton,  where  the  absolute  quantity  of  heat  produced  is  not  very 
significant,  they  constitute  fully  fifty  per  cent  of  the  weight. 

Even  the  perfectly  quiescent  muscles  generate  heat.  Meade-Smith  deter- 
mined simultaneously  the  temperature  of  the  blood  in  the  aorta  and  in  the  leg 
muscles,  diverting  the  blood  meantime  from  the  muscles.  He  was  able  to  show 
that  the  temperature  of  the  muscle  at  the  beginning  of  five-minute  periods 
without  blood  was  as  a  rule  higher,  and  at  the  ends  of  these  periods  invariably 
higher  than  the  temperature  of  the  blood  in  the  aorta;  also  that  the  temperature 
of  the  muscle  always  rose  during  the  period.  The  increase  might  amount  to 
0.1°  C.  and  the  difference  between  muscle  and  blood  might  at  the  end  of  the 
period  be  0.6°  C.  Then  with  every  muscular  contraction,  as  work  is  performed, 
additional  heat  is  generated.  Indeed  the  energy  consumed  as  work  is  never 
more  than  a  fractional  part  of  that  which  appears  as  heat  (cf.  page  113). 

Next  to  the  muscles,  the  glands,  especially  the  liver,  stomach  and  intestines, 
are  great  producers  of  heat ;  but  no  great  importance  is  to  be  ascribed  to  the 
bones  (except  the  red  marrow),  the  skin  or  the  lungs.  Very  active  metabolism 
takes  place  in  the  gray  matter  of  the  central  nervous  system.  But  since  the 
metabolism  in  the  white  matter  is  very  slight  (cf.  Chapter  XV),  and  since 
the  entire  nervous  system  amounts  to  only  about  1.9  per  cent  of  the  body 
weight,  it  is  not  to  be  supposed  that  this  system  produces  any  considerable 
fraction  of  the  total  quantity  of  heat  formed.  It  is  not  yet  possible  to 
determine  more  accurately  the  share  of  the  different  organs  in  this  important 
function. 


LOSS  OF   HEAT  FROM  THE  BODY  403 

§  3.    LOSS   OF   HEAT   FROM   THE   BODY 

The  heat  formed  in  the  body  is  partly  utilized  in  warming  the  food,  in- 
cluding water  ingested  and  the  air  inspired,  is  partly  given  ofE  by  conduction 
and  radiatioti  through  the  skin,  and  partly  disappears  in  the  evaporation  of 
water  from  the  air  passages  and  from  the  skin,  and  in  the  liberation  of  carbon 
dioxide  from  the  lungs.  The  following  estimate,  agreeing  essentially  with 
those  of  Helmholtz  and  Rosenthal,  indicates  approximately  the  proportion  of 
losses  in  an  adult  man  by  these  different  avenues. 

A.  Warming  the  Food  and  Air 

(1)  Water  drunk  at  15°  C.  and  warmed  to  37.5°— raised  therefore  22.5° =    33.75  Cal. 

(2)  1,500  g.  food  eaten  at  25°  C.  (mean)  and  warmed  to  37.5° — raised  therefore 

13.5  ;  specific  heat  0.8 =    15.00    " 

(3)  15,000  g.  (=  11,500  1.)  air  respired  at  15°  C.  and  warmed  to  37.5° — raised 

therefore  22.5° ;  specific  heat  0.237 =    79.75    " 


128.70 


B.  Loss  OF  Water  and  CO3  in  the  Breath 


(4)  It  is  assumed  that  the  inspired  air  is  half  saturated  with  water  vapor  at 

15°  C,  and  that  the  expired  air  is  fully  saturated  at  37.5°  C.  Approxi- 
mately 450  g.  of  water  would  be  given  off,  therefore,  in  the  form  of 
vapor  from  the  respiratory  passages;  the  latent  heat  of  the  water 
vapor  is  0.537  Cal =  241.70    " 

(5)  The  absorption  of  heat  in  the  liberation  of  COa  from  the  lungs  (800  g.) ; 

0.134  Cal.  per  g =  107.20    " 

348r90    " 

From  above 128^0    " 

Total 477.60    ••' 

The  sum  of  heat  losses  specified  under  these  five  headings  amounts  to 
477.60  Cal.  Estimating  the  total  heat  loss  of  an  adult  man  at  2A00  Cal., 
this  sum  represents  only  about  twenty  per  cent  of  the  total.  The  remaining 
eighty  per  cent  (in  round  numbers)  takes  place  through  the  skin. 

The  direct  calorimetric  measurements  by  Atwater  give  approximately  the 
same  result.  In  a  series  of  experiments  lasting  forty  days  the  mean  heat  loss, 
ill  the  case  of  a  resting  man,  by  conduction  and  radiation  was  1,669  Cal.,  through 
the  urine  and  faeces  31  Cal.,  by  evaporation  of  water  550  Cal. — i.  e.,  in  percent- 
ages 74.2,  1.4,  and  24.4  respectively.  In  the  case  of  a  man  at  work,  the  mean 
for  twenty  days  by  conduction  and  radiation  was  2,277  Cal.,  through  urine  and 
fajces  19,  by  evaporation  of  water  1,126;  or  in  percentages,  66.5,  0.6,  and  32.9 
respectively.  The  proportion  of  evaporation  from  the  skin  and  from  the  lungs 
was  not  determined. 

The  skin  gives  off  heat  to  the  surrounding  air,  or  to  other  cold  substances 
coming  in  contact  with  the  body,  by  conduction,  radiation  and  evaporation. 
The  relative  importance  of  these  factors  varies  greatly  under  different  circum- 
stances. The  quantity  of  water  vapor  given  off  from  the  skin  depends  to  a 
great  extent  both  upon  the  temperature  and  humidity  of  the  surrounding  air, 
and  also  upon  the  heat  production  going  on  in  the  body,  which  in  turn  varies 
with  the  kind  and  the  quantity  of  food  eaten  and  the  amount  of  work  done. 


404  AXLMAL  HEAT  AND  ITS  REGULATION 

It  is  therefore  impossible  to  give  definite  figures  for  the  amount  of  water 
given  off  through  the  skin ;  for  all  of  the  twenty-four-hour  determinations 
thus  far  published  have  reference  only  to  the  total  output  of  water  vapor, 
and  not  to  the  apportionment  between  lungs  and  skin. 

Using  the  above-mentioned  figures  (table,  page  403)  for  the  output  of  water 
vapor  in  respiration,  we  can  form  some  approximate  idea  of  the  amount  of 
water  vapor  eliminated  by  the  skin.  Some  examples  are  adduced  here  in  which 
the  necessary  reductions  have  already  been  made.  A  fasting  individual  gave  off 
through  the  skin  on  the  fifth  day  of  his  fast  approximately  350  g.  of  water;  loss 
of  heat  188  Cal.  The  same  individual  on  a  plentiful  diet  gave  off  through  the 
skin  710  g.  water,  loss  of  heat  381  Cal.,  twice  as  much  therefore  as  in  the  first 
case.  Another  subject  at  rest  and  on  a  moderate  diet  excreted  through  the  skin 
480  g.  of  water  (  =  258  Cal.)  ;  on  the  same  diet  at  severe  work,  1,280  g.  water 
(=  686  Cal.)   (cf.  also  page  397). 

According  to  Zuntz,  soldiers  on  the  march  in  cold  weather  eliminate  about 
one-fifth  of  the  total  output  of  water  through  the  respiration,  in  warm  weather 
only  about  one-sixth.  In  extreme  cases  the  loss  of  heat  by  evaporation  may 
reach  the  enormous  value  of  ninety-five  per  cent  of  the  total  heat  loss. 

The  loss  of  heat  by  radiation  and  conduction  also  exhibits  great  variations, 
which  depend  on  the  temperature  of  the  surrounding  air  and  the  heat  produc- 
tion going  on  in  the  body,  as  well  as  upon  the  clothing.  Both  radiation  and 
conduction  are  considerably  greater  on  exposed  parts  of  the  skin  than  on  clothed 
parts.  From  experiments  on  covered  portions,  the  total  heat  loss  by  radiation 
has  been  calculated  for  a  grown  man  at  about  700-800  Cal.,  while  from  obser- 
vations on  the  naked  skin,  it  is  estimated  at  1,700-1,800  Cal.  Similar  differences 
have  been  observed  with  regard  to  loss  of  heat  by  conduction. 


§  4.  PROTECTION  AGAINST  LOSS   OF   HEAT 

Notwithstanding  considerable  variations  in  the  temperature  of  the  sur- 
rounding air,  homoiothermous  animals  maintain  an  even  balance  between  heat 
production  and  heat  loss.  That  this  is  possible  with  so  small  a  quantity  of 
heat  production  in  the  body  is  due  to  the  fact  that  provisions  are  made  in 
warm-blooded  animals  for  restraining  the  loss  of  heat  through  the  skin.  These 
provisions  are,  (1)  the  subcutaneous  adipose  tissue,  and  (2)  the  natural  hairy 
or  feathery  covering  of  the  body. 

We  have  already  seen  that  the  muscles  come  first  in  the  order  of  heat  pro- 
duction. The  heat  formed  in  them,  however,  cannot  be  readily  conducted  to  the 
superjacent  skin  because  the  intervening  adipose  tissue  is  a  very  poor  conductor 
of  heat.  A  piece  of  skin  2  mm.  in  thickness  will  allow  0.00248  cal.  (small)  to 
pass  through  in  one  minute,  when  the  difference  in  temperature  is  18.2°  C.  The 
same  piece  of  skin  plus  a  2  nun.  layer  of  fat  under  the  same  circumstances  will 
allow  only  0.00123  cal.  to  pass.  With  less  difference  in  temperature  on  the  two 
sides  the  protecting  influence  of  the  fat  is  still  greater,  so  that  for  example  with 
a  difference  of  9°  C.  a  layer  of  fat  2  mm.  in  thickness  retains  0.8  of  the  total 
quantity  of  heat  which  would  otherwise  be  allowed  by  the  skin  to  pass  through 
.(King).  In  considering  the  properties  of  fat  deposited  at  different  places  in 
the  body,  Henriques  and  Hansen  have  directed  attention  to  the  lower  melting 
point  of  fat  which  lies  nearer  to  the  outer  surface  of  the  body.     This  is  doubt- 


PROTECTION  AGAINST  LOSS  OF   HEAT  405 

less  connected  with  the  fall  in  temperature  met  with  in  passing  from  the  inte- 
rior toward  the  surface;  for  the  lower  the  temperature  the  lower  must  be  the 
melting  point  of  the  fat  in  order  that  it  may  remain  in  a  fluid  state. 

The  great  Importance  of  the  subcutaneous  fat  is  most  beautifully  seen  in 
the  case  of  the  great  warm-blooded  marine  animals  of  the  arctics.  They  live 
habitually  among  the  ice  blocks  in  a  medium  which  conducts  heat  at  least 
twenty  times  better  than  air.  and  yet  they  are  able  to  maintain  a  body  tem- 
perature of  35°-40°  C.  The  skin  is  subjected  to  conditions  which  would 
abstract  an  enormous  amount  of  heat,  but  the  extraordinarily  thick  layer  of 
subcutaneous  fat  isolates  the  muscles  and  the  organs — in  short,  the  real  body 
— from  the  skin. 

For  warm-blooded  animals  which  live  in  the  air,  the  loss  of  heat  is  greatly 
reduced  by  the  hair  and  feathers ;  and  clothing  serves  the  same  purpose  for 
our  own  bodies. 

Air  is  itself  a  very  poor  conductor  of  heat,  but  when  in  motion  it  may 
carry  away  great  quantities  of  heat.  Let  us  imagine  a  naked  man  in  an 
atmosphere  colder  than  his  skin.  The  layer  of  air  immediately  adjacent  to 
his  skin  is  first  warmed  by  his  body  and  as  a  consequence  it  becomes  lighter. 
It  rises  and  is  replaced  by  fresh,  cold  air,  which  in  its  turn  is  warmed,  re- 
placed, and  so  on  incessantly.  The  body  produces  therefore  by  virtue  of  its 
own  heat  an  uninterrupted  current  of  air,  which  abstracts  great  quantities 
of  heat  from  it. 

This  active  exchange  of  air  is  considerably  restricted  by  the  clothing,  what- 
ever the  material  of  which  it  is  made,  inasmuch  as  it  prevents  free  access  of 
the  air  to  the  skin.  The  air  inclosed  by  the  clothing  is  relatively  stationary 
and  thus,  because  of  its  poor  conducting  qualities,  it  constitutes  a  thermally 
insulating  layer  around  the  body.  Moreover,  not  only  the  air  between  the  cloth- 
ing and  the  skin,  as  well  as  between  the  different  garments,  but  the  air  in  the 
meshes  of  the  clothing  material  itself  is  to  be  taken  into  consideration.  For 
clothing  materials,  like  hair  and  feathers,  are  of  themselves  much  better  con- 
ductors than  air.  The  amount  of  air  held  in  the  meshes  of  the  clothing  of  a 
man  as  ordinarily  dressed  (excluding  wraps)  is  estimated  at  20-301.  (Rubner). 

Important  as  this  layer  of  surrounding  air  is,  it  must  not  stand  absolutely 
still,  but  must  be  kept  in  continual  motion,  even  if  it  be  verj'  slow  motion;  for 
otherwise  the  air  very  quickly  becomes  saturated  with  water  vapor  given  off  by 
the  skin,  and  then  no  further  loss  of  water  vapor  can  take  place.  The  result  is 
great  discomfort  and,  under  some  circumstances,  great  disturbances  in  the  regu- 
lation of  heat. 

The  loss  of  heat  by  radiation  is  likewise  reduced  considerably  by  the  cloth- 
ing. Since  the  clothing  materials  consist  of  substances  which  do  not  permit  the 
passage  of  radiant  heat,  they  absorb  the  heat  radiating  from  the  skin  and  are 
themselves  warmed  by  it.  Consequently  this  heat  remains  longer  in  the  neigh- 
borhood of  the  body  and  thus  helps  to  warm  the  air  immediately  surrounding 
it.  When  one  feels  that  he  is  losing  heat  from  the  immediate  neighborhood  of 
the  body  too  rapidly,  he  covers  the  garment  from  which  the  heat  is  escaping 
with  still  another,  which  catches  the  heat  radiating  from  the  first  and  delays  it 
still  longer.    A  shirt,  vest,  coat,  etc.,  act  in  this  way. 

The  radiation  of  heat  from  the  skin  is  still  further  diminished  by  water 
vapor,  because  it  reduces  the  diathermic  capacity  of  the  air. 


406  ANI\L\L  HEAT  AND  ITS  REGULATION 

As  a  result  of  these  protective  measures,  the  temperature  of  the  air  imme- 
diately surrounding  the  body  is  generally  somewhat  above  30°  C.  The  skin 
itself  in  places  where  it  is  clothed  has  a  temperature  of  33°-35°  C,  on  naked 
places  its  temperature  is  lower  (cf.  page  3'J'J). 

That  warm-blooded  animals  can  maintain  a  constant  body  temperature, 
Avhen  exposed  to  a  very  low  external  temperature,  is  due  to  their  natural  or 
artificial  clothing.  This  is  perfectly  evident  from  the  fact  that  the  tempera- 
ture of  an  animal  declines  more  or  less  when  it  is  shorn,  as  well  as  by  the 
experience  that  a  naked  man  at  rest  can  only  maintain  his  temperature  at 
the  normal  level  when  the  surrounding  temperature  is  at  27°  C.  or  higher 
(Senator). 

By  experiments  with  the  calorimeter  Rubiier  has  determined  the  saving  of 
heat  to  the  body  accomplished  by  clothing  in  some  special  cases.  A  guinea  pig 
lost  normally  by  radiation  and  conduction  on  the  average  3.37  Cal.  per  hour; 
after  being  shorn  the  hourly  loss  was  4.19  Cal. — i.  e.,  33.3  per  cent  more.  Tn  the 
human  subject  the  loss  from  the  naked  arm  by  radiation  and  conduction  at 
ordinary  room  temperature  was  about  thirty  per  cent  more  than  that  from  the 
clothed  arm. 

And  yet  the  saving  actually  accomplished  by  the  clothes  is  somewhat  less 
than  this  would  indicate;  for  the  output  of  water  vapor  from  the  clothed  body 
is  greater  than  from  the  naked  because  of  the  higher  temperature  of  the  air 
immediately  adjacent  to  the  skin.  From  experiments  on  the  naked  forearm 
and  on  the  hand  it  has  been  found  that  in  a  dry  atmosphere  at  a  temperature 
of  15°-20°  C.  about  twenty  per  cent  of  the  total  heat  loss  takes  place  by  evapo- 
ration. From  the  naked  arm  the  elimination  of  water  amounted  to  3.59  g.,  and 
from  the  clothed  arm  4.39  g. — a  difference  of  twenty-two  per  cent.  Using  this 
value  the  saving  of  heat  due  to  clothes  may  be  calculated  as  follows : 

The  total  loss  of  heat  through  the  skin 100 

By  radiation  and  conduction  80 

By  evaporation 20 

The  loss  by  radiation  and  conduction  is  diiniiiislied   liy  the  clothes 

twenty  per  cent,  leaving  therefore 56 

While  the  loss  by  evaporation  is  increased  twenty-two  per 

cent  making 24 

Total 80 

The  saving  according  to  this  amounts  to  about  twenty  per  cent  at  ordinary 
room  temperature,  and  of  course  at  lower  temperature  is  much  greater. 

Just  as  man  seeks  to  reduce  as  much  as  possible  the  loss  of  heat  during 
the  winter  by  wearing  heavier  clothing,  so  the  animals  offset  the  influence  of 
the  lower  temperature  by  a  thicker  coat  of  hair  or  feathers.  What  this  thick 
coat  actualh'  does  for  its  o\\'ner  may  be  seen  in  polar  animals  livin<?  in  the 
air,  which  maintain  a  normal  body  temperature  even  at  an  external  tempera- 
ture of  —40°  C.   (Parry). 

§  5.  REGULATION  OF  THE  BODY'S  TEMPERATURE 

The  facts  thus  far  discussed  relate  only  to  the  necessary  conditions  for 
the  maintenance  of  the  body  temperature,  but  by  no  means  suffice  to  explain 
this  phenomenon  theoretically.     For,  while  both  animals  and  men  are  all  the 


REGULATION  OF  THE  BODY'S  TEMPERATURE  407 

time  .being  exposed  to  greater  or  less  variations  in  the  temperature  of  the 
surrounding  medium,  neither  the  thickness  of  the  clothing  nor  that  of  the 
adipose  tissue  is  being  changed  to  correspond  with  these  variations;  and  3'et 
the  body  maintains  its  temperature  unchanged.  The  sum  total  of  all  those 
processes  by  which  this  constancy  is  maintained  is  comprehended  under  the 
term  heat  regulation  of  the  body.  The.se  processes  can  be  divided  into  two 
groups  according  as  they  relate  to  heat  production  or  to  heat  loss. 

The  way  in  which  the  production  of  heat  varies  under  the  influence  of  the 
surrounding  temperature  has  been  already  presented  in  Chapter  IV  (page 
114).  But  heat  production  is  influenced  also  by  the  amount  of  food,  and  in 
controlling  the  latter  we  have  a  means  of  adapting  the  transformation  of 
substance  in  the  l)ody  to  the  requirements  of  heat  regulation. 

A  noteworthy  illustratiou  is  given  by  Kl  E.  Ranke,  who  studied  his  diet 
both  in  Germany  and  during  a  scientific  expedition  to  Brazil.  Allowing  him- 
self free  choice  of  food,  the  amount  being  controlled  only  by  his  appetite,  his 
total  intake  between  the  temperatures  of  15°  and  22°  C.  was  on  the  average 
3,300-3,500  Cal.  In  a  dry  climate  at  a  temperature  of  25°  C,  it  fell  to  2,800  Cal., 
and  at  an  atmospheric  temperature  of  25°-28°  with  a  humidity  of  about  eighty- 
three  per  cent,  it  reached  the  low  level  of  1,970  Cal.  (  =  20.9  Cal.  per  kg.  body 
weight).  His  body  weight  decreased  however  on  this  low  ration.  In  order  to 
recover  his  original  weight  he  was  obliged  to  adopt  a  richer  diet,  but  various 
disturbances  in  his  general  health  appeared  while  he  was  experimenting  in  this 
direction. 

A.    REGULATION   OF    HEAT  LOSS 

As  we  have  seen  above  the  temperature  of  the  skin  depends  primarily  upon 
the  blood  supply;  the  greater  the  amount  of  blood  flowing  through  it,  the 
warmer  it  becomes.  But  the  warmer  the  skin  becomes,  other  conditions  being 
the  same,  the  greater  is  the  loss  of  heat  from  the  skin  by  radiation  and  con- 
duction. The  heat  loss  by  radiation  and  conduction  therefore  depends  upon 
the  amount  of  Mood  supplied  to  the  shin. 

The  l)lood  vessels  of  the  skin,  like  the  other  vessels  of  the  body,  are  under 
the  influence  of  the  vasomotor  mechanisms,  and  are  constricted  or  dilated 
according  to  the  momentary  requirements  of  the  heat  regulation.  Thus  in 
cold  weather  and  when  the  production  of  heat  in  the  body  is  not  greatly 
increased  by  muscular  work,  they  are  constricted;  and  in  hot  weather  they 
are  dilated. 

These  changes  in  the  blood  supply  of  the  skin  serve  in  another,  and  per- 
haps still  more  important  manner,  to  regulate  the  loss  of  heat.  During  its 
flow  through  the  cutaneous  vessels,  the  blood  naturally  gives  off  heat,  and 
returns  to  the  interior  somewhat  cooled.  When  the  vessels  are  dilated,  more 
blood  flows  through  them,  and  more  heat  is  thus  lost  than  when  they  are 
constricted  and  the  quantity  of  blood  flowing  through  them  is  small.  While 
the  cutaneous  vessels  are  constricted,  the  vessels  of  the  abdominal  viscera  and, 
as  it  appears  from  the  investigations  of  Wortheimer,  those  also  of  the  muscles 
— i.  e.,  of  the  most  important  heat-producing  organs — are  dilated  :  while  dur- 
ing dilatation  of  the  cutaneous  vessels,  those  of  the  abdominal  viscera  are 
constricted. 


408  ANIMAL  HEAT  AND  ITS   REGULATION 

Experience  proves  lluit  a  man  can  maintain  hi.s  body  temperature  without 
increase  in  an  atmosphere  whose  temperature  is  much  higher  than  that  of  his 
body.  This  appears  the  more  remarkable  when  we  consider  that  the  metabo- 
lism and  heat  production  of  the  body  never  cease,  however  high  the  surround- 
ing temperature  may  be.  The  fact,  as  was  first  observed  by  Benjamin  Frank- 
lin, is  to  be  explained  by  the  secretion  of  sweat.  At  a  higher  atmospheric 
temperature  the  sweat  glands  are  stimulated,  and  evaporation  of  the  sweat 
thus  poured  out  upon  the  skin  absorbs  a  large  quantity  of  lieat  from  the  body. 
In  this  way  the  body  is  cooled  and  maintains  its  temperature  unchanged, 
whether  the  outside  temperature  exceeds  or  only  approaches  that  of  the  body. 

But  the  amount  of  sweat  secreted  depends  not  only  upon  the  temperature 
of  the  air,  but  also  upon  the  amount  of  heat  being  produced  in  the  body  at 
the  time.  If  the  heat  production  of  the  body  be  considerably  increased  as  the 
result  of  severe  muscular  work,  the  bod}'  will  sweat  even  at  an  atmospheric 
temperature  of  0°  C.  After  a  full  meal,  owing  to  the  increased  heat  produc- 
tion a  greater  quantity  of  sweat  is  secreted  than  when  the  metabolism  is 
reduced  for  lack  of  food. 


B.    CENTERS  FOR  HEAT  REGULATION 

Among  the  many  so-called  "  heat  centers,'"  located  in  different  parts  of 
the  central  nervous  system.,  which  have  been  mentioned  by  different  authors, 
only  a  single  one  seems  to  be  fairly  entitled  to  the  name.  If  a  fine  needle  be 
thrust  into  the  brain  from  above  downward  in  such  a  direction  as  to  strike 
the  medial  edge  of  the  corpus  striatum,  a  rise  in  temperature  appears  in  the 
skin,  in  the  muscles  and  in  the  rectum;  likewise  an  increase  of  metabolism 
and  of  heat  loss  as  determined  by  the  calorimeter  (Aronsohn  and  Sachs, 
Richet).  The  increase  of  temperature  amounts  to  more  than  2°  C,  the  in- 
crease of  metabolism  and  of  heat  loss  to  about  20  per  cent.  The  maximum 
effect  appears  within  twenty-four  to  seventy-three  hours  after  the  puncture, 
unless  the  needle  be  pressed  through  to  the  base  of  the  cranium,  in  which  case 
it  appears  within  two  to  seven  hours.  The  results  of  electrical  stimulation  by 
means  of  electrodes  insulated  to  the  ends  show  that  the  effect  of  puncture 
is  due  to  stimulation  and  not  to  destruction  of  the  parts  encountered. 

We  cannot  form  any  definite  opinion  at  present,  as  to  the  significance 
which  this  and  other  "  heat  centers  "  have  in  the  regulation  of  this  important 
function. 

How  the  centers  for  heat  regulation  (wherever  they  may  be  located)  are  stimu- 
lated, is  another  question  which  cannot  be  conclusively  answered  as  yet.  It  is 
indeed  fairly  certain  that  the  cold  and  heat  nerves  of  the  skin  play  a  great  part, 
since  heat  production  and  heat  loss  are  reflexly  influenced  in  one  direction  or 
the  other  according  to  conditions  reported  by  these  nerves.  Changes  in  the 
temperature  of  the  blood  also  might  play  a  part ;  that  is,  cold  might  by  direct 
action  on  the  heat  centers  bring  about  an  increase  of  metabolism  and  a  con- 
striction of  the  cutaneous  vessels,  or  warmed  blood  might  rouse  the  sweat  centers 
to  increased  activity.  This  mechanism  does  actually  participate  in  some  such 
way  in  the  regulation  of  heat,  for  in  muscular  work  the  sweat  breaks  out  only 
when  the  body  temperature  has  increased  0.3°-0.5°   C.    (Fredericq).     Likewise 


REGULATIOX  OF  THE  BODY'S  TEMPERATURE  409 

the  augmented  respiration  appearing  with  a  high  external  temperature  (page 
318)  is  caused  by  a  direct  exciting  effect  of  the  blood,  for  it  can  be  reproduced 
in  all  its  essential  features  by  locally  warming  the  blood  in  the  carotids  on  the 
way  to  the  brain ;  but  it  will  not  appear,  notwithstanding  a  very  strong  heat 
stimulus,  when  the  head  is  cooled. 

The  ability  to  maintain  a  constant  temperature  in  certain  species  of  ani- 
mals, including  man,  is  not  fully  developed  immediately  after  birth.  In  such 
warm-blooded  animals  as  have  a  well-developed  nervous  system  at  birth — 
e.  g.,  guinea  pig  and  chick — the  heat-regulating  mechanism  also  is  completely 
functional  at  this  time.  But  those  which,  like  rats  and  pigeons,  are  born 
blind  and  helpless,  only  acquire  the  power  of  regulating  their  own  temperature 
in  the  course  of  the  second  week  (Pembrey).  The  newborn  child  also  has 
not  yet  come  into  full  possession  of  its  power  to  regulate  its  heat  (Raudnitz). 
It  is  probable  that  this  post-embryonic  development  of  the  regulatory  mecli- 
anism  is  intimately  connected  with  the  development  of  the  neuromuscular 
apparatus  going  on  at  the  same  time. 


CHAPTEK    XV 

THE    FUNCTIONS    OF    CROSS-STRIATED    MUSCLES 

The  purpose  of  the  cross-striated  muscles  is  twofold :  first  to  provide  for 
the  bodily  movemenis,  and  secondly  to  participate  in  the  production  and  regu- 
lation of  heat  in  the  body.  In  this  chapter  we  shall  first  inquire  into  the 
general  properties  of  the  muscles  and  shall  then  briefly  discuss  their  relations 
to  other  organs. 

FIRST    SECTION 

GENERAL  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

Inasmuch  as  the  general  properties  of  muscles  and  of  nerve  fibers  agree 
in  many  respects,  and  the  information  gained  from  nerves  very  often  throws 
light  on  the  corresponding  phenomena  of  muscles,  it  seems  best  to  discuss 
them  here  together. 

Physiologists  have  for  a  long  time  given  preference  to  the  study  of  the  gen- 
eral properties  of  muscles  and  nerves  because  at  first  it  promised  to  yield  very 
important  results  bearing  on  the  fundamental  properties  of  the  living  substance 
in  general.  A  great  number  of  facts  have  been  collected  by  the  work  done  in 
this  field,  but  unfortunately  they  do  not  as  yet  afford  us  a  basis  for  any  con- 
sistent theory  of  nervous  and  muscular  activity.  Significant  as  these  facts  are, 
we  must  be  content  to  mention  only  the  most  important  of  them,  a  more  exhaust- 
ive presentation  being  quite  beyond  the  possibilities  of  a  text-book  of  this  size. 

When  not  otherwise  expressly  stated,  the  facts  given  may  be  understood 
as  applying  to  the  surviving  nerves  or  muscles  of  the  frog,  exsected  from  the 
body  (cf.  page  6).  A  motor  nerve  is  generally  employed  in  investigation 
of  the  general  properties  of  nerves,  and  in  most  cases  the  muscle  connected 
with  it  serves  as  the  indicator  of  the  state  of  the  nerve.  The  changes  in  the 
form  of  the  muscle  are  usually  registered  by  the  graphic  method  (cf.  page  6). 

§  1 .    FUNDAMENTAL   LAWS   OF   NERVOUS   ACTIVITY ' 

A  nerve  is  irritable  to  ordinary  artificial  stimuli  at  all  points  of  its  course, 
and  it  transmits  the  stimulus  in  both  directions  from  the  point  of  stimula- 
tion. This  is  best  sho\ATi  by  means  of  the  action  current  (page  48).  If  a 
nerve  be  stimulated  at  its  middle,  each  of  the  two  ends  being  at  the  same 

*  The  properties  of  different  kind.s   of  nerve  fibers  will  be  discussed   more  fully  in 
Chapter  XXII. 
410 


FUNDAMENTAL  LAWS  OF   NERVOUS  ACTIVITY  411 

time  connected  with  a  galvanometer,  the  action  current  appears  in  both.  This 
is  true  not  only  of  mixed  nerve  trunks  composed  of  both  afferent  and  efferent 
fibers,  but  can  be  demonstrated  on  the  anterior  roots  of  the  spinal  nerves 
which  contain  only  efferent  fibers   (Du  Bois-Re}Tnond ) . 

If  a  living  nerve  be  severed,  it  of  course  no  longer  has  the  power  to 
transmit  the  stimulus.  But  the  same  is  true  if  the  nerve  be  simplv  tied  off. 
To  be  capable  of  conducting,  a  nerve  must,  therefore,  he  intact,  not  only  in 
the  physical,  but  also  in  the  physiological  sense. 

The  conductivity  of  a  nerve  may  be  diminished  or  abolished  for  a  time  by 
various  agents:  external  pressure — e.g.,  when,  as  we  saj-,  the  limbs  "go  to 
sleep  " ;  chloroform ;  alcohol,  etc.  All  such  agents  have  this  in  common,  that 
they  reduce  or  even  abolish  the  physiological  continuity  of  the  nerve,  without 
destroying  its  physical  integrity.  x\nd  yet  the  local  excitability  of  the  nerve 
in  the  same  place  may  persist.  Under  certain  circumstances  it  may  happen  also 
that  a  segment  of  the  nerve,  which  for  some  reason  is  not  excitable,  still  has  the 
power  to  transmit  the  stimulus  received  at  some  other  point  on  the  nerve.  This 
is  witnessed,  for  example,  in  certain  stages  of  regeneration  of  a  nerve  that  has 
been  cut.  Moreover,  the  excitability  of  the  nerve  does  not  always  keep  even 
pace  with  its  conductivity,  possibly  because  the  nerve  responds  in  a  different 
manner  to  its  natural  stimulus  propagated  from  one  segment  to  another,  from 
what  it  does  to  the  artificial  stimuli. 

A  stimulus  once  received  by  a  nerve  fiber  is  transmitted  only  within  the 
same  fiber  and  its  branches,  never  passing  to  the  fibers  running  beside  it  in 
the  same  trunk  (law  of  isolated  conduction) . 

This  law  holds  also  for  the  conducting  pathways  in  the  central  nervous  sys- 
tem. One  can  convince  himself  of  its  validity  in  a  very  simple  way.  If,  for 
example,  he  touch  the  tip  of  his  tongue,  at  each  of  tw'o  places  about  1  mm.  apart, 
with  a  sharp  point,  he  can  distinguish  the  two  points  very  accurately,  which  of 
course  would  not  be  possible  if  the  two  stimulated  the  same  nerve  fiber. 

In  very  close  relation  with  this  law  belongs  the  discovery  of  the  specific 
character  of  the  respo7ise  to  excitation — i.e.,  that  stimulation  of  a  definite 
nerve  produces  an  effect  in  its  own  answering  organ  and  in  that  organ  only. 
By  the  answering  organ  we  mean  that  particular  organ  connected  with  the 
nerve  and  specially  influenced  by  it.  The  answering  organ  of  an  ordinary 
motor  nerve  is  the  muscle  which  it  innervates,  the  answering  organ  of  a 
secretory  nerve  is  the  gland  which  it  controls,  etc.  The  answering  organs 
of  the  afferent  nerves  are  nerve  cells  situated  in  the  central  nervous  system. 
From  these  new  nerve  paths  originate,  and  end  in  other  nerve  cells,  and  thus 
stimulation  of  a  single  afferent  nerve  may  rouse  a  whole  series  of  different 
nerve  cells  united  together.  Finally,  a  nerve  cell  connected  with  an  efferent 
nerve  may  be  set  in  action  by  an  afferent  nerve,  and  a  peripheral  organ  may 
thus  be  stimulated  without  the  participation  of  the  will  or  even  of  conscious- 
ness. Such  a  phenomenon  we  call  a  reflex  (Chapter  XXII).  Because  of  the 
manifold  wav  in  which  the  nerve  fibers  are  combined  with  one  another  in  the 
central  nervous  system,  very  complex  effects  may  result  from  a  single  afferent 
stimulus,  without  in  any  way  invalidating  the  law  of  specific  response. 


1 


412 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


§  2.    THE    PROPERTIES   OF    RESTING   MUSCLE 

A.    ELASTICITY 

If  a  metallic  wire  vertically  suspended  be  loaded  with  a  certain  weight, 
almost  immediately  it  assumes  the  maximum  length  for  that  load  and,  prac- 
tically speaking,  is  not  extended  further  however  long  the  weight  remains. 
A  muscle  or  other  organic  tissue  behaves  very  differently.     If  we  load  a  fresh 

muscle  with  a  weight,  for  a  moment  it 
takes  a  certain  length  according  to  the 
size  of  the  load,  but  thereafter  as  long 
as  the  weight  remains  it  continues  to 
stretch,  at  first  rapidly  and  then  more 
and  more  slowly.  This  secondary  stretch- 
ing is  spoken  of  as  the  after  extension. 
When  a  muscle  already  stretched  Ijy  a  cer- 
tain weight  is  unloaded,  it  shortens  rap- 
idly at  first,  then  more  and  more  slowly. 
In  this  case  it  is  said  to  exhibit  secondary 
elasticity,  or  after  shortening  (Fig.  150). 

These  secondary  phenomena  render  the 
investigation    of   the   elasticity   in    muscles 
and   the    influence   of   load    rather   difficult. 
In  order  to  reduce  the  effect  of  after  exten- 
sion as  much  as  possible,  Marey  and  Blix 
have  hit  upon  a  device  by  which  the  load  can  be  increased  or  diminished  contin- 
uously  and   verj'   rapidly,    and  the  variations  in  length  of   the   muscle   can  be 
recorded  at  the  same  time  (Fig.  151). 

The  support  (i)  bears  the  muscle  lever  (c)  on  which  the  muscle  is  fastened 
at  m.  The  lever  is  loaded  by  means  of  the  weight  h,  and  is  counterbalanced  by 
the  weight  k.  The  plate  (f)  with  the  recording  surface  (J)  attached  to  it  can 
be  moved  back  and  forth  between  the  two  ledges  screwed  fast  to  the  base.  At 
the  same  time  the  weight  h  controlled  by  the  bar  h  is  moved  along  the  lever. 


Fig.  150. — Curves  repre.senting  the  ex- 
tension, .4,  and  elastic  shortening, 
B,  of  two  adductor  muscles,  after 
Blix.  ,4  was  suddenly  loaded  with 
100  g.  of  weight  and  B  was  sud- 
denly relieved  of  its  weight. 


Fig.  151.— Apparatus  of  Blix  and  Lov^n  for  recording  the  elasticity  curs-e  of  a  muscle. 


and  in  this  way  the  load  acting  on  the  muscle  is  changed  in  proportion  to  the 
excursion  of  the  writing  surface.  Curves  obtained  with  the  apparatus  represent 
the  extensibility  and  elasticity  of  the  muscle  with  a  uniformly  increasing  and 
uniformly  diminishing  load. 


THE  PROPERTIES  OF  RESTING  MUSCLE  413 

Such  a  curve  is  given  in  Fig.  153.  We  see  that  the  increase  in  length 
of  the  muscle  with  a  load  increasing  at  a  uniform  rate  is  less,  the  greater 
the  absolute  load — i.  e.,  the  coefficient  of  elasticity  becomes  greater  as  the  ten- 
sion of  the  muscle  increases.  Moreover,  it  appears  from  the  figure  that  the 
elasticity  curve  runs  below  the  extension  curve,  a  circumstance  not  due  to 
after  extension.  The  elasticity,  it  will  be  observed,  is  very  complete,  since  the 
muscle  when  it  is  released  resumes  its  original  length.  Permanent  lengthen- 
ing appears  to  a  noticeable  extent  only  when  the  muscle  substance  is  torn 
by  too  great  an  extension. 

B.    CHEMISTRY   OF   MUSCLE 

The  reaction  of  fresh,  resting  muscle  was  for  a  long  time  regarded  as 
acid.  But  Du  Bois-Reymond  pointed  out  that  the  reaction  of  the  flesh  of 
different  mammals  is  more  or  less  alkaline.  Further  investigation  has  shown 
that  there  is  no  one  reaction  for  resting  muscle,  but  rather  two :  alkaline  to 
laemoid  and  neutral  or  faintly 
alkaline  to  curcuma.  The 
aqueous  extract  of  cross- 
striated  muscle  reacts  in  the 
same  way.  According  to  Roh- 
mann,  the  acid  reaction  of  the 
water  extract  to  curcuma  is 
essentially  due  to  sodium 
monophosphate,  and  the  alka- 
line reaction  to  laemoid  to  the 
acid  carbonate  of  sodium,  to 
the  diphosphate  of  sodium  and 

to    alkaline  compounds    of    the         ^'G.  152.— Extension  and  elasticity  curves  of  the  frog's 

.  .  1  gastrocnemius,  after  Nerander.  This  tracing  was 
nroteios 

^                 ■  obtained   with   the   apparatus   shown    in    Fig.    151. 

The  upper  line  represents  the  curve  of  extension  and 
Among  the  proteids   which  the  lower  line  the  curve  of  elastic  shortening. 

make  up  the  insoluble  stroma 

of  muscle,  there  are  two  bodies,  one  a  globulin  {myosin,  v.  Fiirth;  paramyo- 
sinogen, G.  N.  Stewart)  and  the  other  a  globulin-like  substance  {myogen, 
V.  Fiirth;  myosinogen)  which  can  be  extracted  from  fre.>ih.  lilood-free  rabbit's 
muscle  Avith  normal  salt  solution.  In  dead  muscle  both  pass  over  spontane- 
ously into  insoluble  modifications  (myosin  fibrin  and  myogen  filirin)  but  they 
are  distinguished  by  their  precipitation  reactions  and  the  temperature  at 
which  they  coagulate.  ^lyosin  coagulates  at  44°-50°  C,  myogen  at  o5°-65° 
C.  Of  the  total  quantity  of  proteid  which  goes  into  solution  with  normal 
salt,  myosin  constitutes  about  twenty  per  cent  and  myogen  about  eighty  per 
cent  (v.  Fiirth). 

Other  nitrogenous  constituents  of  muscle  represent  the  decomposition  prod- 
ucts of  proteid:  creatin  (0.1-0.4  per  cent  in  fresh  muscle),  hypoxanthin,  xanthin, 
and  guanin  (0.23,  0.05  and  0.02  per  cent  of  dry  substance  respectively). 
Here  belong  also  the  phosphocarnic  acid  (0.1-0.2  per  cent) ;  inosinic  acid 
(C,„H,3X<P0,)  from  which  hypoxanthin  can  be  split  off;  camosin  (C^H^X^Oj) 
closely  related  to  arginin;  and  carnin  (CJTsNiOj). 

The  nonnitrogenous  organic  constituents  are:  inosit  (hexa-hydroxy -benzol, 
C„He(OH,+HjO),  glycogen,  sugar,  fat,  etc. 


414 


THE  FUNCTIONS  OF  CROSS-STRIATED   MUSCLES 


Muscles  owe  their  color  to  a  peculiar  red  pigment  (myochrome)  which 
is  closely  related  to  haemoglobin  but  does  not  agree  with  it  spectroscopically 
(K.  A.  H.  Morner). 


§  3.    STIMULATION   OF   MUSCLES  AND    OF   NERVES 

A.    THE  MUSCLE  CURVE 

1.  Method. — A  muscular  contraction  can  be  recorded  in  several  ways  which 
differ  in  principle  but  which  finallj'  reduce  to  two  groups,  according  as  the  short- 
ening induced  bj-  the  stimulus  is  allowed  to  take  place  or  not.    In  the  latter  case 


Fig.  153. — Apparatus  of  Fick  for  recording  variations  in  the  length  and  in  the  tension  of  a  muscle 
artificially  stimulated.  By  unhooking  the  tension  recorder  the  lever,  HH ,  is  allowed  to  m.ove 
freely  up  and  down  like  an  ordinary  muscle  lever.      For  further  e.xplanation,  see  text. 

the  tension  of  the  muscle  increases  as  a  result  of  the  excitation,  but  its  length 
remains  constant.  For  this  reason  such  contractions  are  called  isometric  con- 
tractions, and  the  variations  of  tension  are  recorded  after  Fick's  method  as 
follows  (Fig.  153).  The  muscle  (M)  is  attached  to  a  strong  steel  spring  (f) 
which  bears  a  long  writing  point  (h)  for  magnifying  and  recording  its  move- 
ments. When  the  muscle  is  stimulated,  it  attempts  to  bend  the  spring,  but  since 
the  latter  yields  but  slightly,  the  muscle  cannot  shorten  to  any  appreciable 
extent ;  consequently  the  whole  effect  of  the  muscular  activity  is  to  increase  the 
tension. 

In  the  other  method  a  lever  loaded  with  a  weight  is  commonly  u.5ed,  and 
the  weight  is  so  chosen  that  the  effort  of  the  muscle  to  shorten  when  stimulated 
is  effective.  The  lever  is  lifted,  therefore,  and  the  resulting  curve  is  a  record 
of  variations  in  the  length  of  the  muscle  during  the  contraction. 


STIMULATION  OF  MUSCLES  AND  OF  NERVES 


415 


A  loaded  lever  lifted  in  this  way  suffers  a  certain  acceleration  in  its  move- 
ment upward,  which  is  often  so  great  that  from  a  certain  moment  onward  the 
lever  moves  of  its  own  inertia,  and  not  at  the  instance  of  the  muscle.  It  is 
evident  that  a  muscle  curve  recorded  under  such  circumstances  can  be  trusted 
only  for  information  as  to  the  very  beginning  of  the  contraction.  In  order  to 
prevent  this  "  throw  "  due  to  inertia  a  very  light  lever  is  employed,  and  the  load 
is  applied  as  near  to  the  axis  as  possible  (Fig.  160),  while  the  muscle  is  attached 
at  a  greater  distance  therefrom.  Since  it  is  assumed  that  the  tension  of  the 
muscle  remains  the  same  throughout,  this  sort  of  a  contraction  is  called  isotonic. 
An  actual  condition  of  isotony,  however,  is  scarcely  ever  to  be  had  (cf.  page  435). 

To  be  able  to  analyze  the  temporal  course  of  the  muscular  contraction  ex- 
actly, one  must  record  it  on  a  writing  surface  moving  with  sufficient  speed  (300- 
600  mm.  per  second). 

2.  The  simple  contraction.  The  muscular  contractions  caused  by  the  vari- 
ous stimuli  are  either  simple  or  summated.  By  simple  contraction,  or  merely 
contraction,  we  mean  that  act  of  the  muscle  which  is  discharged  by  a  single 


Fig.  1.54. — Simple  contraction  curve  of  the  frog's  ga.?trocnemiu.s.  The  vertical  line  at  the  left 
marks  the  movement  of  stimulation.  The  interval  between  this  line  and  the  point  at  which 
the  contraction  curve  leaves  the  base  line  is  the  latent  period. 

stimulus.  By  summated  contractions  we  understand  the  contractions  dis- 
charged by  a  series  of  stimuli  following  each  other  in  rapid  succession  (cf. 
page  51). 

When  a  muscle  receives  a  stimulus,  a  measurable  time  always  elapses  be- 
tween the  instant  of  stimulation  and  the  appearance  of  a  visible  effect,  and 
this  time  is  designated  as  the  latent  period  (Helmholtz.  1850). 

The  general  procedure  in  making  exact  determinations  of  this  as  well  as  of 
other  physiological  periods  may  be  explained  by  the  following  method :  On  the 
lower  edge  of  the  drum  of  a  kymograph  a  metallic  peg  is  securely  fastened,  so 
that  when  the  drum  is  revolving  this  peg  can  break  an  electric  contact.  The 
contact  forms  a  part  of  the  primary  current  to  an  induction  coil.  If  now  the 
secondary  current  be  conveyed  to  the  muscle,  and  the  drvim  be  set  going  so  that 
the  muscle  lever  makes  a  tracing,  it  is  clear  that  the  instant  the  peg  opens  (or 
closes)  the  primary  current  the  muscle  will  receive  a  shock.  But  it  is  equally 
clear  that,  owing  to  the  latent  period,  the  instant  the  resulting  contraction  begins 
will  not  be  the  instant  of  stimulation.  To  find  on  the  tracing  the  instant  when 
the  muscle  receives  the  shock,  let  the  drum  be  moved  very  slowly  until  the  peg 
once  more  breaks  the  primary  current.  Since  the  drum  is  now  as  good  as  stand- 
ing still  the  resulting  contraction  will  trace  a  vertical  line  (Fig.  154)  which 
marks  the  instant  of  stimulation.  The  interval  between  this  vertical  line  and 
the  rise  of  the  muscle  curve  above  the  base  line  is  the  latent  period.  The  period 
can  of  course  be  measured  in  fractions  of  a  second  if  the  vibrations  of  a  tuning 


416  THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

fork  be  reeovdcd  while  the  drum  is  going  at  the  same  rate  of  speed.  Sometimes 
it  is  difficult  to  say  just  when  the  muscle  curve  rises  from  the  base  line.  The 
exact  moment  can  be  determined  if  the  experiment  be  so  devised  that  the  mus- 
cular contraction,  the  instant  it  begins,  opens  the  current  to  an  electric  signal. 

The  length  of  the  latent  period,  which  has  generally  been  determined  on 
the  frog's  muscle,  depends  upon  various  circumstances.  With  a  maximal 
break  induction  shock  and  at  ordinary  room  temperature  (17°-19°  C),  the 
mean  length  is  al)out  0.004  second ;  at  a  higher  tem})erature  it  is  shorter,  at 
a  lower  temperature  longer.  The  latent  period  increases  also  as  the  height 
of  the  contraction  decreases.  On  the  other  hand,  under  circumstances  other- 
wise the  same,  it  is  influenced  very  little  by  the  load  or  by  the  tension  of  the 
muscle  (i.  e.,  up  to  a  certain  limit). 

If  a  muscle  prepared  for  stimulation  be  placed  in  a  horizontal  position 
and  a  lever  be  attached  to  each  of  its  two  ends  in  such  a  way  that  any  increase 
in  the  thickness  of  the  muscle  at  either  end  will  be  recorded,  and  if  the  muscle 
be  now  stimulated  at  one  end,  it  is  found  that  the  response  spreads  from  the 
point  of  stimulation  throughout  the  muscle  at  a  measurable  rate  of  speed 
(Abey).  This  rate  of  propagation^  which  according  to  Engelmann  is  inde- 
pendent of  the  strength  of  the  stimulus,  amounts  in  the  frog  muscle  to  3-4  m. 
per  second  (Bernstein,  Hermann),  or  5-0  m.  (Engelmann),  and  in  human 
muscles  to  10-13  m.  per  second  (Hermann). 

If  in  an  experiment  like  the  one  cited  above  for  the  determination  of  the 
latent  period,  the  two  electrodes  be  placed  on  opposite  ends  of  the  muscle,  the 
excitation  will  start  from  the  negative  electrode  (cf.  page  59),  and  will  spread 
from  there  throughout  the  muscle.  But  before  the  lever  can  be  raised,  the  exci- 
tation must  have  reached  the  entire  muscle;  whence  it  is  evident  that  the 
mechanical  latent  period  of  the  jiart  first  excited  must  be  shorter  than  that  indi- 
cated for  the  whole  muscle. 

After  the  latent  period  the  muscle  curve  rises  to  its  maximum  height  and 
then  falls.  Accordingly  in  every  muscular  contraction  we  have  to  distinguish : 
(1)  latent  period,  (2)  period  of  shortening,  (3)  the  summit,  and  (4)  the 
period  of  relaxation.  In  the  frog's  gastrocnemius  the  period  of  shortening 
lasts  0.05-0.07  second,  the  period  of  relaxation  somewhat  longer. 

The  course  of  the  simple  contraction  may  be  very  difi'crent  in  different 
muscles,  and  in  point  of  time  we  meet  with  all  possible  gradations  from  the 
extremely  short  twitch  of  certain  insects'  muscles,  lasting  only  0.0033  second, 
to  the  contraction  of  smooth  muscles  continuing  for  several  seconds. 

Ranvier  first  directed  attention  to  the  fact  that  the  skeletal  muscles  of  the 
same  animal  which  differ  in  color,  differ  also  in  their  physiological  properties. 
Thus  in  such  animals  as  the  rabbit,  we  can  easily  distinguish  red  and  white 
muscles.  With  the  red  the  latent  period  is  longer,  the  height  of  the  contrac- 
tion is  less — the  descending  limb  of  the  curve  especially  ])eing  very  much 
drawn  out ;  but  the  force  and  endurance  are  greater  than  in  the  white  muscles. 
The  former  are  therefore  more  capable  of  severe  work.  Griitzner  showed 
later  that  individual  muscles  generally  are  composed  of  red  and  white  sec- 
tions, and  that  the  mixture  of  the  two  kinds  of  fibers  is  often  very  intimate. 


STIMULATION  OF  MUSCLES  AND  OF   NER\'ES 


417 


B.    RATE   OF  TRANSMISSION   OF   A  NERVE    IMPULSE 

It  is  necessary  for  the  sake  of  a  more  complete  study  of  the  excitation  of 
nerves  that  we  discuss  here  the  rate  of  transmission  of  the  stimulus  within 
them.  The  first  researches  bearing  on  this  subject  we  owe  again  to  Holm- 
holtz.  The  principle  of  his  method  is  very  simple.  The  latent  period  is 
determined  as  above  described,  but  instead  of  stimulating  the  muscle  directly 
the  stimulus  is  applied  to  its  nerve:  (1)  as  near  as  possible  to  the  muscle 
and  (2)  as  far  as  possible  from  it.  We  find  that  the  latent  period  is  greater 
in  the  second  case  than  in  the  first.  If  the  two  contractions  are  the  same 
size  (Fig.  155),  this  difference  can  only  be  due  to  the  greater  length  of  nerve 


Fig.  155. — Curves  illustrating  the  method  of  determining  the  rate  of  conductivity  in  the  sciatic 
nerve  of  a  frog.  A,  marks  the  point  of  stimulation.  The  first  curve  which  leaves  the  base  line 
at  B  (really  a  little  farther  to  the  right  than  indicated)  was  obtained  by  direct  stimulation; 
the  second  curve  (C)  was  obtained  by  stimulating  the  nerve  as  close  as  possible  to  the  muscle ; 
the  third  curve  (D)  by  stimulating  the  nerve  as  far  away  from  the  muscle  as  possible.  The 
lag  of  the  third  curve  behind  thesecond  should  give  the  time  necessary  for  the  stimulus  to  travel 
from  the  second  point  of  stimulation  on  the  nerve  to  the  first  point — in  this  case  about  55  mm. 
Since  one  complete  vibration  of  the  tuning  fork  (below)  represents  sJoth  of  a  second  and 
this  is  (almost  exactly)  the  time  from  C  to  D,  the  rate  of  transmission  in  this  particular 
case  is  only  about  11  meters  per  second  (200  x  .055). 

traversed  by  the  stimulus  in  the  second  case.  Knowing  the  difference  of 
length  in  millimeters  and  the  difference  of  time  in  hundredths  of  a  second, 
we  can  easily  calculate  the  rate  of  transmission  in  meters  per  second.  In 
the  motor  nerves  of  the  frog  at  room  temperature  this  rate  is  20-26  m.  per 
second.  At  lower  temperatures  it  is  less ;  besides,  there  is  a  certain  dependence 
upon  the  strength  of  the  stimulus,  a  stronger  stimulus  increasing  the  rate 
sometimes  very  considerably. 

In  the  invertebrates  the  rate  is  very  much  lower  and  appears  to  be  less  the 
slower  the  normal  movements  of  the  animal.  In  a  mussel  (Anodonta)  it  is  only 
1  cm.  per  second,  in  an  octopus  3-5  m.  per  second.  The  nonmedullated  fibers 
of  the  olfactory  nerve  of  a  fish  (pike)  transmit  a  stimulus  at  20°  C.  at  the  rate 
of  14—24  m.  per  second  (Nicolai). 

By  recording  the  contractions  of  the  muscles  in  the  ball  of  the  thumb  on 
stimulation  of  the  median  nerve  at  different  points  the  rate  of  transmission  in 


418 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


human  motor  nerves  has  been  estimated  at  33  in.  per  second.     Lately  much 
higher  figures,  up  to  66  m.  per  second,  have  been  given. 

The  stimulus  passes  from  the  motor  nerve  to  its  muscles  through  the 
motor  end  plates.  Here  a  delay  is  experienced  which  with  a  maximal  stimulus 
amounts  to  about  0.0U2-U.003  of  a  second  (Bernstein). 

C.    MECHANICAL  STIMULATION    OF   NERVES 

All  kinds  of  mechanical  disturbances,  provided  they  take  place  with  suffi- 
cient abruptness,  have  a  stimulating  etfect  on  a  nerve. 

A  light  hammer  let  fall  from  different  heights  upon  the  nerve,  resting  upon 
a  solid  support,  is  commonly  used  for  demonstrating  the  mechanical  stimula- 
tion. If  the  nei-ve  be  subjected  to  a  slowly  increasing  pressure  or  tension,  its 
excitability  at  first  increases,  then  as  the  pressure  or  tension  becomes  still  greater 
it  falls.  Beyond  a  certain  limit  pressure  applied  to  a  nerve  entirely  abolishes 
its  power  of  conducting  impulses  (see  page  411).  According  to  Kiihne  and 
tJxkull,  stimulation  may  occur  on  releasing  a  nerve  from  pressure. 


D.    ELECTRICAL   STIMULATION   OF  MUSCLE  AND   NERVE 

1.  Method. —The  kinds  of  electrical  stimuli  the  effects  of  which  have  been 
most  fully  studied  are  the  constant  and  induction  currents. 

In  applying  the  electric  current  to  a  muscle  or  nerve,  or  in  leading  off  elec- 
trical currents  generated  by  animal  tissues  to  a  galvanometer,  nonpolarizahle 
electrodes  are  used  wherever  it  is  practicable.  Metal  electrodes— e.  g.,  of  plati- 
num— are  not  well  adapted  to  such  a  purpose,  partly  because  it  is  difficult  to 
find  two  pieces  of  metal  between  which  there  would  be  no  differences  of  poten- 


FiG.  156. — Schema  of  the  rheocord  of  Du  Bois-Reymond.  The  battery  wires  and  the  electrodes 
are  connected  with  the  rheocord  by  means  of  the  binding  posts  O  and  P.  The  current 
coming  to  the  binding  post  P  splits  into  two  lesser  currents,  one  going  through  the  rheocord, 
the  other  through  the  electrode.  The  strength  of  current  which  will  pass  through  the 
electrodes  will  depend  on  the  amount  of  resistance  in  the  rheocord.  This  resistance  is  increased 
by  mov-ing  the  slide  2,  from  left  to  right,  also  by  thro^-ing  into  the  circuit  other  coils  of  wire 
by  means  of  the  metal  connections  1,  2,  3,  4,  etc. 

tial,  and  partly  because  the  contact  of  such  electrodes  with  moist  animal  tissues 
may  very  easily  set  up  a  difference  of  potential.  In  either  case  the  nerve  would 
be  subjected  to  an  extraneous  current  g-enerated  by  the  electrodes  themselves, 
which  often  perhaps  would  make  no  essential  difference  in  the  results  of  the 
experiment,  since  such  a  current  would  necessarily  be  very  weak;  but  in  many 
investigations,  especially  when  exact  determinations  of  potential  differences  aris- 


STIMULATION   OF  MUSCLES  AND  OF  NERVES 


419 


ing  in  the  nerve,  muscle,  etc.,  are  desired,  the  polarization,  -which  after  a  time 
would  be  produced  by  the  extraneous  current,  would  greatly  vitiate  results. 

The  discovery  by  Jules  Regnauld  that  zinc  in  a  concentrated  solution  of 
zinc  sulphate  gives  no  polarization  was  of  very  great  service  in  the  development 
of  the  methods  of  general  nerv^e-muscle  physiolog5\     The  fluid,  however,  must 


Fig.  157. — Xonpolarizable  electrode.s,  after  Porter.  Each  electrode  consists  of  a  porous  clay 
"  boot,"  which  may  be  filled  with  saturated  solution  of  Zn  SOt.  Connection  with  the  battery 
is  made  to  the  zinc  bars  placed  inside  the  boot.  A  hollow  place  on  the  surface  of  the  "  toe  " 
is  filled  with  normal  saline  and  the  nerve  is  laid  across  those  two  reservoirs  in  such  a  way 
as  to  keep  it  continually  moistened  with  the  sahne.  The  entire  nerve-muscle  preparation 
can  be  kept  moist  by  covering  boots  and  all  with  a  glass  top  which  fits  in  the  groove  around 
the  edge  of  the  porcelain  base. 


not  come  in  contact  with  the  animal  tissues,  for  they  are  completely  destroyed 
by  so  concentrated  a  solution.  The  current  therefore  is  applied  to  the  tissues 
through  porous-clay  points  molded  into  a  suitable  shape,  and  soaked  with  0.6-per- 
cent solution  sodium  chloride  (Fig.  157).  Such  a  mass  is  but  slightly  polariz- 
able.  Often  the  clay  tip  is  sealed  into  the  end  of  a  glass  tube  filled  with  zinc- 
sulphate  solution  into  which  amalgamated  zinc  bars  connected  with  the  source 
of  electricity  are  dipped.  The  boot-shaped  electrodes  represented  in  Fig.  157 
themselves  serve  at  once  as  the  clay  tip  and  the  containers  for  the  zinc  sulphate. 
When  it  is  desired  to  localize  the  stimulus,  or  the  connection  with  the  galvanom- 
eters very  sharply,  the  tissue  is  connected  with  the  porous-clay  tips  of  the  non- 
polarizable  electrodes  by  means  of  woolen  threads  wet  with  0.6  per  cent  NaCl. 

It  is  presumed  that  the  student  is  already  acquainted  with  the  principles  of 
the  induction   coil.     If  not,  a  text-book  of  physics  should  be  consulted. 

Since  the  strength  of  the  induction  current  depends  on  the  abruptness  with 
which  the  primarv'  current  is  changed,  it  is  ver>'  important  that  closing  and 
opening  the  circuit  should  take  place  with  equal  precision.  Many  different  kinds 
of  keys  have  been  devised  to  supply  this  requirement ;  one  is  shown  in  Fig.  160. 


420  THE   FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

Often  it  is  neccssarj'  to  have  the  stimuli  follow  one  another  very  rapidly. 
The  device  most  commonly  employed  for  this  purpose  is  that  kno\\Ti  as  the 
Wafrner  hammer  (Fig.  159).  The  current,  starting  from  the  battery  A',  passes 
through  the  post  g,  the  spring  h  provided  with  an  armature,  and  the  screw  f  to 
the  primary  coil  c,  and  from  there  through  the  electro-magnet  b  back  to  the 
battery.  If  the  current  is  closed  at  the  screw  f,  h  is  magnetized  and  draws  the 
armature  of  the  spring  h  down;  in  this  way  the  current  is  broken  at  f,  the  mag- 


FiG.  158.— Induction  coil  of  Du  Bois-Rejonond,  after  Porter.  The  strength  of  the  induced  cur- 
rents is  varied  by  sliding  the  secondary  coil  on  the  horizontal  bars  and  also  by  revolving  it 
about  its  axis. 

net  consequently  is  demagnetized,  the  spring  h  is  released  until  it  again  touches 
/,  when  the  current  is  once  more  closed,  and  so  on.  The  number  of  interruptions 
per  second  can  be  varied  by  the  position  of  the  screw  f.  The  make  and  break 
shocks  from  such  an  interrupter  are  not,  however,  of  equal  strength.  In  order 
to  equalize  them  a  side  wire  is  inserted  between  g  and  f  and  the  screw  at  f  is 
raised  until  the  hammer  can  no  longer  touch  it.  The  screw  f  on  the  other 
hand,  is  raised  so  that  the  spring  in  its  downward  motion  comes  in  contact 
with  it.  Now  when  the  hammer  vibrates  the  primary  current  is  never  entirely 
broken,  but  varies  between  two  extreme  values.  Consequently  the  make  and 
break  shocks  are  weaker  but  (for  reasons  which  we  cannot  go  into  here)  they 
are  also  more  nearly  equal  in  strength. 

2.  The  General  Law  of  Electrical  Stimulntion. — All  the  effects  of  an  elec- 
tric current  upon  the  medium  through  which  it  flows  depend  upon  the  strength 
and  the  density  of  the  current.  With  the  same  conductor  the  density  of  course 
is  directly  proportional  to  the  strength. 

In  1843  Du  Bois-Eeymond,  on  the  basis  of  his  discoveries  concerning  the 
electrical  stimulation  of  motor  nerves,  laid  do\\Ti  the  following  general  law : 
The  electric  current  does  not  stimulate  by  means  of  its  absolute  density,  but 
by  means  of  the  alterations  which  it  undergoes  from  one  moment  to  another ; 
hence  the  impetus  toward  a  movement  which  results  from  these  alterations 
is  greater  the  more  rapidly  they  occur,  or  the  more  extensive  the  alteration 
in  a  unit  of  time.  The  contraction  of  a  muscle  produced  by  an  increasing 
density  of  the  current  was  called  the  "  closing  contraction,"  that  produced  by 
decreasing  density,  the  "  opening  contraction." 

This  law  was  supported  by  such  facts  as  the  following :  a  current  passing 
through  a  nerve  may,  if  increased  very  gradually,  reach  a  high  density  without 


STIMULATION   OF  MUSCLES   AND  OF   NERVES 


421 


producing  any  contraction ;  whereas  a  much  weakei*  current  closed  suddenly  pro- 
duces a  maximal  effect.  And  conversely,  a  stronger  current  if  reduced  very 
gradually,  may  be  brought  down  to  nil  without  causing  an  excitation ;  whereas 
the  sudden  opening  of  a  much  weaker  current  is  accompanied  by  a  strong 
contraction. 

But  under  certain  circumstances  a  constant  current  flov/ing  through  a  motor 
nerve  may  stimulate  not  only  at  the  moment  of  closing,  but  during  the  entire 
period  of  closure.  This  happens  for  example  with  frog's  nerves  when  the  latter 
are  taken  from  frogs  which  have  been  kept  for  a  long  time  at  a  temperature 
below  10°  C.  (v.  Frey)  ;  also  with  the  nerves  of  warm-blooded  animals  when  the 
current  is  not  too  weak.  Again,  if  a  constant  current  has  been  flowing  through 
a  nerve  for  a  sufficient  time,  on  opening  the  current  there  often  appears  a  pro- 
longed contraction  instead  of  a  simple  short  contraction.  This  continued  state 
of  contraction  is  often  spoken  of  as  "  Bitter's  tetanus."  Often  also  after  the 
summit  of  the  closing  contraction  has  been  passed,  a  cross-striated  muscle  does 
not  recover  its  natural  length  immediately,  but  remains  more  or  less  shortened 
{^'  Wundt^s  tetanus"),  and  only  returns  to  its  resting  condition  when  the  cur- 
rent is  broken — i.  e.,  in  case  no  opening  contraction  occurs.  If  the  stimulus  is 
very  weak,  the  constant  excitation  is  only  a  local  one,  spreading  over  a  limited 


Fig.  1.50. — Details  of  the  Wagner  hammer  or  interrupter  of  the  induction  coil.  c,  prima^' 
coil ;  ?,  secondary  coil.  The  primary  current  is  generated  in  the  battery  K  and  the  .secondary 
or  induced  currents  are  led  off  by  electrodes  attached  to  the  ends  of  the  secondary  coil. 


portion  of  tlie  muscle.  Finally,  when  a  constant  current  is  applied  to  an  afferent 
nerve,  a  distinct  sensation  is  felt  during  the  entire  period  of  closure,  even  when 
the  peripheral  end  organs  are  excluded  (Griitzner,  Langendorif,  BiedeiTnann). 

Wo  find  therefore  so  many  exceptions  to  Du  Bois-Reymond"s  law,  that  in 
its  original  form  it  can  no  longer  bo  regarded  as  of  general  application, 
although,  so  far  as  nuisele  alone  is  concerned,  the  excitation  of  large  masses 
appears  to  depend  upon  sudden  changes  at  the  place  of  direct  stimulation. 
Moreover,  the  law  must  take  into  account  the  nature  of  the  irritable  tissue: 
2G 


422 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


the  more  irritable  it  is,  the  more  do  the  visihle  phenomena  of  continuous 
excitation  remain  in  the  background,  whereas  the  effects  of  variation  in  the 
current  become  the  more  apparent   ( Biedermann ) . 

For  all  irritable  tissues  there  is  a  minimum  duration  of  the  electric  cur- 
rent necessary  to  give  a  stimulus.  Other  things  being  equal,  the  more  this 
time  is  shortened,  the  less  becomes  the  stimulating  effect  until  finally  it  fails 
altogether.  The  length  of  time  necessary  to  produce  the  maximal  effect  de- 
pends primarily  on  the  strength  of  the  current.  The  greater  the  strength 
the  shorter  the  time  may  be.  A  constant  current  of  medium  strength  re- 
quires 0.016  second  to  produce  its  maximal  effect  on  motor  nerves  (J,  Konig)  ; 


Fig.  160. — A  convenient  arrangement  of  the  apparatus  for  sending  induction  shocks  through 
a  muscle  is  shown  in  this  Figure.  BC,  the  battery  cell ;  K,  key  for  closing  and  opening  the 
primary  current.  When  the  wires  are  connected  with  binding  posts  1  and  2  of  the  induction 
coil,  single  make  and  break  shocks  are  obtained  from  the  secondary  coil  and  are  conveyed 
by  the  wires  connected  therewith  to  the  muscle.  When  the  wires  are  connected  with  binding 
posts  1  and  3  of  the  induction  coil  the  automatic  interrupter  is  brought  into  play  and  a  series 
of  rapidly  repeated  (tetanic)  shocks  is  obtained.  By  means  of  hand  electrodes  connected  with 
the  secondary  end  of  the  induction  coil,  stimuli  may  be  applied  in  various  other  ways. 

no  contractions  are  obtained  if  the  time  be  reduced  below  0.002  second.  In- 
duction shocks  are  still  shorter  than  this;  nevertheless,  because  of  their  high 
tension  they  are  the  most  effective  stimuli  for  the  nerves. 


So  far  we  have  considered  only  the  effects  of  currents  suddenly  turned  on 
in  their  full  strength.  It  is  possible  also  by  means  of  special  apparatus  to  arrange 
the  experiment  so  that  starting  from  nil  the  current  will  increase  gradually 
and  only  reach  its  maximum  after  a  certain  measured  time.  When  this  meas- 
ured time  does  not  exceed  TTrV^s^th  of  a  second  the  effect  is  the  same  as  that  of  a 
current  of  equal  intensity  suddenly  opened  in  full  force.  When  it  is  more  than 
Tirinrth  of  a  second  the  effect  varies  with  the  intensity  of  the  current,  being  for 
a  weak  current  less  effective  than  the  sudden  opening,  and  with  a  strong  current 
more  effective   (Gildemeister).     But  the  most  characteristic  thing  about   these 


STIMUL.\TION   OF  MUSCLES  AND  OF  NERVES  423 

"  time  stimuli,"  as  they  are  called,  is  that  the  contractions  which  they  induce 
continue  for  a  noticeably  longer  time,  and  the  nerves  and  muscles  can  there- 
fore be  thrown  by  them  into  a  state  of  excitation  which  lasts  longer,  than  is  the 
case  with  the  sudden  stimuli.  This  peculiarity,  as  we  shall  see  later,  is  of  great 
importance  for  the  theoretical  explanation  of  voluntary  muscular  contraction. 

The  nature  of  the  irritable  tissue  again  has  much  to  do  with  the  length 
of  time  required  to  stimulate  it :  the  more  slowW  it  reacts,  the  longer  must 
the  stimulus  act  to  produce  a  visible  effect. 

A  single  induction  shock,  which  is  so  effective  for  the  nerve,  is  but  slightly 
effective  for  smooth  muscles.  In  certain  stages  of  degeneration  the  skeletal 
muscles  exhibit  a  veiy  much  reduced  or  even  absolute  lack  of  sensitivity  toward 
induction  currents,  whereas  their  excitability  to  constant  currents  remains  unim- 
paired or  may  even  be  increased  (Erb).  With  the  rapidly  contracting  frog's 
muscles,  stimulation  of  the  nerve  by  the  break-induction  shock  is  much  stronger 
than  by  the  make-induction  shock,  because  the  former  is  a  more  sudden  stimulus. 
Kerve-muscle  preparations  of  the  turtle,  which  are  much  more  sluggish  in  their 
action,  behave  in  exactly  the  reverse  manner. 

3.  Law  of  Contraction. — The  stimulating  effect  of  the  constant  current 
depends  not  only  upon  the  strength  but  also  upon  the  direction  of  the  cur- 
rent in  the  nerve.  If  the  current  is  weak  it  generally  produces  a  contraction 
only  when  it  is  closed,  no  difference  in  which  direction  it  is  flowing.  If  the 
current  is  increased  in  strength  (medium  current),  contractions  occur  also 
when  it  is  opened,  whether  the  current  is  flowing  toward  the  muscle  (de- 
scending) or  away  from  it  (ascending),  although  opening  contractions  do 
not  always  appear  with  the  same  strength  of  current  in  the  two  cases.  In- 
creasing the  strength  still  more  (strong  current)  we  find  that  with  the 
ascending  current  the  closing  contraction  gradual!}-  becomes  smaller  until  it 
finally  (Msappears,  while  the  opening  contraction  continues  at  its  maximum. 
With  the  descending  current  we  find  the  reverse  condition :  the  closing  con- 
traction remains  at  its  maximum  however  strong  the  current  be  made,  but 
the  opening  contraction  becomes  smaller  and  smaller  as  the  strength  increases, 
and  not  infrequently  it  disappears.  However,  the  strength  at  which  the  clos- 
ing contraction  disappears,  when  the  current  is  ascending,  is  not  alwaj's  the 
same.  And  sometimes  when  the  current  is  descending  the  opening  contrac- 
tion does  not  disappear  at  all  but  persists  at  a  certain  minimal  size. 

These  generalizations  may  be  summarized  in  the  following  formula,  known 
as  Pfliiger's  law  of  contraction : 


Strength  of  Current.  Ascending  current  Descending  current. 

Weak      i  Closing  C  C 

■  I  Opening  O  0 

-,   ,.        (  Closing  C  C 

Medium  i  ^       .  *  r«  n 

(  Opening  C  C 

Stron       ^  <^losing  0  C 

^  ■  }  Opening  C  O  or  weak  C 

C  —  contraction  ;  0  =  no  contraction. 


424  THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

It  will  be  understood  that  the  terms  weak,  medium,  and  strong  as  applied 
to  the  current  in  this  discussion  do  not  designate  any  absolute  values  of  the 
current,  since  what  is  medium  current  for  one  nerve-muscle  preparation  may 
be  strong  for  another.    The  terms  are  purely  relative  to  any  given  preparation. 

This  peculiar  behavior  of  a  nerve-muscle  preparation  to  currents  of  dif- 
ferent strength,  which  finds  expression  in  the  law  of  contraction,  depends 
upon  another  law  enunciated  bv  Pfliiger,  namelv,  that  a  constant  current  has 


Fig.  101. — Catclectrotoiuis.  The  tracing  is  to  be  read  from  right  to  left.  The  nerve  was  first 
stiuiulateil  in  the  neigliborliood  of  the  catiiode  of  the  polarizing  current  with  stimuli  too  weak 
to  produce  any  effect  while  the  polarizing  current  was  not  running.  The  polarizing  current 
wa.s  then  turned  on,  and,  without  changing  the  strength  of  the  stimuli,  thej'  became  effective. 
When  the  polarizing  current  was  again  turned  off,  the  stimuli  were  again  subminimal. 

no  stimulating  action  on  the  nerve  between  the  poles,  but  acts  only  at  the 
poles.  O71  closing  the  current  the  stimulus  starts  from  the  cathode,  on  opening 
from  the  anode. 

This  2>otar  law  of  excitation  may  be  illustrated  by  the  following  experimental 
facts.  If  in  stimulating  with  the  constant  current  the  electrodes  be  applied  to 
the  nerve  as  far  apart  as  possible,  and  the  latent  period  of  the  closing  contrac- 
tions be  determined  both  for  the  ascending  and  descending  currents,  we  find 
this  period  to  be  longer  for  the  former  than  for  the  latter  (v.  Bezold^.  With 
the  descending  current  the  cathode  is  nearer  the  muscle  than  with  the  ascend- 
ing current ;  hence  the  stimulus  has  a  shorter  distance  to  travel  to  reach  the 
muscle  with  the  former  than  with  the  latter.  In  a  similar  way  it  can  be  shown 
that  the  stimulus  starts  from  the  anode  when  the  current  is  broken. 

The  law  of  contraction  may  be  illustrated  by  carrying  the  experiment  far- 
ther. Thus  if  from  the  determinations  of  the  latent  period  just  mentioned 
the  rate  of  transmission  of  the  stimulus  be  calculated,  it  will  be  found  consider- 
ably lower  than  when  it  is  determined  on  the  same  nei-ve,  by  the  method  (de- 
scribed on  page  417)  of  stimulating  at  two  points  with  the  induction  cur- 
rent. The  reason  is  that  Avith  the  ascending  current  the  stimulus  on  its  way 
to  the  muscle  has  experienced  some  resistance  at  the  anode.  This  resistance 
varies  considerably  in  amount  according  to  the  strength  of  the  stimulating  cur- 
rent. When  the  current  is  weak  or  of  medium  strength  the  stimulus  at  the 
cathode  on  closing  the  current  is  strong  enough  to  overcome  the  resistance  at 
the  anode.  But  when  the  current  is  strong  the  resistance  at  the  anode  is  too 
great  to  be  overcome  by  the  stimulus  at  the  cathode,  and  it  constitutes  therefore 
a  complete  block.  It  can  be  shown  also  that  when  the  cathode  intervenes  between 
the  anode  and  the  muscle,  it  creates  a  resistance  to  the  anodic  stimulus. 

The  polar  law  of  excitation  was  deduced  by  Pfliiger  mainly  on  the  ground 
of  the  alterations  in  excitability  produced  in  the  nerve  by  a  constant  current. 


STIMULATION   OF  MUSCLES  AND  OF   NERVES  425 

While  the  current  is  flowing  the  excitahUity  is  increased  on  both  sides  of  the 
cathode ;  on  both  sides  of  the  anode  it  is  decreased.  These  alterations  appear 
immediately  (within  O.OUUUT  second  at  most)  after  closing  the  current.  In 
the  intrapolar  region  there  is  found  an  indifferent  point  where  the  excita- 
bility of  the  nerve  is  iiot  changed :  and  as  the  constant  current  increases  in 
strength  this  point  moves  toward  the  cathode.  At  the  same  time  the  extra- 
polar  alterations  of  excital)ility  spread  over  greater  lengths  of  the  nerve. 

Likewise  during  the  first  few  moments  after  the  current  is  opened  altera- 
tions in  the  excitability  appear,  but  they  are  Just  the  reverse  of  those  which 
occur  while  the  current  is  closed — i.  e.,  reduced  at  the  cathode  and  increased 
at  the  anode. 

These  alterations  may  be  studied  in  the  following  manner.  A  nerve  is 
stimulated  rhytlimically,  say  once  a  second,  with  a  current  of  constant  strength, 
and  the  resulting  contractions  are  recorded  in  the  usual  manner.  If  now  while 
the  stimulation  is  going  on  at  the  regular  rhythm,  a  constant  current  be  led  into 
the  nerve,  and  the  stimuli  fall  in  the  neighborhood  of  the  cathode  of  this  cur- 
rent, the  contractions  at  once  become  stronger;  if  they  fall  in  the  neighborhood 
of  the  anode,  the  contractions  decrease  in  size  and  disappear  altogether  (see 
Figs.  IGl  and  1G2).  When  the  current  being  led  through  the  neiwe  is  broken, 
contractions  from  stimuli  applied  at  the  cathode  become  smaller,  those  from 
stimuli  at  the  anode  become  larger. 

The  increase  of  excitability  at  the  cathode  while  the  current  is  closed  soon 
fails  and  passes  over  into  a  depressed  condition,  which,  as  Biedermann  observes, 
is  probably  the  expression  of  a  local  fatigue  of  the  nerve. 

The  phenomena  comprehended  under  the  law  of  contraction  may  then  be 
explained  through  the  law  of  polar  excitation  as  follows:  Weak. currents  give  a 
closing  contraction  because  when  the  current  is  closed,  the  sudden  rise  in  irri- 
tability of  the  neiwe  at  the  cathode  is  great  enough  to  constitute  a  stimulus  of 
itself.  The  stimulus  is  effective  whether  the  current  be  ascending  or  descend- 
ing, for  in  the  one  case  the  cathode  is  toward  the  muscle,  and  in  the  other  the 


Fig.  162. — Anclectrotonus.  The  tracing  to  be  read  from  right  to  left.  A  series  of  stimuli  just 
strong  rnougli  to  produce  slight  contractions  were  applied  in  the  neighborhood  of  the  anode 
for  tlie  polarizing  current.  When  the  polarizing  current  was  turned  on  the  stimuli  became 
ineffective.     When  it  was  again  turned  off  the  stimuli  again  became  effective. 

resistance  at  the  anode,  due  to  the  decrease  in  irritiibility,  is  not  groat  enough 
to  block  the  stimulus.  The  sudden  increase  in  excitability  produced  in  the  nerve 
at  the  anode  when  the  current  is  broken  is  not  yet  sufficient  to  constitute  a 
stimulus. — With  the  medium  current  the  increase  in  excitability  at  the  cathode 
on  closing  and  at  the  anode  on  opening  are  both  sufficient  to  produce  a  stimulus, 
and  in  neither  case  is  the  opposite  pole  strong  enough  to  block  it.  The  strong 
current  is  distinguished  from  the  medium  by  the  circumstance  that  while  the 
current  is  closed  the  resistance  at  the  anode  is  stronger  than  the  excitation  at 
the  cathode  and  vice  versa  when  the  curreot  is  opened.  Consequently  with  the 
ascending  current   the   excitation  started   at  the  cathode  cannot    break  through 


426 


THE  FUXCTIOXS  OF  CROSS-STRIATED  MUSCLES 


the  anode,  and  the  closing  contraction  is  wanting.  With  the  descending  cur- 
rent the  excitation  started  at  the  anode  meets  with  a  resistance  at  the  cathode 
which  may  or  may  not  completely  hlock  it ;  hence  the  opening  contraction  either 
fails  altogether  or  is  greatly  diminished. 

Exactly  the  same  laws  hold  for  the  induction  currents  as  for  the  constant 
current.  They  also  stimulate  at  the  cathode  as  they  appear  and  at  the  same 
time  produce  a  resistance  at  the  anode.  When  they  are  strong  enough,  they 
have  a  stimulating  effect  also  as  they  disappear  and  then  the  stimulus  starts 
from  the  anode. 

The  fact  that  the  induction  currents  produce  a  resistance  at  their  anode  is 
demonstrated  by  the  following  experiment :  a  nerve  is  stimulated  with  ascend- 
ing' induction  currents  which,  beginning  with  very  weak  shocks,  are  gradually 


Fig.  163. — Stimulation  of  a  nerve  by  a  series  of  ascending  make-  and  descending  break-induction 
shocks  of  increasing  strength.  To  be  read  from  right  to  left.  The  first  contraction  of  each 
pair  was  obtained  by  the  ascending  closing  and  tlie  second  by  the  descending  opening 
shock.      There  are  no  "gaps"  in  the  latter  series. 


increased  in  strength  (Fig.  163).  The  height  of  the  contractions  at  first  increases, 
but  after  a  time  decreases,  and  with  a  certain  strength  the  muscle  remains  at 
rest  (Fig.  1G3;  Nos.  11-18).  If  the  strength  of  the  shocks  be  raised  still  fur- 
ther, contractions  appear  again,  ^\hich  at  first  are  weak  (Nos.  19,  20),  but  gradu- 
ally become  stronger  until   they   finally   may  become  supramaximal.     With   a 


STIMULATION  OF  MUSCLES  AND  OF  NERVES  427 

series  of  shocks  of  increasing  strength  we  have  therefore  a  gap  in  the  resulting 
contractions  (Fick).  This  is  only  observed  with  the  ascending  currents,  and 
is  the  result  of  a  block  at  the  anode.  The  absence  of  the  contractions  is  there- 
fore entirely  analogous  to  the  corresponding  phenomena  for  the  strong  ascending 
constant  current.  The  contractions  coming  after  the  gap  and  gradually  increas- 
ing in  size  are  produced  really  by  the  excitation  taking  place  at  the  disappear- 


FiG.  164. — Schematic  representation  of  the  distribution  of  an  electric  current  in  a  human  arm 
on  application  of  two  electrodes  over  a  nerve,  after  de  Watteville. 

ance  of  the  induction  current,  and  are  to  be  regarded  for  this  reason  as  a  sort 
of  opening  contractions.  But  further  discussion  of  their  nature  here  would 
carry  us  too  far  afield. 

The  stimulating  effects  and  the  alterations  of  excitability  produced  by 
the  electric  current  follow  the  same  laws  in  human  nerves  as  in  the  exsected 
frog's  nerves  (Waller  and  de  Watteville). 

In  experiments  on  living  men,  the  electrodes  of  course  cannot  be  applied  to 
the  nerves  themselves,  but  can  only  be  placed  on  the  skin;  the  nerve  is  stimu- 
lated then  only  by  the  threads  of  current  which  penetrate  that  far.  It  will  be 
clear  at  once  that  the  density  of  that  portion  of  the  current  reaching  a  par- 
ticular nerve  will  be  greater  the  nearer  the  nerve  lies  to  the  surface  of  the  skin. 
Consequently  in  using  the  current  for  therapeutic  purposes  the  electrodes  are 
applied  to  the  skin  at  those  points  where  the  nerve,  which  it  is  desired  to  stimu- 
late, can  be  reached  most  directly. 

The  effective  anode  is  of  course  the  place  where  the  current  enters  the  nerve 
itself,  the  effective  cathode,  the  place  where  it  leaves  the  nerve.  If  both  poles 
were  to  be  placed  on  the  skin  over  the  nerve,  as  in  Fig.  164,  anodes  and  cathodes 
would  be  present  at  almost  every  possible  point  along  the  nerve,  as  indicated 
by  the  radiating  lines.  Evidently  such  an  experiment  would  not  be  adapted  to 
the  study  of  electrical  effects  on  human  nerves.  The  monopolar  method  is  there- 
fore used,  the  current  being  conveyed  to  and  away  from  the  body  by  electrodes 


428  THE  FUNCTIONS  OP^  CROSS-STRIATED  MUSCLES 

of  different  size,  a  large  one  (12  X  G  em.)  applied  to  the  breast,  and  a  small  one 
(0.5-2  cm.  diameter)  applied  over  the  motor  point  to  be  tested.  Suppose  now 
the  large  electrode  is  the  anode:  the  current  enters  then  with  relatively  low 
density,  spreads  out  through  the  body  with  still  less  density  and  finally  collects 
at  the  cathode  with  great  density.  Since  now  the  effects  of  a  current  depend 
upon  its  density,  it  follows  that  with  currents  of  moderate  strength  these  effects 
will  appear  only  at  the  smaller  electrode.  Some  of  the  many  threads  of  current 
reaching'  the  smaller  electrode  from  all  parts  of  the  body,  will  necessarily  pass 


Fig.   165. — Schematic  representation  of   the  entrance  into  and  exit  from  a  nerve  of  a  current 
applied  to  the  skin  over  the  nerve,  after  de  Watteville. 

through  the  nerve  under  it.  The  effective  cathode  of  the  current  lies  where  these 
threads  pass  out  of  the  nerve,  and  if,  as  we  have  assumed,  the  smaller  electrode 
is  the  cathode,  other  things  being  eqmd,  the  current  will  have  its  greatest  possi- 
ble density  there.  If  the  current  is  revei"sed  so  that  it  now  enters  the  body  by  the 
smaller  electrode  (which  is  still  over  the  nerve),  the  places  where  the  threads  of 
current  leave  the  nerve  constitute  as  before  the  effective  cathode;  the  density 
of  the  current  now  however  is  less  than  in  the  first  case  (Fig.  165). 

The  polar  lav:  of  excitation  applies  also  to  muscle,  both  with  the  constant 
and  induction  current  (v.  Bezold,  Engelmann,  Biedermann  :  cf.  page  416). 

We  have  a  very  instructive  proof  of  this  in  the  "  polar  failure  "  of  excita- 
tion discovered  by  Biedermann  and  Engelmann.  If,  for  example,  the  end  of  a 
frog's  sartorius  muscle  be  narcotized  and  the  cathode  be  applied  to  this  injured 
place,  on  closing  the  current  the  muscle  remains  at  rest.  The  normal  muscle 
substance  is  not  stimulated  by  the  closure  of  a  current  as  it  passes  from  the 
normal  to  the  paralyzed  or  dead  muscle  substance,  and  the  mere  passage  of  a 
current  is  not  sufiicient  to  discharge  the  contraction  (Locke  and  Szymanowski). 
Similar  phenomena  may  be  shown  on  opening  of  the  current  when  the  anode 
is  placed  at  the  injured  place. 


E.    EFFECT   OF    A   RAPID   SERIES    OF   STIMULI 

If  a  nerve  or  a  niu.scle  he  affected  by  two  stimuli  in  rapid  .'^nccossion.  so 
that  the  action  resulting  from  the  first  has  not  yet  come  to  an  end  when  the 
second  becomes  effective,  the  relaxation  which  would  otherwise  follow  the 
first  contraction  is  interrupted  and  the  effect  of  the  second  stimulus  is  added 
to  the  first:  consequently  the  contraction  of  the  muscle  is  greater  than  it 
commonly  would  he  as  the  result  of  a  single  stimulus.  It  is  only  when  the 
load  of  the  muscle  is  very  light  that  it  contracts  as  strongly  to  a  single  stimulus 
as  to  rapidly  repeated  stimuli  (v.  Frey). 


STLMULATIOX  OF  MUSCLES  AND  OF   NERVES 


429 


lu  summated  contractions  the  ascending  limb  of  the  second  contraction  curve 
is  steeper  than  that  of  the  first,  hence  the  summit  of  the  second  appears  earlier 
than  would  be  expected  if  its  course  were  the  same  as  the  first  (v.  Kries).  The 
latent  period  of  the  superimposed  contraction  is  also  said  to  be  Aery  much 
shorter  than  that  following  the  first  stimulus  (Fick). 

In  order  that  successive  stimuli  may  produce  a  summation  they  must  not 
follow  one  another  too  rapidly.  The  smallest  interval  possible  for  any  given 
preparation  depends  upon  the  temperature  and  the  strength  of  the  stimuli :  for 
the  nerves  of  the  frog  at  ordinary  room  temperature  it  may  be  estimated  at 
about  0.001  to  0.005  second.  We  have  a  refractorij  period  therefore  in  nerves 
and  skeletal  muscles  just  as  we  have  in  heart  muscle  (cf.  page  183). 

If  more  than  two  stimuli  affect  the  nerve  or  muscle  at  sufficiently  short 
intervals  the  contraction  of  the  muscle  becomes  still  greater,  and  its  curve 
is  perfectly  continuous,  showing  no  separate  summits  (cf.  Fig.  166).  This 
form  of  contraction  is  called  tetanus. 

Complete  tetanus  appears  only  when  the  stimuli  follow  one  another  so  rap- 
idly that  the  interval  between  them  is  less  than  the  time  occupied  by  the  active 
shortening  of  the  muscle  when  that  is  maximal.     The  frequency  depends  there- 


o, 

1 

Tt 

ft 

■        i 

\y 

0 

1^b     20          30          W           50           60           70                   S5 

Yu;.   166. — Tetanus  curve    of  the  frog's  gastrocnemius,  after  Bolir. 

second. 


Twenty-seven  stimuli  per 


fore  primarily  \\\m)\\  the  behavior  of  the  muscle  to  single  stimuli ;  tlie  more 
rapidly  a  single  contraction  runs  its  course,  the  more  frequently  must  the  stimuli 
be  given  to  produce  complete  tetanus.  This  is  beautifully  shown  by  the  behavior 
of  mu.scles  of  warm-blooded  animals  composed  mainly  of  red  or  white  fibers. 
The  red  salens  muscle  of  the  rabbit  falls  into  almost  complete  tetanus  with  ten 
stimuli  per  second,  while  the  white  (fastrncnemius  medius  with  the  same  fre- 
quency of  stimulation  gives  very  evidf^it  single  contractions.  A  frequency  of 
six   stimuli    per  second    permits   the   white  muscle   to   relax   almost    completely 


430  THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

between  contractions,  whereas  it  keeps  the  red  muscle  almost  continuously  con- 
tracted (Ranvier,  Kronecker  and  Stirling;  cf.  Fig.  167). 

Everything  which  tends  to  make  the  single  contractions  occupy  more  time 
operates  to  reduce  the  frequency  of  stimulation  necessary  to  evoke  complete 
tetanus.  Thus  fatigued  muscles  are  thrown  into  tetanus  with  a  lower  frequency 
than  unfatigued,  because  their  contractions  are  slower. 

The  more  the  frequency  is  reduced  below  that  which  is  just  sufficient  to 
produce  tetanus,  the  more  distinctly  do  the  contractions  produced  by  the  indi- 
vidual stimuli   stand  out  from  one  another,  until  finally  below  a   certain  fre- 


FiG.  167. — Tetanus  curves  of  the  white  (lower  tracings)  and  of  the  red  (upper  tracings)  muscles 
of  the  rabbit,  after  Kronecker  and  Stirling.  To  be  read  from  right  to  left.  A.  ten  stimuli 
per  second.     B,  six  stimuli  per  second. 

quency  there  is  no  fusion  whatever.  We  have  therefore  all  possible  gradations 
between  the  isolated  contractions  and  complete  tetanus.  This  suggests  that  teta- 
nus itself,  notwithstanding  the  continuous  curve  by  which  it  is  represented 
graphically,  is  really  a  discontinuous  process,  and  complete  proof  of  this  is 
furnished  by  the  electrical  variations  accompanying  tetanus  (page  433). 

How  are  we  to  conceive  of  the  processes  going  on  in  the  muscle  in  tetanus? 
One  significant  fact  is  that  by  artificially  supporting  the  muscle,  so  that  it  does 
not  lift  its  weight  until  it  has  contracted  some  distance,  the  single  contractions 
can  be  made  to  reach  the  same  height  as  tetanus  with  the  same  strength  of  cur- 
rent (v.  Frey).  We  may  say,  therefore,  that  in  tetanus  the  muscle  contracts 
to  its  utmost,  because  to  a  certain  extent  it  is  supported  on  itself.  In  addition  to 
this  the  irritahility  of  both  nerve  and  muscle  is  increased  by  a  previous  stimu- 
lation— i.  e.,  if  the  excitation  is  not  too  strong  or  does  not  continue  so  long  as 
to  involve  much  fatigue.  Hence  not  infrequently  it  happens  that  stimuli,  which 
of  themselves  are  ineffective,  become  effective  merely  by  being  repeated  with 
sufficient  frequency. 

Tetanus  may  be  looked  upon  therefore  as  a  sort  of  heaping  tip  of  small  con- 
tractions due  to  the  rapidity  of  the  stimuli  and  to  increased  irritability. 

F.    VOLUNTARY   CONTRACTIONS 

If  we  compare  voluntary  contractions  on  the  same  drum  with  the  rapid, 
twitchlike  muscular  contraction  produced  by  a  single  artificial  stimulus,  we 
discover  that  the  former  are  both  slower  and  less  abrupt.  Comparing  them 
with  the  contractions  obtained  by  rapidly  repeated  shocks,  we  find  more  in 
common.  Many  other  circumstances  strongly  support  this  resemblance,  the 
most  important  of  them  being,  that  the  voluntary  contraction  as  well  as  the 
contractions  which  appear  reflexly  with  strychnine  poisoning  are  accompanied, 


SIGNS   OF   ACTIVITY   IX   MUSCLE   AND   NERVE  431 

just  as  tetanus  is,  by  action  currents  which  signify  a  discontinuous  excitation 
(Loven).  But  it  is  worthy  of  note  that  the  rhythm  of  these  action  currents 
in  voluntary  contractions,  and  others  produced  under  the  influence  of  the 
central  nervous  system,  is  only  about  half  as  rapid  as  the  frequency  of  stimu- 
lation necessary  to  produce  a  complete  tetanus.  And  yet  the  voluntary  con- 
traction as  ordinarily  recorded  is  quite  continuous.  This  must  be  due  to  the 
fact  that  the  single  impulses  sent  out  to  the  muscles  from  the  central  organs 
to  produce  a  voluntary  contraction  last  longer  than  the  ordinary  instantaneous 
stimuli  (Loven),  and  that  the  separate  twitches  are  therefore  more  readily 
fused.  We  know,  indeed,  that  a  ""  time  stimulus"  (page  423)  is  longer  drawn 
out  than  a  momentary  stimulus  and  that  it  is  therefore  better  adapted  to 
produce  summation  with  a  low  frequency  of  stimulation. 

The  trembling  of  the  muscles  which  accompanies  a  strained  effort  to  over- 
come some  great  resistance  or  an  attempt  to  hold  a  muscle  contracted  voluntarily 
to  its  utmost,  are  generally  regarded  as  expressions  of  the  individual  impulses 
discharged  from  the  central  nervous  system.  The  regulation  of  the  innervating 
mechanisms  would  seem  in  these  cases  to  be  disturbed  in  some  way  so  as  to 
affect  the  fusion  of  the  separate  contractions.  It  has  been  shown  that  the  num- 
ber of  such  oscillations  per  second  varies  in  man  from  seven  or  eight  to  twelve 
or  thirteen  (Loven,  v.  Kries,  Schiifer).  The  greatest  muscular  efforts  are  made, 
it  appears,  with  a  frequency  of  ten  to  twelve  impulses  per  second. 


4.    SIGNS   OF   ACTIVITY   IN   MUSCLE   AND    NERVE 


A.    ELECTRICAL  PHENOMENA 

1.  Action  Current. — The  general  law  of  the  electrical  variation  known 
as  the  action  current,  which  makes  its  appearance  when  nerve  or  muscle  is 
active,  has  already  been  given  on  page  48.     In  view  of  its  great  importance 


^      u7l>i  "ilij  "jts  (iifiit ■ 

Fig.   168. — Schema  illustrating  a  rheotome  experiment. 

for  the  general  physiology  of  muscles  and  nerves,  however,  we  must  discuss 
it  here  somewhat  more  in  detail. 

In  order  to  study  time  relations  of  the  action  current,  one  can  use  either 
the  capillary  electrometer  whose  excursions  can  be  recorded  by  the  photographic 
method,  or  the  repeating  rheotome  of  Bernstein. 

Suppose  we  have  an  electrical  variation  of  the  form  represented  in  Fig.  168. 
The  galvanometer  is  too  slow  to  reproduce  this  form  correctly.  But  if  we 
arrange  the  experiment  so  that  a  definite  portion  of  each  variation  of  the  cur- 
rent— e.  g.,  that  included  between  a,  and  h,  in  Fig.  168 — affects  the  galvanometer, 
and  this  is  repeated  many  times,  from  the  excursion  of  the  galvanometer  we  can 
learn  the  extent  of  the  electrical  variation  during  this  portion.  If  now  we  can 
determine   in  the  same  way  the  excursion   of   the  galvanometer  for  the  other 


432 


THE  FUNCnoXS  OF  CKOSS-STRIATED   MUSCLES 


portions,  say  b^  to  c„  c,  to  d„  d,  to  e„  etc.,  of  course  it  will  be  possible  to  obtain 
the  form  of  the  entire  variation.  An  apparatus  which  would  enable  us  to  make 
such  determinations  must  permit  of  connection  with  the  galvanometer  at  a 
definite  moment  after  the  beginning  of  the  variation,  and  of  breaking  this  con- 
nection at  any  desired  moment  during  the  variation.  Since  the  electrical  varia- 
tion in  muscles  and  nerves  is  started  by  the  excitation,  the  requirements  will  be 
met  if  the  galvanometer  circuit  can  be  closed  or  broken  at  any  given  interval 
after  the  instant  of  stimulation. 

The  rheotome  of  Bernstein  (Fig.  169)  consists  of  a  wheel  (r)  revolving  about 
a  vertical  axis,  and  carrying  on  its  circumference  three  metal  pegs,  one  of 
which  (c)  gives  the  stimulus  to  the  nei*ve  by  closing-  or  opening  the  primary 
current  to  an  induction  coil;  the  other  two  pegs  insulated  from  the  first,  but 
in  electrical  connection  with  each  other,  serve  to  close  and  open  the  galvanometer 
circuit.  At  each  revolution  of  the  wheel  the  pegs  c,  and  r,  dip  into  the  mercury 
troughs  (7,  and  q,)  respectively  which  are  connected  with  the  muscle  on  the  one 

hand  and  the  galvanometer  on 
B^  _  the  other.    The  mercury  troughs 

are  movable  with  respect  to 
each  other,  so  that  the  dura- 
tion of  the  galvanometer  cur- 
rent can  be  varied  within  wide 
limits.  If  now  the  wheel  is  re- 
volved at  a  certain  speed,  with 
each  revolution  the  muscle  will 
receive  a  stimulus  and  the  gal- 
vanometer circuit  will  be  closed 
for  a  certain  definite  time  after 
each  stimulus.  If  we  have  the 
two  contacts  so  arranged  that 
the  galvanometer  is  connected 
with  the  muscle  at  the  same 
instant  that  the  stimulus  is 
given,  the  excursion  of  the 
galvanometer  will  represent 
the  first  part  of  the  variation 
evoked  by  the  stimulus.  Then 
by  shifting  the  contacts,  the  galvanometer  can  be  connected  at  different  inter- 
vals following  the  instant  of  stimulation  until  the  entire  variation  is  recorded. 

If  a  muscle  (or  the  heart)  or  a  nerve  be  connected  at  two  uninjured 
places  (a  and  h,  Fig.  170)  with  a  galvanometer,  and  it  be  then  stimulated 
at  some  outside  point  (c),  the  galvanometer  shows  that  the  point  a  situated 
nearer  the  point  of  stimulation  becomes  electrically  negative  to  h.  and  then 
the  current  is  reversed  and  /;  IxT-omes  negative  to  a  (of.  pages  4,S  and  179). 
The  action  current  therefore  consists  of  tiro  plidsrs.  oneli  oif  which  gives  ex- 
pression to  the  general  law,  that  every  active  point  of  a  muscle  or^nerve  is 
electrically  negative  to  every  resting  point  (page  -IS).  When  the  excitation 
spreads  from  the  point  c,  the  nearer  of  the  two  points  natural! v  becomes 
active  first,  while  the  more  distant  point  (h)  is  still  resting;  hence  the 
first  phase.  When  the  excitation  reaches  the  point  h  and  the  point  a  first 
stimulated  has  gradually  passed  into  a  resting  state,  the  second  phase 
appears. 


Fig.   169. — Rheotome  of  Bern.stein. 


SIGNS   OF  ACTIVITY  IX  MUSCLE  AND  NERVE 


433 


The  action  current  does  not  represent  an  artificial  product,  but  is  a  process 
intimately  connected  with  the  process  of  excitation,  for  it  is  produced  by  all 
kinds  of  stimuli ;  it  is  propagated  at  the  same  rate  of  speed 
as  the  excitation  and  varies  in  strength  to  a  certain  ex- 
tent with  the  strength  of  stimulation. 

If  the  nerre  or  the  muscle  be  led  off  to  the  galvanometer, 
not  from  two  points  on  the  longitudinal  surface,  but  from 
the  longitudinal  surface  and  a  cross  section,  the  second 
phase  of  the  action  current  no  longer  appears,  but  the  cur- 
rent is  now  directed  from  the  longitudinal  surface  over  to 
the  cross  section.  It  was  in  this  form  that  the  action  cur- 
rent was  first  discovered.  Since  it  runs  in  the  opposite 
direction  from  the  current  of  rest  (see  page  48)  it  was 
designated  by  Du  Bois-Eeymond  as  the  negative  variation 
of  the  current  of  rest. 

The  action  current  is  the  only  functional  change 
which  we  have  thus  far  been  able  to  observe  in  living 
nerves.  It  is  of  great  importance  also  for  the  reason 
that  it  permits  us  to  determine  the  nature  of  any  mus- 
cular contraction. 


Fig.  170. — Schema 
illustrating  spread 
of  an  excitation 
causing  an  action 
current. 


We  have  already  become  acquainted  with  an  example  of 
this  in  studj'ing  the  heart.    The  action  current  there  showed 

us  that,  notwithstanding  its  long  duration,  the  contraction  of  the  heart  is  in 
reality  a  simple  muscidar  twitch  (cf.  page  179). 

There  are  other  kinds  of  contractions,  like  tetanus  and  voluntaiy  contrac- 
tions, which  as  we  have  seen  are  apparently  continuous,  but  which  the  action 
current  proves  to  be  discontinuous.  If  by  the  use  of  the  rheotome,  a  muscle  be 
stimulated  often  enough  to  produce  complete  tetanus,  the  excursions  of  the  gal- 
vanometer will  show  that  each  separate  stimulus  produces  a  special  action  cur- 
rent of  its  own — i.  e.,  every  excitation  causes  a  molecular  change  in  the  muscle, 
although  the  change  may  not  be  apparent  in  the  mechanical  behavior  of  the 
muscle. 

Tlie  action  current  of  muscle  as  well  as  of  nerve  is  strong  enough  to  have 
a  stimulating  action  of  its  own  (Matteucci).     If  the  nerve  of  one  muscle,  B,  be 
laid  across  the  belly  of  another  muscle,  A,  and  the  second  muscle  be  then  stimu- 
lated through  its  own  nerve,  with 
,,_  each  contraction  of  A,  B  also  con- 

tracts, and  this  even  in  case  A  is 
so  tense  that  it  no  longer  changes 
its  form.  The  contractions  of  B 
agree  minutely  in  number,  strength 
and  sequence  with  those  of  A.  If 
A  is  tetanized.  B  also  is  tetanized. 
These  phenomena  are  called  sec- 
nndary  cmttrnctions,  secondary  tet- 
anus, etc. 

2.      Electrotonir      Currents. — 
When   an  electric  current   is   con- 
ducted  tlirougli   a  c-crtiiin    length  of   a  medullated   nerve   and  another   portion 
of   the   nerve   outside  of   this  length   is   connected   with    the   galvanometer,   an 


Ftg.  171. — Illustrating   the   theory   of    cloctrotonic 
currents,  after  Hermann. 


434  THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

excursion  of  the  needle  is  seen  which  indicates  the  presence  of  a  current  in  the 
portion  led  off.  This  current  is  in  the  same  direction  as  the  current  applied  to 
the  nerve  .(called  the  polarizing  current),  and  is  spoken  of  as  an  electro  tonic 
current.  The  strength  of  this  current  depends  upon  many  different  circum- 
stances; it  is  stronger,  the  less  the  distance  from  the  portion  of  the  nerve  trav- 
ersed by  the  polarizing  current,  and  the  stronger  the  latter  is;  moreover,  the 
change  (in  the  frog)  is  greater  in  the  region  of  the  anode  than  in  the  region 
of  the  cathode. 

The  electrotonic  currents  are  branches  of  the  polarizing  current.  According 
to  Griinhagen,  they  arise  because  the  inner  parts  of  the  nei-ve  libers,  the  axis 
cylinders,  are  better  conductors  than  the  medullary  sheaths.  Consequently  the 
current  (E  in  Fig.  171)  spreads  out  over  great  lengths  of  the  nerve,  and  when 
connection  is  made  from  these  extrapolar  parts  with  the  galvanometer  (G,  G"), 
the  threads  of  current  break  through  to  the  surface.  It  may  be  fairly  doubted 
now  whether,  as  Hermann  imagined,  a  polarization  between  the  inner  and  outer 
parts  of  the  nerve  plays  any  part  in  producing  these  electrotonic  currents. 

B.    THE  MUSCLE  TONE 

If  a  person  sticks  his  finger  in  his  ear  and  then  contracts  his  arm  vigor- 
ously, he  hears  a  dull  sound,  the  pitch  of  which  has  been  determined  by  Wallasten 
and  others  to  be  about  thirty-two  to  thirty-six  vibrations  a  second.  Helmholtz 
observed  that  the  same  sound  is  heard  very  clearly  if  the  ears  (best  at  night)  be 
stopped  with  drops  of  sealing  wax  and  the  masseter  muscles  be  powerfully  con- 
tracted. So  long  as  the  muscles  remain  at  a  uniform  tension,  one  hears  a  dull, 
roaring  sound,  whose  fundamental  tone  is  not  changed  materially  by  increasing 
the  tension,  whereas  the  accompanying  roar  becomes  both  stronger  and  higher. 

Helmholtz  demonstrated  further  that  the  vibrations  of  voluntary  muscles 
which  produce  the  muscular  sound  do  not  occur  so  regularly  as  those  of  a 
musical  tone,  nor  so  rapidly  as  thirty-two  to  thirty-six  per  second.  He  found 
on  the  average  only  about  nineteen  per  second.  The  muscular  sound  is  there- 
fore an  overtone  of  the  true  muscle  vibrations.  Since  the  pitch  of  this  sound 
changes  also  with  the  condition  of  the  ear  drum,  it  follows  that  the  sovind  experi- 
enced is  a  resonance  tone  of  the  tympanic  membrane,  produced  by  the  irregular 
concussions  of  the  muscles.  From  these  facts  it  is  not  difficult  to  understand 
why  the  simple  contraction  of  a  muscle  produced  by  a  single  stimulus,  and  the 
systole  of  the  heart  as  well,  is  accompanied  by  a  muscular  sound  (cf.  page  168). 

C.    THE  CHEMICAL  ALTERATIONS  IN  MUSCLE  DUE  TO  ITS  ACTIVITY 

Active  muscle  acquires  an  acid  reaction.  This  is  probably  due  in  part  to 
an  increased  percentage  of  monophosphates,  and  in  part  to  the  formation  of 
lactic  acid.  According  to  Helmholtz,  working  muscle  contains  less  substance 
soluble  in  water  and  more  substance  soluble  in  alcohol  than  resting  muscle. 
Again  it  is  stated  that  in  work  the  total  quantity  of  creatin  and  creatinin 
increases  and  that  of  the  xanthin  bases  decreases.  Finally,  the  percentage  of 
glycogen  in  the  muscle  diminishes. 

An  acid  reaction  has  been  obsei-ved  in  the  neighborhood  of  the  electrodes 
when  nerves  are  stimulated.  Since  however  no  such  change  can  be  demon- 
strated at  points  of  the  nerve  which  have  not  been  touched  by  the  stimulating 
current,  this  acid  reaction  must  be  regarded  as  a  direct  effect  of  the  current — 
i.  e.,  electrolysis.  Waller  concludes  from  certain  phenomena  with  the  action  cur- 
rent that  the  nerve  forms  carbon  dioxide  during  its  activity. 


SIGNS  OF  ACTIVITY   I\   MUSCLE   AND   NERVE 


435 


D.    MECHANICAL    WORK 

The  amount  of  mechanical  work  done  by  a  muscular  contraction  depends 
primarily  upon  the  strength  of  the  stimulus,  and  upon  the  load. 

1.  Effect  of  the  Streyigth  of  Stimulus. — If  a  muscle  bearing  a  constant 
load  be  stimulated  with  a  graded  series  of  shocks  beginning  at  a  very  low 
level  and  increasing  slowly,  it  is  found,  both  with  direct  electrical  stimulation 
of  the  muscle  and  with  mechanical  or  electrical  stimulation  of  the  nerve,  that 
the  height  of  the  contractions  increases  more  and  more  slowly  with  a  uniform 
increase  in  the  strength  of  the  stimuli,  and  that  it  finally  approaches  its 
maximum  after  the  manner  of  an  asymptote  (Fig.  172).  The  maximum 
shortening  which  can  be  obtained  under  the  most  favorable  circumstances 
with    a    single    contraction    is 

about  twenty  per  cent  of  the 
natural  length  of  the  muscle. 

The  muscular  tension  ob- 
tained with  a  maximal  stimulus 
applied  to  the  nerve  is  consider- 
ably smaller  than  that  obtained 
by  a  maximal  stimulus  applied 
directly  to  the  muscle  itself 
(Dean).  If  this  is  true  of  the 
natural  stimulation  from  the 
central  nervous  system  also,  it 
means  that  the  muscles  are  al- 
ways capable  of  more  work 
than  can  ever,  under  normal  cir- 
cumstances, be  obtained  from 
them. 

2.  Effect  of  Load  with  Con- 
stant Stiinulus. — We  shall  con- 
sider only  the  case  of  a  maxi- 
mal stimulus. 


Fig.  172. — Frog's  gastrocnemius.  Stimulation  of  the 
nerve  with  break-induction  shocks;  load  constant. 
The  abscissae  represent  the  strength  of  the  stimuli, 
the  ordinates  the  height  of  the  contractions. 


One   can    vary    the    way    in 
which  the  power  of  the  muscle 

is  taken  up  by  making  the  contraction:  (1)  isotonic — i.e.,  where  the  load  is 
constant  throughout  the  contraction ;  (2)  auxotonic,  where  the  load  increases 
constantly  throughout;  and  (3)  by  supporting  the  load  so  that  it  is  not  lifted 
until  the  muscle  has  contracted  a  certain  distance  (after-loading'). 

A  perfect  isotonic  contraction  is  probably  never  obtained.  Even  when  the 
mechanical  conditions  of  the  experiment  fulfill  the  requirements  for  isotony 
as  completely  as  possible,  the  contraction  is  retarded  at  its  beginning  by  the 
inertia  of  the  masses  to  be  moved,  consequently  the  tension  of  the  muscle  is 
greater  at  the  start  than  later. 

We  designate  as  auxotonic  contractions,  first  those  in  which  the  muscle 
works  against  a  stiff  spring,  where  the  tension  naturally  increases  as  long  as 
the  muscle  continues  to  contract,  and  secondly,  those  contractions  in  which  the 
tension  of  the  muscle  is  purposely  increased  by  retardation  of  the  movement  at 
its  beginning.     Here  belong  the  so-called  simple  projectile  motion  (Helmholtz), 


436 


THE   FUNCTIONS  OF  CROSS-STRIATED   MUSCLES 


in  which  the  muscle  lifts  a  weight  fastened  directly  to  its  free  end,  and  the 
projectile  motion  irith  dead  weights  (Fick),  where  the  muscle  pulls  on  a  lever 
with  balanced  weights. 

In  Figs.  173  and  174  are  given  examples  of  some  of  the  different  forms  of 
motion,  namely:  Fig.  173  a,  an  isotonic  contraction.  Fig.  173  h,  a  simple  pro- 
jectile motion.  Fig.  174,  projec- 
tile motions  with  dead  balanced 
weights. 

In  curves  approximately  iso- 
tonic, Fig.  173  a,  as  well  as  in 
pure  auxotonic  curves,  which 
naturally  reproduce  the  changes 
in  length  of  the  muscle  most  ex- 
actly, we  find  in  the  ascending 
limb  a  break,  which  is  not  an 
artifact  but  which,  on  grounds 
that  cannot  be  discussed  here,  is 
probably  due  to  the  more  slug- 
gish contraction  of  the  red  mus- 
cle fibers  (cf.  page  416).  In  the 
projectile  curve  this  irregularity 
does  not  appear,  at  least  not  so 
clearly,  because  the  movement 
of  the  lever  does  not  record  the 
finer  details  of  the  contraction.  The  contraction  produced  by  a  single  stimulus 
is,  therefore,  to  a  certain  extent  compound,  owing  to  the  fact  that  the  different 
kinds  of  fibers  composing  the  muscle  become  active  at  different  times.  In  an 
exact  analysis  of  muscular  contractions,  it  is  necessary  to  give  this  circumstance 
its  proper  weight. 

Fig.  175  represents  the  single  contraction  of  a  muscle  poisoned  with  vera- 
trin,   recorded  on  a  slow-moving  drum.     Veratrin  affects  the  red  muscle  fibers 


Fig.  17.3. — Frog's  gastrocnemius,  a,  isotonic  con- 
traction; b,  simple  projectile  contraction.  Both 
were  obtained  with  tlie  same  loads,  80  g.,  after 
Santesson. 


Fig.  174. — Frog's  gastrocnemius.      1,  loaded  with  4  g.,  i.  e.,  with  the  bare  lever;    2,  40  g.  dead 
weight;    3,  100  g.  dead  weight;    4,  200  g.  dead  weight. 

so  that  they  contract  much  more  slowly  than  is  normal.     The  first  rapid  curve  is 
referable  to  the  white  fibers,  the  second  long-drawn-out  cui-ve  to  the  red  fibers. 


SIGNS   OF   ACTIVITY   IN   MUSCLE   AND   NERVE 


437 


After  these  preliminary  remarks  we  can  proceed 
with  the  discussion  of  the  effect  of  load  on  the  work  of 
a  muscle.  We  can  say  in  general  that  the  height  of 
the  contraction  is  less  the  greater  the  load.  But  this 
rule  cannot  stand  without  qualification.  For  under 
the  isotonic  arrangement  we  find  the  height  less  with 
a  very  ligrht  load  than  it  is  with  one  somewhat  heavier 
(v.  Frey),  and  under  the  purely  auxotonic  arrange- 
ment the  height  increases  with  the  load  up  to  a  fairly 
high  primary  tension.  Moreover,  even  if  the  height 
of  the  contraction  does  decrease  as  the  load  increases, 
it  does  so  much  more  slowly  than  the  load  increases ;  so 
that  up  to  a  certain  limit  the  work  done  (product  of 
the  load  hy  the  height  of  contraction)  is  greater,  the 
greater  the  load  (E.  F.  Weher). 

Again,  a?!  increase  in  the  tension  of  a  muscle  dur- 
ing its  contraction  has  a  decidedly  favorable  effect  on 
its  performance.  Under  some  circumstances  the  con- 
tractions against  a  stiff  spring  are  Just  as  high  or  even 
higher  than  isotonic  contractions  obtained  with  a  pri- 
mary tension  of  the  same  amount  (Santesson)  ;  and 
projectile  contractions  are  sometimes  higher  than  iso- 
tonic contractions  with  the  same  primary  tension  (cf. 
Fig.  173).  Finally,  cases  have  been  recorded  where 
auxotonic  contractions  which  l)egin  with  the  same  ten- 
sion are  higher  with  a  strong  spring  than  with  a  weak 
one.  We  can  say,  therefore,  that  within  certain  limits 
the  work  done  by  a  muscle  is  increased  both  by  a  higher 
primary  tension  and  by  an  increase  in  the  tension  dur- 
ing the  contraction. 

In  close  connection  with  this  comes  the  additional 
fact  that  under  the  isometric  arrangement  the  increase 
in  tension  takes  place  much  more  rapidly  than  does 
the  shortening  under  the  so-called  isotonic  arrange- 
ment ;  or,  in  other  words,  its  length  remaining  the 
same,  the  muscle  reaches  its  maximum  tension  mucli 
earlier  than  it  reaches  its  maximum  shortening  when 
the  tension  remains  the  same  (Fick,  Fig.  17(j). 

A  muscle  appears  therefore  to  have  the  power  of 
regulating  the  amount  of  work  done  under  a  given 
stimulus,  -according  to  the  requirements  of  the  case. 
We  must  forego  a  complete  theoretical  disciission  of 
these  facts  here;  but  we  would  direct  attention  to  the 
significance  of  the  red  fibers  in  this  connection.  They 
are,  as  it  appears,  the  most  important  source  of  the 
additional  work  done  as  the  result  of  an  increased 
tension.  Thus  we  find  that  the  secondary  lift  due  to 
these  fibers,  in  contractions  against  a  tense  spring  in- 
27 


438 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


creases  as  the  tension  rises,  whereas  the  primary  lift  caused  by  the  white 
muscle  fibers,  decreases  as  a  rule  with  a  rising  tension  (cf.  page  436). 

3.  The  Absolute  Power  of  a  Muscle. — The  method  of  after-loading-  has  been 
used  for  the  purpose,  among  other  things,  of  determining  the  so-called  absolute 
power  of  the  muscle.  A  muscle  is  loaded  only  with  a  lever,  and  the  lever  is 
supported  mechanically  so  that   the  weights  hung  on  it,  which  constitute  the 


Fig.  176. — Isotonic  (upper)  anil  isometric  (lower)  contraction  curves  under  the  same  primary 
tension,  after  Fick.  To  be  read  from  left  to  right.  The  curves  a,  b,  c,  d,  represent  the  short- 
ening of  the  mu.scle  corresponding  to  the  isometric  contractions  a,  ^,  y,  S. 


after-load,  do  not  affect  the  muscle  so  long  as  it  is  resting.  It  is  loaded  by 
the  weights  oidy  when  contraction  begins,  and  lifts  them  only  when  its  tension 
overcomes  the  after-load.  By  adding  weights  one  reaches  finally  a  mass  which 
the  muscle  no  longer  has  the  power  to  lift.  This  weight  is  taken  as  the  absolute 
power  of  the  muscle  (E.  F.  Weber). 

It  is  evident  that,  other  things  being  equal,  the  absolute  power  of  a  muscle 
must  be  proportional  to  its  cross  section,  or  in  other  words,  among  muscles  com- 
posed of  the  same  kind  of  fibers  the  thickest  is  the  strongest.  In  tetanus  the 
absolute  power  is  greater  than  in   simple  contractions,  and  for  the  voluntary 


SIGNS   OF   ACTIVITY   IN    MUSCLE   AND   NERVE  439 

contractions   of  human  muscles  it   amounts,   according  to   various  authors,  to 
10  kg.  per  square  centimeter  of  cross  section. 

If  an  experiment  be  so  arranged  that  the  muscle  lifts  its  load  after  it  has 
contracted  to  different  heights,  and  the  absolute  power  for  these  successive  heights 
be  determined,  we  find  that  it  grows  steadily  less  (Schwann's  experiment). 

4.  The  Work  of  Tetanized  Muscles. — In  tetanus  it  is  evident  that  the 
work  done  after  the  tetanus  has  reached  its  full  height  is  from  a  mechanical 
point  of  view  nothing  at  all.  Since,  however,  the  contracted  state  always 
calls  for  an  expenditure  of  energy,  tetanus  is  accompanied  by  a  relatively 
great  consumption  of  substance,  which  in  its  turn  leads  to  rapid  fatigue. 

The  work  of  tetanus  as  related  to  its  shortening  is  in  general  similar  to 
that  of  a  single  contraction,  only  it  is  more  extensive,  so  that  under  favorable 
circumstances  the  shortening  may  amount  to  as  much  as  sixty-five  to  eighty- 
five  per  cent  of  the  muscle's  length.  Moreover  the  ratio  of  shortening  in 
tetanus  to  shortening  in  simple  contraction  is  very  different  for  different  kinds 
of  muscles;  thus  it  is  stated  that  the  maximum  shortening  in  tetanus  of  the 
white  muscles  of  the  frog  is  two  to  three  times  the  maximum  shortening  in 
a  simple  contraction ;  of  the  red  muscles  eight  to  nine  times. 

The  height  of  tetanus  with  a  constant  load  depends  on  the  strength  of 
stimulus,  but  not  upon  the  frequency  of  stimulation. 


E.    HEAT   FORMATION   IN   MUSCLE 

By  employing  the  thermo-electrical  method,  Helmholtz  (1S47)  demon- 
strated the  formation  of  heat  in  the  tetanus  of  the  exsected  frog's  muscle. 
Later  the  production  of  heat  in  a  simple  contraction  was  demonstrated  by 
Heidenhain.  And  Blix  has  shoAivn  that  heat  is  formed  even  in  resting  muscle. 
Even  with  the  most  delicate  methods  no  heat  production  can  he  demonstrated 
in  nerves. 

Since  the  performance  of  mechanical  work  and  the  production  of  heat 
-are  the  two  chief  functions  of  muscle,  and  since,  as  we  have  seen  above,  the 
mechanical  work  done  under  a  constant  stimulus  increases  up  to  a  certain 
limit  with  the  load,  it  might  be  supposed  that  the  heat  production  going  on 
at  the  same  time  would  be  in  inverse  relation  to  the  load,  so  that  the  dissimi- 
latory  process  evoked  in  a  muscle  by  a  given  stimulus  would  be  independent 
of  the  load,  and  the  latter  therefore  would  influence  only  the  apportionment 
of  the  total  output  of  energy  by  the  muscle  to  the  two  functions.  But  this 
is  not  the  case.  Since  the  investigation  of  Heidenhain,  we  know  that  the 
total  output  of  energy  in  an  exsected  frog's  muscle  under  a  constant  stimulus, 
increases  up  to  a  certain  limit  tvith  the  load. 

This  property  of  the  muscle  appears  to  be  of  very  great  importance.  For 
if  the  total  performance  of  the  muscle  were  independent  of  the  load  and  were 
dependent  only  on  the  strength  of  stimulus,  the  development  of  energy  in  the 
muscle  might  often  be  out  of  all  proportion  to  the  work  to  be  done.  The  rela- 
tionship discovered  by  Heidenhain  is  to  be  looked  upon  as  a  regulatory  mechanism 
which,  independently  of  the  nervous  impulses,  controls  the  metabolism  in  the 
muscle  according  to  its  momentary  needs  (cf.  also  page  4-il). 


440 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


Fick  and  his  pupils  have  made  absolute  determinations  of  the  amount 
of  heat  developed  in  muscular  activity,  and  the  amount  of  work  done  at  the 
same  time.  Some  of  their  results  are  brought  together  in  the  following  table. 
In  these  experiments  the  load  was  allowed  to  fall  again  after  each  contraction, 
so  that  the  observed  quantity  of  heat  expresses  the  total  output  of  energ}^ 
Each  experiment  consisted  of  three  maximal  contractions  following  one 
another  in  rapid  succession. 


Load, 

Ileatprodiiction  in 

Work, 

Thermal  equivalent 

Ratio  of  work 

g- 

micro-calories. 

g.  mm. 

of  work. 

to  heat. 

0 . 

14.6 

20 

18.3 

465 

i.()9 

i(5.7 

40 

19.7 

802 

1.88 

10.5 

80 

23.9 

1.420 

3.34 

7.1 

120 

24.2 

1.914 

4.50 

5.4 

160 

25.8 

2.402 

5.64 

4.6 

200 

23.6 

2.005 

6.83 

3.7 

160 .. 

26.2 

2.402 

5.64 

4.6 

120 

23.3 
21.9 
19.5 

18.0 

1.914 

1,430 

819 

465 

4.50 
3.34 
1.92 
1.09 

5.2 

80 

6.6 

40 

10.2 

20.. 

16.6 

0 

13.4 

.... 

We  see  that  under  a  maximal  stimulus  and  with  increasing  load  the  ratio 
of  work:  heat  changes  in  favor  of  the  former.  With  the  least  load  the  total 
production  of  energy  is  16.7  times  the  amount  of  work  done,  whereas  with 
the  heaviest  load  it  is  only  3.7  times  as  much.  In  other  experiments  a  still 
greater  part  of  the  total  production  of  energy  appeared  as  mechanical  M^ork. 
But  as  a  rule  in  the  frog's  muscle  cut  out  of  the  body  by  far  the  greatest 
part  of  the  energy  developed  in  contraction  is  used  for  the  production  of  heat. 


§  5.  THE  CENTRAL  INNERVATION  OF  A  SKELETAL  MUSCLE 

Each  one  of  the  muscles  of  the  extremities  receives  motor-nerve  fibers 
from  several  successive  nerve  roots.  This  is  most  clearly  seen  in  the  case  of 
the  sterno-cleido-mastoid  and  the  trapezius  of  man  which  are  innervated  by 
both  the  spinal  accessory  and  the  cervical  nerves.  This  fact  alone  appears 
to  indicate  that  under  normal  circumstances  some  of  the  fibers  of  a  muscle 
are  not  thrown  into  action,  but  that  the  muscle  has  the  power  of  contracting 
partially.     The  following  experiment  by  Gad  confirms  this  conclusion. 

The  lumbar  plexus  of  the  frog  conveys  nerve  fibers  to  the  gastrocnemius  by 
two  roots.  If  with  a  light  load  the  muscle  be  given  a  tetanic  stimulus  directly 
or  indirectly  by  one  or  by  both  of  these  roots  the  contractions  are  of  equal  size. 
But  if  the  tension  developed  in  the  muscle  in  tetanus  be  studied  by  means  of 
the  apparatus  figured  on  page  414,  it  is  found  to  be  less  w^hen  the  stimulus  is 
applied  to  only  one  root  than  when  applied  to  both  or  to  the  muscle  directly, 
and  that  in  the  latter  two  cases  the  tension  is  equal  to  the  sum  of  the  tensions 
developed  by  separate  stimulation  of  the  two  roots.  The  result  goes  to  show 
that  on  stimulation  of  different  nerve  roots,  not  the  Avbole  muscle  but  only  cer- 
tain of  its  fibers  are  excited,  or  in  other  words  that  each  nerve  root  produces  a 


FATIGUE   AND   RECOVERY   OF   MUSCLES  AND   NERVES 


441 


partial  contraction.  There  can  be  no  doubt  that  such  partial  contractions  occur 
also  normally  under  the  influence  of  the  nervous  system,  although  probably  with 
still  nicer  gradations.  In  this  way  the  activity  of  the  muscle  is  adapted  to  the 
work  to  be  performed.  If  no  great  degree  of  tension  is  called  for,  only  a  few 
muscle  fibers  contract,  the  others  remain  quiet  and  do  not  become  fatigued. 
Since  on  the  other  hand  the  extent  of  the  contraction  does  not  depend  upon 
the  cross  section,  but  upon  the  length  of  the  muscle,  we  may  get  just  as  much 
shortening  with  a  partial  contraction  as  when  the  whole  muscle  is  active. 


§  6.    FATIGUE   AND    RECOVERY   OF   MUSCLES   AND    NERVES 
A.    GENERAL   PHENOMENA 

If  a  frog^s  muscle  be  stimulated  repeatedly  with  single  shocks  given  every 
one  to  two  seconds,  at  first  its  contractions  increase  in  size,  even  if  the  stimulus 
remain  of  the  same  strength  ("  treppe  "  of  Bowditch  and  Buckmaster),  and  then 
they  gradually  decrease  until 
complete  exhaustion  is  reached. 
From  the  first  of  the  series  the 
contractions  become  more  pro- 
longed, since  both  the  ascending 
and  the  descending  limbs  of  the 
curve,  but  especially  the  latter, 
occupy  more  time.  As  fatigue 
progresses  and  the  longer  stimu- 
lation is  kept  up,  there  gradu- 
ally develops  a  new  condition  of 
the  muscle :  at  the  end  of  the 
contraction  it  does  not  return  to 
its  resting  position  but  remains 
more  and  more  shortened.^  The 
muscle  finally  becomes  a  slug- 
gish, stubborn  mass  yielding  to 
the  traction  which  strives  to  re- 
store it  to  its  original  form,  with 
extreme  slowness  (Funke).  In 
the  series  represented  in  Fig. 
177  a  muscle  kept  perfused  with 
blood  was  stimulated  every  1.5 
seconds.  Only  the  first  ten  of 
every  fifty  contractions  are  here 
reproduced,  the  six  series  rejire- 

senting  all  told  some  three  hundred  separate  movements.  When  the  interval 
between  stimuli  is  made  still  shorter,  say  0.5  second,  as  fatigue  continues  the 
descending  limb  of  the  curve  does  not  reach  the  base  line,  before  it  is  met  by 
the  following  stimulus,  and  the  curve  becomes  much  like  an  incomplete  tetanus. 
With  a  longer  interval,  say  six  seconds,  the  contraction  is  not  prolonged,  or  only 
slightly  so.  and  the  reduction  in  the  height  of  the  curve  is  the  only  expression 
of  fatigue. 

The  muscle  of  warm-hJooded  animals,  kept  perfused  with  blood,  show,  accord- 
ing to  Rollet,  only  this  latter  form  of  fatigue,  with  no  material  increase  in 
the  duration  of  the  contraction  even  when  the  interval  between  stimuli  is  verj' 


Fig.  177. — Changes  in  the  character  of  the  contraction 
produced  by  fatigue,  after  Rollet. 


•This  condition  is  called  contracture — Ed. 


442 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


short.    Consequently  in  these  muscles  the  above-mentioned  incomplete  tetani  are 
entirely  wanting. 

[According  to  F.  S.  Lee  this  difference  in  the  mode  of  fatigue  between  the 
excised  muscles  of  cold-blooded  and  of  warm-blooded  animals  is  due  to  a  real 
physiological  difference  and  not,  as  had  been  supposed  by  Sehenck  and  Lohmann, 
to  a  mere  difference  of  temperature.  Lee  finds  that  the  muscles  of  the  former 
exhibit  the  same  characteristic  slowing  of  the  contraction  process  (cf.  Fig.  178) 
both  at  low  and  at  high  temperatures  (though  at  the  high  temperature  to  some- 
what less  extent  than  at  the  low) ;  whereas  the  muscles  of  the  latter  do  not 
exliibit  this  phenomenon  at  either  high  or  low  temperatures.  "  The  poikilother- 
mal  condition  (cf.  page  46)  is  more  primitive  than  the  homoiothermal,  and  it 
would  seem  that  the  constant  influence  of  a  uniform  temperature  acting  for  ages 

on  the  skeletal  muscles  of 
warm-blooded  animals  has  im- 
pressed on  them  certain  pro- 
nounced peculiarities."  Pos- 
sibly the  part  which  these 
muscles  themselves  play  in 
the  production  of  heat  is  in 
some  way  associated  with 
this  physiological  difference. 
—Ed.] 

With  regard  to  the  fa- 
tigue of  nerves  we  must  dis- 
tinguish very  clearly  between 
the  local  fatigue  which  takes 
place  in  artificial  stimula- 
tion at  the  point  where  the 
stimulus  is  applied,  and 
which  in  part  at  least  is  due 
to  the  injurious  effects  of 
the  stimulating  agent,  and 
the  fatigue  which  is  pro- 
duced possibly  by  the  trans- 
mission of  stimuli.  Since 
only  the  latter  determines 
the  normal  behavior  of  nerve, 
we  shall  discuss  it  alone. 

In  order  to  observe  the 
fatigue  of  nerve,  it  is  neces- 
sary to  so  arrange  the  ex- 
periment that  its  muscle  is 
not  stimulated.  Bernstein  fulfilled  these  requirements  by  stimulating  the  sciatic 
nerve  of  the  frog  a  long  distance  from  the  muscle,  at  the  same  time  conducting 
through  the  nerve  between  this  point  of  stimulus  and  the  muscle  a  strong  con- 
stant current.  The  resistance  at  the  anode  of  the  constant  current  prevented 
the  stimulus  applied  farther  up  from  reaching  the  muscle.  In  this  way  Bern- 
stein found  that  the  nerve  was  miich  less  capable  of  fatigue  than  the  muscle. 
By  the  same  method  Wedensky  was  able  to  stimulate  a  motor  nerve  of  the  frog 
for  six  hours  without  exhausting  it. 

This  same  resistance  of  nerves  to  fatigue  has  been  demonstrated  also  by 
Langendorff,  Bowditch  and  others,  on  warm-blooded  animals.  If  curare,  which 
throws  out  of  action  the  end  plates  of  the  motor  nerves,  be  administered  to  an 


Fig.  178. — Isotonic  contractions  of  a  frog's  gastrocne- 
mius, after  F.  S.  Lee,  showing  changes  due  to  fatigue. 
Only  every  fiftieth  contraction  is  recorded. 


FATIGUE   AND  RECOVERY   OF   MUSCLES   AND  NERVES  443 

animal,  the  poison  will  be  gradually  thrown  off  from  the  body,  and  the  end 
plates  will  again  recover  their  function.  But  several  hours  intervene,  and  a 
stimulus  applied  during  the  interval  is  of  course  without  effect  on  the  muscle. 
But  when  the  poison  wears  off,  the  effect  of  stimulation  returns  with  all  its  orig- 
inal force,  which  means  that  stimulation  continued  for  hours  has  not  fatigued  the 
nerve.  Brodie  and  Halliburton  observed  likewise  that  nonmedullated  nerves,  such 
as  the  splanchnic,  were  not  fatigued  by  artificial  stimulation  lasting  six  hours. 

Besides  this  any  number  of  natural  phenomena  show  that  nerves  have  a 
much  greater  endurance.  We  know,  indeed,  that  several  efferent  nerves,  espe- 
cially the  vagus  branches  to  the  heart,  are  all  the  time  under  a  tonic  excitation 
of  greater  or  less  intensity,  also  that  the  same  is  true  of  the  afferent  nerves, 
examples  of  which  we  have  in  the  constant  pains  of  certain  nervous  maladies. 

From  these  facts  the  conclusion  has  been  drawn  that  nerves  in  general  are 
not  fatigued,  and  it  cannot  be  denied  that  this  conception  is,  to  a  certain  extent, 
well  founded.  Nevertheless,  one  must  not  imagine  that  no  metabolic  processes 
are  taking  place  in  an  active  nerve  or  that  it  mediates  the  transmission  of 
stimuli,  as  for  example  a  wire  does  an  electric  current;  such  a  supposition  has 
little  probability  in  its  favor  on  purely  antecedent  grounds,  for  a  nerve  is  a 
living  tissue.  Moreover,  there  are  a  number  of  direct  observations  at  hand  which 
show  the  presence  of  chemical  processes  in  nerve  with  perfect  definiteness. 

For  example,  a  nerve  deprived  entirely  of  oxygen  becomes  completely  inex- 
citable  within  three  to  five  hours,  but  recovers  its  excitability  again  within  three 
to  ten  minutes  when  oxygen  is  supplied.  This  phenomenon  as  well  as  the  pro- 
duction of  carbon  dioxide  in  active  nerves  (cf.  page  434)  substantiates  the  view 
that  a  nerve,  so  far  as  processes  taking  place  within  it  are  concerned,  presents 
no  essential  difference  from  the  other  organs  of  the  body.  On  the  other  hand 
its  extraordinary'  resistance  to  fatigue  presupposes  a  very  low  state  of  metabolism 
and  a  very  great  power  of  recuperation.  This  ability  to  recover  is  probably 
different  also  in  different  nerves ;  for  in  the  olfactory  nerves  of  the  pike  unmis- 
takable signs  of  fatigue  make  their  appearance  after  only  a  short  period  of 
excitation  (Garten). 

Contractions  can  still  be  induced  by  direct  stimulation  long  after  the  mus- 
cle fails  to  respond  to  a  tetanizing  stimulus  applied  to  its  nerve.  Since  the 
nerve  itself  does  not  fatigue  we  must  suppose  that  the  nerve  endings  fatigue 
much  earlier  than  the  muscle  substance  itself  (Waller). 


B.    FATIGUE   OF   HUMAN   MUSCLES   AND   NERVES 

The  phenomena  of  fatigue  in  man  have  recently  been  studied  by  several 
authors  by  means  of  the  ergograph,  an  apparatus  first  constructed  by  Mosso. 

This  ergograph  is  especially  constructed  for  the  flexion  of  the  middle  finger, 
and  consists  of  two  parts,  one  to  which  the  hand  is  fastened  and  another  which 
records  the  contractions  of  the  muscle.  The  whole  apparatus  is  shown  in  Fig. 
179.  The  forearm  is  fixed  in  position  by  means  of  the  clamps  and  the  hand  by 
means  of  the  two  tubes  into  which  the  index  and  ring  fingci-s  are  thrust.  A 
string  fastened  to  the  middle  phalanx  of  the  middle  finger,  carries  the  load  and 
moves  the  writing  lever.  The  latter  records  the  contraction  of  the  muscle, 
enlarged  about  twice,  on  a  slowly  rotating  drum.  The  work  of  the  muscle  is 
of  course  the  product  of  the  actual  height  of  contraction  by  the  load. 

If  now  the  load  be  not  too  light  and  the  interval  between  contractions  not 
too  great,  the  height  continually  declines  until  finally  the  subject  is  no  longer 


444 


THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 


able  to  lift  the  load ;  but  if  the  load  be  diminished,  he  can  continue  the  work 
immediately.     The  fatigue  curve  either  declines  rapidly  at   first  and  more 


Fig.    179. — Ergograph,   after  Mosso. 

slowly  at  the  end,  as  in  Fig.  180,  A,  or  the  fall  at  the  beginning  is  slight  and 
is  rapid  toward  the  end  (Fig.  180,  B).  Judging  by  Mosso's  results  every  indi- 
vidual has  his  own  peculiar  form  of  fatigue  curve. 

Of  the  factors  which  influence  the  progress  of  fatigue  we  shall  investigate 
first  the  effect  of  frequency  of  contraction  with  a  constant  load.     Figs.  181,  A  to 


A  B 

Fig.  180. — Fatigue  tracings  obtained  with  the  ergograph  of  Mcsso.     To  be  read  from  right  to  left. 


FATIGUE   AND  RECOVERY   OF   MUSCLES   AND   NERVES 


445 


D  show  that  exhaustion  comes  on  more  rapidly  the  smaller  the  interval  between 
contractions.  In  Fig.  181,  A  we  find  only  fourteen  contractions  before  complete 
exhaustion,  mechanical  work  =  0.912  kg.  m.  In  Fig.  181,  B  the  number  of  con- 
tractions is  eighteen,  and  the  mechanical  work  done  1.080  kg.  m.  In  Fig.  181,  C 
the  number  of  contractions  is  thirty-one  and  the  mechanical  work  1.842  kg.  m. 
With  a  rhythm  of  one  contraction  every  ten  seconds  no  fatigue  at  all  appears 
(Fig.  181,  D).  An  interval  of  ten  seconds,  therefore,  is  sufficient  to  permit  a 
skeletal  muscle  to  recover  completely. 

When  a  muscle  is  worked  at  a  rapid  rhythm  to  the  point  of  complete  exhaus- 
tion, it  requires  a  rather  long  time  to  recover  completely — in  the  experiments  of 
Maggiora  from  one  and  one-half  to  two  hours.  It  was  also  shown  in  these 
experiments  that  the  last  contractions  of  a  series  ending  in  complete  exhaustion, 
are  the  most  fatiguing.     If  only  the  first  part,  say  the  first  fifteen  contractions. 


D 

Fig.  181. — The  onset  of  fatigue  under  stimuli  of  the  same  strength,  given  at  different  intervals, 
after  Maggiora.  ^1,  once  a  second;  B,  once  every  two  seconds;  C,  once  in  four  seconds; 
D,  once  in  ten  seconds.     To  be  read  from  right  to  left. 


of  a  fatigue  series  be  carried  out  and  rest  be  then  permitted,  the  muscle  will 
recover  in  a  much  shorter  time  proportionally  than  if  it  were  completely  fatigued. 
Consequently  the  total  amount  of  work  which  can  be  done  in  a  day  is  consider- 
ably greater  if  the  muscles  be  not  pushed  at  any  time  to  the  limit  of  their 
powers.  For  example,  a  muscle  making  fifteen  contractions  every  thirty  min- 
utes for  fourteen  hours  did  mechanical  work  of  2G.9  kg.  m. ;  the  same  muscle 
when  made  to  perform  the  whole  series  of  fatigue  curves  every  two  hours  accom- 
plished a  mechanical  work  of  only  14.7  kg.  m.;  a  difference  of  12.2  kg.  m. 

Ancemia,  fasting,  want  of  sleep,  among  other  things,  reduce  the  working 
power,  and  favor  the  onset  of  fatigue.  The  capability  of  work  is  increased,  on 
the  other  hand,  by  rest,  by  taking  food,  and  by  massage — the  latter  even  in 
case  the  muscle  be  previously  not  fatigued.  The  effect  of  massage  after  work 
therefore  consists  not  only  in  the  removal  of  products  arising  from  the  expendi- 
ture of  energy,  but  also,  and  to  a  considerable  extent,  in  the  more  active  circu- 
lation  of  the  blood  and  lymph  and  possibly  in  some  alteration  of  metabolism 


446  THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

thereby  produced.  Experiments  on  exsected  frog's  muscles  indicate  that  there 
is  a  direct  influence  on  the  contractile  substance  (Ruge). 

Fatigue  of  one  group  of  muscles  exercises  an  unmistakable  influence  on 
other  muscles — e.g.,  fatigue  of  the  legs  hastens  fatigue  of  the  arms;  but  mus- 
cular training  reduces  such  effects. 

It  has  been  shown  also  that  purely  mental  work  hastens  muscular  fatigue 
to  a  very  great  extent.  It  might  be  supposed  that  this  part  of  fatigue  is  purely 
central ;  but  the  matter  is  not  so  simple.  The  same  result  is  obtained  where  an 
artificial  stimulus  is  applied  to  the  median  nerve  or  directly  to  the  flexor  mus- 
cles of  a  person  fatigued  by  mental  work. 

Finally,  by  other  experiments  which  cannot  be  described  here,  ^losso  has 
shown  that  while  the  mechanical  work  performed  by  a  muscle  decreases  as 
fatigue  comes  on,  the  nervous  effort  and  the  intensity  of  the  processes  which 
call  forth  the  contractions  progressively  increase.  By  a  method  especially 
adapted  to  the  purpose,  it  may  even  be  shown  that  the  nervous  mechanism 
is  being  greatly  strained  before  there  is  any  sign  of  fatigue  in  the  external 
work  done.  This,  as  Treves  remarks,  would  explain  the  fact  that  athletes 
not  infrequently  are  attacked  by  severe  neurasthenic  pains. 

An  increase  in  the  output  of  COj  and  in  the  consumption  of  Oj  is  another 
characteristic  of  fatigued  muscle ;  that  is,  the  utilization  of  energy  becomes  more 
and  more  unfavorable  with  the  progress  of  fatigue. 

What  has  been  said  here  concerning  fatigue  and  recovery  applies  especially 
to  the  skeletal  muscles.  Other  muscles  fatigue  much  more  slowly  and  require 
a  much  shorter  time  of  recovery  in  order  to  remain  permanently  in  functional 
condition.  The  best  example  of  this  is  the  heart,  which  throughout  life  works 
uninterruptedly  with  rest  periods  of  only  about  0.4  second.  That  the  smooth 
muscles  also  are  capable  of  long-continued  work  is  shown  by  the  tonus  which 
they  maintain  in  the  arterial  walls. 

In  view  of  the  facts  presented  here  it  becomes  a  matter  of  interest  to 
inquire  under  what  circumstances  the  greatest  amount  of  muscular  work  can 
be  performed.  This  question  cannot  be  answered  fully  at  present,  but  we  have 
some  facts  bearing  on  the  subject  which  are  of  considerable  interest.  When 
one  does  the  same  amount  of  external  work  in  two  sets  of  experiments  which 
differ  only  in  the  circumstance  that  the  load  and  the  distance  through  which 
it  is  lifted  vary  in  reverse  order  (e.  g.,  20  kg.  X  0.3  m.  and  30  kg.  X  0.2  m.) 
it  is  found  that  the  fatigue  comes  on  much  more  rapidly  with  the  heavier  load 
(Stupin).  The  conclusion  is  that  the  size  of  the  load  and  not  the  absolute 
amount  of  muscular  work  done  determines  how  long  the  movement  can  be 
continued.  But  if  the  load  is  too  small  the  muscle  evidently  cannot  accom- 
plish much  work.  We  may  say,  therefore,  in  general  that  the  greatest  quantity 
of  work  can  be  done  when  the  load  is  of  medium  size. 

This  medium  load  may  be  found  (Treves)  by  choosing  a  weight  with  which 
a  person  while  perfectly  fresh  can  do  the  greatest  absolute  amount  of  work  and 
observing  the  record  until  the  contractions  exhibit  evidence  of  fatigue.  If  now 
the  weight  be  diminished  so  that  the  contractions  of  the  same  extent  can  con- 
tinue, and  so  on,  a  weight  will  finally  be  found  with  which  the  person  can 
continue  the  work  at  the  same  rhythm  indefinitely. 


SMOOTH  MUSCLES 


447 


The  following  table,  compiled  by  Blix,  contains  some  data  on  the  maximal 
muscular  capacity  of  man  at  different  kinds  of  work : 


Kind  of  Work. 

Time. 

Kg.  m.  per  second. 

Observer. 

Climbing  mountain  and  stairs. . . 
Turning  crank 

8  hours 
U  hours 
15  minutes 

10.5 
12.5 
17.0 
19.5 

27.7 

101.2 

95.4 

Weissbach 
Sjostrom 

(1            if 

5  minutes 
H  hours 

(( 

i(            (( 

» 

Climbing  stairs  without  load. . . . 
Climbing  stairs  with  load 

4  seconds 
4.5  seconds 

Blix 

It  is  evident  that  the  capacity  for  work  calculated  per  second  is  greater,  the 
shorter  the  total  time  occupied.  The  highest  record  of  endurance  yet  made  was 
observed  in  a  six-day  bicycle  contest  in  Kew  York.  According  to  Atwater's  cal- 
culation the  victor  performed  during  his  first  day  of  twenty-three  hours  and 
ten  minutes  an  average  of  25  kg.  m.  per  second,  and  in  the  whole  time,  one 
hundred  and  eight  hours  and  forty-four  minutes,  an  average  of  20.2  kg.  m.  per 
second. 

§  7.    RIGOR   MORTIS 

A  muscle  cut  out  of  the  body  or  excluded  from  the  circulation  passes 
sooner  or  later  (ten  minutes  to  several  hours)  into  a  rigid  condition  known 
as  the  death  stiffening  or  rigor  mortis.  It  is  now  shorter,  thicker  and  firmer, 
turbid,  opaque  and  less  extensible;  its  reaction  is  acid,  probably  owing  to  the 
transformation  of  a  portion  of  the  diphosphates  into  monophosphates  brought 
about  by  the  lactic  acid  formed. 

Rigor  of  muscle  is  produced  also  by  warming  to  48°-50°  C,  by  the  effects 
of  distilled  water,  by  acids  and  by  various  other  substances.  It  appears  more 
readily  after  heavy  muscular  work  than  otherwise,  but  on  the  other  hand  appears 
later  if  the  muscle  has  been  paralyzed  by  section  of  its  nerve.  Rigor  mortis  is 
the  cause  of  the  rigidity  of  the  body  after  death.  Under  certain  circumstances, 
which  have  not  yet  been  successfully  imitated,  the  stiflFening  comes  on  immedi- 
ately after  death,  so  that  the  body  becomes  fixed  in  the  position  it  had  at  the 
instant  of  death. 

Rigor  is  regarded  by  most  authors  as  coagulation  of  the  muscle  proteids. 
But  the  processes  taking  place  in  rigor  are  only  partially  explained  in  this 
way,  for  we  do  not  even  know  definitely  how  the  proteids  obtainable  from 
muscle  plasma  occur  in  the  living  muscle.  Besides,  the  phenomena  of  coagu- 
lation in  a  muscle  extract,  and  the  rigidity  brought  about  artificially  by  dif- 
ferent reagents,  present  several  points  of  difference  from  the  natural  death 
stiffeninsr. 


§8.    SMOOTH   MUSCLES 

The  most  satisfactory  smooth  muscles  for  study  are  those  whose  fibers  run 
parallel,  like  the  retractor  penis  of  the  dog  and  the  circular  muscles  in  the  stom- 
ach of  the  frog.  The  extensibility  of  such  muscles  is  relatively  great  and  the 
elastic  after-effect  is  very  considerable.    A  small  weight  acting  for  a  long  time 


448  THE  FUNCTIONS  OF  CROSS -STRIATED  MUSCLES 

will  produce  the  same  amount  of  extension  as  a  large  weight  acting  for  a  short 
time.  When  a  muscle  has  been  extended  greatly,  its  original  length  is  recovered 
by  a  single  contraction  and  can  be  maintained  for  some  time  if  several  contrac- 
tions follow  one  another.  The  activity  of  smooth  muscles,  therefore,  is  intimately 
related  to  their  elastic  properties  (P.  Sehultz). 

Smooth  muscles  cut  out  of  the  body  immediately  fall  into  a  tonic  state  of 
contraction,  and  exhibit  in  addition  spontaneous  rhythmical  contractions.  These 
seem  to  be  of  purely  muscular  origin,  for  they  appear  in  the  rectractor  penis 
which  has  no  ganglia,  and  have  been  observed  as  much  as  twenty-four  hours  after 
the  removal  of  the  muscle  from  the  body  (Sertoli).  They  continue  for  an  equal 
length  of  time  in  the  exsected  frog's  stomach  (Woodsworth).  In  resting  prepa- 
rations they  can  be  induced  by  a  single  mechanical  stimulus,  and  also  by  appli- 
cation of  a  constant  current  (Winkler). 

A  simple  contraction  of  a  smooth  muscle  runs  a  very  different  course  from 
that  of  a  skeletal  muscle.  The  latent  period  is  very  long :  in  the  musculature 
of  the  frog's  stomach  one  to  ten  seconds,  in  the  retractor  penis  0.8  second,  in  the 
urinary  bladder  of  the  cat  0.25  second,  and  in  the  smooth  muscles  of  the  nicti- 
tating membrane,  after  stimulation  of  the  nerve,  0.3-0.5  second.  With  artificial 
stimulation  of  the  vasomotor  nerve  we  get  about  the  same  value — 0.3-0.5  sec- 
ond— for  the  latent  period  of  the  vascular  muscles.  The  contraction  reaches  its 
summit  very  slowly — in  the  frog's  stomach  fifteen  to  twenty  seconds,  and  then 
falls  still  more  slowly,  sixty  to  eighty  seconds.  With  the  same  muscle  the 
amount  of  shortening  in  a  single  contraction  is  forty-five  per  cent  of  its  orig- 
inal length,  in  tetanus  fifty-nine  per  cent. 

Summation  phenomena  may  be  obtained  if  the  stimuli  follow  one  another 
with  sufficient  rapidity;  but  they  must  not  be  identified  with  corresponding 
processes  in  skeletal  muscles.  Here  instead  of  a  simultaneous  contraction  of 
all  of  the  muscular  elements  becoming  stronger  and  stronger,  we  have  to  do 
rather  with  repeated  contractions  of  the  different  cells  in  varying  sequence 
(Zilwa,  Sehultz). 

Finally,  inhibition  of  tonic  contractions  can  be  demonstrated  on  smooth 
muscles.  The  tonus  of  the  retractor  penis  can  be  intercepted  by  means  of  the 
constant  current  (Sertoli),  and  corresponding  phenomena  have  been  obtained 
in  the  frog's  stomach.  Furthermore,  we  know  that  the  smooth  musculature  of 
the  blood  vessels  and  of  the  intestinal  wall  are  under  the  influence  of  inhibi- 
tory nerves. 


SECOND    SECTION" 

RECIPROCAL  RELATIONS  BETWEEN   THE   MUSCLES  AND 
OTHER   ORGANS   OF   THE   BODY 

In  the  performance  of  their  functions  the  muscles  influence,  and  in  many 
ways  are  influenced  by,  the  other  organs  of  the  body.  A  muscle  degenerates 
if  its  connection  with  the  central  nervous  system  be  interrupted,  and  within 
a  relatively  short  time  it  becomes  transformed  into  a  mass  of  connective  tissue. 
The  same  thing  happens  if  the  motor  cells  in  the  anterior  horn  of  the  spinal 
cord  be  destroyed  by  a  lesion.  The  cause  of  degeneration  under  these  circum- 
stances is  not  that  the  muscle  is  inactive.  Inactivity,  as  it  appears,  for  ex- 
ample, as  the  result  of  brain  disease,  involves  a  reduction  of  the  muscle 
substance,  an   atrophy,   but  the  muscle  does  not  degenerate;   it   retains  its 


THE  MUSCLES  AND  OTHER  ORGANS  OF  THE  BODY  449 

characteristic  properties.  On  the  other  hand,  a  muscle  increases  in  mass 
by  work,  and  there  is,  generally  speaking,  no  other  means  of  strengthening 
a  muscle.  We  see  therefore  that  a  muscle  receives  impulses  from  the  central 
nervous  system  which  are  of  the  greatest  possible  importance  for  the  mainte- 
nance of  its  substance  and  of  its  natural  properties  (see  Chapter  XXII). 

A  resting  muscle  has  a  relatively  small  supply  of  blood,  but  during  work 
the  quantity  increases  considerably,  owing  to  the  widening  of  the  blood  stream 
produced  by  the  action  of  the  vasodilator  nerves  (cf.  page  240).  Besides, 
we  find  as  an  accompaniment  of  muscular  work  an  acceleration  of  the  heart 
beat  (cf.  page  197)  and,  as  a  rule,  an  increase  of  arterial  blood  pressure.  The 
latter  is  caused  primarily  by  a  contraction  of  blood  vessels  in  other  organs, 
especially  those  of  the  splanchnic  region,  which  more  than  compensates  for 
the  dilation  in  the  muscles.  The  increase  in  amount  of  blood  expelled  from 
the  heart  in  a  unit  of  time  likewise  contributes  to  the  same  end. 

It  is  impossible,  on  the  basis  of  observations  thus  far  recorded,  to  make 
a  closer  analysis  of  the  mechanisms  concerned. 

Vasodilatation  in  the  muscles  accompanying  work  is  for  the  purpose  of 
supplying  them  with  an  increased  amount  of  oxygen  and  combustible  mate- 
rials ;  for  a  working  muscle  uses  large  quantities  of  oxygen  and  produces  large 
quantities  of  carbon  dioxide.  In  order  to  supply  the  necessary  quantity  of 
oxygen  and  to  remove  the  great  excess  of  carbon  dioxide,  the  respiration  must 
of  course  be  augmented,  and  this  should  be  mentioned  as  one  of  the  accom- 
paniments of  muscular  work  (cf.  page  332). 

Muscular  work  evidently  calls  for  an  increased  supply  of  food  in  order  to 
meet  the  demands  on  the  body,  and  increased  appetite  as  the  result  of  exercise 
is  an  experience  with  which  everyone  is  familiar. 

Whatever  the  effect  of  work  on  the  digestive  process  may  be,  it  appears  from 
the  experiments  of  Rosenberg  on  dogs  and  of  Wait  on  men  that  the  absorption 
of  food  is  equally  good  at  rest  and  at  moderately  vigorous  work. 

With  all  voluntary  muscular  movements  work  is  being  done  also  in  the 
central  nervous  system.  When  we  learn  a  particular  muscular  movement,  of 
whatever  kind,  the  brain  is  always  active.  The  newborn  child  can  move  all 
of  his  muscles,  but  lacks  the  power  to  coordinate  them  into  purposeful  acts. 
This  can  only  be  acquired  by  the  gradual  formation  of  central  connections 
between  the  different  nerve  paths.  We  know,  for  example,  that  many  muscles 
are  necessary  to  keep  the  body  in  an  upright  position,  but  the  cooperation  of 
these  different  muscles  is  perfected  only  b}^  long-continued  practice.  So  it  is 
with  all  of  the  other  muscular  movements  which  we  make. 

Unless  we  make  a  special  study  of  the  subject  we  are  not  aware  of  the 
position  or  arrangement  of  our  muscles.  We  cannot  therefore  merely  will 
that  one  muscle  or  the  other  shall  become  active  but  can  only  resolve  upon 
carrying  out  a  certain  movement.  For  example,  if  we  bend  the  arm,  the 
movement  takes  place  chiefly  by  the  contraction  of  the  biceps  muscle;  but 
the  act  of  volition,  which  we  are  conscious  of,  is  not  a  direct  impulse  to  this 
particular  muscle,  but  a  command  that  the  arm  be  moved.  In  short  we  carry 
out  our  bodily  movements  with  reference  to  the  result,  without  troubling 
ourselves  about  how  the  result  is  attained. 


450  THE  FUNCTIONS  OF  CROSS-STRIATED  MUSCLES 

In  practicing  any  particular  movement  therefore  we  are  striving  to  bring 
about  in  our  central  nervous  system  such  a  combination  of  physiological  fac- 
tors as  will  accomplish  the  desired  effect.  The  more  complicated  a  movement 
is,  the  more  difficult  it  is  of  course  to  discover  this  combination.  But  after 
the  connection  has  once  been  established,  the  movement  can  be  carried  out 
with  the  greatest  ease  in  almost  a  purely  mechanical  manner. 

Here  comes  in  another  peculiarity.  When  we  practice  a  particular  move- 
ment for  the  first  time,  we  use  a  number  of  muscles  which  have  no  impor- 
tance whatever  for  the  movement  intended,  but  rather  interfere  with  it,  since 
they  fatigue  the  body  to  no  purpose.  The  further  the  practice  is  carried, 
however,  the  more  we  learn  to  suppress  these  useless  movements;  and  at  the 
same  time  the  respiration  and  circulation  become  more  and  more  exactly 
adapted  to  the  actual  needs.  It  has  been  observed  that  the  increase  in  com- 
bustion from  a  given  additional  amount  of  work  becomes  steadily  less  (down 
to  a  certain  limit),  as  practice  continues. 

Eeferences. — W.  Biedermann,  "  Electro-Physiology,"  translated  by  Welby, 
New  York  and  London,  1898. — R.  Du  Bois-Reymond,  "  Spezielle  Muskelphysiolo- 
gie  und  Bewegungslehre,"  Berlin,  1903. — A.  Fick,  "  Mechanische  Arbeit  und 
Warmeentwickelung  bei  der  Muskeltatigkeit,"  Leipzig,  1882. — A.  Mosso,  "  Fa- 
tigue," English  edition  by  Margaret  and  W.  B.  Drummond,  New  York  and 
London,  1904. 


CHAPTER    XYI 

ON    SENSATIONS    IN    GENERAL 

FIRST    SECTION 

QUALITATIVE   RELATIONS   BETWEEN   STIMULUS 
AND   SENSATION 

We  obtain  our  knowledge  of  the  outside  world  entirely  through  our  senses. 
The  sense  of  touch,  taken  in  its  widest  acceptation,  teaches  us  to  recognize 
the  nature  of  those  objects  about  us  which  come  into  actual  contact  with  our 
bodies,  and  gives  us  information  concerning  the  temperature  of  these  and 
more  distant  objects. 

By  the  sense  of  taste  w^e  can  distinguish  certain  properties  of  such  sub- 
stances as  can  be  placed  in  the  mouth. 

The  sense  of  smell  enables  us  to  judge  something  of  the  nature  of  the 
atmosphere.  For  certain  animals  this  sense  is  of  very  great  importance,  in 
that  it  furnishes  the  possessor  with  knowledge  of  prey  or  of  enemies  even 
at  a  considerable  distance. 

By  the  sense  of  hearing  we  are  made  aware  of  those  vil)rations  of  solid, 
fluid  or  gaseous  bodies,  which  strike  the  ear.  Through  this  sense  we  obtain 
knowledge  not  only  of  what  goes  on  immediately  about  us,  but  also  of  what 
takes  place  at  a  distance. 

The  sense  of  sight  reaches  out  to  a  still  greater  distance.  By  its  help 
we  can  penetrate  to  the  farthest  point  from  which  light  rays  can  reach  the  eye. 

But  our  sensations  ^  do  not  all  relate  to  the  outside  world.  From  all  the 
organs  of  the  body  information  of  their  condition  and  of  the  processes  taking 
place  within  them  is  all  the  time  being  brought  by  appropriate  nerves  to  the 
central  nervous  system.  Some  of  these  messages  never  rise  into  consciousness, 
but  have  a  controlling  influence  on  the  functions  of  the  body  through  the 
lower  nerve  centers.     Others  rise  to  the  plane  of  consciousness  and  eventuate 

*  By  sensation  we  mean  the  simplest  possible  state  of  consciousness,  one  which  cannot 
be  analyzed  into  simpler  components.  But  a  sensation  corresponding  to  this  definition 
probaJ)Iy  never  exists,  for  psychological  analysis  has  demonstrated  that  even  the  simplest 
conscious  processes  are  really  composed  of  several  simple  sensations.  For  example,  the 
simple  sensation  of  sweetness  is  always  associated  with  the  feeling  that  we  have  something 
in  the  mouth;  the  sensation  of  a  color  likewise  is  complicated  by  its  projection  to  a  certain 
place  in  the  outside  world,  etc.  These  processes  in  consciousness  we  shall  designate  as 
ideas. 

451 


452  OX   SENSATIONS   IN   GENERAL 

in  sensations  which  are  more  or  less  present  to  the  mind.  Sensations  by  which 
we  have  knowledge  of  the  position  in  space  of  our  bodies  and  their  members, 
also  of  the  extent  of  their  movements  and  the  intensity  of  muscular  contrac- 
tions— in  short,  all  those  sensations  which  are  comprehended  as  belonging  to 
the  sense  of  motion  come  under  this  class.  The  sensations  from  other  internal 
organs  like  the  heart,  stomach,  intestines,  bladder,  etc.,  also  belong  here. 
The  latter  are  not  sharply  defined  unless  intensified  b}'^  some  special  cause; 
then  they  sometimes  become  very  painfully  conspicuous.  As  a  rule,  however, 
they  are  wholly  indefinite  and  contribute  in  consciousness  only  toward  the 
general  state  of  feeling,  which  not  only  varies  greatly  according  to  the  nature 
of  these  vague  sensations,  Init  may  very  profoundly  influence  our  wliole  being. 

One  of  the  most  significant  facts  in  connection  with  the  physiology  of 
sensation  is  that  our  conscious  sensations  do  not  arise  in  the  organs  to  which 
the  afferent  nerves  are  distributed  and  to  which  the  stimuli  are  applied.  The 
sensation  of  sight,  for  example,  is  not  in  the  eye,  the  sensation  of  sound  is 
not  in  the  ear,  etc.  The  peripheral  sense  organs  and  the  peripheral  endings 
of  afferent  nerves  in  general  are  for  the  sole  purpose  of  transferring  the  stimuli 
which  strike  them  to  the  appropriate  nerves.  The  nerves  transmit  the  excita- 
tions thus  aroused  to  the  central  organs  of  the  nervous  system  and  the  con- 
scious sensation  arises  only  by  the  activity  occasioned  in  the  brain.  Different 
parts  of  the  brain  are  set  in  action  directly,  according  as  one  afferent  nerve  or 
another  is  excited  (cf.  Chapter  XXIII). 

How  can  a  material  change  in  the  hrain  give  rise  to  a  conscious  sensation  ? 
Philosophers  of  all  times  have  tried  to  answer  this  question.  Since  w^e  are 
discussing  it  here  only  from  the  standpoint  of  natural  science,  we  cannot 
enter  into  the  philosophical  considerations.  It  is  likely,  indeed,  that  the 
question  can  never  be  answered  from  the  standpoint  of  natural  science  alone, 
for,  as  Du  Bois-Reymond  especially  has  pointed  out,  the  question  is  at  bottom 
a  metaphysical  one. 

If  our  knowledge  of  nature  were  so  far  advanced  that  all  the  movements  in 
the  world  could  be  resolved  into  the  movements  of  atoms,  and  our  explanation 
of  nature  could  thus  be  reduced  to  the  mechanics  of  atoms,  we  would  of  course 
be  in  a  position  to  describe  the  material  changes  taking'  place  in  the  brain  in 
definite  psychical  processes  very  exactly.  Satisfactory  as  this  knowledge  would 
be,  it  would  nevertheless  be  unable  to  give  us  any  conclusive  information  con- 
cerning the  relation  of  such  movements  to  such  ultimate  facts  as :  "I  feel  com- 
fortable," "  I  feel  pain,"  and  the  proposition  immediately  dedueible  therefrom : 
"  I  think,  therefore  I  am."  That  is  to  say,  it  is  impossible  to  conceive  scien- 
tifically how  consciousness  and  thought  can  arise  out  of  the  interplay  of  atoms. 
Indeed  we  could  imagine  a  world  similar  to  our  own,  in  which  everything  would 
take  place  exactly  as  in  our  world,  but  where  there  were  no  consciousness  and 
no  thought;  and  yet  the  mechanics  of  atoms  would  be  just  as  valid  for  such  a 
world  as  for  our  own.' 

In  what  sense  do  our  sensations  produced  hy  external  stimuli  correspond 
to  reality?    Philosophy  and  natural  science  attack  this  problem  from  opposite 

'  Cf.  Du  Bois-Reymond,  "  Limits  of  Our  Knowledge  of  Nature,"  translated  by  J.  Fitz- 
gerald in  Popular  Science  Monthly,  May,  1874. 


RELATION'S  BETWEEN   STIMULUS  AND  SENSATION  453 

sides  and  yet  the  two  have  the  same  task  in  common.^  The  former,  which 
considers  the  psychical  side,  seeks  to  eliminate  from  the  cognitive  and  per- 
ceptive processes  everything  which  proceeds  from  the  effects  of  the  objective 
world,  in  order  to  obtain  in  its  purity  that  which  is  proper  to  the  mind  itself. 
Natural  science  on  the  contrary  seeks  to  remove  the  relative  and  the  formal 
elements  of  thought,  definition,  notation,  forms,  hypothesis,  etc.,  in  order  to 
secure  what  belongs  to  the  world  of  actuality,  the  laws  of  which  it  seeks  to 
know.  In  order  to  give  a  theoretical  explanation  of  sensations  from  the  scien- 
tific standpoint  we  must  bear  in  mind  the  following  propositions. 

1.  There  are  two  different  degrees  of  distinction  among  sensations.  The 
one  most  essential  is  the  distinction  between  those  belonging  to  the  different 
senses,  as  between  the  sensations  of  blue,  sweet,  warm,  and  loud.  This  differ- 
ence is  designated  as  the  difference  in  inodaJitij  of  sensation,  and  is  so  complete 
that  it  precludes  any  transition  from  one  to  the  other  or  any  relation  of 
greater  or  less  similarity  between  them.  For  example,  one  cannot  say  whether 
sweet  is  more  like  blue  or  red.  The  second  difference,  which  Helmholtz  limits 
to  a  difference  in  quality  between  sensations  belonging  to  the  same  sense,  is 
less  exclusive.  Within  the  same  sense  transition  and  comparison  are  possible. 
From  blue  we  can  pass  through  violet  and  carmine  red  to  scarlet  red  and  can 
say,  e.  g.,  that  yellow  is  more  like  orange  than  like  blue. 

We  distinguish  the  following  modalities :  pressure  and  touch ;  heat  and  cold ; 
taste;  smell;  hearing;  and  sight.     (With  regard  to  pain  cf.  Chapter  XVII,  §4.) 

2.  Experiment  has  shown  that  the  profound  difference  between  the  senses 
does  not  depend  in  any  wise  upon  the  kind  of  external  stimuli  by  which  the 
sensations  are  aroused,  but  is  determined  solely  hy  the  hind  of  sensory  nerve 
affected. 

For  illustration,  physics  considers  light  as  extremely  rapid  vibrations  of  a 
hypothetical,  imponderable  medium,  the  ether,  which  is  distributed  throughout 
all  space.  When  these  vibrations  of  the  ether  strike  the  retina,  the  latter  is 
excited  and  in  its  turn  produces  through  the  optic  nerve  an  excitation  in  the 
brain,  which  gives  rise  in  consciousness  to  a  sensation  of  light.  But  this  sen- 
sation of  light  has  not  the  least  resemblance  to  the  vibrations  which  constitute 
the  objective  phenomenon  of  light.  This  itself  should  be  fairly  convincing  evi- 
dence that  the  sensation  cannot  agree  in  kind  with  its  external  cause.  Con- 
clusive proof  is  found  in  considerations  such  as  the  following:  If  the  eyeball  be 
pressed  upon,  we  receive  even  in  pitch  darkness  a  sensation  which  is  characterized 
by  a  brilliant  play  of  colors.  A  blow  upon  the  eye  produces  a  flash  of  lig'ht. 
Here  we  have  a  perfectly  typical  sensation,  and  yet  no  light  at  all  has  reached 
the  eye.  The  sensation  is  unquestionably  due  to  an  excitation  of  the  optic 
nerve  produced  by  the  mechanical  pressure  on  the  eyeball.  The  same  thing  is 
experienced  when  an  electric  current  is  conducted  through  the  eye;  we  get  a 
sensation  of  light,  even  though  no  objective  light  may  be  present. 

3.  Since  therefore  sensations  of  exactly  the  same  nature  are  aroused  by 
three  wholly  different  kinds  of  stimuli — light,  mechanical  jiressure.  and  dec- 


»The  following  discussion  is  essentially  a  repetition  of  the  views  of  Helmholtz  as  set 
forth  in  "  Die  Tatsachen  in  der  Wahrnehmungc,"  Berlin,  1879. 

28 


454  OX  SENSATIONS   IN   GENERAL 

tricity — it  is  evident  that  the  character  of  the  sensation  cannot  agree  in  any- 
way with  the  external  cause  by  which  it  is  produced. 

This  conclusion  is  confirmed  by  experiments  demonstrating  that  one  and 
the  same  external  cause  can  produce  entirely  different  sensations,  by  acting  upon 
different  sense  organs.  Thus,  pressure  on  the  skin  gives  a  sensation  of  pressure 
or  of  contact;  pressure  on  the  eyeball  a  sensation  of  light.  When  illuminating 
rays  strike  the  eye,  we  get  a  sensation  of  light ;  when  the  same  rays,  sufficiently 
strong,  strike  the  skin,  they  produce  a  sensation  of  warmth.  The  sensation  which 
is  aroused  by  an  electric  current  applied  to  the  eye  has  an  entirely  different 
character  from  that  which  one  gets  when  the  current  is  applied  to  the  skin. 

4.  Just  as  sensations  have  their  origin  in  the  brain,  so  also  do  they  receive 
their  specific  character  from  the  cerebral  background.  A  sensation  of  light, 
however  produced,  is,  in  the  last  analysis,  conditioned  by  a  material  change 
in  the  brain.  It  follows  that  such  sensations  may  arise,  when  neither  the  eye 
nor  the  optic  nerve  is  stimulated,  if  only  the  seat  of  sensation  in  the  brain  is 
excited  in  some  way,  as  by  a  disturbance  in  the  blood  supply,  etc. 

Herein  lies  the  cause  of  visual  hallucinations.  For  our  subjective  experi- 
ence it  is  a  matter  of  indifference  how  this  particular  place  in  the  brain  is  roused 
to  activity,  whether  mediately  by  the  optic  nerve  or  immediately  by  some  process 
in  the  brain  itself.  The  sensation  of  light  in  the  latter  case  must  be  just  as 
real  for  the  person  experiencing  it  as  a  sensation  produced  in  the  normal  manner 
by  the  action  of  light  on  the  retina. 

What  we  have  said  concerning  the  sensations  of  sight,  will  of  course  apply 
to  those  from  other  senses. 

5.  Although  all  our  sensations  inclusive  of  the  organic  sensations  have  their 
origin  in  the  brain,  they  are  not  consciously  referred  to  the  brain,  but  are 
projected  outward  either  to  other  parts  of  the  body  or  to  the  surrounding 
space.  Thus  we  refer  the  sensations  of  touch  to  the  skin;  the  sensations  of 
taste  to  the  tongue;  those  of  smell  to  the  space  around  us,  to  the  nose,  or  to 
the  mouth ;  the  sensations  of  sound  commonly  to  the  surrounding  space,  in 
exceptional  cases  to  the  ear ;  sensation  of  sight  always  to  the  outer  world. 

The  information  concerning  the  general  condition  of  the  body  brought  to 
the  central  nervous  system,  is  likewise  projected  for  the  most  part  to  differ- 
ent organs.  This  occurs  most  definitely  in  the  case  of  pains  and  motor 
sensations;  but  other  organic  sensations  also  are  referred  to  peripheral 
organs — e,  g.,  the  sensation  of  thirst  to  the  throat,  the  sensation  of  hunger 
to  the  stomach,  et-c. 

Sensations  which  give  us  the  general  feeling  of  bodily  tone,  or  of  good 
spirits  are  not  projected  to  any  definite  organ.  Xeither  are  they  referred  to 
the  brain ;  they  represent  rather  a  general  peculiar  condition  permeating  the 
whole  body,  which  is  present  to  consciousness  as  depression,  vigor,  indisposi- 
tion, comfort,  etc. 

From  all  this  it  follows  that  in  so  far  as  the  nature  of  our  sensation  gives 
us  any  information  of  the  peculiar  external  agency  by  which  it  is  excited,  it 
constitutes  a  sign  rather  than  a  picture  of  that  agency.  A  picture  demands 
some  kind  of  likeness  to  the  thing  pictured,  but  a  sign  need  bear  no  resem- 
blance to  the  thing  signified.     The  onlv  necessary  relation  between  the  two 


RELATIONS  BETWEEN   STIMULUS  AND  SENSATION  455 

is  that  a  given  object,  present  under  the  same  circumstances,  shall  always 
produce  the  same  sign,  and  that  unlike  signs  shall  always  correspond  to 
unlike  agencies. 

To  the  popular  understanding  which  assumes  the  complete  truth  of  the  pic- 
tures represented  to  us  by  our  senses,  this  remnant  of  similarity  may  appear 
very  meager.  But  in  reality  it  is  not  so;  for  services  of  the  greatest  possible 
moment  to  us,  such  as  the  portrayal  of  uniformity  in  the  processes  of  nature, 
can  be  performed  for  us  by  mere  signs.  Every  natural  law  declares  that  condi- 
tions which  are  the  same  in  a  certain  respect  are  always  followed  by  results 
which  are  the  same  in  a  certain  other  respect.  Since  likeness  in  our  world  of 
sense  is  signified  to  us  by  like  signs,  the  natural  sequence  of  cause  and  effect 
will  have  its  counterpart  of  a  perfectly  uniform  sequence  in  the  realm  of  sense. 
If  therefore  even  the  qualities  of  our  sensations  are  nothing  but  signs  which  are 
entirely  dependent  in  kind  upon  our  nervous  organization,  they  are  not  to  be 
discarded  as  mere  worthless  counterfeits.  They  are  signs  of  something,  whether 
of  something  merely  existing,  or  something  occurring,  and  what  is  more  im- 
portant, they  are  able  to  portray  to  us  the  law  of  occurrence. 

Physiology,  therefore,  acknowledges  that  the  nature  of  sensation  is,  in  the 
last  analysis,  subjective.  In  essence  it  is  transcendental.  But  since  experi- 
ence proves  that  excitation  of  different  afferent  nerves  produces  different  sen- 
sations, since  we  know  further  that  sensation  has  its  correlative  physical 
process  not  in  the  excitation  of  the  peripheral  sense  organ  or  that  of  the 
afferent  nerves,  but  in  the  activity  of  the  brain,  and  finally  since  investigation 
has  shown  that  different  afferent  nerves  terminate  in  different  fields  of  the 
cerebral  cortex,  which  in  their  turn  are  connected  with  other  parts  of  the 
brain,  it  follows  that  the  specific  character  of  a  sensation  is  determined  by 
the  part  of  the  brain  roused  to  action.  It  is  in  this'  sense  that  we  shall  under- 
stand the  doctrine  of  specific  sensations,  as  used  in  this  book. 


SECOND    SECTION 

THE  QUANTITATIVE   RELATIONS  BETWEEN  STIMULUS 

AND   SENSATION 

In  order  that  an  external  stimulus  may  produce  a  sensation,  it  must  exceed 
a  certain  lower  limit  of  strength,  which  is  called,  after  Herbart,  the  threshold 
value  of  the  stimulus.^  If  the  stimulus  be  increased  above  this  limit,  the 
sensation  increases  also;  but  while  the  strength  of  the  external  stimulus  may 
be  increased  indefinitely  the  intensity  of  the  sensation  never  exceeds  a  certain 
^pper  limit.  This  maximum  sensation  follows  a  relatively  weak  stimulus 
and  a  further  rise  not  only  does  not  produce  a  quantitative  increase  in  the 
sensation  but  on  the  contrary  and  in  ascending  degree  produces  fatigue  and 
exhaustion  of  the  peripheral  sense  organ. 

'  The  threshold  value  of  the  stimulus  for  the  different  modalities  of  sensation  varies 
greatly  according  to  circumstances.  In  absolute  terms  it  may  be  given  as  follows :  for  the 
sensation  of  pressure  Tiyr'innjth  of  an  erg;  for  sensations  of  sound  -nroocoriroth  of  an  erg;  for 
sensations  of  sight  (green)  rffrrrriinnnjth  of  an  erg. 


456  ON   SENSATIONS   IN   GENERAL 

Between  the  minimum  and  the  maximum,  as  thus  defined,  variations  in 
the  strength  of  the  stimulus  will  produce  variations  in  the  intensity  of  the 
sensation. 

§  1.    WEBER'S   LAW 

In  estimating  differences  in  the  intensity  of  sensations  we  meet  with  a 
peculiar  difficulty.  We  can  say  that  a  certain  sensation  is  stronger  or  weaker 
than  another  of  the  same  kind,  hut  we  cannot  say  hoiv  much  stronger  or 
weaker  it  is;  for  every  sensation  constitutes  a  whole  in  itself  and  cannot 
be  represented  as  the  sum  of  several  individual  sensations.  If,  for  example, 
a  white  surface  is  illuminated  at  one  time  by  1  candle  power  and  at  another 
by  n  candle  powers,  we  can  say  perhaps  that  the  sensation  in  the  second  case  is 
stronger  than  in  the  first ;  but  we  cannot  tell  how  much  stronger  it  is. 

The  relation  between  the  strength  of  the  stimulus  and  the  intensity  of  the 
sensation  is  not  to  be  determined  by  merely  setting  arbitrary  stimuli  over 
against  the  sensations  evoked  by  them.  We  can  better  approach  the  problem 
by  inquiring  Jiow  much  a  given  stimulus  must  be  changed  to  produce  a  per- 
ceptible change  in  the  intensity  of  the  sensation.  E.  H.  Weber  who  made  the 
first  observations  along  this  line  (1831)  laid  down  the  following  law  known 
by  his  name:  The  increase  in  the  stimulus  necessary  to  produce  a  perceptible 
change  in  a  given  sensation  must  always  bear  the  same  relation  to  the  size 
of  the  initial  stimulus. 

Thus,  if  to  a  weight  of  1  unit  a  person  must  add  a  weight  of  sVh  in  order 
to  make  the  second  load  perceptibly  heavier  in  his  own  subjective  appreciation 
of  weight  than  the  first,  then,  according  to  Weber's  law,  with  an  initial  load 
of  10  the  superadded  weight  must  be  ^|-ths  to  enable  him  to  detect  the  dif- 
ference. 

By  placing  weights  on  both  hands  at  the  same  time,  the  hands  being  sup- 
ported on  the  table,  Weber  found  that  the  "  threshold  difference  "  was  one-third 
of  the  initial  stimulus,  but  when  the  same  hand  was  successively  weighted  it 
was  only  one-fourteenth  to  one-thirtieth  of  the  initial  stimulus.  In  estimating 
weights  by  the  muscular  sense — i.  e.,  by  lifting  them — the  threshold  difference 
goes  down  to  one-fifteenth  to  one-twentieth  when  both  hands  are  used  simul- 
taneously, and  to  one-fortieth  when  the  weights  are  lifted  successively  with  the 
same  hand. 

According  to  experiments  by  Merkel  with  fairly  pure  pressure  stimuli,  the 
threshold  difference  for  50,  100,  200,  500  and  1.000  g.  was  yf^,  y^,  yir^, 
-^^ ,  and  ^^  respectively.  For  weights  above  and  below  these  values  it  is 
not  so  constant. 

Another  illustration  of  the  law  is  the  following :  When  one  looks  at  a  draw- 
ing with  shadings  tmder  different  degrees  of  illumination,  the  fine  gradations 
of  brightness  come  out  with  about  the  same  clearness.  For  example,  if  he  look 
at  the  drawing  first  with  the  naked  eye,  then  through  a  gray  glass  which 
diminishes  the  intensity  of  the  light  rays  from  different  parts  of  the  drawing  to 
the  same  extent  proportionally,  the  different  parts  of  it  are  still  seen  in  their 
proper  relations  as  regards  light  and  shade.  This  would  not  be  true  if  the 
same  proportional  decrease  in  the  intensity  of  the  stimuli  coming  from  dif- 


WEBER'S  LAW  457 

ferent  parts  of  the  drawing  produced  proportionally  different  variations  in 
the  resulting  sensations.  It  is  owing  to  this  same  peculiarity  of  our  organ 
of  vision  that  we  do  not  see  the  stars  in  daylight.  The  amount  of  light  which 
the  stars  contribute  to  the  illumination  of  the  heavens  is  too  slight  in  propor- 
tion to  the  total  illumination  for  us  to  detect  them. 

^ilerkel  has  shown  that  the  same  law  holds  for  the  sense  of  hearing,  and 
Camerer  and  Kepler  for  the  sense  of  taste. 

Weber's  law  is  true  within  fairly  wide  limits  for  all  the  senses,  but  for 
very  high  or  very  low  degrees  of  intensity  certain  variations  come  in.  How- 
ever, since  the  stimuli  of  medium  intensity  are  the  ones  that  occur  most  com- 
monly in  our  everyday  life,  we  may  say  that  in  general  our  estimates  of 
differences  in  intensity  follow  this  law. 

In  attempting  a  theoretical  explanation  of  Weber's  law  it  must  not  be  for- 
gotten that  the  conscious  sensation  aroused  bj-  an  external  stimulus  occurs  only 
when  the  excitation  begun  at  the  sense  organ  reaches  the  cerebral  cortex.  It  is 
possible  that  in  the  purely  physiological  events  taking  i)lace  in  the  peripheral 
sense  organ,  in  the  nerves  and  in  the  central  nervous  system  a  certain  increase 
in  the  stimulus  produces  the  same  absolute  increase  in  the  excitation  aroused. 
If  so,  the  relationship  expressed  in  Weber's  law  would  be  due  to  something  which 
is  peculiar  to  the  process  of  arousing  a  conscious  sensation  from  a  physiological 
excitation.  But  it  is  also  conceivable  that  the  peripheral  sense  organ,  nerves, 
etc.,  themselves  react  in  accordance  with  Weber's  law,  and  that  the  law  is  there- 
fore a  purely  physiological  one.  The  latter  alternative  is  probably  correct,  for 
approximately  the  same  relationship  of  excitation  to  intensity  of  stimulus  has 
been  observed  in  many  purely  physiological  processes.' 

References. — W.  James,  "Principles  of  Psychology,"  Xew  York,  1905. — 
0.  Kiilpe,  "  Outlines  of  Psychology,"  translated  by  E.  B.  Titchner,  New  York 
and  London,  1901. 

*  Fechner  sought  to  deduce  from  this  law  of  Weber  a  more  general  one.  known  as  the 
psychophysical  law.  By  giving  the  former  an  algebraic  expression  and  using  the  dif- 
ferential calculus  he  arrives  at  the  formula  E  =  C  log.  nat.  r.  (where  E  is  the  sensation,  C  a 
constant,  and  r  the  stimulus),  which  means  that  the  sensation  is  proportional  to  the  natural 
logarithm  of  the  stimulus.  So  many  objections  have  been  urged  against  this  formulation 
that  its  further  consideration  here  seems  unwarranted  by  its  importance  for  the  physiolog- 
ical side  of  the  questions  involved. — Ed. 


CHAPTER    XVII 

THE    SEXSORY    FUNCTIONS    OF    THE    SKIN 

Aside  from  serving  as  the  outer  covering  of  the  body  and  in  addition  to 
what  it  does  in  the  service  of  heat  regulation,  the  skin  has  very  important 
sensory  functions.  Notwithstanding  that  much  has  been  explained  by  work 
done  within  the  last  decade,  the  intimate  mechanism  of  these  functions  still 
appears  to  be  very  enigmatical.  We  shall  divide  them  into  three  different 
groups,  namely:  (1)  sensations  of  temperature,  (2)  sensations  of  pressure  and 
touch,  (3)  sensations  of  pain. 

§  1.    SENSATIONS   OF   TEMPERATURE 

Temperature  sensations  are  of  two  kinds,  cold  and  heat  sensations,  and 
both  are  probably  related  to  the  regulation  of  heat  in  our  bodies.  The  nerves 
which  mediate  these  sensations  produce  reflex  effects,  which  manifest  them- 
selves as  variations  in  the  intensity  of  combustion,  in  the  distribution  of 
blood,  and  in  the  activity  of  the  sweat  glands.  The  conscious  sensations  of 
temperature  inform  us  how  the  thickness  of  our  clothing  and  the  temperature 
of  our  rooms  need  to  be  changed  one  way  or  the  other,  although  it  must  be 
allowed  that  this  information  not  infrequently  leads  us  astray. 

Until  a  few  years  ago  it  was  generally  supposed  that  the  diametrically 
opposite  sensations  of  heat  and  cold  were  mediated  alike  by  all  parts  of  the 
skin  and  that  only  one  kind  of  nerve  fibers  was  concerned  in  both  sensations. 
Blix  and  Goldscheider  independently  of  each  other  (1883,  18S4)  demon- 
strated, however,  that  not  all  points  on  the  skin  are  capable  of  arousing  tem- 
perature sensations  of  both  kinds,  but  that  the  nerves  which  mediate  sensations 
of  heat  have  their  end  organs  at  different  points  from  those  which  mediate 
sensations  of  cold. 

This  proposition  is  proved  by  the  following  experiments.  A  metallic  tube 
drawn  out  to  a  fine  point  is  filled  with  water  of  the  desired  temperature.  When 
cold  water  is  used  and  the  tip  of  the  tube  is  applied  to  the  skin,  care  being  taken 
not  to  exert  pressure,  one  observes  that  the  point  can  only  be  felt  cold  at  certain 
spots,  while  at  others  it  produces  no  sensation  of  temperature  at  all.  If  the 
experiment  be  repeated,  using  this  time  warm  water  instead  of  cold,  we  find  that 
sensations  of  heat  can  be  received  only  from  certain  points. 

Marking  off  cold  spots  and  heat  spots  on  the  skin  with  different  f^olors,  we 
find  that  the  two  do  not  coincide,  although  it  must  be  said  that  a  perfectly  exact 
determination  of  their  relative  positions   is  very  difficult  or  quite  impossible, 
owing  to  the  conduction  of  heat  by  the  skin  (cf.  Fig.  182). 
458 


SENSATIONS  OF  TEMPERATURE  459 

The  presence  of  different  temperature  points  has  been  established  not  only 
by  use  of  the  appropriate  temperature  stimuli  but  also  by  mechanical,  electrical 
and  chemical  stimulation. 

The  sensation  which  is  produced  l)y  stimulation  of  a  single  temperature 
point  is  not  "  pointlike  " ;  instead,  one  experiences  a  sort  of  irradiation  of 
the  feeling,  so  that  the  sensation  is  more  extensive  than  the  temperature  point 
— i.  e.,  it  appears  to  be  disklike  and  at  the  same  time  to  have  depth.  It  is 
on  this  account  that  the  temperature  sensations  aroused  by  contact  with  warm 
and'  cold  objects  appear  to  be  perfectly  continuous,  giving  no  indication  of 
the  pointlike  arrangement  of  the  end  organs.  Then  we  are  inclined  also  to 
fill  up  unconsciously  all  the  gaps  in  our  special  sensations  (cf.  the  blind  spot 
in  the  eye,  Chapter  XXI). 

The  number  of  cold  spots  in  the  skin  of  an  adult  is  found  to  be  6-23  per 
square  centimeter  of  surface ;  the  number  of  warm  spots  0-3.    The  entire  surface 
of  the  body  would  contain,  therefore,  about  250,000  cold  spots,  and  about  30,000 
warm  spots.    In  a  child  the  temperature  points  appear  to 
stand  closer  together,  and  this  may  be  taken  to  mean  that 
the  child  is  born  with  his  complete  equipment  of  such 
points. 

In  order  to  obtain  a  more  accurate  idea  of  the  topogra- 
phy of  the  temperature  senses,  Goldscheider  has  stimulated 
different  portions  of  the  skin  with  the  ends  of  cold  and 
hot   rods   3-4  cm,   in  diameter.     One  cannot  obtain  the 


number  of  temperature  points  by  this  method,  but  can      Fig.  182. — Tlie  arrange- 
test  the  relative  sensitivity  of  different  regions  very  well.  ment    of    cold    spot.s 

Thus  if  there  be  no  temperature  points  in  a  certain  por-  /  '^j?'^       j^** 

,.        .           r    1            1         -n            1                               -J-  (red),     and     pressure 

tion,  application  of  the  rods  will  produce  no  sensation  of  spots    (black)   on     a 

temperature  at  all ;  if  points  are  present,  they  may  vary  small  area  of  the  dor- 

both  in  number  and  excitability,  so  that  the  degree  of  sal   side   of   the   left 

sensitivity  will  vary.     A  surface  with  only  a  few  intense  wrist,  after  Bhx. 
points  would  give  a  stronger  sensation  than  another  with 

many  weak  points,  etc.     Fig.  183  is  given  as  an  example  of  the  topographical 
distribution  of  the  cold  and  heat  senses. 

Goldscheider  summarizes  his  numerous  experiments  on  this  subject  as 
follows:  (1)  The  cold  sense  is  everywhere  more  perfectly  developed  both 
extensively  and  intensively  than  the  heat  sense.  (2)  This  relationship  holds 
as  well  for  the  parts  of  the  skin  habitually  clothed  as  for  the  parts  habitually 
naked.  Goldscheider  finds  the  cause  of  this  regional  difference  in  the  varying 
number  of  nerve  fibers  supplied  to  the  different  places.  Of  course  there  should 
be  added  also  the  varying  thickness  of  the  epidermis  covering  the  end  organs. 

The  experiments  of  different  authors  agree  fairly  well  with  regard  to  the 
acuteness  of  the  temperature  senses  in  the  different  regions.  Those  most  sen- 
sitive to  temperature  stimuli  are  the  nipi)les,  and  the  breast  in  general,  the  aliB 
nasap,  the  anterior  parts  of  the  arm;  then  follow  the  outer  angle  of  the  eye,  the 
upper  lip,  the  abdomen,  the  volar  side  of  the  forearm,  the  inner  parts  of  the 
thigh,  the  foreleg,  etc.    Least  sensitive  of  all  is  the  scalp. 

The  hand  is  but  slightly  sensitive  to  temperature  and  in  general  it  can  be 
said  that  those  regions  of  the  skin  which  are  used  especially  for  touch  are  less 
sensitive  to  temperature  than  other  regions. 


460 


THE  SENSORY   FUNCTIONS   OF  THE   SKIN 


The  temperature  sense  is  about  equally  developed  at  symmetrical  points  on 
the  two  sides  of  the  bodj^  but  there  is  no  special  congruence  exhibited  between 
such  points. 

The  mucous  membranes  possess  as  a  rule  but  a  feebly  developed  temperature 
sense,  or,  as  is  true  of  the  cornea,  none  at  all.  Especially  is  the  heat  sense  poorly 
developed  in  such  places. 

A  given  cold  stimulus  will  evidently  produce  a  greater  cooling  in  a  unit  of 
time  and  will  therefore  constitute  a  stronger  stimulus  for  the  cold  nerves,  on 


a.    Cold  sense.  ...  Spat  inter    OsmeU-    Spatrun 

Osmeta        ^^^^^^     carp.   >Merofseum  ^smetdcarpifl    Sp^f 

...  S9a<""_      carpi    '»■  ,        „,^ j — nj^j •. ,_/ ^, ,   ofse,, 

J©       \ 


...  S»a<"";i      carpi 


-  „irwr-osme«Mn>i,Jo'saum.   carp,  III  ^    ofseum  II. ,  "^ '"eiacarp, ,?     Sp^t  , 
Ota-  i9*      „«  v'*-  _J1j— ' '  ~^ -— -L    °^^e 


Fig.  183. — Topographical  distribution  of  the  cold  and  heat  senses  over  the  middle  region  of  the 
back  of  the  hand,  after  Goldscheider.     The  relative  sensitivity  is  indicated  by  depth  of  shade. 

parts  of  the  body  which  are  ordinarily  clothed  than  on  unclothed  parts.  The 
relation  of  the  heat  sense  to  the  cold  sense  is  for  this  reason  somewhat  different 
on  clothed  and  unclothed  parts. 

So  long  as  the  temperature  of  the  surrounding  atmosphere  changes  liut 
little,  we  do  not  as  a  rule  experience  any  sensation  of  temperature,  although 
some  parts  of  the  skin,  according  as  they  are  clothed  or  not.  may  be  very 
much  warmer  or  colder  than  others.  When  a  person  goes  from  one  room 
in  which  he  feels  neither  cold  nor  warm  into  another  which  is  colder  (or 
warmer),  he  immediately  feels  cold  (or  warm).  But  if  the  difference  bet.reen 
the  t\yo  rooms  is  not  very  great,  all  sensations  of  temperature  disappear  within 
a  short  time.  If  now  he  returns  to  the  first  room,  his  experience  of  tem- 
perature will  be  just  the  reverse  of  the  former  change,  until  again  the  sensa- 
tion gradually  wears  off. 

The  temperature  of  the  surrounding  atmosphere  therefore  may  vary  within 
certain  limits  without  producing  in  us  any  corresponding  sensation.  One 
might  suppose  that  this  ability  of  the  skin  to  adapt  itself  to  slight  changes 
of  temperature  would  be  due  to  variations  in  the  distribution  of  blood,  so 


PRESSURE  AND  TOUCH  461 

that  the  end  organs  would  have  a  uniform  temperature  in  spite  of  the  varia- 
tions outside.  But  this  is  not  the  case,  for  Thunberg  has  shown  that  the 
adaptation  is  to  be  observed  even  after  a  large  quantit}^  of  blood  has  been 
drawn  from  the  vessels, 

E.  H.  Weber,  to  whom  we  owe  the  first  careful  studies  on  the  sensory  func- 
tions of  the  skin,  was  of  the  opinion  that  the  heat  spots  are  stimulated  specifically 
by  an  increase  in  the  temperature  of  the  skin  and  the  cold  spots  by  a  fall. 
Hering,  on  the  other  hand,  conceives  that  the  determining  factor  is  not  the 
temperature  of  the  skin  but  of  the  thermal  apparatus  itself.  We  cannot  here 
enter  into  a  discussion  of  the  merits  of  these  two  hypotheses.  We  may  merely 
mention  one  phenomenon  which  can  scarcely  be  explained  by  either  of  them. 

It  is  a  common  experience  that  one  sometimes  feels  a  sensation  of  chill  on 
getting  into  a  hot  bath.  This  is  because  the  cold  spots  of  the  skin  respond  to 
the  heat  stimulus  with  their  own  peculiar  sensation.  Excitation  of  these  spots 
by  heat  occurs  only  with  stimuli  of  45°  C,  and  upward  (Lehman,  v,  Frey),  The 
reverse  process  of  stimulating  the  heat  spots  by  cold  gives  no  reaction. 

The  end  organs  of  the  temperature  nerves  share  with  other  nervous  end 
organs  a  peculiar  property,  in  virtue  of  which  the  strength  of  the  excitation 
aroused  depends  upon  the  rapidity  of  the  stimulation,  in  this  case  upon  the 
rapidity  of  the  increase  or  decrease  of  temperature.  The  strength  of  the  sensa- 
tion depends  also  upon  the  size  of  the  skin  area  stimulated:  if  the  whole  hand  is 
dipped  into  water  at  37°  C.  the  water  feels  warmer  than  water  at  40°  into  which 
only  one  finger  is  dipped. 

If  a  piece  of  metal  at  2-3°  C,  be  placed  in  contact  with  the  skin  of  the 
brow  for,  say,  thirty  seconds  and  then  removed,  the  sensation  of  cold  on  that 
part  of  the  skin  is  experienced  for  some  twenty  seconds  afterwards  (E,  H,  W^eber) 
— i,  e,,  the  temperature  sensation  persists  after  the  stimulus  is  removed, 

A  change  in  the  temperature  of  the  skin  reduces  the  excitability  of  both 
kinds  of  temperature  nerve  endings.  If  one  hand  be  held  in  moderately  cold 
water  and  the  back  of  the  other  hand  be  dipped  in  the  same  water,  it  seems 
colder  to  the  latter  hand.  If  the  skin  be  overheated  then  dipped  in  cold  water 
the  water  seems  warmer  than  otherwise. 

If  hot  and  cold  stimuli  he  applied  simultaneously  to  the  same  skin  area  the 
sensation  of  cold  appears  first.  Likewise  on  stimulation  of  the  cold  spots  the 
sensation  is  sharper  and  reaches  its  maximum  sooner  than  the  sensation  aroused 
by  stimulation  of  the  heat  spots.  This  difference  is  not  observed  on  stimulation 
of  the  temperature  spots  by  electricity.  From  these  facts  v.  Frey  concludes  that 
the  heat  endings  lie  in  the  deeper  layers  of  the  skin,  the  cold  endings  in  the  more 
superficial  layers. 

§2.    PRESSURE   AND   TOUCH 

Uy  the  pressure  sense  we  not  only  distinguish  pressure  and  contact,  hut 
learn  also  whether  the  surface  of  an  object  is  smooth  or  rough,  whether  an 
object  is  sharp  or  dull,  hard  or  soft,  solid  or  liquid,  etc.  Here  belong  also 
itching  and  tickling  sensations  and  the  like. 

It  is  perfectly  certain  that  these  different  sensations  are  not  all  mediated 
by  the  true  nerves  of  pressure,  but  that  other  afferent  nerves  play  an  im- 
portant part.  If  for  example,  we  perceive  an  object  to  be  hard,  this  sensation 
of  hardness  is  caused  not  only  by  the  effect  produced  on  the  nerves  of  pressure, 
but  there  is  experienced  also  a  sensation  of  resistance  which  is  evoked  by  the 


462  THE  SENSORY   FUNCTIONS  OF  THE  SKIN 

so-called  motor  sense  (ef.  Chapter  XVII 1).  Since,  however,  these  different 
kinds  of  pressure  sensations  have  not  been  sufficiently  differentiated  either 
physiologically  or  psychologically,  we  shall  limit  the  following  discussion  to 
pressure  sensations  in  their  simplest  form. 

Blix  was  the  first  to  demonstrate  by  mechanical  stimulation  of  the  skin 
with  fine  points,  that  the  pressure  sense  like  the  temperature  sense  is  not 
continuously  rej)resented  over  the  entire  skin,  but  that  the  end  organs  of  the 
nerves  mediating  the  sensation  of  pressure  are  separate  from  one  another 
and  are  not  identical  with  the  end  organs  of  the  temperature  nerves  (see 
Fig.  182). 

Stimulating  the  pressure  points  as  lightly  as  possible  with  a  bristle  pro- 
duces a  delicate  but  vivid  and  often  somewliat  tickling  sensation,  such  as  is 
experienced  when  one  of  the  fine  hairs  on  the  skin  is  moved.  According  to 
Kiesow  this  shows  that  the  tickling  sensation  is  a  sensation  of  pressure  of  a 
peculiar  shade  occurring  under  special  conditions  (and  in  certain  cases  con- 
nected with  sensations  of  contraction).  With  a  little  stronger  pressure  the 
sensation  takes  on  a  perfectly  characteristic  quality,  as  if  it  were  produced 
by  a  small,  hard  grain  being  pushed  into  the  skin,  hence  the  name  "  granu- 
lar "  used  by  Goldscheider. 

The  pressure  spots  can  be  sought  out  also  by  means  of  induction  shocks. 
By  monopolar  stimulation  of  the  spots  a  prickling  sensation  is  experienced  with 
a  strength  of  current  which  gives  no  sensation  at  all  if  applied  in  the  intervals 
between  the  spots,  v.  Frey,  who  has  studied  exhaustively  the  electric  stimula- 
tion of  the  pressure  points,  observes  that  induction  shocks  produced  by  as  many 
as  130  interruptions  of  the  primary  current  per  second  are  felt  as  independent 
shocks,  also  that  the  constant  current  causes  a  discontinuous  excitation.  On 
certain  regions  of  the  skin  (fingers,  tip  of  tongue,  red  edges  of  lips),  Sergi  has 
found  that  mechanical  shocks  can  still  be  appreciated  as  distinct  if  they  occur 
at  intervals  of  0.001-0.002  second. 

The  pressure  points  are  arranged  with  special  reference  to  the  hairs.  Each 
hair  has  a  pressure  point  near  its  point  of  exit  and  directly  above  the  deepest 
part  of  the  follicle  (v.  Frey).  It  cannot  be  said  however  that  the  number 
of  pressure  points  coincides  exactly  with  the  numl^er  of  hairs.  In  the  first 
place  the  hairs  often  stand  in  twos  and  threes  and  then  are  so  close  together, 
that  it  is  not  always  possible  to  demonstrate  the  presence  of  pressure  points 
belonging  to  them.  Besides,  one  finds  here  and  there  within  the  regions  clothed 
by  hairs  some  pressure  points  standing  quite  apart  and  wholly  unrelated  to 
any  hair. 

The  number  of  pressure  points  varies  in  different  parts  of  the  skin — e.  g.,  on 
the  flexor  surface  of  the  wrist  28  per  sq.  cm.,  on  the  anterior  surface  of  the  fore- 
leg 5  per  sq.  cm.  (Kiesow).  According  to  v.  Frey's  estimate,  the  entire  surface 
of  the  adult  body,  with  the  exception  of  the  head,  would  probably  contain  about 
500,000  pressure  points. 

Excitation  of  the  pressure  points  appears  to  be  accomplished  by  deforma- 
tion of  the  skin.  When  a  perfectly  uniform  pressure  is  applied  to  the  skin 
no  sensation  is  produced,  the  best  illustration  of  which  is  the  fact  that  we 
do  not  feel  the  pressure  of  the  atmosphere.     The  following  experiment  also, 


THE   LOCAL  SIGN  463 

first  made  by  Meissner,  illustrates  the  same  point.  If  the  hand  be  dipped 
into  water  or  mercury  at  the  temperature  of  the  skin,  no  sensation  is  produced 
in  any  part  of  the  skin  submerged  so  long  as  the  hand  is  kept  perfectly  still 
and  contact  with  the  vessel  is  avoided.  But  a  sense  of  pressure  is  felt  at  the 
boundary  line  between  air  and  liquid. 

A  weight  allowed  to  rest  upon  the  skin  for  a  long  time,  is  felt  continuously, 
but  with  less  and  less  distinctness  as  time  goes  on.  Should  the  weight  be  very 
small,  it  may  be  felt  only  at  the  moment  of  its  application.  Removal  of  the 
weight  is  not  of  course  appreciated  uidess  it  is  heavy  enough  to  be  felt  all  the 
time  it  is  present.  Often  the  sensation  outlasts  the  stimulus,  probably  owing 
to  the  persistence  of  the  deformation  in  the  skin. 

Kiesow  gives  the  following  data  with  regard  to  the  sensitiveness  of  the  dif- 
ferent parts  of  the  skin.  The  relative  strength  of  the  tetanizing  induction  cur- 
rent necessary  for  the  threshold  stimulus  is :  on  the  tip  of  the  tongue,  1 ;  lips, 
1.1;  anterior  half  of  the  tongue,  5;  tips  of  the  fingers,  14-17;  tip  of  the  thumb, 
19-21 ;  edge  of  the  kneepan,  21 ;  styloid  process  of  the  ulna,  34r-37. 

Stimulating  the  skin  of  the  frog  with  pressure,  Steinach  was  able  to  observe 
an  action  current  in  the  corresponding  nerves,  the  strength  of  which  was  found 
to  depend  upon  that  of  the  stimulus. 


§  3.    THE    LOCAL    SIGN 

A  person  pricked  on  the  skin  wath  the  point  of  a  needle  can  tell  with  the 
eyes  closed  exactly  where  the  needle  is  applied.  This  ability  to  refer  a  cutane- 
ous stimulus  to  the  correct  place  is  often  described  for  brevity  as  the  sense 
of  location,  but  is  better  described  as  the  power  of  JocaUzation.  E.  H.  Weber, 
who  was  the  first  to  investigate  this  sense  with  any  completeness,  applied  the 
two  points  of  a  draughtsman's  compass  to  the  skin  and  determined  the  least 
distance  from  each  other  at  wiiich  they  could  be  distinguished  by  the  subject 
as  two  distinct  ])oints  when  applied  to  different  parts  of  the  skin.  The  less 
this  distance  was  found  to  be  the  greater  was  the  ability  of  the  skin  to  localize 
the  stimulus  accurately. 

The  following  are  some  of  Weber's  results,  given  in  millimeters:  tip  of  the 
tongue,  1 ;  tips  of  the  fingers,  2 ;  lips,  4.5 ;  dorsal  side  of  the  third  joint  of  the 
fingers,  7 ;  side  of  the  tongue,  9 ;  outer  surface  of  the  eyelids,  11 ;  dorsal  side  of 
.the  first  finger  joint,  16 ;  brow,  23 ;  back  of  the  hand,  31 ;  sternum,  45 ;  middle 
of  the  back,  68. 

We  see  that  the  distance  is  greatest  on  the  trunk  and  decreases  more  and 
more  as  we  pass  toward  the  ends  of  the  extremities.  It  is  least  on  the  tips  of 
the  fingers  (neglecting  the  tip  of  the  tongue) — i.  e.,  just  where  the  skin  is 
used  for  the  most  delicate  touch  and  where  the  discernment  of  slight  intervals 
between  ol^jocts  is  most  necessary. 

Our  ability  to  distingui-li  sliglit  intervals  of  space  with  the  skin  is,  how- 
ever, not  (juite  so  limited  as  it  might  appear.  In  the  first  place  as  we  know 
from  numy  experiences,  it  can  be  improved  hi/  practice :  in  the  second  place 
slight  intervals  are  much  more  sharply  distinguished,  if  the  two  places  on 
the  skin  are  stimulated  not  simultaneously,  but  fmccessivehj  (Judd.  v.  Frey)  : 
and  in  the  third  place,  this  ability  is  much  greater  when  two  isolated  pressure 


464  THE  SENSORY  FUNCTIONS  OF  THE  SKIN 

points  are  stimulated  than  when  the  needles  are  applied,  as  in  Weber's  experi- 
ments, quite  at  random.  Under  suitable  conditions  of  the  experiment  the 
smallest  distance  at  which  any  two  stimuli  applied  to  the  skin  can  be  recog- 
nized as  distinct,  corresponds  closely  with  the  distance,  as  determined  by 
successive  stimulation,  of  neighboring  tactile  points  from  each  other  (v.  Frey 
and  Metzner). 

The  differences  already  observed  between  different  points  of  the  skin,  obtains 
also  for  the  stimulation  of  isolated  pressure  points,  as  the  following  summary 
will  show.  The  smallest  perceptible  distance  for  the  nail  joints,  volar  side  is 
0.1  mm. ;  for  the  balls  of  the  fingers,  0.1-0.2  mm. ;  palm  of  the  hand,  0.1-0.5 ; 
ball  of  the  thumb,  0.2-0.4 ;  nose  and  chin,  0.3 ;  back  of  the  hand,  0.3-0.8 ;  cheek, 
arm,  brow,  O.i-l.O;  foreleg,  abdomen,  1.0-2.0;  thigh,  3.0;  back,  4.0-6.0  mm. 

It  has  been  found  also  that  the  smallest  perceptible  distances  are  shorter 
when  the  points  applied  simultaneously  are  placed  in  the  transverse  direction 
from  each  other  than  when  the  line  joining  them  lies  in  the  longitudinal 
direction  of  the  part,  and  that  they  decrease  with  the  distance  of  the  points 
tested  from  the  axis  of  rotation  of  the  members;  thus,  on  the  arm  above, 
53.8  mm.;  below,  44.6;  on  the  forearm  above,  41.2;  below,  22.5;  on  the  hand 
above,  20.4;  below,  7.8;  on  the  third  finger  above,  7.5;  below,  2.5  (Vierordt). 

The  power  of  localization  is  reduced  by  fatigue,  anaemia,  low  temperature, 
etc.,  and  is  intensified  by  hypertemia  of  the  skin.  Children  have  a  more  precise 
power  of  localization  than  adults. 

It  is  really  very  remarkable  that  we  have  the  power  to  distinguish  two 
points  as  two  when  they  are  applied  to  the  skin  simultaneously.  For  the 
mere  excitation  from  the  one  must  be  Just  like  that  aroused  from  the  other. 
But  the  fact  that  we  have  the  power  to  feel  them  as  two  must  mean  that  the 
two  sensations  of  pressure  differ  in  some  definite  property.  Since  now  we 
can  distinguish  simultaneously  stimulated  points  better  the  farther  they  are 
apart,  it  follows  further  that  this  difference  between  the  sensations  produced 
from  different  points  is  greater,  the  farther  they  are  apart. 

This  difference  between  the  resulting  sensations  which  enables  us  to  locate 
the  place  of  stimulation  is  known,  since  Lotze,  as  the  local  sign.  Since  every 
sensation  arises  in  the  last  analysis  through  cerebral  processes,  we  may  con- 
ceive of  the  local  sign  as  a  difference  in  some  property  of  the  different  sections 
of  the  brain,  excited  by  stimulation  of  the  different  pressure  nerves.  In  a 
crudely  schematic  way  we  may  imagine  that  every  pressure  nerve  is  connected 
in  some  way  with  a  special  nerve  cell  and  that  excitation  of  this  nerve  cell 
produces  a  specific  shade  of  sensation  which  differs  from  all  other  sensations 
of  pressure. 

The  temperature  nerves  of  the  skin  likewise  possess  this  power  of  localiza- 
tion, but  it  is  not  so  highly  developed  for  temperature  as  it  is  for  pressure. 
The  cold  spots  appear  to  have  a  more  precise  power  of  localization  than  the 
heat  spots. 

The  power  of  localization  of  the  retina,  especially  of  the  fovea  centralis,  will 
be  taken  up  in  Chapter  XXI. 


PAIN  465 


4.    PAIN 


If  too  strong  a  stimulus  be  applied  to  the  skin  or  if  it  be  continued  too 
long  or  be  repeated  too  often,  a  peculiarly  disagreeable  sensation,  which  we 
call  pain,  is  aroused.  With  a  sufficiently  strong  stimulus  the  sensation  is 
diffused  in  our  perception  more  or  less  beyond  the  part  of  the  skin  directly 
excited.  And  from  pain  of  very  great  intensity  convulsions,  loss  of  conscious- 
ness, or  even  mental  derangement  may  result. 

Sensations  of  pain,  whose  important  function  it  is  to  direct  our  attention 
to  all  kinds  of  influences,  which,  if  neglected,  might  bring  us  into  great 
danger,  are  mediated  not  by  the  skin  alone,  but  by  all  other  parts  of  the 
body  as  well.  Pathological  processes  in  the  internal  organs  of  the  body  or  in 
its  members  are  often  accompanied  by  pain.  Cramps  of  the  muscles  give  rise 
to  severe  pains,  and  the  feeling  of  great  fatigue  in  the  muscles  after  severe 
work  lies  on  the  borderland  of  painful  sensations.  Pressure  on  the  eye  causes 
pain,  a  bitterly  cold  wind  causes  pain.  Then  there  are  toothache,  earache^ 
headache,  labor  pains,  and  many  others  of  which  we  have  no  need  to  be 
reminded. 

It  is  very  difficult  to  draw  a  sharp  line  between  actual  pain  and  a  mere  feel- 
ing of  displeasure.  High  tones,  e.  g.,  are  extremely  unpleasant ;  so  also  are 
vibrations  and  rapid  variations  in  the  intensity  of  light;  bad-smelling  and 
bad-tasting  substances  produce  nausea.  Several  of  these  and  other  analogous 
sensations  produce  in  certain  individuals  eifects  quite  similar  to  those  of  pro- 
nounced pains. 

Only  the  painful  sensations  aroused  by  the  skin  have  been  subjected  to 
exact  analysis. 

The  cutaneous  pains  are  not  always  of  the  same  character,  but  exhibit 
differences  which  are  due  mainly  to  different  combinations  of  the  various 
sensations  mediated  by  the  skin,  but  also  to  the  extent  and  duration  of  the 
stimulus.  Thus  a  burning  pain  is  accompanied  by  a  sensation  of  heat;  in 
a  stinging  pain  the  disturbance  is  confined  to  a  small  area  of  the  skin;  we 
call  a  pain  cutting  if  it  is  distributed  over  some  extent  of  the  body  with  a 
certain  speed ;  a  throbbing  pain  is  aroused  when  the  pain  comes  and  goes 
with  the  pulse,  as.  e.  g..  in  the  case  of  inflammatory  pains,  where  the  pulsa- 
tions cause  an  increase  in  the  pressure  of  the  tissue. 

Pain,  more  than  any  other  sensation,  has  immediate  reference  to  oneself, 
and  likewise  the  intensity  of  pain  more  than  that  of  any  other  sensation  is 
influenced  by  the  mind.  When  a  person  cuts  himself  accidentaUij  with  a 
knife,  the  cut  produces  no  pain  worth  mentioning  even  though  the  wound 
be  a  deep  one.  But  let  him  know  beforehand  that  a  slight  operation,  be  it 
nothing  more  than  a  prick  of  the  finger  for  a  blood  count,  is  to  be  performed 
on  him,  and  it  may  cause  him  real  agony.  From  this  it  follows  that  the 
imagination  of  pain  increases  its  intensity  very  greatly. 

By  directing  the  attention  very  intently  to  a  certain  part  of  the  body,  a  per- 
son may  evoke  creeping  sensations,  sensations  of  tension,  pressure,  etc.,  due  to 
the  dilatation  of  the  arteries  with  the  cardiac  systole,  to  pressure  of  the  clothes, 
etc.,  which  otherwise  he  would  not  be  conscious  of  at  all,  and  by  continued  atten- 


466  THE  SENSORY  FUNCTIONS  OF  THE  SKIN 

tion  to  them  they  gradually  become  more  and  more  unpleasant  and,  finally,  actu- 
ally painful. 

In  diseases  accompanied  by  pain,  the  pain  is  often  more  severe  at  night  than 
during  the  day.  This  is  probably  due  to  the  fact  that  in  the  daytime  our  atten- 
tion is  distracted  by  many  things  outside  ourselves,  and  is  not  directed  so  exclu- 
sively to  the  body. 

By  purposely  fixing  one's  attention  on  a  definite  object  or  idea  it  is  possible 
to  suppress  not  only  the  expression  of  pain,  but  to  a  large  extent  the  pain  itself. 
The  following  story  of  Immanuel  Kant  is  much  to  the  point.  Kant  suffered 
from  time  to  time  with  attacks  of  gout  which,  as  many  know,  may  be  very 
painful.  "  Out  of  patience  at  feeling  myself  deprived  of  sleep,"  he  writes,  "  I 
soon  seized  upon  the  stoical  expedient  of  fixing  my  thought  intently  on  some 
chance  object,  whatever  it  might  be  (e.  g.,  on  the  many  ideas  associated  with 
the  name  of  Cicero),  and  of  consequently"  diverting  my  attention  from  all  sen- 
sations. In  this  way  the  sensation  speedily  became  blunted,  so  that  the  natural 
tendency  to  sleep  overcame  them.  And  this  I  could  repeat  with  equally  good 
results  each  time  in  the  little  interruptions  in  my  night's  rest  occasioned  by 
recurring  attacks.  But  in  the  morning  the  shiny  redness  of  the  toes  of  my  left 
foot  was  sufficiently  convincing  to  myself  that  these  sensations  had  not  been 
purely  fanciful." 

Although  all  men  have  not  the  same  will  power  as  Kant  had,  we  may  never- 
theless learn  from  his  example  that  it  is  possible  actually  to  suppress  pain  to  a 
certain  extent,  just  as  it  is  possible  for  us  to  accustom  ourselves  to  bear  a  neces- 
sary pain  without  sounding  it  abroad  with  loud  wailings. 

The  expression  of  pain,  therefore,  is  not  to  be  accepted  as  a  measure  of  its 
intensity.  A  strong-willed  person  may  feel  very  severe  pain  without  wincing, 
while  another  may  cry  out  at  a  pin  prick.  On  the  other  hand,  we  must  not 
forget  the  experience  oft  confirmed  in  animals  as  well  as  in  men  that  sensitive- 
ness to  pain  is  very  different  in  different  individuals.  And  since  nobody  can 
tell  with  certainty  how  strong  is  the  pain  which  another  feels,  we  ought  not  to 
withhold  our  sjTnpathy  from  others  when  they  give  expression  to  pain. 

It  is  very  difficult  to  decide  just  wherein  lies  the  real  physiological  cause 
of  pain.  Since  we  know  that  the  pain  aroused  by  any  adequate  stimulus  has 
an  altogether  different  character  in  different  parts  of  the  body — as.  e.  g.,  those 
aroused  by  a  high  temperature  differ  from  those  aroused  by  a  low  temperature, 
as  the  pain  of  muscle  cramps  is  of  a  different  kind  from  that  of  high  pressure 
inside  the  eye.  and  the  pains  occiirring  in  inflammatory  processes  differ  accord- 
ing to  the  organ  inflamed — the  assumption  is  undoubtedly  suggested  that  pain 
is  produced  by  an  excessive  excitation  of  the  ordinary  afferent  nerves  from 
different  parts  of  the  body. 

The  fact  that  in  certain  diseases  of  the  nervous  system  the  sensations  of  pain 
are  lost  while  the  ordinary  tactile  sensations  do  not  suffer  any  considerable 
diminution,  does  not  militate  against  this  hypothesis.  One  might  readily  im- 
agine that  the  maximum  excitation  necessary  for  the  production  of  pain  were 
not  reached,  although  the  threshold  stimulus  remained  approximately  the  same; 
and  this  supposition  could  be  brought  into  line  with  Schiff's  observation  that 
section  of  the  gray  matter  of  the  spinal  cord  abolishes  sensations  of  pain  with- 
out affecting  the  tactile  sensations. 

Proceeding  from  this  observation  it  has  repeatedly  been  conjectured  that 
painful  impressions   are  conducted  through  the  gray  matter,   and  that  the 


PAIN  467 

sensations  of  pain  are  aroused  by  a  sort  of  summation  taking  place  in  the 
cells  of  the  gray  matter,  and  there  is  any  number  of  observations  at  hand 
which  show  that  tactile  stimuli,  of  themselves  wholly  painless,  produce  severe 
pain  if  repeated  frequently  enough.  Likewise  the  irradiation  of  pain,  as 
well  as  the  occurrence  in  pathological  processes  of  many  accessory  sensations 
of  a  painful  character,  appear  to  speak  for  the  participation  of  the  gray 
matter. 

While  these  and  other  observations  can  l)c  explained  on  the  ground  that 
the  sensory  cutaneous  nerves  already  discussed  mediate  the  sensations  of  pain, 
they  do  not,  however,  constitute  positive  proof  of  that  proposition.  Let  us 
see  what  we  may  learn  from  investigation  of  the  different  sense  points  of 
the  skin. 

There  prevails  among  authors  who  have  I>usied  themselves  with  this  ques- 
tion a  most  gratifying  agreement  on  one  point,  namely,  that  neither  stimula- 
tion of  the  temperature  points  by  their  appropriate  stimuli  nor  mechanically 
(by  a  needle  thrust)  produces  any  pain  ( Goldscheider  et  aJ.).  Likewise  when 
a  heat  spot  is  tested  with  very  warm  water,  it  gives  a  burning  hot  sensation 
but  no  pain.  The  heat  pain  might  be  regarded  therefore  as  a  separate  sensa- 
tion of  pain  merely  colored  by  the  excitation  of  the  heat  nerves,  unless  we 
suppose  that  the  analgesia  of  the  heat  spots  is  due  to  the  fact  that  the  surface 
stimulated  is  too  small ;  for  it  is  a  well-known  fact  that  the  size  of  the  surface 
stimulated  is  a  very  important  factor  in  the  production  of  pain. 

Blix  demonstrated  that  on  many  parts  of  the  body  a  needle  can  be  thrust 
deep  into  the  skin  without  producing  any  pain.  The  nerves  which  mediate 
pain  therefore  do  not  occur  everywhere  in  the  skin.  Neither  Blix  nor  Gold- 
scheider however  felt  impelled  to  assume  the  existence  of  special  nerves  of 
pain  with  their  own  end  organs,  but  conceived  that  sensations  of  pain  have 
their  origin  in  excitation  of  pressure  nerves,  v.  Frey,  on  the  other  hand, 
entered  the  lists  for  special  pain  nerves  and  adduced  the  following  weighty 
reasons,  among  others,  for  their  existence. 

(1)  By  obserA'ing  certain  precautions,  mechanical  stimulation  of  the  skin 
with  a  bristle  produces  a  pure  sensation  of  pain  without  any  preliminary  or 
accompanying  sensation  of  pressure.  (It  will  be  readily  understood  that  the 
pain  spots  cannot  be  stimulated  singly  by  mechanical  means  when  they  lie  in 
the  immediate  neighborhood  of  pressure  points.) 

(2)  If  a  bristle  be  placed  over  a  pressure  point,  the  sensation  appears  imme- 
diately, but  at  once  fades  away  again  and  usually  becomes  unnoticeable  after  a 
short  time.  Over  the  pain  point  the  effect  appears  later,  gradually  increases  in 
strength  and  decreases  again  after  reaching  a  maximum.  If  the  sensation  is 
still  present  after  the  stimulus  has  ceased,  it  disappears  slowly.  Intimately  con- 
nected with  this  behavior  is  the  fact  that  rapidly  repeated  electrical  or  mechani- 
cal stimuli  (from  five  per  second  upward)  applied  to  the  pain  point  fuse  as  a 
rule  into  a  continuous  sensation,  whereas  through  the  pressure  point  we  can 
distinguish  very  well  130  shocks  per  second   (page  462). 

(3)  "When  the  head  of  a  pin  is  pressed  for  a  moment  into  the  skin,  there 
follows  ver>-  often  after  the  sensation  of  pressure  and  separated  from  it  by  a 
short  interval,  a  second  sensation  which  is  painful.  Only  pain  points  in  the 
neighborhood  of  pressure  points  exhibit  this  phenomenon.  On  isolated  pressure 
points  the  painful  after-effect  is  wanting,  and  on  isolated  pain  points  the  sen- 


468  THE  SENSORY   FUNCTIONS  OF  THE  SKIN 

sation  of  pressure  accompanying  the  stimulus  fails,  while  the  painful  after-effect 
appears  very  vividly. 

With  regard  to  the  topographical  distribution  of  the  pain  spots  we  learn 
from  V.  Frey  and  others  that  on  the  back  of  the  hand  over  the  metacarpus 
of  the  ring  finger  16  pain  points,  as  against  2  pressure  points,  can  be  demon- 
strated within  12.5  sq.  mm. — i.  e.,  1.3  pain  points  to  the  square  millimeter. 

From  reasoning  which  we  need  not  enter  into  here  v.  Frey  has  reached 
the  following  conclusions  with  regard  to  the  anatomical  structures  which  may 
possibly  serve  as  the  end  organs  of  the  different  cutaneous  nerves: 

(1)  Among  the  well-known  sensory  nerve  endings  on  parts  devoid  of  hair 
there  is  only  one  form  which  occurs  in  sufficient  number  to  fulfill  the  require- 
ments of  an  end  organ  of  the  pressure  points,  namely,  the  tactile  corpuscles  of 
Meissner.  According  to  this  discoverer  there  are — e.  g.,  over  the  metacarpus 
of  the  little  finger  in  1  sq.  mm.  one  to  two  of  these  corpuscles — which  agrees  well 
with  the  number  of  pressure  points  in  the  same  place. 

(2)  These  corpuscles  however  are  quite  exclusively  confined  to  the  parts 
devoid  of  hair.  Anatomical  investigations  have  brought  to  light  the  presence 
of  a  wreath  of  nerve  fibers  encircling  the  hair  follicles  down  close  under  the 
opening  of  the  sebaceous  glands,  their  terminal  processes  penetrating  the  walls 
of  the  follicle  as  far  as  the  glassy  layer.  This  wreath  of  nerve  fibers  which 
occurs  with  the  greatest  regularity  in  every  hair  follicle  may  be  the  end  organ 
of  the  pressure  points  associated  with  the  hairs. 

(3)  The  sensation  of  pain  is  probably  aroused  by  stimulation  of  some  mech- 
anism lying  nearer  the  surface.  Since  only  free  intraepithelial  nerve  endings 
are  found  external  to  the  tactile  corpuscles,  we  may  look  upon  these  as  the  organs 
of  the  (superficial)  sensations  of  pain  in  the  skin. 

(4)  Finally,  v.  Frey  and  Thunberg,  the  latter  by  careful  analysis  of  the 
different  phenomena  attending  stimulation  with  heat,  have  made  it  probable  that 
the  end  organs  of  the  heat  nerves  lie  deeper  than  those  of  the  cold  nerves,  also 
that  the  latter  lie  deeper  than  the  end  organs  of  the  pain  nerves. 

References. — M.  G.  Blix,  Zeitschrift  fiir  Biologic,  Bd.  xx,  xxi,  1884,  1885. — 
M.  V.  Frey,  Abhandl.  d.  mathem.-phys.  CI.  der  konigl.  sachs.  Ges.  d.  Wiss.,  Bd. 
xxiii,  No.  3,  1896. — A.  Goldsch'eider,  Archiv  fiir  Anat.  und  Physiol.,  physiol. 
Abt.,  1885,  suppl.   Bd.— A.   Goldscheider,  "  Ueber  den  Schmerz,"  Berlin,  1884. 


CHAPTEE    XVIII 

ORGANIC    SENSATIONS 

We  include  as  organic  sensations  all  those  sensations  aroused  independently 
of  external  stimuli  by*  internal  processes  going  on  in  the  various  peripheral 
organs.  Sensations  excited  from  the  sense  organs  normally  by  external  agen- 
cies or  abnormally  by  pathological  processes  evidently  do  not  belong  in  this 
category. 

Among  the  sensations  thus  defined  we  may  mention  first  those  which  con- 
stitute the  source  of  our  general  bodily  feelings  (page  452).  But  analysis  of 
this  class  of  sensations  has  not  progressed  far  enough  as  yet  to  entitle  them 
to  further  consideration  here.  We  should  mention  also  certain  occasional 
sensations  of  pain  arising  within  the  internal  organs  concerning  the  exact 
cause  of  which  nothing  positive  is  yet  known. 

The  only  organic  sensations  thus  far  studied  critically  are  those  by  which 
we  form  ideas  of  the  position  of  our  bodies  and  their  parts  (head,  trunk  and 
extremities)  in  space,  and  those  by  which  we  are  made  aware  of  the  extent, 
intensity  and  direction  of  our  movements.  These  sensations  play  a  consider- 
able part  in  the  regulation  of  our  movements  and  besides  are  very  important 
in  the  psychological  elaboration  of  our  sense  impressions  (even  of  those  which 
arise  through  external  agencies),  although  they  appear  as  a  rule  to  be  indis- 
tinct and  indefinite  in  comparison  with  the  last  named. 

The  two  groups  of  organic  sensations  just  mentioned  are  not,  however, 
everywhere  sharply  distinct  from  one  another.  The  impulses  by  which  we 
are  made  aware  of  our  bodily  movements,  their  direction  and  intensity,  merge 
into  the  less  distinct  afferent  impulses  by  which  we  form  ideas  concerning 
the  orientation  of  our  bodies.  The  anatomical  substratum  of  our  motor  sensa- 
tions and  of  our  sense  of  position  is  furnished  in  part  by  the  sensory  nerve 
endings  of  the  muscles,  tendons,  joints,  skin  and  in  part  by  those  of  certain 
portions  of  the  inner  ear  (semicircular  canals  and  otolith  sacs). 

§  1.    MOTOR   SENSATIONS 

Even  with  the  eyes  closed  we  have  a  very  definite  idea  of  the  position  of 
our  limbs.  If,  for  example,  one  arm  be  passively  placed  in  a  certain  position, 
the  person  can  with  his  eyes  closed  place  the  other  arm  in  exactly  the  same 
position.  Likewise  a  person  has  a  perfectly  precise  idea  with  respect  both  to 
direction  and  speed  of  the  changes  in  the  position  of  his  limbs.  Finally,  one 
can  estimate  weights  very  accurately  by  lifting  them. 

These  and  other  similar  sensations  are  described  by  different  authors  by 
different  names,  such  as  motor  sensations,  muscular  sense,  sense  of  force,  etc. 

469 


470  ORGANIC  SENSATIONS 

This  difference  in  terminology  alone  is  evidence  that  views  differ  greatly  as 
to  the  real  cause  of  these  sensations.  According  to  some  authors,  like  Ch.  Bell 
and  E.  H.  Weber,  they  are  produced  by  excitation  of  the  sensory  nerves  to  the 
muscles;  others,  like  Lotze  and  Schiff,  conceive  that  they  are  evoked  by  the 
different  foldings  of  the  skin  incidental  to  different  positions;  according  to 
Bernhardt  the  sensory  nei-ves  of  the  skin,  of  the  fascias  and  of  the  periosteum 
as  well  as  the  nerve  trunks  running  through  the  muscles  occasion  muscular  sen- 
sations; Lewinsky  seeks  their  cause  in  the  excitation  of  the  nerves  of  the  joints 
and  bones ;  and  many  authors  like  Leyden,  Meynert,  Nothnagel  and  others  assume 
that  several  different  kinds  of  afferent  nerves  have  a  share  in  their  production. 

As  for  lifting  an  object  with  the  hand,  in  a  greai  majority  of  cases  we 
send  an  impulse  to  the  muscles  which  is  exactly  suited  to  the  purpose,  being 
neither  too  weak  nor  too  strong.  That  is,  if  the  object  is  a  familiar  one,  we 
can  adjust  the  voluntary  impulse  very  exactly  to  the  work  to  be  performed. 
From  this  the  conclusion  has  been  drawn  that  the  feeling  of  fffort  is  the 
all-important  thing  in  the  perception  of  active  movements  (J.  Miiller.  Wundt). 

As  a  matter  of  fact  it  is  easy  to  show  that  we  do  associate  immediately  with 
a  voluntary'  impulse  an  idea  of  the  movement  as  if  it  were  already  performed. 
Persons  who  have  suffered  amputation  of  a  leg  assert  very  positively  that  when 
they  will  to  bend  the  lost  part  they  experience  a  distinct  feeling  that  muscles 
are  being  contracted. 

But  the  central  feeling  of  effort,  however  important  it  may  be,  is  not  the 
only  determining  factor.  The  mere  development  of  our  ability  to  adapt  the 
necessary  motor  impulses  to  the  lifting  of  different  objects,  involves  the  con- 
stant participation  of  afferent  impulses  which  keep  us  informed  of  the  results 
of  the  impulses  sent  out.  It  can  be  shown  also  without  difficulty  that  the 
result  of  a  voluntary  impulse  is  usually  controlled  by  afferent  impulses.  Thus, 
if  we  misjudge  the  weight  of  an  object — e.  g.,  overestimate  it — we  give  too 
strong  an  impulse,  as  a  consequence  of  which  the  object  is  lifted  considerably 
higher  than  we  intended  it  should  be  and  we  are  immediately  aware  of  the 
fact  even  without  the  use  of  our  eyes.  Similarly  we  are  aware  of  the  fact, 
if  the  impulse  is  too  weak.  Naturally  if  these  afferent  impulses  participate 
in  bringing  aljout  active  movements,  they  must  be  the  more  necessary  for 
making  us  aware  of  passive  movements. 

Let  us  see  what  are  the  afferent  nerves  mediating  motor  sensations.  Ana- 
tomical proof  of  the  presence  of  afferent  miiscnhir  nerves  has  been  furnished 
by  Eeichert,  Kolliker,  Odenius  and  others.  We  know  too  from  the  perfectly 
definite  sensations  of  fatigue  as  well  as  from  the  pains  of  muscle  cramps  that 
these  nerves  are  unquestional)ly  al)le  to  mediate  conscious  sensations.  They 
also  give  rise  to  reflexes,  among  which  those  producing  vasodilatation  and 
those  involving  the  skeletal  muscles  as  answering  organs  are  the  most  impor- 
tant (Tengwall).  It  seems  probable  therefore  that  these  nerves  do  play  a 
prominent  part  in  the  motor  sensations. 

In  the  case  of  the  eye  muscles  the  afferent  nerves  are  of  great  importance. 
We  shall  see  later  (Chapter  XXI")  that  we  have  a  very  delicate  appreciation  of 
the  slightest  contraction  of  the  eye  muscles.  This  could  onlj'  be  true,  if  afferent 
nerves  from  the  muscles  or  their  tendons  were  present. 


MOTOR  SENSATIONS  471 

Likewise  the  thyroarytenoid  muscle,  whose  finely  graduated  contractfons  de- 
termine the  pitch  of  the  vocal  tones,  appears  to  possess  a  very  delicate  muscular 
feeling  produced  by  the  afferent  nerves;  there  is,  however,  no  feeling  of  move- 
ment connected  with  this. 

According  to  the  view  which  Goldscheider  in  particular  has  worked  out, 
the  most  important  nerves  for  the  perception  of  passive  movements  are  the 
afferent  nerves  of  the  joints.  The  sensations  of  pressure  and  tension  in  the 
soft  parts  of  the  limbs  not  only  do  not  produce  the  sensation  of  movement, 
they  even  interfere  with  it.  Again,  since  the  threshold  value  of  the  sensation 
— i.  e.,  the  smallest  passive  movement  which  one  can  perceive — is  not  influ- 
enced in  any  way  by  the  degree  of  contraction  of  the  muscles  when  the  passive 
movement  begins,  cooperation  of  the  muscular  sensibility  as  a  factor  appears 
to  be  excluded.  Finally  the  distance  described  by  the  moving  force  bears  no 
relation  to  the  amount  of  sensation  which  one  experiences;  the  determining 
factor  is  the  amount  of  rotation  at  the  joint. 

Lewinski  made  some  experiments  on  ataxic  patients  (cf.  page  472)  by  mov- 
ing their  limbs  very  slowly  and  very  slightly  at  the  ankle,  knee  and  hip  joints, 
part  of  the  time  pressing  the  parts  together  at  the  joint,  part  of  the  time  not. 
When  the  parts  were  thus  pressed  the  patients  always  perceived  the  movement 
very  exactly,  when  not  they  could  form  no  idea  of  the  motion. 

The  perception  of  active  movements  likewise  results  from  the  rotation  of 
the  joints.  To  this  are  to  be  added,  however,  as  contributing  factors  the 
sensations  connected  with  the  tension  of  the  tendons  and  their  epiphyses, 
possibly  also  the  sensations  aroused  through  the  sensory  nerves  of  the  mus- 
cles. These  sensations  concern  not  merely  the  tendons,  etc.,  of  the  active 
muscles,  but  also  their  antagonists.  In  a  passive  movement  the  tendons  simply 
follow  the  pull;  some  are  stretched,  others  are  only  under  the  tonic  resistance 
of  their  own  muscles. 

In  active  movements,  especially  if  the  joint  to  be  moved  is  loaded,  we 
also  experience  sensations  of  weight  and  of  resistance.  The  nerves  of  the 
joints  and  of  the  tendons  are  again  of  the  first  importance,  the  pressure  on 
the  surface  of  the  joints  and  the  tension  of  the  tendons  varying  according  to 
the  resistance  or  the  weight. 

Jacobi  has  called  attention  to  still  another  circumstance  to  which  he  ascribes 
great  importance  in  the  determination  of  the  size  of  a  weight,  namely,  the  com- 
parison of  the  amount  of  nerve  force  employed  with  the  latent  period  of  the 
movement — i.  e.,  the  time  which  elapses  between  the  act  of  volition  and  the  incep- 
tion of  the  movement.  The  latent  period,  in  his  opinion,  depends  upon  the 
amount  of  nerve  force  employed,  and  with  the  same  amount  of  nerve  force  is 
proportional  to  the  size  of  the  weight. 

The  sensory  nerves  of  the  skin  appear  commonly  to  be  of  but  slight  im- 
portance in  any  kind  of  motor  sensations.  The  sensation  of  weight  remaiiis 
unchanged  after  the  skin  is  rendered  insensitive  to  touch.  And  yet  cutaneous 
sensations  appear  to  contribute  something  to  the  quantitative  refinement  of 
ft  sensation  of  resistance  as  well  as  to  the  localization  of  the  sensation  and 
so  to  the  formation  of  a  clearer  total  impression  (Goldscheider  and  Blecher). 
29 


472  ORGANIC  SENSATIONS 

In  the  case  of  the  face  muscles  and  the  levator  palpehrce  superioris  distinct 
sensations  which  inform  us  of  the  displacements  suffered  by  the  soft  parts 
accompany  the  contractions  (Goldscheider). 

The  sensations  which  make  us  aware  of  the  position  of  the  extremities 
have  their  origin  in  the  skin,  tendons,  and  probably  the  joints.  By  combina- 
tion with  optical  memory  pictures  they  give  us  our  idea  of  position.  Sensi- 
bility of  the  muscles  appears  to  have  little  to  do  with  the  perception  of 
position  in  the  case  of  the  extremities,  but  in  the  case  of  the  eye  muscles  it 
plays  a  very  important  part. 


§2.    PHYSIOLOGICAL   SIGNIFICANCE  OF  THE  MOTOR  SENSATIONS 

Taken  in  their  broadest  sense,  the  motor  sensations  are  of  very  great  im- 
portance for  the  regulation  of  all  bodily  movements.  Whenever  any  part 
of  the  body  suffers  loss  of  the  motor  sensations  or  a  decline  in  their  intensity 
and  fineness,  that  part  of  the  body  exhibits  disturbances  in  the  coordination 
of  its  movements.  In  this  way  are  brought  about  those  pathological  symptoms 
which  are  described  as  ataxia  and  which  are  defined  in  brief  as  a  disturbance 
in  the  harmonious  and  purposeful  cooperation  of  the  muscles. 

One  of  the  most  frequent  forms  of  ataxia  arising  from  lesion  of  afferent 
pathways  is  locomotor  ataxia  occurring  in  tabes  dorsalis.  It  is  characterized  by 
the  peculiar  way  in  which  the  legs  are  swung  and  the  feet  planted  in  walk- 
ing. Instead  of  the  slightly  flexed  position  of  the  normal  leg  as  it  is  swung 
forward,  the  knee  is  extended,  sometimes  excessively,  and  the  leg  is  thrust  for- 
ward, the  heel  being  planted  on  the  ground  with  a  sudden  stamp.  At  the  same 
time  the  legs  are  kept  far  apart,  the  trunk  sways  back  and  forth,  and  the  body 
is  in  momentary  danger  of  losing  its  equilibrium. 

Coordination  of  the  muscles  being  necessary  to  hold  the  body  erect  no  less 
than  to  carry  out  movements  of  the  limbs,  ataxia  is  at  times  noticeable  in  stand- 
ing. Thus  ataxic  persons  are  inclined  to  place  the  legs  far  apart  in  order  to 
increase  the  area  of  support.  If  the  feet  are  placed  close  together  the  body  sways, 
or  may  fall,  especially  if  the  eyes  be  at  the  same  time  closed  so  as  to  shut  out 
control  by  visual  impressions  (Leyden  and  Goldscheider). 

There  are  many  clinical  observations  to  support  this  dependence  of  exact 
movements  upon  different  impulses,  and  they  are  confirmed  in  the  most  beau- 
tiful way  by  experiments  on  animals. 

Thus,  after  section  of  the  afferent  roots  Avhich  supply  one  hind  leg,  a  dog 
is  unable  to  run  on  the  ataxic  leg  when  the  sound  leg  is  tied  up  (Hering,  Jr.). 
When  the  afferent  roots  to  both  hind  legs  are  cut,  a  dog  is  utterly  unable  to 
walk,  and  can  only  pull  himself  along  on  the  abdomen  by  means  of  the  fore  legs, 
the  hind  parts  dragging.  Gradually,  however,  the  dog  can  learn  to  walk  again, 
and  at  the  end  of  three  to  four  weeks  but  few  signs  of  the  original  disturbance 
are  left  (Bickel).  There  is  therefore  a  means  of  compensating  the  loss  of  these 
afferent  impulses. 

J.  R.  Ewald  observed  that  in  cases  of  this  kind  the  animal  could  call  into 
play  certain  aids  not  previously  used  for  regulation  of  his  movements,  and  in 
fact  Bickel  observed  that  a  dog  which  has  recovered  the  use  of  his  legs  after 
an  operation,  exhibits  again  the  original  symptoms  when  he  is  taken  into  a  dark 


OTOLITH  SACS  OF  THE  INNER  EAR  473 

room;  from  which  it  appears  that  the  optical  apparatus  constitutes  the  com- 
pensating medium.  H.  Munk  found  on  monkeys  that  after  section  of  all  the 
nerves  to  one  anterior  extremity,  the  insensitive  arm  could  be  extended  for  food 
on  the  same  day  of  the  operation,  but  the  hand  could  not  be  moved.  During  the 
following  days  the  number  and  extent  of  isolated  movements  steadily  increased 
(more  rapidly  so  with  practice),  and  in  a  few  days  the  animal  could  again  grasp 
bits  of  food  and  convey  them  to  its  mouth.  After  some  months  the  arm  was 
used  for  almost  all  isolated  acts,  but  continued  to  be  more  impulsive  and  cum- 
brous in  its  movements  than  the  normal  arm,  which  as  time  went  on  came  to 
be  used  first  on  most  occasions.  The  associated  movements  of  the  arm  in 
walking,  jumping,  climbing,  etc.,  however,  were  entirely,  or  almost  entirely 
obliterated;  at  all  events  they  were  no  longer  used  to  any  advantage. 

We  mav  sum  up  bv  saying  that  the  messages  conveyed  by  the  afferent  fibers 
to  the  central  organs  are  of  great  importance  not  only  for  the  coordination 
of  movements  but  for  the  movements  themselves,  and  that  this  depends  pri- 
marily on  the  fact  that  it  is  through  these  messages  that  the  individual  learns 
to  what  extent  the  intended  movement  was  carried  out  or  failed  to  be  carried 
out.  The  nerves  of  the  organ  itself  are  the  ones  most  directly  concerned, 
but  they  can  be  replaced  to  a  greater  or  less  extent  by  other  nerves — as,  e.  g., 
the  optic.  When  this  compensation  also  fails  the  motor  disturbance  is  greater 
than  ever  and  it  is  conceivable  at  least  that  if  all  afferent  impulses  were 
completely  inhibited,  purposeful  motor  functions  would  no  longer  be  possible. 

§  3.    THE    SEMICIRCULAR    CANALS   AND    OTOLITH   SACS 
OF   THE   INNER   EAR 

Physiological  experiment  and  clinical  experience  both  seem  to  have  shown 
definitely  that  the  afferent  nerves  of  the  semicircular  canals  and  otolith  sacs 
in  the  internal  ear  convey  impulses  to  the  nerve  centers,  which  have  much  to 
do  with  the  perception  of  position  or  changes  in  the  position  of  the  head  as 
well  as  with  other  processes  of  orientation,  etc. 

We  shall  investigate  these  phenomena  without  for  the  present  raising  the 
question  of  how  far  the  impulses  give  rise  to  conscious  sensations. 

A.    ANATOMICAL 

It  is  not  our  intention  to  describe  the  internal  ear  fully  in  this  place ;  we 
shall  only  mention  l)riefly  the  structural  relations  which  are  important  for 
our  present  purpose.  The  internal  ear  can  be  divided  into  two  portions,  the 
cochlea  and  the  semicircular  canals,  together  with  the  sacciiliis  and  utriculus. 
These  two  divisions  have  as  a  matter  of  fact  entirely  different  functions. 

The  cochlea  unquestionably  represents  the  end  organ  of  those  nerve  fibers 
the  excitation  of  which  arouses  auditory  sensations,  particularly  those  of  musi- 
cal tones.  This  is  especially  well  borne  out  by  the  facts  of  comparative  anat- 
omy. In  fishes  the  cochlea  is  represented  only  by  a  very  small  knoblike 
appendage  to  the  saccule  called  the  lagena.  In  frogs  and  toads  the  cochlea 
reaches  a  somewhat  higher  development  and  in  the  reptiles  a  regular  pro- 
gression of  stages  can  he  followed  from  the  turtles  and  snakes  to  the  lizards 


474 


ORGANIC  SENSATIONS 


and  crocodiles.  In  the  last  named  for  the  first,  and  in  birds  the  cochlea 
becomes  curved  and  slightly  spiral,  while  in  the  mammals  it  reaches  its  highest 
development  by  growing  out  into  a  long  tube  which  describes  upon  itself 
one  and  one-half  to  four  spiral  turns. 

The  semicircular  canals  are  arranged  in  the  three  dimensions  of  space. 
Inasmuch  as  the  ph3'siological  investigations  of  these  structures  relate  mainly 
to  the  pigeon,  we  shall  describe  them  for  this  animal  at  once,  following  the 
work  of  J.  R.  Ewald.  We  find  on  each  side  of  the  head  an  external,  an 
anterior  and  a  posterior  canal  (Figs.  184  and  185).  The  two  external  canals 
lie  almost  exactly  in  the  same  plane,  which  when  the  head  is  in  its  normal 
position  with  the  beak  slightly  lowered,  is  approximately  the  horizontal  plane 
(Fig.  184).  The  planes  of  the  posterior  canal  of  one  side  and  the  anterior 
canal  of  the  other  are  almost  exactly  parallel,  but  the  projection  of  each  is 
about  7  mm.  distant  from  the  other  (Fig.  186)  and  each  forms  an  angle  of 
about  45°  with  the  median  vertical  plane  of  the  head.    This  relationship  being 


Fig.    184. — The  semicircular  canals  of  the  pigeon  laid  bare  in  situ,  after  J.  R.  Ewald.     The  rods 
a,  b  and  c  are  placed  in  the  axes  of  the  eyes,  the  skull  and  the  beak. 

true  for  both  pairs  (the  left  anterior  with  the  right  posterior,  and  the  right 
anterior  with  the  left  posterior),  it  follows  that  the  six  canals  together  mark 
out  three  planes  which  lie  in  the  three  dimensions  of  space. 

This  description  applies  strictly  only  to  the  middle  portion  of  each  canal, 
for  Its  ends  deviate  somewhat  from  the  course  taken  by  the  middle. 
_       Each  canal  bears  at  one  end  an  enlargement,  the  ampulla,  which  contains 
m  Its  crista  acustica  the  nerve  endings  of  the  canal.     The  ampulla;  of  the  two 


OTOLITH  SACS  OF  THE  INNER  EAR 


475 


canals  which  lie  in  the  same  plane  are  so  arranged  that  particles  moving  in  the 

same   direction   in   the   two  move  toward   the  ampulla   of  one   and   away  from 

the  ampulla  of  the  other. 

In  the  sacculus  and  utriculus  likewise  are  nerve  endings  contained  in  the 

maculce  acusticce. 

These  nerve  endings  consist  of  cells  with  hairlike  processes,  which  in  turn 

are  connected  with  the  terminal  filaments  of  the  eighth  cranial  nerve.     In  the 

ampulhe  the  hairs  are  bound  to- 
gether by  a  substance  which  is 
probably  slimy  and  gelatinous  in 
life.  This  substance,  however,  does 
not  reach  down  to  the  epithelial 
surface,  but  is  separated  from  it 
by  a  small  space  filled  with  endo- 
lymph,    through    which    the   hairs 


Fig.  185. 


Fig.  186. 


Fig.  185. — Schema  .showing  the  relations  of  the  planes  of  the  semicircular  canals  of  the  pigeon 
to  each  other,  after  J.  R.  Ewald.  The  open  skull  is  seen  from  behind.  The  anterior  canal 
lies  in  the  plane  A,  the  posterior  in  the  plane  P,  and  the  external  in  the  plane  E. 

Fig.  186. — Schema  showing  the  distance  of  the  planes  of  the  anterior  and  posterior  canals 
(prolonged)  from  each  other. 


project  before  entering  the  slimy  material.  A  small  solid  body,  the  so-called 
otolith,  rests  upon  the  hairs  in  each  of  the  macula  acustieae.  All  vertebrates 
from  the  bony  fishes  up,  with  the  exception  of  the  mammals,  have  three  otolith 
organs  on  each  side  (one  in  each  of  the  three  parts:  utriculus,  sacculus  and 
lagena)  ;  the  mammals  have  but  two,  since  in  them  the  lagena  is  absent,  having 
been  developed  into  the  auditory  cochlea. 

These  three  (or  two)  otolith  organs  bear  to  each  other  the  same  spatial  rela- 
tions as  the  semicircular  canals,  the  macula  utriculi  lying  in  the  plane  of  the 
external  canal,  the  macula  sacculi  in  the  plane  of  the  anterior,  and  the  axis  of 
the  lagena  (where  such  can  be  made  out)  in  the  plane  of  the  posterior  canal. 

It  was  long  supposed  that  the  semicircular  canals  and  the  ear  sacs  were 
called  into  play  in  the  perception  of  noises — i.  e.,  of  sounds  not  produced  by 
regular  periodic  vibrations — while  the  musical  tones  excited  the  nervous  end 


476 


ORGANIC  SENSATIONS 


organs  of  the  cochlea.  Conclusive  proofs  for  this  apportionment  of  the 
acoustic  stimuli  to  two  kinds  of  terminal  auditory  apparatus,  however,  were 
not  forthcoming.  Instead,  it  has  heen  shown  hy  numerous  experiments  that 
the  semicircular  canals  and  the  sacs  play  a  very  important  part  in  the  media- 
tion of  our  sensations  of  position,  orientation,  and  the  like. 


B.    EXPERIMENTAL  SUPPRESSION   OF  THE  SEMICIRCULAR   CANALS 

In  1828  Flourens  published  a  paper  on  the  phenomena  which  follow  de- 
struction of  the  semicircular  canals  of  the  pigeon.  After  transection  of  a 
canal  he  observed  peculiar  pendiilumlil-e  movements  of  the  head  in  the  plane 
of  the  canal  transected.  Thus,  if  the  horizontal  canal  were  the  one  operated 
on,  the  head  was  rotated  incessantly  to  and  fro  in  the  horizontal  plane.  These 
movements  ceased  after  a  time;  but  if  the  corresponding  canal  of  the  other 
side  were  sectioned,  the  movements  began  again  with  still  greater  intensity. 
They  came  on  suddenly,  if  the  animal  was  disturbed  in  any  way.  The 
pigeons  could  no  longer  fly  and  could  only  take  food  with  difficulty.  The  more 
extensive  the  destruction  of  the  canals,  the  more  intense  were  the  disturbances 
produced,  and  the  animals  continued  to  exhibit  such  disturbances  for  years. 

Goltz  performed  a  great  service  for  this  line  of  investigation  when  he 
observed  that  the  result  of  the  operation  can  be  descrilied  primarily  as  a 
disturbance  in  the  ability  of  the  animal  to  keep  its  body  in  equUihrinm. ^  He 


Fig.   187. 


Fig.  188. 


Fig.  187. — Pigeon  witli  botli  membranous  lab5Tintlis  removed,  after  J.  R.  l^wald. 
Fig.   188. — Pigeon  five  days  after  removal   of    the    right    membranous    labyrinth,    after  J.  R. 
Ewald.     The  head  is  inclined  toward  the  operated  side. 

also  laid  stress  on  the  idea  that  since  this  disturbance  persists  for  several 
years  after  the  operation,  it  must  be  regarded  not  as  a  .^^ymptom  of  irritation, 
but  as  a  symptom  of  some  deficiency  caused  by  elimination  of  the  semi- 
circular canals.  This,  moreover,  is  confirmed  by  painting  the  canals  with 
cocaine,  exactly  the  same  phenomena  being  produced  as  by  section  (Ch. 
Koenig.  Gaglio).  Goltz  concluded  that  the  semicircular  canals  constitute  a 
peripheral  sense  organ,  which  supplements  the  visual  and  inotor  senses   in 


OTOLITH  SACS  OF  THE   INNER  EAR  477 

the  perception  of  the  position  of  the  head  and  thus  indirectly  in  perceiving  the 
position  of  the  whole  body. 

After  removal  of  the  entire  membranous  labyrinth  from  both  sides  the 
pigeon  on  casual  examination  exhibits  no  particularly  prominent  symptoms 
for  some  months  after  the  operation.  But  on  closer  investigation  one  finds 
that   all   the   muscles    are   abnor- 

strated    by    the    following    experi-     ?^__  ___^^^^^  —  -^__.-^.^^ 

ment.  A  small  lead  ball  weighing  ^^^  i89.-Pigeon  twenty  days  after  removal  of  the 
20  g.  is  suspended  on  a  thread  and  right  membranous  labyrinth,  after  J.  R.  Ewald. 

the  thread  is  fastened  by  means  of  The  head  has  been  turned  once  around  to  the 

modeler's    wax    to    the    beak    of    a  right, 

pigeon  whose  labyrinths  liave  been 

removed.  If  the  ball  hangs  in  front,  it  draws  the  head  far  downward,  but  the 
relatively  strong  muscles  of  the  back  of  the  neck  are  able  to  lift  it  and  to  dangle 
it  about.  The  head  follows  the  pendulumlike  movements  of  the  ball  apparently 
without  concern  but  in  reality  quite  powerlessly  until  at  last  in  the  course  of 
its  swinging  the  weight  is  thrown  around  over  the  back.  Immediately  this 
happens  the  head  is  held  by  the  ball  in  the  position  shown  in  Fig.  187.  The 
muscles  which  otherwise  would  lift  the  head  from  this  position  are  too  weak  to 
do  so  now  that  the  labyrinths  are  wanting. 

The  following  experiment  shows  how  the  sensations  of  position  are  affected. 
A  pigeon  deprived  of  its  labyrinth  is  blindfolded  by  drawing  a  leather  cap  over 
its  head.  Because  of  the  muscular  weakness  the  head  falls  down  over  the  back 
and  the  muscular  sensation  fails  to  apprise  the  nerve  centers  of  the  fact.  Since 
the  visual  impulses  do  not  now  compensate  for  this  deficiency,  the  animal  no 
longer  has  any  correct  notion  of  the  attitude  of  its  head,  and  will  allow  it  to 
remain  in  this  unnatural  i)osition. 

After  removal  of  the  labyrinth  on  one  side  only  the  disturbances  are  less 
severe,  so  that  the  animals  can  still  fly  and  can  take  food  without  difficulty. 
But  they  are  not  by  any  means  normal,  for  the  peculiar  rotations  of  the  head 
first  described  by  Flourens,  and  which  cease  after  bilateral  extirpation,  at 
times  make  their  appearance. 

During  the  first  days  following  the  operation  the  pigeon  begins  to  incline  its 
head  toward  the  niK'rntcd  side.  The  turning  increases  more  and  more  as  time 
goes  on,  and  finally  may  amount  to  complete  rotation  (Figs.  188  and  189).  The 
explanation  is,  that  by  removing  one  labyrinth,  say  the  right,  the  muscles  which 
normally  prevent  the  bead  from  falling  to  the  right  are  greatly  weakened. 

There  is  a  decline  in  the  funclionnl  power  of  other  muscles  after  extirpa- 
tion of  one  labyrinth.  According  to  Ewald  eacli  labyrinth  is  connected  by  way 
of  the  central   nervous  svstem  with   all   the  voluntary  muscles  of  the  body, 


478  ORGANIC  SENSATIONS 

but  more  directly  with  those  of  the  opposite  side  and  in  particular  with  those 
which  move  the  head  and  vertebral  column.  Accordingly  the  muscles  of  either 
side  would  be  roused  to  activity  in  any  given  case  chiefly  by  the  opposite 
labyrinth.  In  agreement  with  this  is  the  fact  that  if  one  labyrinth  be  left 
intact  and  the  other  be  suppressed,  rigor  appears  sooner  after  the  death  of  the 
animal  on  the  side  opposite  the  normal  labyrinth. 

In  other  species  of  animals  extirpation  of  one  labyrinth  produces  somewhat 
different  results.  In  the  rabbit  rolling  of  the  entire  body  around  its  longitudinal 
axis  sets  in  soon  after  the  operation.  This  is  caused  by  extension  of  the  legs  on 
the  opposite  side,  and  by  the  consequent  rotation  of  the  animal  toward  the 
operated  side  until  it  comes  to  lie  on  its  back.  The  animal  tries  to  regain  its 
feet,  but  as  soon  as  it  succeeds,  begins  once  more  to  roll  over.  The  legs  of  the 
operated  side  are  entirely  passive  all  the  while.  After  bilateral  extirpation  in 
the  dog,  the  animal  exhibits  a  certain  unsteadiness  in  his  gait.  When  he  jumps 
down  from  a  table,  he  falls  sprawling  on  the  floor.  Some  difficulty  in  chewing 
and  in  swallowing  may  also  be  observed.  All  of  which  symptoms  point  to  a 
reduction  of  muscular  strength  and  of  the  ability  to  properly  control  the  muscles. 

The  disturbances  arising  from  bilateral  extirpation  of  the  labyrinths  grad- 
ually disappear  again.  This  occurs  in  all  likelihood  mainly  because  the  animal 
gradually  becomes  accustomed  to  regulating  his  movements  without  the  help 
of  the  afferent  impulses  from  the  semicircular  canals. 

The  cerebrum  appears  to  play  the  most  important  part  in  this  regulation. 
With  pigeons  from  which  the  cerebrum  was  removed,  unilateral  extirpation 
evoked  the  usual  complex  of  symptoms,  but  some  of  them,  especially  the  rota- 
tion of  the  head,  were  no  longer  compensated.  After  the  sj^mptoms  accompany- 
ing bilateral  extirpation  in  the  dog  had  been  improved  as  much  as  possible, 
J.  E.  Ewald  removed  the  surface  of  the  cortex  from  the  motor  zone  of  both  sides. 
The  dog  exhibited  disturbances  of  coordination  of  the  profoundest  kind.  He 
could  no  longer  jump  or  run  or  walk  or  even  stand ;  in  fact  he  could  not  lie  on 
his  belly.  He  lay  rather  on  one  side  or  the  other,  and  despite  his  most  vigorous 
efforts  was  unable  to  raise  himself  with  his  legs.  The  head,  however,  was  used 
to  more  purpose.  Gradually  these  disorders  improved,  but  they  immediately 
returned  and  in  exactly  the  same  fashion,  as  directly  after  the  operation, 
when  the  animal  was  taken  into  a  room  which  was  suddenly  darkened.  The  dog 
showed  therefore  that  after  exclusion  of  the  impulses  mediated  through  the  laby- 
rinths and  through  the  so-called  motor  zone  of  the  cortex,  he  had  been  thrown 
back  upon  his  eyes  for  the  regulation  of  his  movements.  Since  now  no  such 
disturbances  result  from  destruction  of  the  cortex  alone,  even  when  the  visual 
sensations  also  are  excluded,  it  follows  that  after  extirpation  of  the  labyrinth 
the  cerebral  cortex  takes  upon  itself  the  business  of  replacing  the  missing  afferent 
impulses  as  far  as  possible.  Then  when  the  cerebral  cortex  also  is  destroyed,  a 
compensation  can  once  more  be  effected  through  the  eyes,  but  this  fails  on  exclu- 
sion of  the  visual  sensations. 

The  disturbances  which  appear  on  suppression  of  the  labyrinth  are  there- 
fore, (1)  a  reduction  of  muscular  strength,  and  (2)  derangements  in  the 
coordination  of  movements,  which  to  all  appearances  are  due  to  the  loss  of 
afferent  impulses. 


OTOLITH  SACS  OF  THE  INNER  EAR  479 

C.    ARTIFICIAL  STIMULATION   OF  THE  SEMICIRCULAR    CANALS 

Breuer  (1874)  made  the  first  experiments  of  this  kind  and  they  were 
extended  later  by  Ewald.  In  the  following  discussion  we  shall  follow  in  the 
main  Ewald's  results. 

The  anatomical  structure  of  the  semicircular  canals,  as  Breuer  and  Mach 
have  pointed  out,  make  it  highly  probable  that  the  specific  stimulus  for  the 
nervous  end  organs  in  the  ampullae  consists  of  currents  in  the  endolymph. 

When  a  ring-shaped  tube  containing  a  fluid  is  rotated  in  the  plane  of  its 
curvature  the  fluid  remains  for  a  time  at  rest  on  account  of  its  inertia — i.  e.,  a 
current  is  set  up  in  the  opposite  direction  relative  to  the  walls  of  the  tube,  until 
the  fluid  has  had  time  to  acquire  the  speed  of  the  tube.  Such  a  current  must 
result  as  often  as  a  change  in  the  speed  or  direction  of  rotation  takes  place. 
The  same  phenomena  evidently  must  occur  in  the  semicircular  canals  with  every 
rotation  of  the  head.  But  the  eifect  in  the  different  canals  will  depend  upon 
their  position  with  reference  to  the  axis  of  rotation.  Rotation  about  the  vertical 
axis  acts  almost  exclusively  on  the  two  external  canals.  If  the  head  is  turned 
to  the  right  there  arises  in  the  external  canal  of  the  right  side  a  current  directed 
toward  the  end  of  the  canal  containing  the  ampulla,  in  that  of  the  left  side  a 
current  away  from  the  ampulla.  And  thus  there  is  in  the  different  pairs  of  semi- 
circular canals  a  current  of  a  certain  strength  in  a  certain  direction  correspond- 
ing to  every  turn  of  the  head.  The  sensory  hairs  of  the  maculte  are  moved  by 
these  currents  and  in  this  way  the  corresponding  nerve  endings  are  excited. 

These  conclusions  are  capable  of  experimental  proof  by  producing  move- 
ments of  the  endolymph  in  a  given  direction.  For  this  purpose  Ewald  opened 
a  bony  semicircular  canal  at  two  points.  Into  the  opening  farther  from  the 
ampulla  he  introduced  a  plug  so  that  the  movement  of  fluid  in  that  direction 
was  prevented.  He  adjusted  to  the  other  opening  a  small  apparatus  by  means 
of  which  he  could  exert  pressure  on  the  naked  membranous  canal.  Since  the 
fluid  could  not  move  away  from  the  ampulla,  when  pressure  was  applied  a 
current  of  endolymph  was  naturally  produced  toward  the  ampulla.  With 
every  stimulus  of  pressure  the  animal  (pigeon)  invariably  moved  its  head 
and  eyes  in  the  direction  of  the  current  and  exactly  in  the  plane  of  the  canal 
stimulated.  When  the  pressure  was  not  released  the  animal  brought  its  head 
back  after  a  time  to  the  starting  point.  If  now  the  pressure  was  released 
and  thus  a  current  in  the  opposite  direction  was  produced,  the  head  and  eyes 
were  again  turned,  but  this  time  in  the  opposite  direction — i.  e.,  always  in 
the  direction  of  the  current  of  endolymph  and  in  the  plane  of  the  canal 
stimulated. 

Proof  that  the  currents  of  endolymph  give  the  normal  stimulus  to  the 
semicircular  canals  is  furnished  also  by  rotation  experiments.  To  prevent 
complications  witli  the  sense  of  sight  the  animal  must  be  blindfolded.  If  a 
pigeon  be  placed  in  a  rotation  apparatus  in  such  a  way  that  it  is  rotated  to  the 
right  about  a  vertical  axis,  it  turns  its  head  in  the  horizontal  direction  to 
tlie  left,  tliat  is,  in  the  same  direction  as  the  current  produced  by  the  inertia 
of  the  endolymph.  When  the  head  has  lieen  turned  a  certain  distance  to  the 
left,  it  moves  a  certain  distance  to  the  right  toward  the  median  position,  then  is 
again  rotated  to  the  left,  and  so  on.    In  this  wav  the  head  swings  incessantly  to 


480  ORGANIC  SENSATIONS 

and  fro  and  the  eyes  also  take  part  in  the  movements.  Xow  it  is  a  probability 
supported  by  many  facts  that  the  first  phase  of  the  movement  represents  a 
reaction  of  the  animal  to  the  rotation;  the  second  phase  is  produced,  because 
after  the  head  has  been  carried  far  enough  from  the  median  position  the 
afferent  impulses  from  the  joints,  muscles,  etc.,  are  strong  enough  to  arouse 
the  opposite  sets  of  muscles. 

When  the  two  external  canals  are  plugged  up  so  as  to  prevent  movements  of 
the  fluid,  the  reaction  to  rotation  in  the  horizontal  plane  is  almost  entirely  want- 
ing. On  the  other  hand,  one  can  destroy  any  number  of  the  anterior  and  pos- 
terior semicircular  canals  without  changing  the  reaction. 

The  characteristic  eye  movements  occur  also  when  mammals  are  rotated; 
they  are  wanting  after  section  of  the  eighth  cranial  nerve  or  of  the  semicircular 
canals. 

From  these  facts  we  may  conclude  that  the  semicircular  canals  are  influ- 
enced by  movements  of  the  head,  and  in  all  proliability  the  immediate  stimulus 
is  caused  by  currents  set  up  in  the  endolymph;  this  means  that  the  sensory 
hairs  of  the  corresponding  crista  acustica  are  put  on  the  stretch  and  the  ap- 
propriate end  organs  are  consequently  excited.  These  in  their  turn  produce 
reflex  responses  by  which  the  position  of  the  head  and  of  the  eyes  is  regulated. 

The  movements  of  the  eyes  and  of  the  head  which  have  been  seen  to  take 
place  when  the  animal  is  rotated  may  appear  after  extirpation  of  the  labyrinths 
when  the  eyes  of  the  animal  are  open.  At  the  beginning  of  rotation  the  animal 
experiences  a  displacement  of  the  retinal  picture,  and  seeks  to  resist  that  dis- 
placement by  striving  to  hold  the  object  steadily  in  view. 

The  subsequent  motion  of  the  head  in  the  direction  of  the  rotation  is  pure 
reflex,  probably  discharged  by  the  excitation  of  the  retina  due  to  the  displace- 
ment of  the  image  or  by  impulses  coming  from  the  neck  and  eye  muscles. 

The  effects  of  extirpation  of  the  semicircular  canals  which  have  been  sum- 
marized under  B  can  be  brought  into  line  with  these  results  without  serious 
difficulty.  Suppose  a  normal  animal  moves  his  head,  say,  to  the  right.  The 
movement  produces  in  both  external  semicircular  canals  currents  in  the  endo- 
lymph in  the  opposite  direction,  and  these  in  turn  reflexly  induce  a  rotation  of 
the  head  in  the  direction  of  the  current — i.  e.,  in  the  direction  reverse  to  the 
original  rotation  of  the  head.  If  the  two  external  canals  are  now  thrown  out 
of  function,  either  by  being  plugged  or  by  being  sectioned,  the  currents  are  not 
set  up  and  consequently  the  muscular  movements  caused  by  them  do  not  take 
place.  But  the  head  may  swing  to  one  side.  If  so,  it  will  continue  until  the 
motor  sensations  from  the  joints,  etc.,  discharge  compensating  movements.  This 
mode  of  discharge,  however,  is  not  so  finely  graded,  for  the  animal  has  lost  the 
power  of  telling  when  the  head  has  been  returned  to  normal  position;  conse- 
quently it  is  difficult  for  the  animal  to  regain  its  equilibrium  after  that  has 
once  been  disturbed.  When  several  canals  are  suppressed  at  the  same  time  the 
swinging  motions  of  the  head  become  still  more  extensive. 

The  laxness  of  the  muscles  which  has  been  observed  affects  most  the  muscles 
of  greatest  precision — e.  g.,  the  extrinsic  muscles  of  the  eyes — and  is  probably 
due  to  the  absence  of  impulses  normally  roused  by  the  labyrinth  (Jensen). 


OTOLITH   SACS  OF  THE   INNER   EAR  481 


D.    THE  OTOLITH   SACS 

It  will  be  readily  understood  that  a  movement  in  a  straight  line  will  not 
produce  any  current  in  the  semicircular  canals,  for  the  reason  that  the  influence 
of  inertia  in  the  two  halves  of  each  canal  will  be  found  to  be  equal  and  in  oppo- 
site directions.  But,  as  Breuer'has  observed,  it  appears  that  the  otolith  apparatus 
may  be  stimulated  under  these  circumstances.  The  impression  which  the  otolith 
will  make  at  any  time  will  depend  on  the  position  with  reference  to  the  direc- 
tion of  gravity,  of  the  surface  between  the  otolith  and  the  subjacent  epithelium, 
and  will  vary,  therefore,  with  the  position  of  the  head  with  reference  to  the  line 
of  gravity.  On  account  of  the  varying  position  of  the  different  maculae,  the 
impressions  from  the  different  otoliths  for  any  given  position  of  the  head  will 
also  be  different.  Hence,  every  position  of  the  head  would  be  accompanied  by  a 
definite  combination  of  impressions  discharged  by  the  otoliths,  and  hence  the 
otolith  sacs  would  constitute  an  organ  for  the  perception  of  the  position  of  the 
head  with  reference  to  a  plumb  line. 

Again,  if  we  suppose,  as  Breuer  has  sought  to  show,  that  each  otolith  has  a 
definite  "  groove,"  so  to  speak,  in  which  it  may  exert  the  pressure  due  to  its 
inertia,  we  should  have  an  arrangement  by  which  translocation  movements  in 
any  straight  line  could  be  perceived. 

Several  obsei-\'ations  on  fishes  have  been  cited  in  support  of  this  function  of 
the  otolith  sacs,  their  purport  being  that  when  the  sacs  are  injured  or  destroyed 
the  orientation  of  the  animal  with  reference  to  gravity  is  practically  lost. 


E.    OBSERVATIONS   ON   MEN 

The  rotation  experiments  constitute  a  no  less  valuable  means  of  studying 
the  influence  of  the  semicircular  canals  in  man.  When  a  man  with  normal 
ears  is  rotated  about  the  vertical  axis  in  an  apparatus  suitable  for  the  purpose, 
the  eyes  are  moved  first  slowly  in  the  opposite  direction,  then  quickly  in  the 
same  direction  as  the  rotation.  This  reaction  appears  to  be  perfectly  constant 
in  healthy  individuals,  but  is  often  (fifty  per  cent  of  the  cases  ^)  wanting 
in  the  deaf  and  dumb  (Kreidl). 

Kreidl  asserts  furthermore  that  these  same  deaf-and-dumb  persons  who 
failed  to  give  the  eye  reaction,  did  not  suffer  from  dizziness  when  the  rotation 
ceased,  as  the  normal  persons  do.  and  similarly,  we  find  in  James  the  state- 
ment that  out  of  519  deaf-and-dumb  persons  only  199  suffered  from  dizziness 
as  the  result  of  rotation. 

The  explanation  which  Breuer  has  advanced  with  reference  to  the  func- 
tion of  the  otolith  sacs  in  animals,  namely,  that  they  make  the  animal  aware 
of  its  position  with  reference  to  the  line  of  gravity,  appears  to  apply  also  to 
man.  Certain  positions  of  the  eyes  are  unquestionably  dependent  upon  the 
position  of  the  head  with  reference  to  the  line  of  gravity.  Thus,  for  example, 
in  the  blind  the  bending  of  the  head  forward  is  accompanied  by  an  elevation 
of  the  plane  of  vision  with  reference  to  the  head,  and  bending  the  head 
backward  by  a  corresponding  lowering  of  the  plane  of  vision  (Breuer).  In 
persons  with  normal  eyes  these  movements  do  not  occur.     But  we  meet  with 

'  Mygind  ha^s  ascertained  that  in  Copenhasren  about  fifty-six  per  cent  of  the  deaf 
and  dumb  have  the  semicircular  canals  affected. 


482  ORGANIC  SENSATIONS 

a  wheel-like  rotation  of  the  eye  about  its  axis  when  the  head  is  bent  to  one 
side  or  the  other.  This  is  not  caused  by  the  nerves  which  convey  muscular 
sensations,  for  the  same  rotation  appears  when  the  whole  body  is  inclined  one 
way  or  the  other  without  bending  the  head  or  neck.  When,  for  example,  a 
person  lying  horizontally  on  his  back  turns  his  head  to  the  right  his  eyes  turn 
to  the  left,  while  with  the  same  rotation  of  the  head  in  a  standing  position  no 
rotation  of  the  eyes  takes  place.  Such  phenomena  appear,  therefore,  to  de- 
pend upon  the  changed  position  of  the  head  with  reference  to  the  line  of 
gravity.  Since  they  are  very  different  in  character  from  those  aroused  from 
the  semicircular  canals,  we  should  probably  not  go  far  astray  in  assuming 
that  they  are  mediated  by  the  otolith  sacs,  that  is,  that  the  latter  furnish 
impressions  which  inform  us  of  the  direction  of  the  line  of  gravity. 

These  impressions  do  not  figure  prominently  except  under  circumstances 
which  exclude  the  ordinary  visual,  motor  and  tactual  impressions,  as  for  example 
in  diving.  It  is  said  that  many  deaf-and-dumb  persons  lose  all  sense  of  direc- 
tion when  the  body  is  submerged  (James),  also  that  such  persons  have  great 
difficulty  in  standing  on  one  leg,  and  when  the  eyes  are  closed  find  it  quite  impos- 
sible. We  may  suppose  that  in  these  persons  the  otolith  sacs  have  undergone 
pathological  changes. 

The  dizziness  produced  by  sending  an  electric  current  transversely  thiough 
the  head  is  also  thought  to  be  due  to  stimulation  of  the  labyrinth.  When  the 
current  is  closed  the  person  feels  as  if  the  head  and  entire  body  were  inclined 
toward  the  cathode;  when  it  is  opened  one  has  the  sensation  of  falling  toward 
the  anode. 

From  the  observations  and  experiments  here  presented  it  appears  quite 
probable  that  the  labyrinth  is  a  peripheral  organ  which  reflexly  regulates 
various  finely  graduated  movements  especially  of  the  eyes  and  of  the  head,  and 
in  general  is  of  considerable  importance  for  the  tonus  and  functional  capac- 
ity of  the  skeletal  muscles.  If  the  conclusion  is  correct  that  conscious  im- 
pressions as  to  the  position  of  the  head  and  orientation  of  the  body  are 
obtained  from  the  labyrinth,  it  ought  to  be  regarded  also  as  an  actual  sense 
organ  analogous  to  the  organs  of  the  motor  sensations.  Tliat  these  impres- 
sions are  usually  indistinct  says  nothing  against  their  occurrence,  for  super- 
ficially considered,  the  sensations  aroused  through  the  nerves  of  the  tendons, 
joints  and  muscles,  in  spite  of  their  demonstrably  great  importance,  appear 
to  us  much  less  vividly  than  the  sensations  which  proceed  from  sense  organs 
stimulated  by  external  agencies. 

References. — St.  von  Stein,  "  Die  Lehre  von  den  Funktionen  der  einzelnen 
Teile  des  Ohrlabyrinthes,"  Jena,  1894.— J.  B.  Ewald,  "  Physiologische  Unter- 
suchungen  iiber  das  Endorgan  des  Nervus  oetavus,"  Wiesbaden,  1892, — J.  Breuer, 
Wiener  Sitzungsher.,  November,  1903. 


CHAPTER    XIX 


TASTE    AXD    SMELL 


By  means  of  the  sense  of  taste  we  learn  something  of  the  solid  and  fluid 
substances  taken  into  the  mouth,  and  bv  means  of  the  sense  of  smell  some- 
thing of  the  nature  of  the  atmosphere  entering  the  nasal  cavities.  The  two 
senses  very  often  work  together,  and  many  impressions  which  we  ordinarily 
describe  as  sensations  of  taste,  have,  as  a  matter  of 
fact,  nothing  whatever  to  do  with  the  sense  of  taste, 
being  mediated  solely  by  the  organs  of  smell. 

§  1.    SENSATIONS   OF   TASTE 

Ordinarily  only  the  upper  surlace  of  the  tongue 
is  described  as  the  peripheral  organ  of  taste.  But 
this  appears  to  be  incorrect,  for  according  to  dif- 
ferent authors  the  under  surface  of  the  tip  of  the 
tongue,  the  soft  and  hard  palate,  the  anterior  pillars 
of  the  fauces,  the  tonsils,  uvula,  posterior  wall  of 
the  pharynx,  posterior  side  of  the  epiglottis  and  of 
the  larynx,  as  well  as  the  mucous  membrane  of  the 
cheeks,  mediate  sensations  of  taste.  However,  this 
is  true  only  of  children ;  in  adults  the  mucous  mem- 
brane of  the  cheeks,  the  uvula,  tonsils  and  middle 
of  the  tongue  no  longer  react  to  sapid  substances; 
in  exceptional  cases  the  anterior  pillars  of  the 
fauces  and  the  under  surface  of  the  tip  of  the 
tongue,  both  sides  of  the  frenum.  continue  to  be 
percipient.     According  to  Hanig  the  central  zone 

of  the  tongue  which  is  not  percipient  is  surrounded  on  all  sides  by  a  "taste 
girdle  "'  within  which  the  sensitiveness  decreases  more  and  more  from  the  edge 
toward  the  middle  line  (cf.  Fig.  190.  where  the  sensitivity  of  the  different 
portions  is  schematically  represented  by  the  number  of  l)lack  spots). 

The  end  orp-ans  of  the  gustatory  nerves  are  the  taste  buds  or  taste  goblets 
discovered  by  Loven  and  Schwalbe.  They  are  ovoid  bodies,  0.08  mm.  long  and 
0.04  mm.  thick,  which  lie  imbedded  in  the  epithelium  of  the  mucous  membrane. 
They  consist  in  part  of  outer,  sustentacular  or  tegumental  cells  and  in  part  of 
inner  taste  cells  which  represent  the  true  neuroepifheUiim  connected  in  one  way 
or  another  with  the  gustatory  nerve  iibers.  In  order  to  stimiilate  these  taste  cells 
the  sapid  substance  must  come  into  actual  contact  with  them,  and  this  is  made 
possible  by  tlie  presence  of  a  small  taste  pore  at  the  top  of  the  taste  bud,  into 
which  the  attenuated  ends  of  the  taste  cells  project. 

483 


Fig.  190. — The  taste  zone  oa 
the  upper  surface  of  the 
tongue,  after  Hanig. 


484 


T.\STE  AND  SMELL 


Because  of  the  anatomical  structure  of  the  taste  organ  the  entrance  of  the 
sapid  substances  in  sufficient  quantity  to  arouse  gustatory  sensations  is  rendered 
difficult,  especially  if  the  tongue  is  covered  by  a  thick  layer  of  mucus. 

The  taste  buds  are  found  chiefly  in  the  circumvallate  papillte  and  in  the  sides 
of  the  foliate  papillie,  but  occur  also  in  the  fungiform  papilla\  and  are  scattered 
here  and  there  over  the  various  parts  of  the  mucous  membrane  of  the  mouth 
and  thi'oat  endowed  with  the  sense  of  taste. 

The  tongue  possesses  also  nerves  of  touch,  heat  nerves,  and  cold  nerves. 
What  nerves  supply  gustatory  fibers  to  the  tongue  can  of  course  only  be  answered 
by  observations  on  men  in  whom  the  afferent  nerves  from  the  tongue  have  been 
paralyzed  in  some  way.    It  appears  from  such  obsei'vations  summarized  by  Cas- 


ggl.spheno 


Fig.   191. — Course  of  the  facial  nerve  and  its  communications  with  the  trigeminal  and  glosso- 
pharyngeal nerves.      The  chief  gustatory  fibers  are  indicated  in  red,  after  Leube. 

sirer  that  in  by  far  the  greater  number  of  cases  the  gustatory  fibers  for  the  pos- 
terior part  of  the  tongue  traverse  the  glossopharyngeal,  those  for  the  anterior 
part  the  basal  trigeminal  nerve  (Fig.  191).  In  certain  cases  it  appears,  how- 
ever, that  the  glossopharyngeal  represents  the  gustatory  nerve  of  the  whole 
tongue,  while  in  others  it  may  happen  that  all  the  gustatory  fibers  traverse 
the  trigeminal. 


Only  four  qualitatively  different  kinds  of  sensation  are  mediated  by  the 
sense  of  taste;  namely,  sweet,  acid,  hitter  and  salt,  to  which  alkaline  and 
metallic  are  added  by  some  authors. 

These  six  qualities  however  cannot  be  regarded  as  pure  taste  qualities,  for 
all  of  our  gustatory  impressions  are  accompanied  by  tactile  sensations  (Kiesow). 


SENSATIONS   OF   TASTE  485 

It  is  impossible  to  classify  the  gustatory  impressions  any  further.  For 
example,  if  we  use  solutions  of  HCl.  HXO3  H2SO4,  acetic,  tartaric  and  oxalic 
acids  of  such  strength  as  to  produce  sensations  of  the  same  intensity,  they 
all  taste  alike.  The  same  is  true  of  bitter  substances  like  strychnin,  quinin, 
morphin  and  picric  acid,  and  of  sweet  substances  such  as  milk  sugar,  grape 
sugar,  cane  sugar.  On  the  base  of  the  tongue  we  can  distinguish  all  the  taste 
qualities,  but  on  the  tip  there  are  considerable  differences  in  this  respect  in 
different  individuals,     v.  Yintschgau  recognizes  four  groups  of  individuals: 

(1)  those  who  distinguish  with  the  tip  of  the  tongue  all  the  four  qualities; 

(2)  those  who  distinguish  sweet,  salt  and  acid  readily,  but  bitter  less  easily; 

(3)  those  who  distinguish  none  of  the  qualities  easily;   (4)   those  who  have 
no  sense  of  taste  at  all  on  the  tip  of  the  tongue. 

Moreover,  the  same  substance  placed  on  different  parts  of  the  tongue  may 
have  a  different  taste.  Thus  according  to  Howell  and  Castle  brom-saccharin 
tastes  bitter  on  the  base  of  the  tongue,  but  sweet  on  the  tip.  Shore  found 
that  a  five-per-cent  solution  of  MgSO^  has  a  faintly  sweetish  taste  on  the 
tip  of  the  tongue  followed  by  an  acid  taste,  an  acid  and  bitter  taste  on  the  edge 
and  a  pure  bitter  taste  on  the  base. 

By  means  of  cocaine  the  sensibility  of  the  tongue  to  gustatory  stimuli  can  be 
considerably  reduced.  But  the  effect  is  different  for  the  different  taste  qualities. 
A  five-per-cent  solution  of  cocaine  acts  most  markedly  on  the  sense  of  bitter, 
then  on  sweet  and  acid,  while  it  is  entirely  without  effect  on  salt  (Shore, 
Kiesow).  The  faintly  toxic  substance  eucain  has  approximately  the  same  effect. 
GjTnnemic  acid  obtained  from  Gymnema  sylvestre  placed  on  the  tongue  in  a 
sufficiently  concentrated  form  obliterates  every  trace  of  sensitiveness  for  sweet 
(Edgeworth)  ;  it  acts  secondarily  on  bitter  and  to  a  much  less  degree  on  salt 
and  acid  (Shore,  Kiesow). 

It  is  very  proljable,  from  such  observations  as  those  just  mentioned,  that 
the  different  taste  qualities  are  mediated  by  different  nerves,  just  as  in  the 
case  with  the  different  qualities  of  the  temperature  sense.  This  inference 
has  been  directly  confirmed  by  Ohrwall. 

By  means  of  a  very  fine  brush  he  placed  solutions  of  sugar,  quinin  and 
tartaric  acid  on  different  fungiform  papillae,  and  found  that  out  of  125  such 
papillae  on  the  anterior  part  of  the  tongue  27  (21.6  per  cent)  did  not  react 
to  either  of  these  substances.  Of  the  remaining  98,  12  reacted  only  to  tartaric 
acid,  3  only  to  sugar,  12  only  to  tartaric  acid  and  sugar,  7  only  to  quinin 
and  tartaric  acid.  4  only  to  sugar  and  quinin.  Xo  definite  results  were  ob- 
tained with  reference  to  the  sensitivity  of  different  papillae  for  salt.  Kiesow 
has  reached  similar  conclusions. 

Hoeber  and  Kiesow  have  discussed  the  significance  of  electrolytes  as  gusta- 
tory excitants,  and  have  reached  the  conclusion  that  the  specific  sensations  are 
aroused  in  part  by  ions.  For  example,  the  salty  taste  of  KCl  NaCl.  MgClj, 
NaBr,  NaT,  Xa,SO<  is  caused  by  the  electronegative  ions  (CI,  Br,  etc.)  ;  the 
threshold  stimulus  is  given  by  a  concentration  of  0.020-0.025  g.  of  the  ion  per 
liter;  a  sweet  taste  produced  by  a  very  weak  solution  is  caused  by  the  OH-ions, 
the  threshold  value  of  the  stimulus  being  given  by  0.006-0.009  g.  ions  per  liter. 

The  acid  taste  produced  by  the  anode  of  a  constant  current  is  probably  due 
to  electrolytic  dissociation  of  the  saliva. 


486  TASTE   AND  SMELL 

§2.    SENSATIONS   OF   SMELL 

While  the  olfactory  organ  of  man  is  particularly  sensitive  to  certain  odors, 
it  in  general  is  much  less  sensitive  than  that  of  many  other  mammals.  The 
organ  of  smell  is,  in  fact,  much  more  important  for  the  whole  life  of  the 
lower  animals,  because  it  is  mainly  by  this  sense  that  they  find  and  select 
their  food.  Among  civilized  men  this  sense  plays  but  a  small  part  for  such 
purposes,  although  it  is  stated  that  some  so-called  wild  people  are  possessed 
of  a  very  highly  developed  sense  of  smell.  Thus  Humboldt  relates  that  the 
Peruvian  Indians  can  follow  the  trail  by  scent  with  as  much  accuracy  as  a 
hunting  dog.  Among  civilized  people  the  sense  of  smell  serves  to  test  the  air 
inhaled  or  furnish  information  as  to  the  nature  of  the  food  to  be  eaten.  As 
a  rule  it  is  of  no  very  great  service  even  in  this  respect  for  the  olfactory  sense 
very  soon  becomes  ])lunted  for  a  certain  odor  and  then  gives  us  no  indication 
of  the  presence  of  harmful  substances  in  the  air.  This  is  notably  true,  for 
example,  of  those  who  live  in  close,  poorly  ventilated  dwellings.  The  report 
made  by  the  sense  of  smell  as  to  the  quality  of  the  food  is  influenced  largely 
by  conventional  customs,  and  these  differ  according  to  times  and  places.  The 
olfactory  sensations  probably  serve  us  most  by  arousing  and  promoting  the 
desire  for  food. 

It  has  long  been  known  that  only  the  uppermost  part  of  the  mucous  mem- 
brane lining  the  nasal  passages  is  provided  with  the  olfactory  epithelium. 
The  investigations  of  v.  Brunn  have  shown  that  the  region  actually  supplied 
with  olfactory  nerves  extends  over  only  a  relatively  small  part  of  the  superior 
turbinated  bone  and  the  opposite  face  of  the  nasal  septum.  The  epithelium 
here  covers  an  area  somewhat  smaller  than  a  ten-cent  piece  each  side  of  the 
olfactory  cleft,  situated,  therefore,  in  the  roof  of  the  nasal  cavity  as  far 
removed  as  possible  from  the  external  nares. 

Unless  the  act  of  inspiration  is  modified  so  as  to  carry  the  air  directly 
to  the  upper  part  of  the  nose  the  air  current  never  goes  higher  than  the 
anterior  lower  edge  of  the  superior  turbinated  bone  (Franke)  and  conse- 
quently does  not  pass  over  the  olfactory  region.  Since,  however,  we  experi- 
ence olfactory  sensations  in  ordinary  respiration  and  since  we  have  convincing 
evidence  that  the  normal  excitation  of  the  olfactory  organ  takes  place  by 
means  of  material  particles  in  the  air  (see  below)  we  must  suppose  that  the 
odoriferous  particles  reach  the  olfactory  cleft  by  diffusion. 

Since  the  nose  is  always  in  open  communication  with  the  throat,  odoriferous 
substances  can  of  course  always  pass  thence  into  the  nose  and  so  reach  the 
olfactory  cleft.  This  is  what  happens  when  we  eat.  While  a  morsel  of  food  is 
being"  masticated  vapors  pass  into  the  nasopharynx  and  are  then  carried  upward 
into  the  olfactory  region  by  the  expired  air.  In  swallowing  the  nasal  cavity  is 
closed  off  from  the  throat  but  immediately  afterwards  communication  is  reestab- 
lished and  the  following  expiration  carries  the  vapor  of  substances  moistening 
the  wall  of  the  pharynx  into  the  nose.  It  is  at  this  moment,  but  not  so  long 
as  the  fluid  remains  in  the  mouth,  that  one  "  tastes  "  the  aroma  or  the  bouquet 
of  drinks. 

It  was  thought  for  a  long  time  that  the  olfactory  organ  is  stimidated  by 
vibrations  of  the  odorous  substances,  and  that  the  organ  of  smell  was,  there- 


SENSATIONS   OF   SMELL 


487 


fore,  analogous  to  the  organ  of  hearing.  The  chief  support  of  this  view  was 
that  with  certain  strongly  odorous  substances  no  loss  in  weight  could  l)e  de- 
tected with  the  balance,  whereas,  if  it  were  true  that  the  olfactory  organ  was 
excited  by  material  particles  set  free  from  them  there  should  be  such  a  loss. 
But  Berthollet  demonstrated  that  material  particles  are  given  off  from  odorous 
substances.  He  placed  a  piece  of  camphor  in  a  vacuum  of  a  barometer;  the 
mercury  of  the  barometer  gradually  fell,  thus  showing  that  small  particles 
of  camphor  were  given  off,  that  they  collected  in  the  empty  space  and  exerted 
pressure  on  the  mercury. 

Another  proof  which  we  owe  to  Tyndall  is  the  following:  Radiant  heat 
passes  through  an  absolutely  empty  space  without  being  absorbed;  if,  how- 
ever, a  gas  is  placed  in  the  path  of  the  heat  rays,  a  greater  or  less  amount 
of  heat,  according  to  the  nature  of  the  gas,  is  held  back  by  it.  Xow  Tyndall 
showed  that  an  atmosphere  which  had  been  in  contact  with  odorous  substances 
and  had  taken  up  its  vapor,  absorbs  radiant  heat  to  a  much  greater  extent 
than  pure  atmospheric  air.  Thus  the 
vapor  of  patchouli  absorbed  thirty-two 
times  as  much  as  air,  oil  of  rose  thirty- 
six  times,  oil  of  anise  three  hundred 
and  seventy-two  times  as  much. 

Odors  are  carried  in  a  quiet  atmos- 
phere by  diffusion.  Of  course  air  cur- 
rents and  the  like  also  aid  much  in  this 
distribution.  The  carrying  power — i.  e., 
the  power  of  diffusion — varies  with  dif- 
ferent odors. 


192. — Olfactometer,    after    Zwaarde- 
maker. 


Johannes  Miiller  and  several  other 
authors  assumed  that  the  particles  of  Fig. 
odoriferous  substance  were  first  dis- 
solved in  the  mucus  covering  the  olfac- 
tory region  and  then  stimulated  the  olfactory  epithelium.  Since,  however,  very 
many  odorous  substances  are  very  slightly,  if  at  all,  soluble  in  water,  Zwaarde- 
maker  has  put  forward  the  hypothesis  that  stimulation  takes  place  by  direct 
contact  of  the  gaseous  molecules  with  the  cilia  of  the  olfactory  cells.  The  fact 
that  fishes — e.  g.,  the  dogfish — have  a  well-developed  sense  of  smell  speaks 
pretty  definitely  in  favor  of  Miiller's  view. 

Zwaardemaker  has  constructed  a  small  apparatus,  the  olfactometer  (Fig.  192). 
for  the  purpose  of  testing  the  acuteness  of  the  sense  of  smell.  The  essential  parts 
of  this  apparatus  are  a  paper  cylinder  and  a  tube  through  which  one  may  inhale. 
The  cylinder,  which  can  also  be  made  of  filter  paper,  is  dipped  in  the  scented 
fluid,  and  when  its  pores  are  filled  with  this,  it  is  withdrawn,  dried  out  and 
hastily  blown  through.  The  smelling  tube,  which  fits  exactly  into  the  tubulure 
of  the  cylinder,  is  then  inserted  and  the  other  end  placed  in  the  nasal  opening. 
The  small  wooden  shield  serves  to  keep  the  odor  out  of  the  other  nasal  opening. 

When  air  is  inhaled  through  the  tube  from  the  cylinder  impregnated  with 
the  odorous  substance  the  number  of  odoriferous  particles  reaching  the  nose 
will  vary  inversely  as  the  depth  to  which  the  smelling  tube  is  inserted  into  the 
cylinder.     By  graduating  the  tube,  one  can  thus  make  veiy  rapid  and  very  exact 


488  TASTE  AND  SMELL 

relative  detenninations  as  to  the  acuteness  of  the  olfactory  sense  in  different 
individuals. 

The  following  data  by  Passy  give  some  idea  of  the  quantitative  capacity 
of  this  sense  in  man.  All  the  sources  of  error  involved  tend  to  make  the 
results  rather  too  high  than  too  low: 

Mg.  per  liter  of  air. 

Essence  of  orange 0.00005-0.001 

Ether 0.0005-0.004 

Camphor 0.005 

The  smallest  value  thus  far  published  for  the  threshold  value  of  the  sense 
of  smell  is  that  of  Fischer  and  Penzoldt.  They  observed  that  0.01  mg.  of 
mercaptan  uniformly  distributed  through  an  air-tight  room  of  230  cubic 
meters  capacity  still  gave  a  faint  but  distinct  odor.  This  would  be  only 
0.00000004  mg.  of  mercaptan  per  1.  of  air. 

Attempts  have  often  been  made  to  find  a  natural  classification  of  the  odors, 
and  it  cannot  be  denied  that  recent  efforts  in  this  direction  as  well  as  the 
observations  of  Haycraft  on  the  relation  between  the  chemical  constitution 
and  the  odor  of  various  substances  give  promise  that  we  shall  some  day  have 
a  real  classification.  For  the  present  I  shall  only  remark  that  many  vaporous 
or  gaseous  substances  act  to  a  greater  or  less  extent  upon  the  organs  of  taste 
connected  with  the  trigeminal  nerve  so  that  the  resulting  sensation  is  in  large 
part  iit  least  the  result  of  a  gustatory  excitation.  This  is  true  of  all  the  so- 
called  pungent  substances  like  chlorin,  iodin.  bromin,  nitric  acid,  acetic  acid, 
ammonia,  oil  of  mustard,  etc.  According  to  Zwaardemaker  structures  are 
found  in  the  olfactory  region  which  resemble  the  taste  buds  and  which  mediate 
the  sweet  odor  of  chloroform.  According  to  Xagel  we  have  to  do  in  this  case 
with  a  stimulation  of  gustatory  nerves  on  the  posterior  side  of  the  uvula. 

Although  we  cannot  yet  erect  a  natural  system  of  odors  we  can  say  defi- 
nitely that  different  kinds  of  olfactory  sensations,  to  a  certain  degree  at  least, 
are  mediated  by  different  nerves.  Certain  individuals  who  possess  a  well- 
developed  sense  of  smell  for  some  substances  are  unable  to  perceive  the  odor 
of  others.  For  example,  there  are  people  who  cannot  smell  vanilla  and  yet 
are  sensitive  enough  to  other  odors.  The  same  is  true  of  the  odor  of  violets. 
We  must  suppose  that  in  these  people  certain  nerve  fibers  or  end  organs  are 
wanting. 

The  presence  of  diffrrcnt  olfactory  nerves  is  more  definitely  proved  by  the 
phenomena  of  fatigue  of  the  olfactory  organ.  For  example,  Aronsohn  has 
shown  that  when  this  organ  becomes  fatigued  for  one  odor  it  still  remains 
entirely  functional  for  others.  Again,  when  the  sense  of  smell  is  temporarily 
lost  as  the  result  of  injury  to  the  olfactory  organ,  it  is  not  recovered  for  all 
odorous  qualities  within  the  same  time — e.  g.,  in  one  case,  for  creosote  three 
days,  skatol  and  mercaptan  four  days,  musk  seventeen  days,  roast  beef  two 
months,  etc.   (Eollet). 

References.— F.  Kiesow,  "  Geschmackssinn,"  "  Wundt's  Philosophische  Stu- 
dien,"  vols,  x,  xii,  1894,  1896.-^7;.  Ohrwall,  "Geschmackssinn,"  Skandinavisches 
Arch,  fur  Physiologic,  vol.  ii,  1897. — H.  Zwaardemaker,  "Die  Physiologic  des 
Geruehes,"  Leipzie,  1895. 


CHAPTER    XX 

HEARING,    VOICE   AND    SPEECH 

FIRST    SECTION 

AUDITORY    SENSATIONS 

§  1.    STIMULI   APPROPRIATE   FOR   THE    ORGAN   OF   HEARING 

The  organ  of  hearing  is  stimulated  by  the  vibrations  of  elastic  bodies 
which  we  perceive  as  sound.  Helmholtz,  whose  presentation  of  the  subject  ^ 
we  shall  follow  here  in  the  main,  divides  auditory  sensations  into  two  groups: 
namely,  noises  and  musical  tones. 

A  musical  tone  is  produced  by  regular  periodic  movements  of  the  sounding 
body,  which  are  communicated  by  it  to  the  air  or  some  other  elastic  medium. 
By  a  regular  periodic  movement  we  mean  a  movement  which  is  repeated  at 
exactly  the  same  interval  of  time,  and  always  exactly  in  the  same  manner. 
The  length  of  the  interval  from  the  beginning  of  one  movement  to  the  next 
repetition  of  it  is  called  the  wave  length  or  the  period. 

As  a  rule,  the  vibrations  are  conveyed  to  the  ear  through  the  air.  The 
particles  of  air  must  therefore  execute  regular  periodic  vibrations,  moving  to 
and  fro  within  narrow  limits  so  that  the  air  is  alternately  condensed  and 
rarefied  (wave  crest  and  wave  trough).  Sound  is  propagated  in  the  form  of 
concentric  spherical  waves,  new  particles  of  air  in  all  directions  from  the 
sounding  body  being  successively  set  in  motion. 

Three  qualities  of  sound  are  to  be  distinguished :  loudness,  pitch  and 
timbre. 

A.    LOUDNESS 

The  loudness  of  a  sound  depends  upon  the  ampJitude  of  the  vihratiojis. 
The  greater  the  excursions  which,  for  example,  a  vibrating  piano  string 
descri])es,  the  louder  is  the  sound  at  a  given  distance  from  its  source.  The 
greater  the  distance  from  the  source,  the  weaker  is  the  sound,  the  loudness 
being  inversely  as  the  square  of  the  distance. 

B.    PITCH 

Pitch  is  determined  by  the  vibration  frequency,  or  in  other  words  by  the 
number  of  vibrations  per  second,  and  is  independent  of  the  form  of  the  vibra- 

'  "  Lehre  von  den  Tonempfindungen  als  physiologische  Grundlage  fiir  die  Theone  der 
Musik." 

30  489 


490 


HEARING,  VOICE  AND  SPEECH 


tion  during  the  period.    The  more  frequent  the  vibrations  in  a  unit  of  time — 
i.  e.,  the  shorter  the  period — the  liigher  is  the  tone. 

For  an  exposition  of  the  fundamental  facts  of  this  subject  it  is  very  con- 
venient to  have  a  special  apparatus,  like  the  siren  (Fig.  193),  which  permits 
an  easy  <letermination  of  the  number  of  atmospheric  vibrations  producing 
different  tones. 

A  is  a  thin  disk  of  pasteboard  or  metal  which  is  provided  with  holes  in 
several  concentric  rows  and  at  equal  distances  from  each  other  in  the  same  row. 
It  can  be  set  in  rapid  rotation  by  means  of  the  string  f  which  runs  over  the 
pulley  b.  By  means  of  the  tube  c  a  blast  of  air  of  proper  strength  is  directed 
toward  one  of  the  rows  of  holes.  Each  hole  therefore  as  it  passes  the  mouth  of 
the  tube  lets  out  a  single  puff  of  air  and  thus  when  the  disk  is  rotated  rapidly 
enough   a   tone    is   produced   whose    pitch   depends    upon   the   number   of   holes 

blo-wn  through  in  a  second  of  time. 
This  number  can  be  found  by  count- 
ing the  rotations. 

Now  experiment  has  sho^\Ti  that 
pitch  is  entirely  independent  of  the 
size  of  the  holes  or  the  strength  of 
the  blast  and  thus  it  is  proved  that 
pitch  depends  only  on  the  number 
of  vibrations. 

The  nearer  the  row  of  holes  to 
the  center  of  the  disk — i.  e.,  the 
smaller  the  number  blown  through 
in  a  single  rotation — the  lower  will  be  the  tone,  the  rate  of  rotation  remaining 
the  same.  If  one  row  with  8  and  another  with  16  be  employed  the  tone  pro- 
duced by  the  latter  is  the  octave  of  that  produced  by  the  former — i.  e.,  the 
tone  which  constitutes  the  higher  octave  of  the  other  contains  within  a  given 
time  exactly  twice  as  many  vibrations  as  the  other,  and  the  ratio  of  the  two 
is  as  1 :  2. 

In  the  same  way  the  following  ratios  have  been  found  to  obtain  between 
the  number  of  vibrations  of  the  different  tones  used  in  music :  1 :  2  =  octave ; 
2  :  3  ^  a  fifth  ;  3  :  4  ^  a  fourth  ;  4  :  5  =  major  third  ;  5:6=  minor  third ; 
5:8  =  minor  sixth ;  3:5  =  major  sixth.  These  are  all  consonant  intervals 
— i.  e.,  in  the  octave  every  second  vibration  of  the  upper  note  begins  at  the 
sanie  time  with  one  of  the  lower;  in  the  fifth,  every  third;  in  the  fourth, 
every  fourth,  etc. 

There  is  an  upper  and  a  lower  limit  to  the  frequency  of  periodic  vibrations 
capable  of  exciting  the  auditory  organ. 

The  smallest  number  per  second  which  can  be  heqrd  by  the  human  ear  is 
given  by  Preyer  as  15-24,  by  Helmholtz  as  28,  by  Bezold  using  highly  improved 
experimental  methods  as  11 ;  but  sounds  only  begin  to  acquire  a  definite  musical 
pitch  at  about  40  vibrations  per  second.  The  highest  number  which  can  be 
heard  as  a  distinct  sound  according  to  Edelmann  is  in  the  neighborhood  of  50,000. 
The  whole  range  of  perceptible  sounds  (11-50,000)  amounts  therefore  in  the 
most  favorable  case  to  over  12  octaves.  In  music  only  about  7  octaves  (40-4,700 
vibrations)  are  used. 


Fig.    19.3. — Seebeck's  siren. 


STIMULI  APPROPRIATE   FOR  THE   ORGAN   OF   HEARING  491 


C.    TIMBRE 

If  the  same  tone  be  struck  successively  on  different  instruments,  as  the 
violin,  piano,  clarinet,  flute,  etc.,  even  a  musically  untrained  ear  can  readily 
distinguish  the  instruments.  This  property  of  a  musical  tone  which  differs 
with  the  instrument  producing  it  is  described  as  the  timbre  or  quality.  It  is 
this  property  also  by  which  we  distinguish  human  voices. 

Inasmuch  as  the  cause  of  timbre  cannot  lie  in  the  frequency  nor  the 
amplitude  of  the  vibrations,  it  must  be  referred  to  dissimilarities  in  their 
form.  To  a  certain  extent  also  it  is  due  to  the  way  in  which  the  tone  is 
struck. 

How  is  this  difference  in  form  of  the  vibration  to  be  explained?  When 
a  piano  string  is  set  in  vibration  the  pitch  of  the  tone  produced  depends  upon 
two  things :  the  length  of  the  part  vibrating,  and  the  tension  of  the  string. 
The  tension  remaining  the  same,  the  longer  the  vibrating  part  the  deeper  the 
pitch.  If  the  operator  touch  the  middle  of  a  string  lightly  with  his  finger 
and  then  cause  it  to  vibrate,  each  half  will  vibrate  independently  and  so 
twice  as  many  vibrations  per  second  are  made  as  by  the  whole  string.  The 
tone  produced  is  therefore  the  octave  of  the  tone  given  by  the  whole  string. 
In  the  same  way  a  string  can  be  caused  to  vibrate  in  thirds  and  fourths,  etc., 
and  the  number  of  vibrations  of  the  corresponding  tone  will  then  be  three, 
four,  etc.,  times  as  high  as  that  of  the  whole  string. 

Now  whenever  the  string  vibrates  as  a  whole,  it  divides  itself  spontane- 
ously into  two,  three,  four,  five,  etc.,  vibrating  parts.  Hence,  it  gives  in 
addition  to  its  fundamental  tone  other  tones  whose  vibration  frequencies  are 
two,  three,  etc.,  times  as  great  as  the  fundamental,  all  of  them  fused  into 
the  peculiar  sound  of  that  particular  string.  The  tones  produced  by  the 
partial  vibrations  of  the  string  are  called  the  overtones  or  partial  tones,  and 
when  the  vibration  frequency  of  the  overtones  is  a  multiple  of  that  of  the 
fundamental,  they  are  called  harmonious  overtones.  The  harmonious  over- 
tones for  c  are  given  in  the  following  example: 

^        P-a         ^         £         = 


3 


i 


p^ 


12  3456789  10 

Numberof      132        2X133  3X132     4X132     5><?^132     6X132     7X132     8X132     9X132    10X132 

vibrations 

What  has  been  said  of  the  piano  string  is  true  for  musical  instruments 
in  general,  inclusive  of  the  human  voice.  But  there  are  sounds  which  are 
fairly  free  of  overtones  and  so  consist  of  a  simple  tone  only — as,  e.  g..  the 
proper  sound  of  a  tuning  fork.  Such  tones  are  unusually  soft,  and  free  from 
sharpness  or  roughness.  Comparing  the  timbre  of  a  simple  tone  with  that 
of  a  compound  tone,  including  its  lower  harmonious  overtones,  the  latter  is 
found  to  be  fuller  sounding,  more  metallic  and  brighter  than  the  simple  tone. 

Since  by  far  the  greater  number  of  tones  are  compound  it  is  evident  that 
anv  variation  in  the  number  or  intensity  of  the  overtones  will  produce  some 
difference  in  the  character  of  the  tone;  hence  we  may  point  to  differences 


492  HEARING,  VOICE  AND  SPEECH 

in  the  accompanying  overtones  as  ven*  probalily  the  cause  of  difference  in 
timbre. 

There  remains  for  us  yet  to  consider  how  it  is  possible  for  the  ear  to 
perceive  the  differences  in  the  form  of  vibration  caused  by  the  overtones. 

The  effect  of  overtones  in  altering  the  form  of  vibration  may  be  repre- 
sented diagrammatically  as  in  Fig.  194.  a'  a'  is  the  base  line  of  reference,  the 
dotted  lines  a.  b,  and  c  represent  the  vibrations  of  a  fundamental  tone  (a) 
and  its  first  two  overtones ;  the  solid  line  d  is  the  resulting  vibration  produced 
by  interference  of  the  three.  It  is  evident  that  notwithstanding  the  change 
in  form  of  the  vibration  the  period  of  the  fundamental  tone  remains 
unchanged. 

But  if  these  partial  tones  are  not  to  be  regarded  as  mere  mathematical 
fictions,  if  they  have  a  real  existence,  they  should  produce  some  mechanical 
effect  which  is  recognizal^le.  Such  an  effect  we  find  in  the  phenomenon  of 
sympathetic  vibration  (resonance),  occurring  in  all  bodies  which,  once  they 
are  given  the  impetus,  run  through  a  series  of  different  vibrations  before  they 
come  to  rest.  The  simplest  example  of  this  is  witnessed  when  a  certain  note 
is  sung  into  a  piano.  The  same  note  is  given  back  by  the  piano,  its  intensity 
bearing  a  direct  relation  to  the  exactness  with  which  the  note  of  a  particular 
string  is  struck  by  the  voice.  Sympathetic  vibrations  between  bodies  pro- 
ducing compound  tones  can  be  aroused  even  in  case  the  vibration  frequency 
is  not  exactly  reproduced,  and  this  takes  place  more  readily  the  smaller  the 
mass  of  the  sympathetic  body   (e.  g.,  a  catgut  string  responds  more  readily 


Fig.  194. — Schema  illustrating  the  relation  of  overtones  to  their  fundamental  tone,  after  Hensen. 

than  a  wire  string  of  the  same  diameter).  But  it  is  much  more  difficult  to 
induce  sympathetic  vi])rations  from  a  body  which  gives  no  overtones — e.  g., 
from  a  tuning-fork — because  it  will  respond  only  to  its  own  particular  form 
of  vibration. 

It  has  been  shown  that  a  membrane  adapted  to  a  certain  tone  also  exhibits 
the  phenomenon  of  sympathetic  vibrations,  if  a  lower  tone,  which  contains 
the  tone  of  the  membrane  among  its  overtones,  is  sounded.  The  tympanic 
membrane  of  the  ear  is  not  adapted  to  any  one  tone — i.  e.,  has  no  fundamental 
tone — hence  does  not  select  any  single  tone  by  resonance. 


TRANSMISSION   OF   SOUND   IN  THE   EAR  493 

The  actual  presence  of  overtones  can  be  demonstrated  still  more  clearly 
by  the  use  of  the  Helmholtz  resonators.  These  may  have  different  forms.  The 
one  shown  in  Fig.  195  has  the  form  of  a  hollow  sphere,  one  opening  (o)  of 
which  ends  abruptly,  while  the  other  (h)  is  drawn  out  funnellike  and  so  shaped 
as  to  tit  into  the  ear.  The  air  of  such  a  resonator  in  conjunction  with  that  of 
the  auditory  passage  and  the  eardrum  forms  an  elastic  system,  which  intensifies 
the  fundamental  tone  of  the  sphere.  Of  course,  one  can  have  a  whole  series 
of  resonators  adapted  to  the  different  tones.  If  now  a  certain  resonator  be 
placed  to  the  ear  and  the  attention  is  directed  to  a  sound  or  series  of  sounds 
in  which  the  particular  tone  of  that  resonator  occurs,  this  tone  will  be  intensi- 
fied to  so  great  an  extent  that  it  can  readily  be  heard  above  the  others. 

These  and  other  observations  which  we  cannot  go  into  here  make  it  per- 
fectly certain  that  the  different  overtones  actually  exist  in  compound  tones. 

The  following  experiment  shows  di- 
rectly that  the  ear  also  can  receive  these 
overtones  and  is  therefore  sensitive  to  each 
and  every  simple  vibration  of  this  kind. 
If  the  tone  g  of  the  first  octave  be  struck 
on  the  piano  and  immediately  afterwards 
the  tone  c  of  which  g  is  the  second  over- 
tone and  the  attention  be  directed  steadily 
to  g,  one  can  hear  it  in  the  tone  c,  after  the 
g  string  has  ceased  vibrating.  In  the  same 
way  one  can  convince  himself  that   e  of 

the   second  octave   is  one  of   the   overtones  Fig.   195.— Resonator  of  Helmholtz. 

of  c.     Often  the  overtones  become  clearer 

as  the  string  ceases  to  vibrate,  for  it  appears  that  they  die  out  more  slowly 

than  the  fundamental  tone. 

The  ability  of  the  ear  to  analyze  sounds  into  their  constituents  is  attested 
by  our  every-day  experiences  that  we  can  easily  distinguish  the  individual 
tones  of  an  organ  though  only  a  person  musically  trained  can  name  them. 

The  facts  which  make  it  possible  for  the  ear  to  analyze  sound  may  be 
summarized  briefly  as  follows.  Every  movement  of  the  atmosphere  which 
represents  a  compound  of  tones  can  he  resolved  into  a  number  of  simple 
pendulumlike  vibrations,  and  for  each  such  vibration  there  is  a  tone  per- 
ceptible to  the  ear  whose  pitch  is  determined  by  the  vibration  frequency  of 
the  atmospheric  movement  (Ohm's  law). 

How  does  the  ear  accomplish  this  analysis?  Since  the  endings  of  the 
auditory  nerve  are  found  in  the  internal  ear.  it  is  plain  that  analysis  of  sound 
must  take  place  there,  also  that  sounds  must  l)e  transmitted  thither  without 
any  consideral)le  change.  These  phenomena  will  occupy  us  in  the  pages  imme- 
diately following. 

§  2.    TRANSMISSION    OF   SOUND    IN   THE    EAR 

The  external  and  middle  ear  together  constitute  merely  an  apparatus  for 
the  transmission  of  sound,  and  careful  investigation  of  auditory  sensations 
has  shown  that  this  apparatus  is  able  to  transmit  sound  waves  to  the  internal 
ear  without  any  considerable  modification. 


494 


HEARING,  VOICE  AND  SPEECH 


A.    THE  EXTERNAL  EAR 

• 

Since,  owing  to  the  feeble  development  of  the  ear  muscles,  the  human 
pinna  cannot  be  turned  in  different  directions,  it  is  of  but  slight  service  in 
the  collection  of  sound  waves.  It  has  been  shown  also  that  the  reflection 
of  sound  waves  by  the  pinna  is  of  no  importance  (Harless,  Mach). 

The  external  auditory  meatus  ought  probabl}'  to  be  described  as  a  means 
of  protection  for  the  eardrum.  The  indirect  course  of  the  canal  itself  favors 
this  view,  since  in  order  to  see  the  drum  the  pinna  must  be  drawn  considerably 
upward  and  backward.  Besides,  this  canal  is  provided  with  sensitive  hairs 
which  together  with  the  disagreeable  odor  of  the  earwax  secreted  in  the  canal 
serve  to  prevent  the  entrance  of  insects.  The  passage  also  protects  the  middle 
and  internal  ear  from  variations  of  temperature. 

Like  every  hollow  space  of  the  kind  the  external  auditory  meatus  has  its 
own  resonance  tone,  situated  between  c'^  and  a'^ '  (Helmholtz,  Hensen).  If  this 
tone  be  contained  in  a  sound,  naturally  it  will  be  intensified  above  other  tones 

by  the  sympathetic  vibration  of  the  air 
in  the  canal,  but  owing  to  its  high 
position  in  the  scale  its  resonance  is 
of  no  great  consequence  from  a  practi- 
cal standpoint. 

A  tuning  fork  allowed  to  die  out 
until  the  vibrations  are  just  impercep- 
tible when  it  is  held  close  to  the  ear, 
can  be  heard  again  if  the  handle  be 
placed  between  the  teeth.  In  this  case 
the  sound  is  conducted  in  part  directly 
through  the  bones  of  the  head  to  the 
internal  ear  and  in  part  is  transmitted 
from  the  bones  to  the  eardrum  and 
propagated  thence  as  usual  through 
the  auditory  ossicles. 

B.    THE  MIDDLE  EAR 

1.  Vibrations  of  the  Eardrum. — 
The  tympanic  membrane  or  eardrum 
is  a  fibrous  membrane  0.1  mm.  in 
thickness,  formed  mainly  of  external 
radial  and  internal  circular  fibers.  It 
is  obliquely  placed  across  the  internal 
end  of  the  external  auditory  meatus 
and  is  drawn  inward  at  its  middle  by 
the  long  process  of  the  malleus  which 
is  inserted  into  its  tissue  along  one  of 
given  the  form  of  a  shallow,  irregular 
(Fig.  196). 


Fig.  196. — Transverse  section  through  the  left 
auditory  canal  and  tympanic  membrane  of 
man,  enlarged  four  times,  after  Hensen. 
The  section  is  taken  just  behind  the  handle 
of  the  hammer  in  a  plane  parallel  to  the 
handle.  G,  external  auditory  meatus;  C, 
tympanic  cavity;  S,  the  stapes;  H,  the  ham- 
mer; a  ledge  projects  at  L,  to  which  the 
ligaments  are  attached.  Between  the  long 
process  of  the  anvil  and  the  handle  of  the 
hammer  the  tendon  of  the  tensor  tjTiipani 
may  be  seen;  LS,  ligament um  superior. 

its  radii.     In  this  way  the  membrane  is 
funnel  with  an  aperture  of  about  125° 


*  The  small  Roman  numerals  designate  octaves. 


TRANSMISSION   OF   SOUND   IN   THE   EAR 


495 


The  membrane  is  set  in  vibration  by  the  oscillations  of  the  atmosphere 
and  is  so  arranged  that  it  does  not  favor  any  particular  tone. 

Fick  has  worked  out  the  following  conception  of  the  mechanics  of  the 
drum.  The  radii  from  the  tip  of  the  long  process  of  the  malleus  to  the 
periphery  of  the  drum  being  of  different  lengths,  the  different  sectors  of 
the  drum  may  be  looked  upon  as  to  a  certain  extent  independent  of  each 
other.  If  they  were  entirely  independent  strands,  each  would  vibrate  in  re- 
sponse to  its  own  particular  tone.  Being  joined  together  into  a  membrane 
they  do  not  thus  select  individual  tones,  although  separate  parts  can  be  thrown 
into  action  without  moving  distant  parts  very  much.  Consequently,  because 
of   the    summation   of   successive 

vibrations,  regular  periodic  move-  -   ■^^ 

ments  are  more  favorably  received 
by  the  drum  than  single  vibra- 
tions. And  yet  vibrations  of  any 
form  or  frequency  are  faithfully 
transmitted  to  the  handle  of  the 
malleus,  for  among  the  sectors 
and  segments  of  the  membrane 
there  are  always  some  which  are 
suited  to  the  component  vibra- 
tions. Since,  however,  the  mal- 
leus is  a  rigid  body  and  can  only 
vibrate  as  a  whole,  all  the  com- 
ponents will  be  represented  in  the 
form  of  its  movements. 

The  peculiar  form  of  the  tym- 
panic membrane  is  of  special  sig- 
nificance in  another  respect  also ; 

tlie  sound  waves  converging  toward  the  middle  point  are  damped — i.  e.,  dimin- 
ished— in  amplitude,  but  are  increased  in  intensity.  This  aids  greatly  in  the 
transmission  of  vibrations  to  the  perilymph  (Helmholtz). 

2.  The  Auditory  Ossicles. — For  the  anatomical  details  of  the  auditory 
ossicles  the  reader  is  referred  to  text-books  of  anatomy.  We  give  here  briefly 
only  the  facts  with  reference  to  their  mode  of  attachments,  as  made  out  by 
Hensen  and  Schwalbe,  which  are  of  most  importance  for  an  understanding 
of  their  physiological  purpose  (Figs.  196  and  197). 

The  malleus,  or  hammer,  is  attached  to  the  wall  of  the  tympanic  cavity  by 
three  ligaments  (Fig.  197).  The  first  of  these,  the  anterior,  passes  from  the 
processvs  Jongus  and  around  its  base  partly  to  the  larger  spine  of  the  tym- 
panum {Sp.  m.),  partly  through  the  Glaserian  fissure  to  the  angular  spine  of 
the  sphenoid  bond.  Tbo  second  or  external  ligament  (Lifj.  e.rf.)  is  a  short  tense 
band  which  springs  from  the  whole  posterior  half  of  the  notch  of  Rivinus  as 
far  as  the  smaller  spine  of  the  tympanum  opposite  the  hammer,  and  from  this 
relatively  long  line  of  insertion  its  fibers  converge  to  the  crista  mallei.  The 
third  or  superior  ligament  (Fig.  196,  LS)  limits  the  movability  of  the  ossicles 
downward. 

The  tip  of  the  short  leg  of  the  incus  is  fixed  by  means  of  a  strong  ligament 
(ligamentum  incudis  posterius)   to  the  opposite  wall  of  the  tympanic  cavity. 


.j.«t 


Fig.  197. — Nearly  horizontal  section  through  the 
tympanic  cavity,  CT,  of  the  right  ear,  enlarged 
four  times,  after  Ilensen.  The  section  is  taken 
just  above  the  notch  of  Rivinus  and  vertical  to 
the  plane  of  Fig.  196.  H,  medial  edge  of  the 
head  of  the  hammer.  A.  anvil.  The  ligamen- 
tum anterius,  Liij.  a.,  is  seen  springing  from  the 
larger  process,  Sp.  m,  of  the  wall  of  the  tympanic 
cavity  and  passing  to  the  hammer  where  it  be- 
comes continuous  with  the  ligamentum  laterale. 
LI  of  the  anvil-hammer  joint.  The  ligamentum 
externum,  Liy.  c.vt.  springs  the  notch  of  Rivinus 
and  passes  to  the  hammer. 


496 


HEARING,   VOICE   AND  SPEECH 


When  the  tympanic  membrane  moves  in  and  out  in  response  to  the  at- 
mospheric vibrations  tlie  handle  of  the  hammer  naturall}'  moves  with 
it ;  but  the  head  of  the  hammer  moves  in  the  opposite  direction.  Too 
great  an  excursion  of  the  handle  outward  is  prevented  l)v  the  external 
ligament. 

The  incus  articulates  with  the  head  of  the  malleus  by  means  of  a  peculiar 
saddle-shaped  joint,  the  physiological  significance  of  which  has  been  pointed 
out  b}^  Helmholtz.  This  joint  is  provided  with  ratchet  teeth,  which,  as  will 
be  evident  from  inspection  of  Fig.  198,  engage  each  other  in  such  a  way  that 
the  incus  is  carried  along  with  every  movement  of  the  manubrium  inward, 
while  they  are  disengaged  when  the  manubrium  moves  outAvard.     In  this  way 

the  danger  of  tearing  the  stapes  from  its 
fastening  in  the  foramen  ovalis  when  the 
tympanic  membrane  is  for  an}^  reason  pushed 
outward,  is  diminished.  Helmholtz  estimates 
that  the  hammer  can  be  rotated  five  degrees 
outward  without  carrying  the  anvil  with  it. 
If  we  imagine  the  hammer  and  anvil 
locked  together  by  their  ratchet  teeth  so  that 
the  tM'o  move  inward  as  one  solid  body,  the 
system  formed  by  the  two  ossicles  can  be 
regarded  as  a  one-armed  lever,  the  fulcrum 
of  which  lies  where  the  apex  of  the  short 
process  of  the  anvil  is  supported  against  the 
wall  of  the  tympanic  cavity.  The  tip  of 
the  manubrium  constitutes  the  point  where 
the  ])ower  is  applied,  the  apex  of  the  long 
process  of  the  an\'il  the  point  where  the  load 
— i.  e.,  the  stapes — is  acted  upon.  These 
three  points  lie  almost  exactly  in  a  straight 
line,  the  joint  between  the  stapes  and  anvil 
lying  only  a  little  inside  the  line  joining 
the  other  two.  The  lever  a  a  (Fig.  198)  is  about  9.5  mm.  long,  the  short  arm 
between  the  two  apices  of  the  anvil  being  about  6.3  mm. — i.  e.,  just  two-thirds 
of  the  long  arm. 

It  follows  that  when  the  hammer  and  anvil  are  firmly  engaged,  the  excur- 
sion of  the  incus-stapes  joint  is  only  two-thirds  that  of  the  apex  of  the  manu- 
brium, but  the  pressure  which  the  stapes  exerts  on  the  oval  window  is  one 
and  one-half  times  as  great  as  that  which  acts  upon  the  apex  of  the  manu- 
brium ( Helmholtz ) . 

The  top  of  the  stapes  is  attached  by  a  strong  ligament  to  the  long  process 
of  the  incus,  and  its  base  is  fastened  into  the  fenestra  ovalis  by  means  of  a 
thin  membrane.  The  stapes  must  accompany  all  the  movements  of  the  long 
process  of  the  incus,  so  that  when  the  tympanic  membrane  moves  inward,  the 
base  of  the  stapes  is  pressed  into  the  labyrinth.  At  the  same  time  there  takes 
place  a  slight  rotation  of  the  stapes  around  the  long  axis  of  its  base.  A  limit 
is  set  to  the  movement  of  the  base  inward  by  the  resistance  of  the  membrane 
holding  it  in  the  oval  window. 


Fig.  198. — Hammer  and  anvil,  after 
Helmholtz.  PE,  processus  Folia- 
nus;  Tt,  tensor  tympani ;  b,  ratchet 
tooth  of  the  anvil. 


TRANSMISSION   OF   SOUND   IN   THE   EAR  497 

Politzer  attached  threads  to  the  malleus  and  incus  and  recorded  their  move- 
ments on  a  revolving  drum.  In  this  way  he  was  able  to  show  by  direct  experi- 
ment what  is  supported  also  by  theoretical  considerations,  namely,  that  sound 
is  transmitted  from  the  tympanic  membrane  to  the  labyrinth  by  molar  move- 
ments of  the  auditory  ossicles  and  not  by  molecular  movements. 

The  round  window  is  closed  by  a  thin  membrane  bathed  on  the  inside  by 
the  perilymph.  The  perihTiiph  being  incompressible,  this  membrane  in  all 
likelihood  constitutes  an  arrangement  by  which  the  movement  of  the  stapes 
inward  can  be  compensated  by  an  equal  movement  outward.  The  endolymph 
has  a  similar  protective  device  in  the  ductus  endolymphaticus,  which  is  con- 
nected on  the  one  hand  with  the  utricle  and  saccule  and  by  these  with  the 
scala  media  of  the  cochlea,  and  on  the  other  passes  through  the  petrous  bone 
and  terminates  on  its  posterior  surface  in  a  little  vesicle  underneath  the  dura 
mater. 

The  round  window  might  also  serve  for  the  purpose  of  conveying  vibrations 
to  the  perilymph,  and  this  in  fact  has  been  observed  when  the  oval  window 
was  rigidly  closed. 

By  means  of  a  capillary  manometer  introduced  into  the  superior  semi- 
circular canal,  Bezold  was  able  to  determine  the  extent  of  the  movements 
described  by  the  conducting  apparatus  of  the  human  ear  with  the  tympanic 
cavity  open.  The  maximum  movement  of  the  manubrium  caused  by  variations 
of  atmospheric  pressure  in  the  external  auditory  canal  was  about  0.76  mm. 
from  one  extreme  to  the  other,  one-third  of  this  being  the  movement  inward 
and  two-thirds  the  movement  outward. 

As  Bezold  remarks,  this  difference  between  the  movement  inward  and  out- 
ward is  difficult  to  harmonize  with  an  exact  transmission  of  sound  waves,  and 
probably  would  not  occur  under  normal  circumstances.  As  a  matter  of  fact 
we  have  in  the  internal  muscles  of  the  ear  a  device  which  in  life  might  correct 
this  lack  of  coordination  observed  after  death. 

These  are  the  tensor  tympani  and  the  stapedius  muscles,  the  former  inner- 
vated in  the  main  by  the  trigeminal  nerve,  the  latter  by  the  facial.  The 
tensor  tympani  draws  the  manubrium  inward  and  thereby  presses  the  stapes 
farther  into  the  labyrinth.  It  serves  thus  to  keep  the  chain  of  ossicles  "  keyed 
up."  Section  of  its  tendon  permits  a  moderate  magnification  of  the  movement 
of  the  whole  chain  and  the  increase  is  almost  exclusively  in  the  outward 
movement  (Bezold). 

E.\pcriments  on  dogs  have  shown  that  the  tensor  tympani  contracts  reflexly 
to  acoustic  stimuli  (Ilensen,  Ilammerschlag  et  at.)  acting  through  subcortical 
centers  not  higlier  than  the  posterior  corpora  quadrigomina   (Ostmann). 

Hensen  looks  upon  the  tensor  tympani  as  an  apparatus  for  accommodating 
the  ear  in  listening  to  faint  sounds,  and  cites  as  evidence  the  fact  that  a  weak 
sound  becomes  stronger  for  the  moment  when  strong  motor  impulses  are  sent 
out,  say  to  the  muscles  of  the  face  or  limbs.  The  explanation  would  be  that 
impulses  are  at  the  same  time  sent  to  the  tensor  tympani  muscle. 

Ostmann  would  ascribe  this  function  to  the  stapedius. 

3.  The  Tympanic  Cavity  and  Eustachian  Tube. — In  order  that  the  middle 
ear  may  fulfill  its  purpose  of  transmitting  the  vibrations  of  the  atmosphere 


498  HEARING,   VOICE  AND  SPEECH 

to  the  labyrinth  to  the  best  advantage,  it  is  necessary  that  all  extraneous 
vibrations  be  excluded  as  far  as  possible.  Moreover,  the  tympanic  cavity 
ought,  if  possible  at  all,  to  have  no  tone  of  its  own,  and  finally  no  difference 
of  atmospheric  pressure,  at  least  no  permanent  difference,  ought  to  obtain 
between  the  tympanic  cavity  and  the  outside  air. 

These  requirements  are  sufficiently  fulfilled,  one  can  readily  see,  by  the 
structure  of  the  tympanic  cavity,  this  being  at  once  rather  small  and  very 
irregular  in  shape,  so  that  resonance  to  special  tones  is  prevented. 

The  pressure  inside  the  tympanic  cavity  is  regulated  through  the  Eusta- 
chian tube  communicating  with  the  throat.  Normally  this  tube  is  rather 
tightly  closed,  but  it  is  often  opened — as,  e.  g.,  in  swallowing.  Since  it  is  in 
this  way  that  the  pressure  inside  and  outside  the  tympanic  cavity  is  equalized, 
it  is  well  for  a  person  inclosed  within  a  pneumatic  cabinet,  where  the  air 
pressure  is  considerably  increased,  to  swallow  frequently.  The  tube  is  opened 
also  in  strong  inspiration  and  in  phonation,  although  to  a  less  extent  than  in 
swallowing. 

The  Eustachian  tube  is  lined  with  a  ciliated  epithelium  which  probably 
serves  to  drive  the  mucus,  etc.,  toward  the  throat. 

§  3.    EXCITATION   OF   THE   AUDITORY   NERVE 

The  vibrations  of  the  stapes  are  transmitted  to  the  perilymph,  and  these 
in  turn  set  the  endolymph  in  vibration. 

A.  THE  RESONATORS  IN  THE  COCHLEA 

We  have  already  remarked  that  the  analysis  of  sound  leads  us  to  assume 
that  the  different  perceptible  sounds  have  their  appropriate  resonators  in  the 
ear.  But  it  is  possible  also  to  imagine  that  the  fibers  of  the  auditory  nerve 
themselves  are  thrown  By  the  endolymph  into  vibrations  which  agree  exactly 
with  those  of  the  conducting  apparatus.  Against  this  hypothesis,  however, 
several  objections  may  be  urged,  chief  of  which  is  that  we  have  nowhere  else 
in  physiology  any  analogous  production  in  a  nerve  itself  of  40,000  or  50,000 
molecular  vibrations  per  second.  Besides,  there  are  some  observations  which 
appear  to  speak  directly  in  favor  of  the  resonance  theory.  For  example, 
Bezold  has  found  by  means  of  an  instrument  which  enabled  him  to  vary  the 
number  of  vibrations  per  second  from  that  of  the  lowest  sound  to  that  of  the 
highest,  without  any  omissions,  that  for  different  individuals  there  are  gaps 
of  greater  or  less  size  in  the  series  of  perceptible  tones.  Some  show  defects 
both  in  the  upper  and  the  lower  ends  of  the  series,  others  only  in  the  lower, 
and  still  others  only  in  the  upper  end.  Gaps  of  varying  extent  occur  also  at 
different  places  along  the  course  of  the  scale.  All  of  them  can  be  explained 
by  supposing  that  the  corresponding  resonators  are  wanting. 

That  the  fibers  of  the  auditory  nerve  are  not  set  in  vibration  directly  by 
the  vibrations  of  the  endolymph  is  indicated  by  the  following  considerations 
M'ith  reference  to  fatigue  of  the  ear : 

If  the  vibrations  of  a  tuninp:  fork  in  a  distant  room  be  transmitted  by 
means  of  two  telephones  to  the  two  ears,  the   tone  will  appear  to  be  located 


EXCITATIOX   OF  THE   AUDITORY   NERVE  499 

exactly  in  the  mid  line  of  the  head.  If  it  be  transmitted  to  only  one  ear  for  a 
time,  and  then  the  two  telephones  be  used  again,  the  tone  appears  now  to  be 
on  the  side  of  the  ear  which  was  resting.  If  in  this  way  the  one  ear  be  fatigued 
for  a  tone  say  of  360  vibrations  per  second,  and  immediately  afterwards  one  of 
365  vibrations  be  transmitted  to  both  ears,  the  one  fatigued  for  360  vibrations 
will  show  no  trace  of  fatigue  for  the  new  tone.  It  is  difficult  to  see  how  the 
nerve  fibers  could  be  excited  directly  by  one  of  these  tones  and  not  by  the  other. 
The  difficulty  disappears  by  supposing  that  each  has  a  resonator  which  is  not 
affected  by  the  other. 

We  can  think  of  the  analysis  of  tones,  therefore,  as  follows :  In  the  internal 
ear  there  are  a  large  number  of  resonators  adapted  for  different  tones,  which 
are  called  into  play  if  the  appropriate  vibrations  are  transmitted  to  the  endo- 
lymph.  Each  of  these  resonators  in  some  way  affects  a  nerve  fiber.  The 
excitation  thus  aroused  is  transmitted  to  the  brain  and  there,  according  to 
the  nerve  fiber  which  brings  it,  gives  rise  to  a  perception  of  one  tone  or  another. 

In  order  to  test  the  plausibility  of  this  hypothesis  it  is  necessary  to  in- 
quire whether  the  structures  which  might  be  regarded  as  resonators  are  present 
in  sufficient  number  to  account  for  the  analytical  powers  of  the  ear. 

Only  exceptionally  does  one  meet  with  a  man  who  cannot  tell  definitely 
which  of  two  successive  tones  is  the  higher,  provided  that  the  interval  between 
them  really  is  great  enough.  In  musically  educated  individuals  this  ability 
is  very  great.  According  to  Preyer  trained  persons  can  recognize  a  difference 
of  0.3-0.5  vibrations  per  second  within  the  range  from  a^  to  c";  above  and 
below  this  range  the  ability  is  much  less — e.  g.,  with  c^  errors  of  as  much  as 
one  hundred  and  more  vibrations  may  occur. 

According  to  Helmholtz's  calculations  some  4,200  resonators — i.  e.,  600 
per  octave — would  be  sufficient  to  account  for  the  best  possible  discernment 
of  fractions  of  a  half  tone.  Besides  this,  300  resonators  would  be  enough  for 
the  tones  not  used  in  music — i.  e.,  4,500  in  all. 

We  have  seen  that  the  semicircular  canals  and  the  otolith  sacs  probably 
have  no  acoustic  functions,  or  that  at  most  they  take  part  only  in  the  percep- 
tion of  noises  (cf.  page  475).  The  whole  structure  of  the  nerve  endings  in 
the  cochlea,  on  the  other  hand,  favors  the  view  that  the  peripheral  organ  for 
the  analysis  of  sound  is  to  be  sought  here. 

On  the  basilar  membrane  (Fig.  199,  mh)  we  find  the  organ  of  Corti.  This 
contains  a  very  large  number  of  rodlike  structures,  the  pillars  of  Corti  (ic  and 
dc),  standing  side  by  side  throughout  the  whole  length  of  the  cochlea  and  bound 
together  by  means  of  a  joint  at  the  top  into  pairs. 

These  pillars  are  surrounded  outside  and  inside  by  peculiar  epithelial  cells, 
some  of  which,  the  outer  (ah)  and  inner  (ih)  hair  cells,  bear  hairlike  processes 
ending  freely  in  the  endolymjih.  These  cells  are  in  connection  with  the  end- 
ings of  the  auditory  nerve.  The  hasilar  membrane  is  of  varying  width  at  differ- 
ent parts  of  the  cochlea  and  contains  fibers  which  are  stretched  transversely  to 
the  cochlear  canal.     These  are  imbedded  in  a  transparent  matrix. 

The  required  resonators  must  be  found  among  these  structures  and  their 
number  is  quite  sufficient  for  the  purpose;. for,  according  to  Retzius,  the  cochlea 
of  man  contains  5,600  inner  pillar  cells,  3,850  outer  pillar  cells,  3,500  inner 


500 


HEARIXG,   VOICE  AND  SPEECH 


hair  cells,,  12.000  outer  hair  cells   (in  four  rows),  and  24,000  fibers  in  the 
basilar  meml)rane. 

We  can  oiily  conjecture  which  of  these  structures  are  the  true  resonators 
Originally,  Helmholtz  ascribed  this  function  to  the  pillars  of  Corti ;  Zlr, 

>  t:  t:  -'s  ^ 


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however,  he  gave  up  this  view  because  it  was  found  that  birds  and  reptile,  h.ve 
fact'that?h  r  -r  '""''^^-^^'^y  -^--  After  Hensen  had  estall  ltd  he 
fact  that  the  basilar  membrane  varies  in  width  in  different  parts  of  the  cochlea 


EXCITATIOX   OF  THE   AUDITORY    NERVE  501 

Helmholtz  sought  the  resonators  in  the  transverse  strands  of  this  structure. 
In  a  menihrane  of  this  kind  where  the  longitudinal  tension  is  small  as  com- 
pared with  the  transverse  tension,  the  radial  fibers  act  like  a  system  of  sepa- 
rate strings.  The  membrane  connecting  them  serves  only  to  give  the  pressure 
of  the  fluid  a  purchase  on  the  strings  and  each  one  will  therefore  vibrate 
independently  of  the  others. 

Finally,  the  hair  cells  might  serve  as  resonators.  In  short,  although  we 
cannot  settle  definitely  on  a  choice  between  these  various  elements,  it  must 
be  evident  that  there  is  no  lack  of  structures  suitable  for  such  a  function. 

B.    OBJECTIONS  TO   THE   RESONANCE   THEORY 

The  resonance  theory  of  Helmholtz  fits  in  remarkably  well  with  the  facts 
mentioned  thus  far.  But  there  are  some  circumstances  under  which  the  the- 
ory cannot  be  applied  so  readil}',  and  these  circumstances  must  not  be  passed 
over  in  silence. 

1.  Beats. — When  two  tones  of  different  vibration  frequencies  are  sounded  at 
the  same  time,  if  the  difference  between  them  is  not  too  great,  the  vibrations 
of  the  two  will  interfere  with  each  other,  producing  what  are  called  beats.  Thus 
if  the  difference  in  the  number  of  vibrations  be  only  one  per  second,  and  if  the 
two  tones  be  struck  at  the  same  instant,  the  air  waves  of  the  deeper  tone  will 
gradually  fall  behind  those  of  the  higher  until  at  the  end  of  a  half  second  the 
summit  of  one  wave  will  coincide  with  the  valley  of  the  other;  after  another 
half  second  the  two  summits  will  coincide,  and  so  on.  And  in  general  if  n 
represent  the  number  of  vibrations  of  a  tone  per  second,  and  n  -\-\  that  of 
another,  then  the  loudness  of  the  tone  will  be  increased  every  second  and  be 
diminished  every  half  second.  The  number  of  beats  per  second  therefore  will 
always  be  equal  to  the  difference  in  the  number  of  vibrations  per  second  between 
the  two  tones. 

Now  if  each  tone  has  only  one  independent  resonator  in  the  cochlea,  it  is 
difficult  to  see  how  it  would  be  possible  for  two  tones  to  influence  each  other 
in  this  way.  There  is,  however,  veiy  good  reason  for  believing  that  each  tone 
excites  several  neighboring  resonators,  and  the  diflSculty  offered  by  beats  for 
the  resonance  theory  is  readily  disposed  of  by  this  supposition.  For  two  tones 
lying  close  together  we  suppose  must  influence  several  resonators  in  common ; 
then  since  the  objective  strength  of  the  tone  varies  incessantly  because  of  the 
interference,  the  sympathetic  vibrations  of  the  resonators  common  to  the  two 
must  likewise  vary  in  strength,  and  hence  the  subjective  sensation  must  present 
similar  variations.  Other  phenomena  connected  with  beats  can  be  explained 
from  the  same  viewpoint. 

2.  Combination  Tones. — When  two  tones  not  too  close  together  in  the  scale 
are  sounded  at  the  same  time,  one  may  hear,  as  was  first  pointed  out  by  Sorge 
(1740)  and  Tartini,  a  true  tone,  the  vibration  frequency  of  which  is  equal  to 
the  difference  in  the  number  of  vibrations  per  second  between  the  two.  For  ex- 
ample, striking  a  fundamental  and  its  fifth  at  the  same  time  (ratio  2:3),  one 
hears  the  lower  duodecimo  of  the  fundamental.  The  first  difference  tone 
then  forms  a  second  difference  tone  with  the  first  primary  tone.  Under  cer- 
tain circumstances  a  tone  may  also  be  perceived  which  represents  the  sum 
of  the  vibration  frequencies  of  the  two  primary  tones  (Helmholtz).  These 
difference  tones  and  summation  tones  are  included  under  the  term  combina- 
tion tones. 


502  HEARING,  VOICE  AND  SrEECH 

Lagrange  and  Young  regarded  the  difference  tones  as  a  kind  of  beats  and 
explained  them  on  the  assumption  of  subjective  interference.  If  this  were 
shown  to  be  true,  it  would  constitute  an  absolute  refutation  of  the  resonance 
theory,  for  these  particular  tones  would  then  have  no  objective  existence  and  so 
could  not,  as  the  theory  demands,  excite  resonators  in  the  ear.  The  summation 
tones  would  constitute  still  greater  difficulty  for  the  theory. 

Helmholtz,  however,  found  an  explanation  for  these  tones  by  supposing  that 
either  the  tympanic  membrane  or  the  incus-malleus  joint,  or  both,  are  not  uni- 
formly elastic,  and  that  the  combination  really  takes  place  therefore  in  the  con- 
ductors of  the  ear.  Several  authors  do  not  find  this  explanation  wholly  satis- 
factor:S'  and,  because  of  this  and  other  difficulties  which  cannot  be  entered  into 
here,  have  given  up  the  resonance  theory-  altogether  and  adopted  other  views. 
When  all  has  been  said,  however,  it  is  the  opinion  of  the  author  that  the  reso- 
nance theory  is  better  able  to  explain  the  essential  features  of  the  auditory 
sensations  than  any  of  its  rivals.  It  is,  of  course,  not  improbable  that  this 
theory  will  need  to  be  modified  or  extended  in  one  way  or  another,  as  has  been 
done  by  Wundt  and  by  Hermann,  for  example,  but  the  ground  principle — the 
analysis  of  sound  by  resonators  in  the  internal  ear — will,  it  is  the  author's 
belief,  endure. 

SECOND    SECTION 

PHYSIOLOGY    OF   VOICE    AND    SPEECH 

The  physiology  of  voice  and  speech  covers  so  wide  a  field  that  it  will  be 
necessary  for  us  here  to  limit  ourselves  to  the  most  important  facts.  Ijet  it 
be  expressly  understood  that  what  follows  is  to  be  regarded  only  as  a  brief 
orienting  survey. 

The  uppermost  part  of  the  trachea,  the  larynx,  is  fashioned  in  a  peculiar 
way  so  as  to  serve  for  the  production  of  the  voice.  The  most  essential  parts 
of  the  larynx  are  the  vocal  cords.  These  are  thin,  elastic  bands  stretched 
across  the  lumen  of  the  larynx,  and  like  other  structures  of  the  kind,  they 
can  be  made  to  produce  distinct  tones  by  being  set  in  vibration.  In  their 
case  the  vibration  is  caused  bv  a  blast  of  air  from  the  lungs  forced  through 
the  chink  (glottis)  between  their  free  edges.  The  pitch  and  other  qualities 
of  the  tones  thus  produced  are  altered  by  varying  the  tension  and  mode  of 
vibration  of  the  cords.  This  function  it  is  the  business  of  the  laryngeal 
muscles  to  discharge. 

§  L    ACTION   OF   THE   LARYNGEAL   MUSCLES 

The  true  vocal  cords  are  attached  at  one  end  to  the  recurrent  angle  of  the 
thyroid  cartilage  and  at  the  other  to  the  vocal  processes  of  the  arytenoid 
cartilages;  consequently  their  tension  and  position  can  only  be  altered  by 
changing  the  distance  from  the  thyroid  cartilage  to  the  arytenoids  and  the 
distance  from  one  arytenoid  cartilage  to  the  other. 

The  arytenoids  are  fastened  to  the  cricoid  cartilage,  so  that  every  move- 
ment of  the  latter  produces  a  change  in  the  position  of  the  former ;  hence,  the 
distance  between  the  thyroid  and  the  arytenoids  can  be  altered  by  moving 
the  cricoid. 

The  action  of  the  separate  muscles  may  be  condensed  somewhat  as  follows : 


ACTION   OF  THE   LARYNGEAL   MUSCLES 


503 


Contraction  of  the  cricothyroid  increases  the  tension  of  the  vocal  cords  by 
rotating  the  cricoid  cartilage  upon  the  thyroid  around  an  axis  running  through 
the  articulation  which  the  small  (lower)  cornua  of  the  thyroid  make  with  the 
cricoid.  Thus  the  broad  posterior  plate  of  the  cricoid  to  which  the  arytenoids 
are  attached  is  moved  dou-nward  and  backward,  and,  the  arytenoids  being 
prevented  by  ligaments  from  slipping  forward,  as  a  consequence  the  vocal 
cords  are  put  on  a  stretch. 

The  glottis  is  widened  by  moving  the  vocal  processes  of  the  arytenoid 
cartilages,  to  which  the  vocal  cords  are  attached,  farther  asunder.  This  is 
accomplished  chiefly  by  contractions  of  the  posterior  crico-arijtenoid  muscle 
springing  from  the  cricoid  cartilage  and  attached  to  the  muscular  processes 
of  the  arytenoid  cartilages.  The  action  of  this  muscle  is  represented  schemat- 
ically in  Fig.  200.  It  contributes  to  the  tension  of  the  vocal  cords  by  holding 
the  arytenoid  cartilage  against  the  muscles  which  tend  to  draw  it  forward 
(Neuman).  In  this  abducting  action  the  posterior  crico-arytenoid  is  aided 
to  some  extent  by  the  vertically  directed  portion  of  the  lateral  crico-arytenoid 
(Riihlmann). 

But  for  the  most  part  the  lateral  crico-arytenoid  is  an  adductor  of  the 
vocal  cords  (Fig.  201)  and  the  ihyro-aryienoid  lying  over  this  muscle  has 
the  same  action. 

The  vocalis  or  internal  thyro-arytenoid  muscle,  regarded  by  several  authors 
as  belonging  to  the  thyro-arytenoid,  runs  from  the  angle  of  the  thyroid  car- 
tilage to  the  arytenoid  cartilage  and  is 
applied  to  the  outer  margin  of  the  vocal 
cord  of  each  side.     It  serves  first  to  relax 


Fig.  200. — Schematic  representation  of  tlie 
action  of  the  posterior  crico-arytenoid 
muscles,  after  Testut.  Tlie  red  color 
indicates  the  position  of  the  vocal 
cords  and  of  the  arytenoid  cartilages, 
when  these  muscles  contract. 


Fig.  201. — Sth(--inatic  representation  of 
the  action  of  the  lateral  crico-aryte- 
noid muscle,  after  Testut.  The  red 
color  indicates  the  position  of  the  vocal 
cords  and  of  the  arytenoid  cartilages 
when  these  muscles  contract. 


the  vocal  cords  by  approximating  the  points  of  their  attachment.  But  a  much 
more  important  function  is  to  impart  the  necessary  internal  tension  and  firm- 
ness, as  well  as  to  give  a  favorable  form  and  position  to  the  whole  mass  of 
the  vocal  cord,  for  intonation  (Griitzner). 


504 


HEARING,  VOICE  AND  SPEECH 


With  the  exception  of  the  crico-thyroid  muscle  which  is  innervated  hy  the 
superior  and  median  lar3'ngeals,  the  latter  arising  from  the  phar^-ngeal  branch 
of  the  vagus,  the  muscles  of  the  larynx  receive  their  nerve  supply  from  the 
recurrent  laryngeal. 

§  2.    VOICE    PRODUCTION 

Production  of  sound  in  the  larynx  presupposes  that  the  glottis  is  closed 
and  that  the  vocal  cords  are  placed  in  a  state  of  tension.  If  then  air  is 
driven  from  the  lungs  under  sufficient  pressure,  it  forces  its  way  through  the 
glottis  and  as  it  does  so  sets  the  vocal  cords  in  vibration. 

Caginard-Latour  and  Griitzner  have  estimated  the  air  pressure  necessary 
for  this  purpose.  On  patients  with  tracheal  fistuUie  they  connected  a  manome- 
ter with  the  trachea  by  means  of  a  tracheal  cannula  and  demonstrated  for 


Fig.  202. — Larj-ngoscopic  picture  of  the  human  throat,  as  seen  during  quiet  inspiration.     En- 
larged twice  (Heitzmann). 

a  tone  of  medium  height  and  strength  a  pressure  of  140  to  240  mm.  of  water ; 
for  very  loud  tones,  as  in  shouting  at  the  top  of  the  voice,  a  pressure  as  high 
as  945  mm.  of  water  was  obtained. 

The  power  which  produces  this  pressure  comes  from  the  muscles  of  expira- 
tion, chiefly  the  abdominal  muscles.  It  is  said  that  good  singers  use  only 
the  thoracic  muscles  of  expiration. 

The  sound  produced  in  the  larynx  is  modified  as  to  its  timbre  but  not  as 
to  pitch,  by  the  resonance  chamber.« — pharynx,  mouth,  nasal  cavities,  etc. — 
and  the  task  of  the  voice  culturist,  besides  that  of  inculcating  correct  habits 
of  breathing,  consists  merely  in  training  the  pupil  to  so  shape  these  cavities 
as  to  impart  the  most  agreeable  quality. 


§  3.    REGISTERS   OF   VOICE 

Before  the  invention  of  the  laryngoscope,  our  knowledge  of  the  beliavior 
of  the  vocal  cords,  etc.,  in  the  production  of  voice  was  based  mainly  on 
observations  made  with  dissected  preparations.     But  with  the  invention  of 


REGISTERS   OF   VOICE 


505 


this  instrument  by  Garcia  (1855)  phy&iological  and  pathological  study  of  the 
larynx  entered  upon  an  entirely  new  era. 

The  laryngoscope  is  a  very  simple  instrument.  A  concave  mirror  held  before 
the  observer  is  provided  with  an  aperture  throufjh  which  the  observer  looks.  It 
receives  light  from  some  artificial  source,  and  reflects 
it  upon  a  plain  mirror  held  at  the  proper  angle  in 
the  pharj'nx.  The  latter  mirror  serves  both  to  illu- 
minate the  interior  of  the  larynx  and  to  form  an 
image  of  the  same  which  can  be  seen  by  the  observer. 


Fig.  203. — The  appearance  of 
the  vocal  cord.s  wliile  pro- 
ducing a  chest  tone,  after 
Mandl. 


Fig.  202  represents  a  laryngoscopic  picture  as 
seen  in  quiet  breathing  and  Fig.  203  that  seen  in 
vocalizing. 

Two  different  registers  are  distinguished  :  the 
chest  voice  and  the  falsetto  or  head  voice.  Tlie 
former  is  fuller  and  richer — i.  e.,  richer  in  lower 
overtones — than  the  falsetto.  The  chest  tones  are 
lower  than  the  head  tones ;  although  within  a  certain  compass  the  same  person 
can  produce  identical  tones  with  either  the  chest  voice  or  the  head  voice. 

In  the  production  of  chest  tones  the  vocal  cords  vibrate  throughout  their 
entire  breadth.     Tliey  are  also  pressed  inward,   thus  narrowing  the  glottis 

so  that  the  air  can  only  escape  very 
slowly.  In  the  production  of  head 
tones  only  the  edges  of  the  vocal 
cords  vibrate  and  the  glottis  is  firm- 
ly closed  posteriorly,  but  is  rather 
widely  open  anteriorly.  The  air 
escapes  therefore  more  readily  than 
in  the  case  of  chest  tones.  For  this 
reason  chest  tones  can  be  held  longer 
than  head  tones. 

We  have  the  following  means 
in  the  larynx  itself  of  altering  the 
pitch  of  the  voice  (Griitzner)  :  (1) 
By  changing  the  longitudinal  ten- 
sion of  the  vocal  cords;  (2)  by  lim- 
iting the  vibrating  length  of  the 
vocal  cords,  which  is  done  by  ap- 
plying the  inner  surfaces  of  the 
arytenoid  cartilages  to  each  other 
progressively  more  and  more  from 
posterior  to  anterior;  (3)  by  chang- 
ing the  form  of  the  vocalis  mu.scle, 
and  thereby  varying  the  width  of  the  vocal  cords;  (4)  In'  altering  the  air 
pressure  in  the  trachea. 

Higher  tones  within  the  same  register  tlierefore  may  be  produced  in  two 
general  ways:  (a)  By  increasing  tlie  tension  and  at  the  same  time  lengthening 
the  vocal  cords;  (h)  by  shortening  the  vibrating  portion.  Different  individ- 
uals use  one  or  the  other  of  these  methods  more  or  less  exclusively. 


Fig.  204. — Position  of  tlie  vocal  organs  in  pro- 
ducing the  sound  of  broad  A,  after  Griitzner. 


506 


HEARING.   VOICE   AND  SPEECH 


§  4.    ELEMENTS    OF    SPEECH 

Language  is  niailo  up  of  words,  words  of  syllables  and  syllables  of  ele- 
mentary sounds  called  vowels  and  consonants.  Vowels  are  produced  when 
the  voice  is  modified  by  merely  changing  the  shape  of  the  resonance  cavities 
— pharynx,  mouth,  and  nasal  passages;  consonants  when  the  air  or  voice 
is  more  or  less  obstructed  by  the  movable  parts  of  the  organs  of  speech — 
lips,  teeth,  tongue  and  palate. 

In  whispering  the  glottis  is  partially  open  and  the  air  is  allowed  to  pass 
through  without  setting  the  vocal  cords  in  vibration.  Since  each  of  the  reso- 
nance cavities  has  a  sound  of  its  own  which  it  emits  when  the  air  contained 
in  it  is  caused  to  vibrate,  and  since  sounds  may  be  produced  by  the  lips,  tongue, 
etc.,  alone,  it  is  possible  to  speak  without  voice. 


A.    VOWELS 

We  cannot  here  discuss  exhaustively  the  changes  of  the  mouth  cavity 
necessary  for  the  production  of  vowels.  Griitzner  summarized  the  most  im- 
portant of  them  as  follows :  If  the  voice  be  sounded  with  the  tongue  well  down 

in  the  mouth,  and  the  lips  at  first 
but  slightly  open,  the  sound  of  U 
(00)  is  produced.  Then  while 
the  voice  is  sounding,  if  the  mouth 
be  opened  more  and  more  witliout 
changing  the  position  of  the  tongue 
the  sound  of  00  gradually  passes 
into  that  of  0  and  finally  into 
that  of  broad  A.  and  vice  versa. 
The  vowels  F,  0,  A,  can  be  uttered 
therefore  merely  by  changing  the 
size  of  the  mouth  opening;  in  or- 
dinary speech,  however,  the  tongue 
and  soft  palate  take  part  in  the 
changes.  If  now  the  sound  of 
])road  A  be  uttered  with  the  mouth 
moderately  open  (Fig.  204)  and  if 
without  changing  the  size  of  the 
opening  the  tongue  be  gradually 
lifted  more  and  more  toward  the 
hard  palate  we  get  successively  the  sounds  of  long  A  and  E  (Fig.  205)  (Ger- 
man E  and  I).  In  this  series  the  space  inclo.sed  between  the  larynx,  posterior 
wall  of  the  pharynx,  soft  palate  and  base  of  the  tongue  (lar^-ngeal  space. 
Purkinje)  gradually  becomes  larger. 

The  other  sounds  of  these^  same  letters  are  produced  by  combination  of 
the  positions  already  mentioned  for  the  two  series.  The  larvnx  and  soft 
palate,  however,  undergo  changes  of  position  also. 

Bonders  has  shown  that  the  buccal  cavity  is  attuned  for  the  production 
of  the  different  vowels  not  at  the  same  pitch,  but  at  different  pitches.     The 


Fig.   205. — Position    of   the  vocal   organs  in  pro- 
ducing the  sound  of  long  E,  after  Griitzner. 


ELEMENTS   OF   SPEECH  507 

tones  which  are  favored  by  the  shape  of  the  cavity  may  be  found  by  blowing 
into  the  mouth  while  the  organs  are  in  the  proper  positions;  then  if  these 
tones  occur  as  overtones  in  the  sounds  emitted  by  the  vocal  cords,  they 
are  selected  by  the  resonance  of  the  cavity  and  are  intensified.  According 
to  Helmholtz  (1803),  each  vowel  has  one  or  two  such  tones  (the  pitch 
of  which  is  constant)  which  are  characteristic  of  it  whenever  it  is  either 
sung  or  spoken.  Those  vowels  which  are  formed  when  the  tongue  is  high  in 
the  mouth,  thereby  dividing  it  into  two  cavities  (viz.,  long  and  short  A  and 
E)  have  two  tones,  and  those  formed  when  the  tongue  is  low  (viz.,  00,  0  and 
broad  A)  have  but  one. 

B.  CONSONANTS 

The  consonants  are  much  more  complicated  in  the  mode  of  their  production 
than  the  vowels,  one  important  feature  in  their  production  consisting  of 
changes  in  the  resonance  quality  of  the  l)ucco-pharyngeal  space.  In  most  of 
the  consonants  the  mouth  and  nasal  cavities  are  separated  from  one  another 
by  the  soft  palate,  but  in  some  not.  But  as  more  or  less  complete  oljstruction 
of  the  air  in  some  part  of  the  passage  is  common  to  all,  the  distinguishing 
character  of  the  sound  depends  on  the  place  and  manner  of  the  obstruction. 
Some  consonants  are  uttered  with  voice,  others  without. 

References. — P.  Griitzner,  "  Physiologie  der  Stimme  und  Sprache,"  Leip- 
zic,  1879  (Hermann^s  Handhiich  der  Physiologie,  i,  2). — //.  Helmholtz,  "Die 
Lehre  von  den  Tonempfindungen,"  fourth  edition,  Braunschweig,  1877. — L.  Her- 
mann, several  articles  in  the  Archiv  fiir  die  rjesamte  Physiologie,  vols,  xlvii, 
xlviii,  liii,  Iviii,  Ixi,  Ixxxiii,  xci,  1890-1902. — H.  Pipping,  articles  in  the  Zeit- 
schrift  fiir  Biologic,  vols,  xxvii,  xxxi,  1890,  1895. 


31 


CHAPTER    XXI 


VISION 


If  we  wish  to  investigate  an  object  hy  means  of  the  tactile  sense,  we  must 
be  able  to  feel  the  ditferent  parts  of  it.  In  doing  this  different  nerve  fibers 
are  stimulated ;  each  nerve  fiber  produces  a  special  sensation,  which,  owing  to 
its  "  local  sign."  differs  from  those  mediated  by  other  nerve  fibers ;  and  the 
sum  total  of  all  these  different  sensations  gives  us  our  idea  of  the  object. 

It  is  the  same  with  the  e3'e.  The  retina  constitutes  a  mosaic  of  nerve 
endings  sensitive  to  the  light ;  each  of  these  nerve  endings  produces  a  sensation 
endowed  with  its  own  peculiar  "  local  sign  " ;  and  just  as  with  the  skin,  the 
total  result  of  all  these  sensations  constitutes  our  idea  of  the  object  as  obtained 
by  vision. 

From  this  it  is  evident  that  a  clear  idea  of  an  object  perceptible  to  the 
eye  can  only  be  obtained,  if  each  point  of  the  object  acts  upon  its  own  particu- 
lar point  of  the  retina. 

Since  light  emanating  from  or  reflected  from  an  ol)ject  radiates  in  all 
directions,  becoming  more  and  more  divergent  the  farther  it  proceeds,  in  order 
to  form  a  sharp  picture  of  the  object  on  the  retina  the  light  must  be  collected 
by  refraction  of  its  rays,  in  such  a  maimer  that  they  will  be  focused  on  the 
retina.     This  is  the  purpose  of  the  refracting  media  of  the  eye. 

The  physiology  of  the  visual  organ  must  begin  therefore  with  a  considera- 
tion of  the  eye  as  an  optical  instrument.  After  that  we  shall  study  the  visual 
sensations,  and  the  movements  of  the  eve. 


FIRST    SECTIO?^ 

THE    EYE    AS    AN    OPTICAL    INSTRUMENT 

§  1.    THE    OPTICAL   CONSTANTS   OF   THE   EYE 

The  eye  contains  a  number  of  refracting  media  separated  from  one  another 
by  approximately  spherical  surfaces.  These  media  named  from  anterior  to 
posterior  are :  (1)  The  layer  of  tears ;  (2)  the  cornea  ;  (3)  the  aqueous  humor; 

(4)  the  crystalline  lens  composed  of  many  layers  of  different  refracting  power; 

(5)  the  vitreous  body. 

In  order  to  follow  the  course  of  light  rays  in  the  eye  we  must  determine 
( 1 )  the  refractive  indices  ^  of  the  various  media ;  ( 2 )  the  radii  of  the  ref ract- 

*  The  ratio  between  the  velocity  of  liorht  in  a  vacuum  and  its  velocity  in  a  gi^'en  me- 
dium, as  glass,  is  the  refractive  index  of  that  medium.     Since  however,  the  velocity  in  air 
508 


THE   OPTICAL  CONSTANTS   OF  THE   EYE 


509 


ing  surfaces;  (3)  the  distances  of  the  different  refracting  surfaces  from  one 
another.     Theh^e  measurements  are  called  the  optical  constants  of  the  eye. 

The  following  table  after  Helmholtz  contains  a  summary  of  values  found 
by  different  authors  for  the  refractive  indices  of  the  various  media  in  the 
human  eye : 

Cornea 1.330-1.357 

Aqueous  humor 1 .335-1 .356 

Vitreous  body 1.336-1.357 

Crystalline  lens,  outer  layer 1 .  338-1 .  474 

"     median 1.352-1.478 

"  "     core 1.390-1.481 

The  lens,  as  appears  from  the  table,  has  a  different  refractive  index  in  its 
different  layers,  the  value  increasing  from  without  inward.  As  a  consequence, 
the  focal  distances  of  the  component  lenses  become  smaller  in  the  same  order 
and  the  total  refracting  power  greater  than  it  would  be,  if  the  whole  lens  had 
the  refractive  index  of  its  core  (Young, 
Listing). 

-  Hence  it  is  a  mistake  to  try  to  re- 
place the  crystalline  lens  by  a  homoge- 
nous lens  of  the  same  form  and  with  an 
average  refractive  index.  Such  a  lens 
must  have  a  higher  total  refractive  in- 
dex than  that  of  its  densest  part. 

In  calculating  the  course  of  the  light 
rays  in  the  eye,  we  shall  follow  Helm- 
holtz in  supposing  the  crystalline  lens  to 
be  replaced  by  a  homogenous  lens  with 
a  refractive  index  of  1.4371. 

The  problem  to  be  solved  is  rendered 
much   easier  by  this  simplification   and 

we  can  now  treat  the  optical  system  of  the  eye  as  if  it  were  composed  of 
two  relatively  simple  systems.  The  first  consists  of  (1)  air,  (2)  cornea, 
(3)  aqueous  humor;  the  second  of  (1)  aqueous  humor,  (2)  crystalline  lens 
and   (3)   vitreous  body. 

The  system  of  the  cornea  can  be  simplified  still  further  for  three  reasons: 
it  is  very  thin,  its  surfaces  are  almost  concentric  and  its  refractive  index  is 
only  a  little  greater  than  that  of  the  aqueous  humor.  Since  the  refractive 
index  of  the  layer  of  tears  on  the  outside  differs  but  slightly  from  that  of 
the  aqueous  humor  inside,  we  may  think  of  the  cornea  as  a  watch-glass-shaped 


is  but  slightly  less  than  in  a  vacuum,  the  refractive  index  of  a  medium  is  ordinarily  given 
as  the  retardation  which  the  light  suffers  in  passing  from  air  into  that  medium.  The  re- 
fractive index  may  be  fo\md  by  measuring  the  angle  of  incidence  and  the  angle  of  refrac- 
tion— e.  g.,  the  angles  a  and  $  formed  by  the  light  ray  f  g  m  Fig.  206.  The  refractive 
index  of  the  medium  below  the  line  a  b,  supposing  the  medium  above  that  line  to  be 


air,  is  given  bv  the  formula  n  =   -. —    . 
*  *  sme  /3 


510 


VISION 


lens  immersed  in  aqueous  humor.  Such  a  lens  does  not  change  the  course 
of  the  light  rays  to  any  appreciable  extent.  According  to  an  estimate  of 
Helmholtz  the  focal  distance  of  the  cornea  embedded  in  the  aqueous  humor 
would  be  8.7  m.,  a  distance  which,  in  comparison  with  the  dimensions  of  the 
eye,  can  be  regarded  as  practically  infinite. 

The  first  refracting  system  is  reduced  therefore  to  a  simple  optical  system 
composed  of  two  media,  the  air  and  the  aqueous  humor,  separated  by  a  surface 
with  the  curvature  of  the  cornea. 

To  be  able  to  follow  the  course  of  the  light  rays  in  the  eye  we  need  there- 
fore, in  addition  to  the  refractive  indices  already  mentioned,  only  the  following 
data:  (1)  The  radius  of  curvature  of  the  cornea;  (2)  the  distance  of  the 
anterior  surface  of  the  lens  from  the  vertex  of  the  cornea;   (3)   the  radius 


Fig.  207. 

of  curvature  of  the  anterior  surface  of  the  lens;  (4)  the  thickness  of  the  lens 
and  (5)  the  radius  of  curvature  of  the  posterior  surface  of  the  lens. 

Some  of  the  values  found  by  different  authors  for  these  dimensions  are 
given  in  the  following  table: 

(1)  Radius  of  curvature  of  the  anterior  surface  of  cornea 6.852-8. 154  mm. 

(2)  Distance  from  vertex  of  cornea  to  anterior  surface  of  the  lens 2.900-4.09       " 

(3)  Distance  from  vertex  of  cornea  to  posterior  surface  of  lens 6.844-7.69       " 

(4)  Radius  of  curvature  of  anterior  surface  of  lens 7.860-12.58     " 

(5)  Radius  of  curvature  of  posterior  surface  of  lens 5.13  -8.49      " 


To  enable  us  the  better  to  follow  light  rays  through  an  optical  system  like 
that  represented  by  the  human  eye,  let  us  suppose  the  refracting  surfaces  S^, 
S„  and  *S'3  in  Fig.  207  to  be  related  to  each  other  as  are  the  refracting  surfaces 
of  the  cornea  and  lens.  The  points  F  and  F*  will  be  the  anterior  and  posterior 
focal  points  of  the  entire  system,  the  line  AAi  its  axis.  Imagine  any  incident  ray 
parallel  to  the  axis  to  be  represented  by  Px.  Since  all  rays  parallel  to  the  axis 
pass  through  the  focal  point,  whatever  course  this  ray  may  take  through  the 
system,  we  know  that  after  it  is  refracted  it  will  pass  through  the  focal  point 
F*.  But  the  incident  and  refracted  rays  must  meet  somewhere  if  prolonged. 
Let  this  point  of  meeting  be  e".  Imagine  the  incident  ray  Px  projected  toward 
Q  and  call  the  portion  e*()  the  incident  ray.  Since  this  is  everywhere  parallel 
to  the  axis  it  must  have  a  corresponding  ray  which  will  pass  through  the  ante- 
rior focus  F.  Prolonging  the  incident  ray  until  it  meets  the  refracted  ray  again, 
we  get  the  point  e. 

The  rays  Px  and  Fx„  therefore,  converge  toward  the  point  e,  the  rays  Qy 
and  F*y^,  toward  e* — i.  e.,  if  we  regard  e  as  a  luminous  point  e*  will  be  its  image. 


THE   OPTICAL  CONSTANTS   OF   THE   EYE 


511 


If  through  these  points  two  planes  be  drawn  perpendicular  to  the  axis  of 
the  system,  then  every  point  in  the  plane  e  will  have  its  image  in  the  plane  e*, 
and  the  image  will  be  on  the  same  side  of  the  axis  and  at  the  same  distance 


from  it.  In  short  an  object  in  the  plane  e  has  an  erect  image  of  the  same  size 
in  the  plane  e*. 

These  two  planes  are  called  the  principal  planes  of  the  system  and  the  points 
at  which  they  cut  the  optical  axis  are  called  the  principal  points. 

All  distances  in  general  are  calculated  from  the  principal  points,  those  which 
concern  the  incident  ray  from  the  first,  those  which  concern  the  refracted  ray 
from  the  second. 

I^ow  what  will  be  the  relation  between  an  object,  whose  rays  are  transmitted 
by  a  system  of  this  kind,  and  its  image?  The  answer  is,  just  the  same  relation 
as  between  the  object  and  image  of  a  simple  system. 

If — e.  g.,  in  Fig.  208,  which  represents  a  simple  optical  system — an  object, 
sp,  be  transmitted  by  a  simple  refracting  surface,  the  size  of  the  image,  tr,  will 
be  to  the  size  of  the  object  as  ar  is  to  pa  (from  the  similar  geometrical  figures 
asp  and  art).     The  point  a  of  such  a  system  is  called  the  nodal  point. 

So  also  in  Fig.  209  where  £"£"*  are  the  principal  points  and  F  and  F*  the 
focal  points,  there  will  be  two  points  K  and  K*  so  situated  (at  equal  distances 
from  E  and  E*)  that  the  size  of  the  object  FA  will  be  to  the  size  of  its  image 
P*At  as  the  distance  AK  is  to  the  distance  A,K*.  These  two  points  are  called  the 
nodal  points  of  the  system.  They  may  be  defined  as  the  two  points  so  situated 
that  a  ray  directed  toward  the  first  will  be  directed  toward  the  second  after 
refraction,  the  rays  before  and  after  refraction  being  parallel. 

It  is  evident  that  if  we  can  locate  accurately  the  nodal  points  of  the  eye 
and  know  the  size  and  distance  of  any  object,  we  can  estimate  the  size  of  its 
image  in  the  eye.     Moser  was  the  first   (1844)   to  make  use  of  theoretical 


Fig.  209. 


results  obtained  by  Gause  and  Bessel  and  on  the  basis  of  these  to  calculate 
the  position  of  the  two  nodal  points.  Somewhat  later  Listing  gave  an  esti- 
mate of  the  numerical  values  according  to  the  best  measurements  completed 
at  that  time.  Since  his  time  the  designation  of  schematic  eye  has  been  applied 
to  an  eye  whose  optical  constants  correspond  approximately  to  the  mean  value 


512  VISION  • 

of  the  prevailing  measurements.     It  must  be  observed,  however,  that,  as  will 
appear  from  the  table  on  page  510,  the  individual  variations  are  considerable. 

In  the  following  table  are  contained  the  optical  constants  from  two  sche- 
matic eyes,  which  have  been  calculated  by  Helmholtz  on  the  Ijasis  of  newer 
measurements. 

The  location  is  in  all  cases  given  as  the  distance  in  millimeters  from  the 
vertex  of  the  cornea,  and  is  reckoned  as  positive  when  it  is  posterior  and 
negative  when  anterior. 

Directly  Determined 

Refractive  index  of  the  aqueous  humor  and  vitreous  body.  1.3376  1.3365 

Total  refractive  index  of  crystalline  lens 1.4545  1.4371 

Radius  of  curvature  of  the  cornea 8.0  7.829 

Radius  of  curvature  of  the  anterior  surface  of  the  lens ....  10.0  10.0 

Radius  of  curvature  of  the  posterior  surface  of  the  lens  ...  6.0  6.0 

Location  of  the  anterior  surface  of  the  lens 3.6  3.6 

Location  of  the  posterior  surface  of  the  lens 7.3  7.3 

Calculated 

I.  II. 

Cornea :  anterior  focal  distance 23 .  692  23 .  266 

Cornea:  posterior    "           "          31.692  31.095 

Lens:  focal  length 43.707  50.617 

Posterior  focal  distance  of  the  eve 19.875  20.713 

Anterior      "            "        "     "     "     14.858  15.498 

Location  of  the    I  principal  point  1 .  9403  1 .  753 

"    "    II         "            "      2.3563  2.106 

«        "     "      Inodalpoint 6.957  6.968 

"    "    II      "         "      7.373  7.321 

"        "     "     anterior  focal  point —12.918  —13.745 

"        "     "     posterior  focal  point 22.231  22.819 

In  Fig.  210  these  values  are  brought  together  in  a  diagram  of  the  human 
eye  enlarged  about  three  times.  We  see  that  the  principal  points  {li^  h,,)  lie 
in  the  middle  of  the  aqueous  chamber  and  the  nodal  points  (k,  k„)  in  the 
posterior  part  of  the  crystalline  lens.  The  posterior  focal  point  F,,  falls  upon 
the  retina. 

By  means  of  these  so-called  cardinal  points,  the  path  of  any  given  inci- 
dent ray  can  be  determined,  as  has  been  seen  on  page  511,  beyond  its  last 
refraction;  likewise,  the  location  of  any  point  occurring  in  the  neighborhood 
of  the  axis.  Since,  moreover,  the  two  principal  points  and  the  two  nodal 
points  lie  very  close  together  (by  the  above  table,  0.410  mm.  and  0.353 
mm.  apart  respectively),  for  many  purposes  the  two  can  l)e  regarded  as 
one  point  and  the  eye  reduced  to  a  single  optical  system.  In  this  reduced 
eye  the  principal  point  lies  (according  to  Listing's  scheme)  2.345  mm.  pos- 
terior to  the  anterior  surface  of  the  cornea  and  the  single  nodal  point  0.476 
mm.  anterior  to  the  posterior  surface  of  the  lens.  If  from  this  point  a  curve 
be  drawn  through  the  reduced  principal  point  (radius  of  5.125  mm.)  it  will 
represent  the  anterior  limiting  surface  of  the  reduced  eye;  in  front  of  it  is 
air,  back  of  it  aqueous  humor  or  the  vitreous  body. 

As  appears  also  from  the  above  table,  the  anterior  focal  distance  of  the 
cornea  (II  eye)  is  23.3  mm.,  that  of  the  entire  eye  15.5  and  the  focal  length 


IMAGES   UPON   THE   RETINA 


513 


of  the  lens  50.6  mm.     The  refracting  power  of  the  cornea  is  therefore  43.2 
diopters^   (1,000 -=- 23.3),  that  of  the  entire  eye  64.5  diopters. 

It  follows  that  the  strongest  refraction  of  light  takes  place  in  the  cornea. 

Occasionally  among  old   people  the   lens  becomes   turbid  and  opaque.     In 
order  to  restore  the  sight  in  such  cases  the  lens  is  removed.    After  the  operation 


Fig.  210. — Position  of  the  cardinal  points  in  the  schematic  eye,  after  Helniholtz. 

the  refracting  power  of  the  eye,  which  can  no  longer  be  accommodated,  is  about 
10  D.  less  than  before — i.  e.,  in  the  normal  eye  of  old  persons  the  lens  raises  the 
refracting  power  of  the  eye  by  about  this  amount. 


§2.    IMAGES   UPON   THE   RETINA 

The  size  and  position  of  an  image  formed  bv  a  centered  optical  system 
depends  not  only  upon  the  size  and  position  of  the  object,  but  also  upon  the 
position  of  the  cardinal  points  of  the  system.  From  Fig.  209  it  is  evident 
that  so  long  as  the  distance  c  P  >  F  E  the  image  will  be  inverted — i.  e.,  so 
long  as  an  object  is  beyond  the  outer  or  anterior  focal  point  of  the  eye  the 
image  on  the  retina  will  be  inverted.  Again,  so  long  as  e  P  >  2  F  E  the  image 
will  be  smaller  than  its  object  or,  applied  to  the  eye,  so  long  as  the  object 
is  more  than  twice  the  distance  of  the  outer  focal  point  from  the  eye,  the 
image  on  the  retina  is  smaller  than  the  object.  This  tallies  with  our  experi- 
ence that  we  cannot  focus  sharply  on  the  retina  rays  from  objects  lying  nearer 
the  eye  than  twice  its  focal  distance. 


'  One  diopter  (D)  is  the  refracting  power  of  a  lens  with  a  focal  distance  of  I  meter: 
the  refracting  power  is  the  reciprocal  of  the  focal  distance. 


514  VISION 

A.    DIRECT   AND   INDIRECT   VISION 

When  we  wish  to  scrutinize  an  object  very  closely,  we  so  direct  the  eye 
that  the  middle  point  of  the  object  is  pictured  on  the  fovea  centralis  of  the 
yellow  spot  in  the  retina.  This  point  is  therefore  designated  as  the  center  of 
exact  vision.  The  diameter  of  the  fovea  according  to  Fritsch  is  1-1.5  mm., 
so  that  it  corresponds  to  a  visual  angle   (see  page  517)   of  4°-6°. 

The  nervous  elements  of  the  retina,  however,  reach  all  the  way  to  the 
era  serrata,  and,  being  also  sensitive  to  light,  can  produce  conscious  sensa- 
tions from  all  parts.  But  these  sensations,  as  compared  with  those  aroused 
from  the  fovea,  are  more  and  more  indistinct  the  farther  the  retinal  cells 
affected  lie  from  the  fovea. 

The  reader  can  convince  himself  of  this  by  a  very  simple  experiment.  If 
one  eye  be  closed  and  the  other  be  directed  intently  at  some  object,  he  will  find 
that  of  all  the  objects  in  the  room  only  that  one  directly  regarded  and  those 
lying  nearest  it  are  seen  distinctly,  others  appear  less  and  less  distinct  the 
farther  they  are  situated  from  the  line  of  vision.  Vision  with  those  parts 
of  the  retina  lying  outside  the  fovea  centralis  is  called  indirect  vision. 

Indirect  vision  is  of  very  great  service,  for  by  it  we  obtain  some  idea  of  the 
space  in  which  the  object  directly  regarded  is  situated.  Especially  is  it  of 
service  in  walking,  as  anyone  can  prove  to  himself  by  trying  to  walk  over  an 
unfamiliar  path  with  one  eye  closed  and  with  indirect  vision  of  the  other 
excluded  by  looking  through  a  tube  or  through  the  half-closed  hand.  He  finds 
it  dithcult  either  to  perceive  or  to  avoid  obstacles.  In  fact  even  close  work, 
such  as  reading  a  printed  page,  is  much  more  difficult  under  such  circum- 
stances, because  only  a  small  part  of  the  print  can  be  seen  at  one  time. 


B.    THE  LIGHT-PERCEIVING  LAYER  OF  THE  RETINA 

The  retina  consists  of  several  different  elements,  part  of  which  are  nervous 
in  nature  and  part  serve  as  a  supporting  substance  for  the  nervous  structures. 
Eamon  y  C'ajal  has  published  not  long  since  a  detailed  investigation  of  the 
structure  of  the  retina.  His  chief  results  so  far  as  the  nervous  elements  are 
concerned,  may  be  summarized  briefly  as  follows   (cf.  Fig.  211)  : 

The  rod  fibers  (h  h)  whose  bodies  together  with  those  of  the  cones,  consti- 
tute the  outer  granular  laj'er  (B)  end  inwardly  in  little  knots  embraced  by  the 
terminal  iibers  of  the  outer  processes  of  the  definitive  bipolar  cells  (c).  These 
cells  together  with  those  belonging  to  the  cones  constitute  the  inner  granular 
layer  (E)  ;  their  outer  tuft  of  dendrites  is  directed  vertically.  Below  the  bipolar 
cell  rests  upon  a  ganglion  cell  (n)  and  clasps  it  with  iingerlike  branches.  These 
ganglion  cells  form  the  so-called  ganglion-cell  layer  (G). 

The  cone  fiber  (a)  ends  in  a  broad  base,  from  which  short  basilar  dendrites 
are  given  off.  With  these  the  dendrites  of  the  spinal  bipolar  cells  (e)  belong- 
ing to  the  cones  come  into  contact.  The  outer  tuft  of  dendrites  of  these  bipolar 
cells,  in  contrast  with  that  of  the  bipolar  cells  belonging  to  the  rods,  is  quite 
flat,  and  widely  spread  out.  The  inner  process  ends  at  various  levels  of  the 
inner  plexiform  layer  (F)  in  a  terminal  arborization  which  comes  into  relation 
with  the  outwardly  directed  branchlets  of  definite  ganglion  cells. 


IMAGES  UPON  THE  RETIXA 


515 


From  the  cells  of  the  ganglion  layer  optic  fibers  are  given  off,  forming  the 
innermost  layer  of  the  retina,  the  nerve-fiber  layer  {H). 

The  lateral  extent  of  the  outer  tuft  of  dendrites  of  the  bipolar  cells  (£"), 
both  of  those  which  correspond  to  the  rods  and  those  -which  correspond  to  the 
cones,  varies  greatly.  In  general  several  rods  or  cones  are  connected  with  each 
of  the  bipolar  cells.  But  each  cone  of  the  fovea  centralis  is  in  contact  with 
the  dendrites  of  but  one  bipolar  cell. 

Compared  with  the  end  arborizations  of  the  ganglion  cells  those  of  the 
bipolar  cells  are  very  small ;  consequently  the  smallest  ganglion  cells  must  be 
in  touch  with  a  relatively  large  number  of  bipolar  cells. 

In  addition  to  these  elements  the  retina  contains  still  other  cells  of  a  nerv- 
ous nature,  lying  either  in  the  inner  granular  layer  (outer  and  inner  horizontal 


Fig.  211. — A  section  through  the  retina  of  a  full-grown  dog,  after  Cajal.  A,  layer  of  rods  and 
cones;  B,  outer  granular  layer,  containing  tlie  bodies  of  the  visual  cells;  C,  outer  plexiform 
layer;  E,  inner  granular  layer,  containing  the  bipolar  cells;  F,  inner  plexiform  layer;  G,  gan- 
glion cell  layer;  H,  layer  of  the  optic  fibers.  a,  cone  fiber;  b,  bodj'  and  fiber  of  a  rod  cell; 
c,  bipolar  cell  with  "brush"  of  fibrils  belonging  to  the  cones;  /,  giant  bipolar  cell  with  wide 
spreading  brush  of  fibrils;  /(,  diffuse  amacrine  cell,  the  varicose  processes  of  which  lie  for  the 
most  part  directly  on  the  ganglion  cells;  i,  ascending  nerve  fibers;  ;,  centrifugal  fiVjers;  7  and 
</',  specialized  cells  which  arc  seldom  imjiregnated;  v.  ganglion  cell  receiving  within  it  the  ter- 
minal brush  of  a  bipolar  cell  from  the  rods;  m,  nerve  fiber  which  is  lost  in  the  inner  ple-xifonn 
laver. 


cells)  or  in  the  inner  plexiform  layer  (amacrine  cells,  /()•     The  former,  accord- 
ing  to    Cajal,   are   for   the   purpose   of  bringing   definite   groups   of   rods   into 
relation  with  other  definite  groups  more  or  less  remote  from  them.     Nothing 
positive  can  be  said  as  to  the  significance  of  the  amacrine  cells. 
Finally,  the  retina  contains  also  centrifugal  nei-ve  fibers   (/). 

Which  of  these  layers  of  the  retina  is  the  one  primarily  noted  upon  by 
theb>ht? 

Certainly  not  the  nerve-fiber  layer,  for  the  optic  nerve  is  ]w<\.  as  insensitive 
to  light  as  other  nerve  trunks.  This  is  shown  especially  by  the  following 
experiment  first  performed  by  !Mariotte  (about  16fi5). 


516  VISION 

If  the  left  eye  be  closed  and  the  light  be  fixed  steadily  on  the  white  cross 
in  Fig.  212  and  the  book  be  held  at  a  distance  of  about  25  cm.  from  the  eye, 
the  white  circle  will  disappear  entirely  from  view,  so  that  the  black  field 
appears  uniform.  There  is,  therefore,  in  the  eye  a  spot  which  is  not  sensitive 
to  light,  and  which  is  called  for  this  reason  the  blind  spot. 

By  measuring  the  apparent  size  of  the  hlind  spot,  and  its  apparent  distance 
from  the  fixation  point  of  the  eye,  it  can  be  shown  to  correspond  exactly  with 
the  point  of  entrance  of  the  optic  nerve,  where  the  mass  of  optic  fibers,  not 
covered  by  the  l)laek  pigment,  spreads  outward  toward  the  transparent  media 


Fig.  212. 

of  the  eye.  The  insensibility  of  the  optic  nerve  fillers  appears  still  more 
directh',  if  by  means  of  a  small  mirror  the  light  of  a  small  flame  be  thrown 
into  the  eye  so  that  it  falls  upon  the  point  of  entrance  of  the  optic  nerve. 
The  subject  experiences  no  sensation  of  light  (Danders). 

The  blind  spot  is  so  large  that  at  a  distance  of  1.7-2  m.  it  can  contain  the 
image  of  a  man's  head.  The  reason  why  we  do  not  ordinarily  miss  the  object 
in  our  field  of  vision  which  falls  upon  the  blind  spot  is,  that  we  unconsciously 
fill  the  gap  with  something  conformable  to  the  rest  of  the  field.  Moreover  the 
distance  of  the  blind  spot  from  the  center  of  exact  vision  is  such  that  objects  in 
that  quarter  would  be  pretty  indistinct  if  the  spot  were  not  blind. 

The  light-perceiving  layer  of  the  retina,  therefore,  must  lie  behind  the 
nerve-fiber  layer,  or  still  more  accurately  behind  the  blood  vessels  of  the  retina, 
as  was  first  shown  by  the  famous  experiment  of  Purkinje. 

If  a  beam  of  light  from  a  short-focus  lens  be  concentrated  on  the  con- 
junctiva of  one  eye  as  far  as  possible  from  the  cornea,  and  at  the  same  time 
the  gaze  of  this  eye  be  directed  toward  a  uniformly  colored  dark  background, 
there  appears  at  once  in  the  field  of  vision  a  network  of  dark,  branching 
vessels.  This  network  is  nothing  else  than  the  shadow  of  the  vessels  of  the 
retina. 

Purkinje's  figure,  as  this  vascular  tree  is  called,  is  rendered  still  more 
plainly  visible  if  the  illuminating  lens  be  moved  to  and  fro;  it  can  also  be 
perceived,  if  Avhile  the  gaze  is  directed  to  a  dark  l)ackgronnd  a  Inirning  candle 
be  moved  to  and  fro  at  one  side  and  a  little  below  the  eye. 

From  the  fact  that  we  can  perceive  the  shadow  of  the  retinal  vessels  in  our 
own  eyes,  it  follows  that  the  vessels  themselves  are  in  front  of  the  light- 


IMAGES   UPOX   THE   RETINA 


517 


perceiving  layer  of  the  retina.  Finally,  by  exact  physiological  measurements, 
H.  Miiller  has  shown  that  the  distance  between  the  vessels  and  the  light- 
perceiving  layer  must  be  from  0.17-0.33  mm.,  and  microscopical  measure- 
ments in  turn  have  shown  that  the  distance  (0.2-0.3  mm.)  takes  us  to  the 
layer  of  rods  and  cones.  Hence  it  follows  with  great  proljability  that  the  latter 
structures,  the  rods  and  cones,  arc  the  light-perceiving  parts  of  the  retina. 

Why  do  we  not  ordinarily  see  the  Purkinje  figures?  Since  the  field  of  vision 
is  always  filled  by  objects  which  give  more  or  less  light  to  the  eye,  the  pupil  may 
be  looked  upon  as  a  luminous  disk  throwing  light  upon  the  retina.  Xow  the 
branches  of  the  central  vein  of  the  retina  are  only  about  0.038  mm.  in  thick- 
ness; and  with  a  pupillary  diameter  of  4  mm.,  the  umbra  of  these  branches 
would  be  only  0.17  mm.  long  and  so  would  not  quite  reach  the  sensitive  layer 
of  the  retina.  The  penumbra  which  does  reach  the  rods  and  cones  remains 
always  in  the  same  place  and  we  have  become  so  accustomed  to  its  presence  that 
we  do  not  perceive  it.  In  Purkinje's  experiment,  on  the  other  hand,  the  shadow 
falls  on  an  unusual  place  and  the  illuminated  point  has  a  smaller  diameter 
than  the  pupil,  both  of  which  circumstances  tend  to  favor  its  perception  in  con- 
sciousness. If  the  source  of  light  be  not 
moved  the  figure  disappears  shortly,  only  to 
reappear  when  the  source  of  light  is  again 
moved,  just  as  other  objects  are  more  read- 
ily perceived  when  moving  than  when  at  rest. 


-  O.i-0. 


Another  circumstance  which  strongly 
favors  the  light-perceiving  function  of 
the  rods  and  cones  is  the  fact  that  the 
other  retinal  layers  gradually  thin  out 
toward  the  yellow  spot,  so  that  in  the  very 
center  of  the  fovea  itself  only  cone  cells 
are  left.  These  are  connected  with  the 
other  layers  of  the  retina  by  oblique, 
lateral  branches  (cf.  Fig.  211). 

Seen  from  the  outside  the  layer  of  rods 
and  cones  forms  a  mosaiclike  surface  (Fig.  213).  an  arrangement  well  adapted 
to  a  light-perceiving  function;  for  every  object  perceptible  to  the  eye  is  trans- 
fornu'd  by  refraction  into  a  mosaic  picture  of  itself. 


a 

Fig.  213. — View  of  the  rods  and  cones  seen 
from  the  outer  surface  of  the  retina, 
after  Max  Schultze.  a,  arrangement  of 
rods  (small  circles)  and  of  cones  (double 
circles)  in  most  parts  of  the  retina;  b, 
arrangement  in  the  region  of  the  mac- 
ula lutea. 


C.    VISUAL  ANGLE   AND  THE   LIMITS   OF   VISION 

When  the  eye  receives  light  from  a  luminous  ])oint,  for  whose  distance 
it  is  not  exactly  accommodated,  the  light  proceeding  from  the  point  is  brought 
to  a  focus  in  front  of  or  back  of  the  retina,  and  an  illuminated  circular  field 
(dis])ersion  circle)  is  formed  on  the  retina,  the  size  of  which  depends  upon 
the  location  of  the  focus.  If  the  focus  of  the  beam  is  close  to  the  retina, 
either  in  front  or  behind  it,  the  dispersion  circle  will  be  small ;  if  farther 
from  the  retina,  the  circle  will  be  larger. 

.Ml  rays  which  nass  through  the  pupil  take  a  course  in  the  vitreous  hody 
as  if  they  proceeded  from  the  ])icture  of  the  pupil  wliieh  the  lens  throws  back 


518  VISION 

into  the  vitreous  body.  The  actual  size  of  tlie  pupil  therefore  is.  other  things 
being  equal,  the  factor  determining  the  size  of  the  dispersion  circle. 

We  have  already  seen  (page  511)  that  the  position  of  the  retinal  picture 
of  a  luminous  point  can  l)e  determined  in  the  schematic  eye  by  drawing  a 
straight  line  from  the  objective  point  to  the  first  nodal  point  and  another 
parallel  to  this  from  the  second  nodal  point  to  the  retina.  In  the  reduced 
eye  the  two  nodal  points  coincide  and  the  retinal  image  falls  where  a  line 
from  the  object  through  the  nodal  point  meets  the  retina.  Lines  of  this  kind 
b}'  which  the  location  of  the  image  on  the  retina  can  he  determined  are  called 
lines  of  direction. 

That  particular  line  of  direction  which  connects  the  middle  point  of  an 
outer  object  with  the  center  of  the  fovea  in  the  retina  is  called  the  line  of 
vision. 

The  lines  of  direction  enable  us  to  determine  the  size  of  the  image  of  an 
object  formed  on  the  retina.  We  have  only  to  draw  lines  of  direction  from 
the  extreme  ends  of  the  object  and  solve  the  similar  triangles  thus  formed 
(see  page  511).  By  such  a  construction  also  we  can  calculate  approximately 
the  distance  from  each  other  of  the  images  of  two  luminous  points  which  are 


Fig.  214. — Diagram  showing  the  visual  angle,  i.  e.,  the  angle  subtended  by  two  lines  of  direction 
a"  a'  and  b"  b'  through  the  first  nodal  point. 

just  distinguishable,  and  can  thus  ol)tain  a  measure  of  the  acuteness  of  vision. 
For  several  reasons,  however,  this  linear  measure  is  not  used,  but  instead  the 
angle  which  the  two  lines  of  direction  subtend  (Fig.  214)  at  the  first  or 
second  nodal  point.     This  angle  is  called  the  visual  angle. 

According  to  an  old  statement  by  Hooke.  two  stars  whose  apparent  dis- 
tance from  one  another  is  less  than  thirty  celestial  seconds  always  appear  as 
one  star,  and  scarcely  one  person  out  of  a  hundred  can  distinguish  the  two 
if  their  apparent  distance  is  less  than  sixty  seconds.  Later  observers  have 
obtained  values  varying  all  the  way  from  fifty  to  ninety  seconds. 

In  Listing's  schematic  eye  a  visual  angle  of  sixty  seconds  corresponds  to  a 
distance  on  the  retina  of  0.00438  mm.  Microscopical  measurements  find  the 
thickness  of  the  cones  in  the  yellow  spot  to  be  from  0.0054-0.0045  mm.  (Kul- 
liker)  to  0.0036-0.002-0.0015  mm.  Counts  of  the  number  of  cones  in  the  fovea 
made  by  Salzer  gave  for  the  eyes  of  stillborn  children  13,200-13.800  per  square 
millimeter. 

The  limits  of  vision — i.  e..  the  ability  to  distinguish  two  points — therefore 
depend  upon  the  diameter  of  the  cones  in  the  center  of  exact  vision.  To  be 
able  to  perceive  points  as  distinct, and  separate,  they  must  fall  upon  cones 
which  are  separated  by  at  least  one  resting  cone. 


STATIC   REFRACTION    IX   THE   EYE  519 


§  3.    STATIC    REFRACTION   IN   THE    EYE 

The  laws  of  refraction  in  an  optical  system  teach  us  that  for  every  different 
position  of  the  ol)ject  the  position  of  the  image  changes.  For  this  reason  in 
order  to  take  a  picture  on  a  sensitive  plate  by  means  of  a  camera,  the  position 
of  the  plate  must  be  adapted  to  the  distance  of  the  object. 

But  if  the  plate  is  immovable,  as  is  trne  of  the  retina,  a  nearer  object  can 
be  focused  by  using  a  stronger  lens — i.  e.,  by  increasing  the  refracting  power 
of  its  system.  This  is  what  happens  in  the  eye.  By  accommodation  (see  §  6), 
the  refractive  power  of  the  crystalline  lens  can  be  increased  to  different  de- 


c 

Fig.  215. — The  static  refraction  of  :    A,&  hypermetropic  eye;  B,  an  emmetropic  eye;  and  C,  a 

myopic  eye. 

grees,  so  that  objects  at  widely  different  distances  can  be  focused  sharply 
on  the  retina. 

An  optical  system  is  characterized  by  the  distance  of  its  posterior  focal 
point;  and  we  can  distinguish  three  kinds  of  eyes  according  as  the  posterior 
focal  point  is  on  the  retina,  in  front  of  or  behind  the  retina  (Bonders). 
Unaccommodated  eyes  with  the  posterior  focal  point  on  the  retina  are  to  be 
regarded  as  normal  and  are  called  emmetropic   (Fig.  215,  B). 

Eyes  of  the  second  kind  where  the  focal  point  of  parallel  rays  falls  in 
front  of  the  retina  are  called  myopic  or  nearsighted,  ])ecause  they  are  onlv 
able  to  focus  on  the  retina  such  light  rays  as  come  from  objects  at  a  finite 
distance  (Fig.  215,  C). 


520  VISION 

Eyes  of  the  third  kind,  where  the  focal  point  falls  behind  the  retina  are 
called  hypermetropic,  or  long-sighted  (Fig.  21o,  A).  In  order  that  incident 
rays  may  be  brought  to  a  focus  on  the  retina  of  such  an  eye,  they  must 
already  be  convergent  as  they  enter  the  eye.  Since,  however,  converging  rays 
never  occur  in  nature,  it  is  evident  that  a  hypermetropic  eye,  not  provided 
with  artificial  lenses,  can  focus  parallel  or  divergent  rays  accurately  only  by 
accommodation ;  in  short,  the  hypermetropic  eye,  if  it  is  to  see  without  glasses 
must  always  be  accommodated. 

Of  the  three  kinds  of  eyes  the  emmetropic  is  without  doubt  the  best  adapted 
to  its  purpose;  for,  as  we  have  seen,  rays  from  objects  more  than  5  m.  distant 
may  be  regarded  as  practically  parallel  for  the  eye  so  that  the  unaccommodated 
emmetropic  eye  can  form  a  distinct  picture  of  all  such  objects.  The  hyper- 
metropic eye  can  adjust  itself  for  far  distant  and  near  objects  by  accommoda- 
tion. But  the  myopic  has  no  means  at  all  of  adjusting  itself  for  distant  objects 
and  from  this  point  of  view  at  least  must  be  regarded  as  the  least  serviceable 
of  the  three. 

The  far  point  of  the  eye  is  that  point  from  which  proceed  light  rays  with 
the  least  divergence  that  can  be  focused  by  the  eye.  In  the  emmetropic  eye 
the  far  point  lies  of  course  at  an  infinite  distance.  The  far  point  of  the 
myopic  eye  lies  at  a  finite  distance  in  front  of  the  e3^e.  The  far  point  of 
the  h}'permetropic  eye  lies  behind  the  e^'e.  It  represents  the  point  of  con- 
vergence of  those  rays  which,  after  refraction  in  the  unaccommodated  eye,  are 
brought  to  a  focus  on  the  retina. 

We  say  therefore  with  reference  to  its  structure  that  the  refracting  power 
of  the  myopic  eye  is  too  strong,  that  of  the  hypermetropic  eye  too  weak. 

By  suitably  chosen  lenses  both  the  myopic  and  the  hypermetropic  eye  can 
be  made  to  focus  parallel  rays  on  the  retina.  If  we  place  before  a  myopic  eye 
a  doulde  concave  lens  of  such  a  strength  as  to  give  the  parallel  rays  the  direc- 
tion they  would  have  if  they  came  from  the  far  point  of  the  eye.  it  is  evident 
that  now  the  combination,  lens  -|-  the  eye,  affects  parallel  ravs,  just  the  same 
as  does  an  emmetropic  eye. 

If  we  place  before  a  hypermetropic  eye  a  double  convex  lens  which  con- 
verges parallel  rays  to  its  far  point,  then  the  com])ination,  lens  -|-  the  eye, 
must  again  be  equal  to  the  emmetropic  eye. 

The  degree  of  myopia  or  hypermetropia  is  measured  by  the  refracting 
power  of  the  lens  necessary  to  make  the  eye  emmetropic.  It  is  evident  at 
once  that  the  focal  point  of  this  lens  coincides  with  the  far  point  of  the  eye 
and  the  degree  of  myopia  or  hypermetropia  is  therefore  expressed  by  the 
reciprocal  value  of  the  distance  of  the  far  point  from  the  eye.  This  correction 
lens  determines  also  the  static  refraction  of  the  eye — i.  e.,  the  amount  of 
refraction  taking  place  without  accommodation. 

§  4.    OPTICAL   DEFECTS   OF   THE   EYE 

In  our  discussion  thus  far  we  have  silently  assumed  that  the  eye  is  a 
perfectly  constructed  optical  instrument — that  its  refracting  media  are  per- 
fectly transparent,  their  surfaces  exactly  spherical  and  the  centers  of  curvature 


OPTICAL   DEFECTS   OF  THE   EYE 


521 


of  the  various  media  all  in  the  same  straight  line.  Strictly  speaking,  how- 
ever, this  is  not  the  case,  for  the  eye  presents  a  number  of  optical  defects, 
some  of  which  in  the  majority  of  cases  are  quite  negligible,  while  others 
occasionally  affect  its  functional  power  to  a  very  great  extent.  We  shall  have 
space  here  to  discuss  only  the  most  important  of  these  defects. 


i 


A.  TRANSPARENCY  OF  THE  MEDIA  OF  THE  EYE 

When  we  remember  how  complicated  is  the  structure  of  the  cornea  and 
of  the  lens,  it  will  not  appear  strange  that  these  media  are  found  not  to  be 
perfectly  transparent.  If  a  strong  beam  of  light  be  thrown  into  the  eye  by 
means  of  a  convex  lens,  the  illuminated  part  of  the  cornea  and  of  the  lens 
immediately  becomes  visible — i.  e.,  these  structures  send  out  from  all  points 
an  irregularly  diffuse  light.  This  diffuse  light 
likewise  passes  to  the  retina,  excites  it  and 
produces  a  mist  of  light  within  which  the 
images  regularly  formed  on  the  retina  appear 
enshrouded.  With  ordinary  illumination  we 
do  not  perceive  this  mist  and  it  does  not  inter- 
fere with  vision,  but  one  may  be  made  aware  of 
its  existence  in  the  following  manner:  If  in 
the  evening  a  person  direct  his  gaze  away  from 
the  artificial  light  and  toward  a  dark  corner, 
the  differences  of  light  and  shadow  from  this 
quarter  are  much  more  readih'  perceptible  than 
equal  differences  coming  into  the  eye  from  the 
direction  of  the  source  of  light.  The  reason  i 
into  the  eye  in  the  latter  case  by  the  highly  illuminated  pupil  interferes  with 
the  contrast  effects  necessary  to  perception  of  such  differences.  Accordingly, 
when  one  wishes  to  distinguish  slight  differences  of  light  and  shade,  he  in- 
stinctively turns  his  back  to  the  source  of  light. 

There  also  exist  in  the  eye  certain  flecks  which  under  certain  circumstances 
may  interfere  considerably  with  perfect  vision,  especially  if  they  lie  in  the 
posterior  part  of  the  vitreous  body.  The  perception  of  these  flecks  in  the 
transmitting  media  is  described  as  "  entoptic"  phenomena.  We  have  already 
had  an  example  of  such  phenomena  in  Purkinje's  figure  (page  516)- 

Under  ordinary  circumstances  these  small  dark  flecks  are  not  noticed ; 
the  reason  is  that  an  almost  uniform  amount  of  light  enters  the  eye  through 
every  portion  of  the  pupil,  and  thus  the  entire  pupil  constitutes  the  illuminat- 
ing surface  alike  for  all  parts  of  the  posterior  portion  of  the  e^^e.  The  flecks 
being  smaller  than  the  pupil,  the  shadows  cast  by  them  are  naturally  very 
short  and  do  not  ordinarilv  reach  the  retina. 


Fig.  216. — Method  of  demonstrat- 
ing entoptic  phenomena  in  one's 
own  eye,  after  Helmholtz. 

that  the  mist  of  lisrht  thrown 


The  following  method  (Helmholtz)  may  be  used  for  demonstrating  these 
entopif  phenomena.  A  convex  lens  of  large  aperture  and  short  focal  distance 
(a.  Fig.  216)  is  placed  before  the  eye;  at  some  distance  in  front  of  the  lens  is 
placed  a  candle,  h,  a  small  image  of  which  is  formed  by  the  lens  at  its  focal 
point.  Then  a  small  screen,  c,  with  a  minute  opening,  is  so  placed  that  the 
reduced   image  of  the   flame  falls   in  the   opening.      If  the  image   lies   in   the 


522  VISION 

anterior  focal  point  of  the  eye,  the  rays  from  it  which  enter  the  eye  will  be 
parallel  after  refraction  and  a  shadow  of  any  object  {h,  in  Fig.  217)  in  the  vitre- 
ous body  which  is  formed  on  the  retina  (^)  will  be  of  the  same  size  as  the 
object  itself. 

B.  FORM  OF  THE  REFRACTING  SURFACES 

To  be  able  to  judge  the  eye  as  an  optical  instrument  we  must  have  more 
detaiUnl  information  of  the  actual  form  of  the  refracting  surfaces.  Our  knowl- 
edge along  this  line  is  limited  for  the  most  part  to  the  cornea,  which,  however, 

as  we  have  already  seen,  is  the  most  important 
of  the  refracting  media  (cf.  page  513). 

The  most  exact  study  of  this  subject  we  owe 
to  Gullstrand  who  used  the  following  method. 
A  disk  with  concentric  circles  (Placido's  kerato- 
scope)  is  so  placed  as  to  be  reflected  by  the 
cornea ;  the  reflected  image  is  photographed  by 
the  instantaneous  method;  and  the  distances  of 
Fig.  217. — After  Helmlioltz.  the  circles   from   one   another  are   measured   on 

the  photograph.  Knowing  the  corresponding 
differences  on  the  object  and  the  distance  of  the  latter  from  the  cornea,  the 
radius  of  cui-vature  of  the  different  sectors  of  the  cornea  can  be  calculated. 

We  find  as  a  result  of  this  method  that  the  optical  zone  of  the  cornea — 
i.  e..  that  part  immediately  in  front  of  the  pupil — always  approaches  the 
spherical  in  form,  but  that  it  is  often  less  sharply  curved  in  one  meridian 
than  another.  Instead  of  being  the  segment  of  a  sphere  with  a  circular 
cross  section,  it  is  then  a  dome  with  an  oval  cross  section. 

If  the  surface  of  the  cornea  were  always  perfectly  spherical,  it  would  share 
with  all  such  surfaces  the  defect  of  splirrical  ahcrration  (Fig.  218).  It  will 
be  evident  from  the  figure  that  spherical  aberration  can  be  corrected  by  flat- 
tening the  refracting  surface  at  the  periphery  enough  to  bring  the  several 
foci  together.  Gullstrand  has  found  from  his  detailed  study  of  the  curvature 
of  the  cornea,  that,  as  a  matter  of  fact,  the  spherical  aberration  in  the  vertical 
plane  is  slightly  offset  by  a  flattening  directly  above  the  line  of  vision,  which 
is  probably  due  to  the  pressure  of  the  upper  eyelid.  Elsewhere  the  flattening 
is  not  sufficient  to  affect  the  aberration.  Hence  we  may  sa}^  that  that  part 
of  the  cornea  which  is  used  for  direct  vision  exhibits  this  defect. 

C.    ASTIGMATISM 

When  the  optical  zone  of  the  cornea  is  not  perfectly  spherical  but  is 
curved  more  sharpl}"^  in  one  meridian  than  another,  the  refraction  of  light 
will  not  be  equal  in  the  two  meridians.  If  this  difference  is  slight  there  will 
Ije  no  disturbance  to  vision ;  l)ut  it  not  infrequently  happens  that  the  asym- 
metr}^  of  structure  is  great  enough  to  interfere  with  the  ability  to  focus 
correctly. 

A  beam  of  light  which  is  not  brought  to  a  single  point  after  refraction, 
but  has  different  focal  distances  for  different  meridians,  is  described  as  astig- 
matic.   If  the  two  meridians  in  which  the  focal  distance  is  greatest  and  least 


OPTICAL   DEFECTS   OF   THE   EYE 


523 


arc  perpendicular  to  each  other,  the  astigmatism  is  described  as  regular.  We 
shall  discuss  onh'  this  kind  of  astigmatism  here. 

An  astigmatic  beam  may  l)e  formed  in  two  wa3^s:  (1)  When  the  optical 
system  is  asymmetrical  and  the  incident  rays  vertical;  and  (2)  when  the 
optical  system  is  symmetrical  and  the  incident  rays  oblique. 

The  first  case  is  the  simplest  (for  the  second  see  page  525).  Suppose  we 
have  a  lens,  which  in  the  horizontal  meridian  has  a  refractive  power  of  10 
diopters;  in  the  vertical  meridian  a  refractive  power  of  13  diopters.  It  is 
evident  that  the  beam  after  refraction  will  no  longer  have  a  common  focus, 
for  the  incident  rays  in  the  horizontal  meridian  are  brought  to  a  focus 
yV  m-  behind  the  lens  and  those  falling  in  a  vertical  meridian  J^  m.  behind 
the  lens. 

Further  study  of  the  ])rol)lem  has  shown  that  if  no  account  be  taken  of 
the  spherical  aberration,  the  light  rays  instead  of  being  converged  to  foci 
at  the  focal  points  of  the  two  meridians  are  converged  into  a  focal  line  per- 
pendicular to  the  principal  ray  at  each  of  those  points.  The  first  focal  line 
corresponds  to  the  focal  point  of  the  meridian  with  the  strongest  refractive 
power  and  is  perpendicular  to  that  meridian — i.  e.,  in  the  plane  of  the  weakest 
meridian.     The  second  focal  line  corresponds  to  the  focal  point  of  the  weakest 


Fig.  21S. — Illustrating  .spherical  aberration.  The  raj's  parallel  to  the  axis  of  the  system  are 
converged  to  foci  nearer  and  nearer  the  convex  surface  the  farther  they  are  removed  from 
the  axis. 

meridian  and  is  perpendicular  to  that  meridian — i.  e.,  in  the  same  plane  as  the 
strongest  meridian. 

In  front  of  the  first  focal  line  the  beam  of  rays  forms  in  a  cross  section 
an  ellii)se  with  the  longer  a.xis  in  the  direction  of  the  first  focal  line,  beyond 
the  second  focal  line  the  beam  forms  an  ellipse  with  the  longer  axis  in  the 
direction  of  the  second  focal  line.  A  transition  from  the  one  elongation 
to  the  other  takes  place  between  the  two  focal  lines,  the  upright  ellipse 
becoming  first  a  circle  and  then  a  procumbent  ellipse   (Fig.  219). 

In  an  astigmatic  eye,  therefore,  a  homocentric  ^  l)undle  of  rays  cannot  be 
brought  to  a  single  focus.  When  the  eye  is  adjusted  for  the  most  refractive 
meridian,  the  images  on  the  retina  are  all  drawn  out  in  tb(>  direction  of  the 


•  That  is.  rays  proceeding  from  a  common  point  or  rays  which  pass  through  a  common 
point  when  prolonged. 
32 


524 


VISION 


first  focal  line;  when  it  is  adjusted  for  the  least  refractive  meridian  the 
retinal  images  are  drawn  out  in  the  direction  of  the  second  focal  line — in 
both  cases,  therefore,  distorted.  To  prevent  this  the  eye  is  adjusted  so  that 
some  point  between  the  two  focal  lines  falls  on  the  retina.  The  distortion 
of  objects  is  thereby  rendered  less,  but  the  distinctness  of  the  image  is  more 
or  less  reduced. 

Astigmatism  may  be  demonstrated  subjectively  by  the  use  of  a  chart  (like 
that  in  Fig.  220)  composed  of  several  radii,  all  of  the  same  width  and  depth  of 


Fig.  219. — Refraction  of  the  light  rays  in  regular  astigmatism,  showing  the  form  of  a  beam  at 
different  cross  sections,  after  Fuchs,  r  v, ,  vertical  meridian  of  the  cornea;  h,  h  the  horizontal 
meridian.  The  focus  for  the  horizontal  meridian  is  at  /, ;  that  for  the  vertical  meridian  at  /; 
the  image  of  a  point  is,  therefore,  not  a  point  but  a  dispersion  circle.  The  shape  of  the  circle, 
however,  is  determined  by  the  spot  at  which  the  retina  is  situated.  At  the  position  2,  the 
image  of  a  point  would  be  a  vertical  line,  at  4  a  circle,  at  6  a  horizontal  line,  etc. 

color.  If  this  chart  be  held  before  the  eye  at  such  a  distance  that  only  one 
meridian  can  be  seen  distinctly,  this  meridian  corresponds  in  direction  to  the 
most  refractive  meridian  of  the  eye,  and  its  image  on  the  retina  to  the  second 
focal  line.  If  now  the  chart  be  brought  as  close  to  the  eye  as  possible,  again 
only  one  meridian  is  distinct.  In  regular  astigmatism  this  meridian  is  at  right 
angles  to  the  first:  it  gives  the  direction  of  the  least  refractive  meridian  of  the 
eye  and  its  image  corresponds  to  the  first  focal  line. 

A  certain  degree  of  astigmatism  occurs  in  all  eyes,  although,  as  a  rule,  it 
is  so  slight  as  to  have  no  practical  importance.  The  astigmatism  which  causes 
a  noticeable  distortion  of  images  is  caused  mainly  by  the  asymmetrical  struc- 
ture of  the  cornea. 


OPTICAL   DEFECTS   OF   THE   EYE  525 

As  a  rule,  however,  the  actual  astigmatism  of  the  cornea  is  greater  than 
the  total  astigmatism  as  determined  by  the  subjective  method.  This  means 
that  it  is  compensated  to  some  extent  by  some  structures  in  the  eye  itself — as, 
6.  g.,  the  lens. 

According  to  measurements  made  by  Xordenson  on  pupils  between  the 
ages  of  seven  and  twenty,  out  of  452  eyes  examined  only  42  (nine  per  cent) 
had  no  astigmatism  of  the  cornea  which  could  be  detected.  Sixty-nine  pupils 
had  an  astigmatism  of  more  than  1  diopter,  and  four  an  astigmatism  of  more 
than  1.5  D.  However,  a  normal  acuteness  of  vision  is  perfectly  possible  with  an 
astigmatism  of  1.5  diopters.  In  85.1  per  cent  of  the  astigmatic  eyes  examined 
the  vertical  meridian  was  the  most  refractive;  in  1.5  per  cent  the  horizontal, 
and  in  13.4  per  cent  an  oblique  meridian.  In  the  majority  of  cases  therefore 
the  vertical  meridian  is  the  most  sharply  curved. 

The  difference  in  static  refraction  between  the  most  refractive  and  the  least 
refractive  meridian   of  the  eye,  expressed  in  diopters,  is  known  as  the  degree 
of  astigmatism.    After  this  has  been  determined  (by  methods  which  we  cannot 
discuss  here)   it  can  be  corrected  by  means  of   cylindri- 
cal lenses — i.  e.,  glasses  which  represent  segments  of  the 
curved  surface  of  a  ej'linder. 

In  using  such  glasses  for  the  correction  of  astigma- 
tism the  glass  is  so  placed  that  its  own  asymmetry  is  the 
reverse  of  that  of  the  eye.  Suppose  an  eye  were  myopic 
in  the  vertical  meridian  and  emmetropic  in  the  horizontal. 
Then  the  eye  could  be  made  emmetropic  by  placing  before 
it  a  suitable  concave-cylindrical  glass  with  a  curvature  in 
the  vertical  meridian.    The  myopia  in  this  meridian  would  Fig.  220. 

be  corrected  by  the  curvature.     Rays  falling  in  the  hori- 
zontal meridian  would  not  be  refracted  at  all,  and  would  not  need  to  be,  for 
the  eye  we  suppose  is  already  emmetropic  in   that  meridian.     Correction   for 
other  sorts   of   astigmatism  and   for   astigmatism   combined   with   myopia    and 
hypermetropia  can  readily  be  devised  by  the  reader. 

D.    THE   ANGLE   BETWEEN  THE   LINE   OF   VISION   AND   THE   VISUAL   AXIS 

The  laws  of  refraction  thus  far  discussed  proceed  on  the  assumption  that 
the  line  of  vision  coincides  with  the  optical  axis  of  the  eye.  But  this  is  not 
the  case.  The  line  of  vision  in  front  of  the  eye  lies  inside  of  and  somewhat 
above  the  optical  axis,  the  center  of  exact  vision  therefore  lying  outside  of  and 
somewhat  below  the  axis.  In  Fig.  210  (page  .513)  (r,  G„  marks  the  line  of 
vision ;  F ,  F „  the  optical  axis. 

The  angle  between  the  line  of  vision  and  the  optical  axis  is  designated  as 
the  angle  a.  Its  size  in  the  horizontal  meridian  is  3.5°-7.0°,  and  in  the  vertical 
approximately  3.5°. 

The  rays  of  light  entering  the  eye  in  the  line  of  vision  therefore  strike  it 
obliquely.  Under  these  circumstances  a  homocentric  beam  remains  no  longer 
liomooontric.  but  becomes  astigmatic  (see  page  523),  the  rays  falling  in  the 
horizontal  meridian  being  most  strongly  refracted.  This  astigmatism  how- 
ever is  more  than  compensated  by  the  ordinary  astigmatism  of  the  opposite 
kind  in  the  cornea. 

Assuming  the  angle  a  to  be  5°,  Gullstrand  calculated  the  influence  of  the 
oblique  incidence  of  the  line  of  vision  for  the  schematic  eye  and  found  that  the 


526  VISION 

distance  between  the  two  focal  lines  was  only  0.03  mm.  and  the  degree  of 
astigmatism  only  0.1  diopter.  These  figures  explain  why,  as  has  long  been 
known,  the  sharpness  of  vision  commonly  suffers  no  reduction  from  this 
kind  of  astigmatism. 

E.    CHROMATIC   ABERRATION   IN   THE   EYE 

The  refractive  index  of  solid  and  liquid  media  is  different  for  rays  of 
different  wave  length — e.  g.,  that  of  water  for  red  (spectrum  line  C)  is  1.331705 
and  for  violet  (spectrum  line  G)  1.341285.  For  a  long  time  it  was  supposed 
to  be  impossible  to  prevent  this  dispersion  of  light  into  its  colors  in  any  optical 
s3-stem.  Later,  however,  it  was  shown  to  be  possible  and  instruments  have 
long  since  been  constructed  in  which  no  color  dispersion  at  all  occurs. 

Our  everyday  experience  teaches  us  that  the  chromatic  aberration  in  the 
eye  cannot  be  very  great,  for  in  ordinary  life  it  is  almost  entirely  unnoticeable. 
But  more  exact  investigation  of  the  subject  shows  that  the  achromatism  of 
the  eye  is  by  no  means  perfect. 

Since,  the  refractive  indices  of  the  optical  media  in  the  eye  for  the  most 
part  do  not  differ  much  from  that  of  water,  Helmholtz  calculated  the  dispersion 
for  the  reduced   eye    (see  page    512),   on   the    assumption   that   water  was   the 


b. 
Fig.  221. — Diagram  illustrating  the  chromatic  aberration  of  an  eye. 

refractive  substance  throughout,  and  found  that  the  posterior  focal  distance  for 
red  (line  C)  was  20.574  nun.  and  for  violet  (line  G)  20.14  mm.  Actually  the 
color  dispersion  in  the  human  eye  appears  to  be  somewhat  gi'eater  (the  distance 
between  the  focal  points  of  red  and  violet  0.58-0.62  mm.  instead  of  0.434  mm.). 
According  to  Einthoven,  the  difference  in  focal  distance  between  the  D  and  F 
lines  in  the  schematic  eye  is  0.272  mm. 

There  is,  however,  a  physiological  reason  as  well  as  a  structural  one  why  the 
color  dispersion  is  not  plainly  noticeable.  When  white  light  enters  the  eye  and 
the  eye  adjusts  itself  for  the  most  strongly  effective  rays  of  medium  wave  length, 
the  latter  come  together  on  the  retina  almost  exactly  in  one  point,  which  is 
surrounded  by  a  fringe  of  red  and  violet  rays.  But  the  exciting  effect  of  rays 
of  very  great  or  very  small  wave  length  is  relatively  slight,  consequently  the 
action  of  the  fringe  zone  in  comparison  with  that  of  the  center  is  negligible. 
Besides,  the  center  is  more  strongly  illuminated  than  the  fringe  zone  because 
lays  of  all  wave  lengths  strike  it. 

The  same  thing  is  true  of  the  dispersion  circles  caused  by  the  spherical 
aberration  when  the  eye  is  adjusted  to  the  focal  point  of  the  central  rays. 

Only  one  experiment  on  color  dispersion  in  the  eye  can  be  described  here. 
If  one  holds  before  an  ordinary  petroleum  flame  a  screen  with  a  narrow  open- 
ing in  it  and  behind  this  a  cobalt-blue  glass  which  shuts  out  most  of  the  orange, 
yellow  and  green  rays,  but  lets  through  an  abundance  of  ultra-red,  indigo-blue 
and  violet  rays,  the  opening  may  be  seen  as  a  luminous  point  sending  out  red 


THE   IRIS  527 

and  violet  rays.  Now  this  point  appears  differently  to  the  observer  according 
to  the  distance  for  which  the  eye  is  adjusted.  If  it  is  adjusted  for  the  red  rays, 
there  appears  a  red  spot  with  a  violet  halo;  if  it  is  adjusted  for  the  violet  rays, 
a  violet  point  with  a  red  halo.  This  will  be  evident  from  Fig,  218  if  one 
imagines  the  retina  in  the  first  case  to  be  located  at  r  and  in  the  second  at  v. 
This  experiment  is  particularly  beautiful  if  an  electric  incandescent  lamp  be  used. 
The  colored  circles  of  subjective  origin  (H.  Meyer's  rings)  which  are  per- 
ceptible around  a  source  of  light  under  certain  abnormal  circumstances,  as  in 
conjunctivitis,  or  after  the  effect  of  osmium  vapor,  are  to  be  explained  by  the 
diffraction  of  the  light  about  dead  epithelial  cells,  mucous  corpuscles,  etc.,  on  the 
surface  of  the  cornea.  A  similar  color  phenomenon  (Bonder's  rings)  is  pro- 
duced by  diffraction  at  the  edges  of  the  lens,  but  this  occurs  normally  only  when 
the  pupil  is  greatly  dilated  (Salomonsohn). 

F.    SUMMARY 

Summarizing  the  optical  defects  of  the  eye,  we  may  say  that  Avhile  it 
exhibits  various  defects  which  could  not  be  permitted  in  a  good  optical  instru- 
ment, yet  its  capacity  as  an  organ  of  vision  is  surprisingly  little  interfered 
with.  The  oblique  incidence  of  the  line  of  vision,  the  difference  in  the  re- 
fraction between  the  different  meridians  of  the  cornea,  the  imperfect  correc- 
tion of  spherical  and  chromatic  aberration — none  of  these  nor  all  of  these 
together  diminish  the  capacity  of  the  eye  to  such  an  extent  as  to  produce  any 
perceptible  disturbances  in  vision.  But  this  is  true  only  of  the  normal  eye. 
It  happens  not  infrequently  that  these  defects  exceed  the  normal  limits  and 
then  the  eye  must  be  descril)ed  as  a  rather  poor  optical  instrument.  Often- 
times in  such  cases,  the  optical  properties  of  the  eye  can  be  very  considerably 
improved  by  practical  treatment. 


§  5.    THE   IRIS 

In  order  that  a  proper  image  formed  in  a  camera  may  not  be  interfered 
with  by  light  reflected  from  the  inner  walls,  the  latter  are  always  covered 
with  a  dull  black  color.  The  retinal  pigment  and  the  strongW  pigmented 
choroid  coat  serve  the  same  purpose  in  the  eye. 

The  iris  which  is  but  the  anterior  prolongation  of  the  choroid  coat  like- 
wise has  an  important  function.  It  has  been  shown  that  the  laws  of  refraction 
in  an  optical  system  hold  good  in  case  only  such  rays  enter  as  form  a  very  small 
angle  with  the  optical  axis,  and  the  peripheral  rays  are  shut  out.  This  exclu- 
sion of  the  peripheral  rays,  so  important  for  the  clearness  of  the  images,  is 
provided  for  by  the  iris.  The  pupil  can  be  constricted  or  dilated  by  con- 
traction of  circular  or  radial  fibers  respectively  in  the  iris.  Such  alterations 
in  the  size  of  the  pupil  serve  the  optical  requirements  of  the  eye  in  two  ways : 
in  near  vision,  if  this  is  accompanied  by  convergence  of  the  optical  axes,  the 
pupil  constricts  and  thereby  contributes  to  the  sharpness  of  the  image;  again, 
wlien  the  asymmetry  of  the  cornea  is  great,  the  resulting  astigmatism  is 
counteracted  to  a  certain  extent  by  constriction  of  the  pupil.  The  pupil  has 
in  addition  the  important  function  of  protecting  the  retina  from  too  intense 
a  light;  it  constricts  in  strong  light  and  dilates  in  weak  light. 


528 


VISION 


Fig.  222. — The  iris  of  a  cat.  A,  at  rest; 
B,  on  stimulating  it  at  the  upper 
right-hand  side  (Langley). 

nerves  to  the  sphincter  piipilUv. 


Constriction  of  the  pupil  is  caused  by  contraction  of  a  circular  muscle, 
composed  in  most  animals  of  smooth  muscle  fibers  and  known  as  the  sphinc- 
ter of  the  pupil ;  dilatation,  by  smooth  radial  fibers  known  collectively  as  the 
dilator  of  the  pupil.  The  existence  of  an  independent  dilator  was  conclu- 
sively proved  several  years  ago  by  the  physi- 
ological experiments  of  Langley  and  An- 
derson; it  has  recently  been  demonstrated 
anatomically  as  well. 

The  muscles  of  the  iris  receive  their 
nerves  by  both  cerebral  and  sympathetic 
pathways.  The  constrictor  fibers  are  found 
in  the  oculo  motor.  From  this  nerve  they 
pass  over  to  the  ciliary  ganglion,  connect 
there  with  nerve  cells  (Langendorff),  and 
continue  thence  through  the  short  ciliary 
Stimulation  of  a  single  one  of  the  short 
ciliary  nerves  causes  only  partial  contraction  of  the  sphincter,  so  that  the 
pupil  takes  an  irregular  form.  It  is  stated  that  the  oculo  motor  at  the  same 
time  inhibits  the  dilator  of  the  pupil. 

The  dilator  fibers  of  the  pupil  come  from  the  sympathetic.  They  pass  out 
of  the  spinal  cord  by  the  anterior  roots  of  the  seventh  to  the  eighth  cervical  and 
the  first  to  the  second  thoracic  spinal  nerves,  go  to  the  first  thoracic  ganglion, 
then  through  the  anterior  arm  of  the  annulus  of  Vieussens  to  the  inferior 
cervical  ganglion,  and  from  this  by  way  of  the  trunk  of  the  cervical  sympathetic 
to  the  superior  cervical  ganglion.  From  the  superior  cerv'ical  ganglion,  the 
fibers  pass  to  the  Gasserian  ganglion,  follow  the  trigeminal  and  traverse  the 
long  ciliary  nerves,  without  connecting  with  the  ciliary  ganglion,  to  the  iris. 
Stimulation  of  the  sympathetic  is  said  to  cause  inhibition  of  the  sphincter  as 
well  as  excitation  of  the  dilator  (Reid). 

Both  constrictor  and  dilator  fibers  of  the  pupil  are  in  a  state  of  tonic 
excitation :  when  the  cervical  sympathetic  is  cut,  the  pupil  constricts ;  when 
the  oculo  motor  is  cut,  it  dilates. 

The  following  experiments  by  Langley  and  Anderson  show  that  the  dila- 
tation of  the  pupil  is  not  merely  a  matter  of  inhibition  on  the  part  of  the 
sphincter  pupillfe.  When  the  sclerotic  was  stimulated  locally  with  the  induc- 
tion current,  a  short  local  dilatation  of  the  pupil  (Fig.  222)  was  obtained. 
Were  the  dilatation  due  solely  to  inhibition  of  the  sphincter, 
the  movement  would  have  been  uniform  all  around  the  pupil. 
Again,  when  a  sector  of  the  iris  is  isolated  except  at  its  ciliary 
attachment  by  two  radial  cuts  (Fig.  223),  this  sector  shortens 
both  on  direct  stimulation  and  on  stimulation  of  the  cervical 
sympathetic. 

.  ,.1  Fig.   223. — After 

Changes  m  the  diameter  of  the  pupil  imder  normal  eir-  Langley. 

cumstances  are  for  the  most  part  produced  reflexly.     The  most 
important  of  these  reflexes  is  mediated  by  the  optic  nerve.     Constriction  begins 
within  0.4-0.5  second  and  reaches  its  maximum  in  about  0.1  second  thereafter 
(Listing).     It  requires  hut  an  instantaneous  flash  of  light  to  call  out  the  reflex 
constriction  (v.  Vintschgau). 

In  all  animals  in  which  only  part  of  the  optic  nerve  fibers  cross  at  the 


ACXOmODATIOX  529 

chiasm  (man,  monkey,  predatory  animals  and  some  rodents)  contraction  of 
both  pupils  results — i.  e.,  the  reflex  excitation  passes  over  from  one  optic  nerve 
to  both  oculo  motor  nerves  when  light  enters  but  one  eye. 

Stimulation  of  other  afferent  nerves,  and  powerful  respiratory  movements, 
as  in  dyspnoea,  etc.,  are  as  a  rule  accompanied  by  dilatation  of  the  pupil, 
although  reflex  constriction  has  also  been  observed  with  such  stimulation. 
Likewise  stimulation  of  the  most  widely  different  parts  of  the  brain,  cerebral 
cortex  (motor  zone  and  temporal  convolutions),  corpora  striata,  optic  thalami, 
anterior  and  posterior  corpora  quadrigemina,  produces  dilatation.  Dilatation 
of  the  pupil  on  stimulation  of  afferent  nerves  as  well  as  on  stimulation  of 
these  various  parts  of  the  l)rain  in  many  cases  persists  after  bilateral  section 
of  both  the  cervical  sympathetic  and  the  trigeminal  nerves.  It  must  be  re- 
garded therefore  as,  in  part  at  least,  the  result  of  inhibition  of  the  constrictor 
center. 

The  tonus  of  the  constrictor  nerves  is  mainly  of  reflex  origin,  for  after 
section  of  the  optic  nerve  section  of  the  oculo  motor  no  longer  produces  dila- 
tation of  the  pupil  (Knoll).  But  stimulation  of  the  optic  nerve  cannot  be 
the  only  cause  of  the  sphincter  tonus,  for  the  pupil  is  strongly  constricted 
in  sleep. 

The  center  for  the  constrictor  nerves  of  the  pupil  is  to  be  sought  in  the 
nucleus  of  the  oculo  motor  nerve.  According  to  Hensen  and  Volckers,  in  the 
dog  it  lies  in  the  floor  of  the  third  ventricle  close  to  the  aqueduct  of  Sylvius  and 
a  little  posterior  to  the  center  for  accommodation  (Fig.  230). 

The  center  for  the  dilatation  of  the  pupil  was  located  by  Budge  in  the 
cervical  cord  (centrum  cilio  spinale)  ;  other  authors  have  been  led  by  their  inves- 
tigations to  conclude  that  the  center  is  located  in  the  brain  and  that  fibers  pass 
thence  down  the  cord  to  the  roots  of  exit.  Since,  however,  after  section  of  the 
cord  high  in  the  neck,  the  pupil  is  dilated  on  stimulation  of  the  sciatic  nerve, 
but  is  always  constricted  by  section  of  the  cervical  cord  alone,  we  may  perhaps 
safely  infer  that  there  is  a  center  in  the  cord,  the  normal  tonic  influence  of 
which  is  to  keep  the  pupil  dilated. 


§  6.    ACCOMMODATION 

A.    RANGE    OF   ACCOMMODATION 

A  point  of  light  starting  from  the  far  point  of  the  eye  and  brought  gradu- 
ally nearer  to  it,  can  be  kept  constantly  focused  on  the  retina.  But  this  is 
possible  only  up  to  a  certain  limit,  there  being  for  every  eye  a  near  point 
whence  it  receives  the  most  divergent  rays  which  can  be  focused  on  the 
retina.  In  order  that  these  most  divergent  rays  may  be  focused  on  the 
retina  the  refraction  of  the  eye  must  be  increased  in  some  way.  The  change 
in  the  eye  by  which  this  is  accomplished  is  called  accommodation.  Know- 
ing the  far  point  and  the  near  point  of  the  eye.  it  is  very  easy  to  calculate 
how  much  the  refraction  is  increased  by  accommodation. 

The  focal  distance  of  the  lens  which  will  give  to  the  rays  proceeding  from 
the  near  point  the  direction  they  would  have  if  they  came  from  the  far  point 
furnishes  the  measure  of  the  ranqe  of  accommodation. 


530 


VISION 


We  have  here  to  distinguish  between  range  of  accommodation  and  line 
of  accommodation.  The  former,  as  just  stated,  is  the  measure  of  the  increase 
in  refracting  power  which  can  be  brought  about  by  accommodation,  whereas 
the  hitter  gives  tluit  depth  of  space  within  which  the  eye  can  form  by  the  help 
of  accommodation  a  clear  picture  on  the  retina.  The  range  of  accommodation 
is  entirely  independent  of  the  static  refraction  of  the  eye;  but  the  line  of 
accommodation  varies  considerably  in  eyes  of  different  refractive  conditions. 

The  range  of  accommodation  decreases  gradually  with  age,  as  the  following 
table  compiled  by  Bonders  will  show : 


Age  in  Years. 

Range  of  accommodation. 
Diopters. 

Age  in  Years. 

Range  of  accommodation, 
Diopters. 

10 

14.0 
12.0 
10.0 
8.5 
7.0 
5.5 
4.5 

45 

3.5 

15 

50 

2.5 

20 

55                 

1  75 

25             

60 

1.0 

30           

65 

0  75 

35          

70 

0.25 

40 

75         .               .... 

0.0 

1 

This  gradual  diminution  in  the  optical  power  of  the  eye  is  called  presby- 
opia.    It  must  not  be  confused  with  hypermetropia,  for  h\^ermetropia  is  a 


A 


^ 


Fig.  224.— After  Helmholtz. 

particular  kind  of  static  refraction,  while  presbyopia  is  caused  by  a  loss  in 
the  power  of  accommodation. 

Presbyopia  is  treated  with  convex  lenses,  the  strength  being  so  chosen 
that  rays  proceeding  from  a  point  lying  conveniently  near  the  eye  appear  to 
come  from  the  actual  near  point.  Objects  can  then  be  held  at  anv  distance 
and  be  clearlv  focused  on  the  retina. 


B.    MECHANISM   OF    ACCOMMODATION 

The  change  in  the  optical  apparatus  which  takes  place  in  accommodation 
consists  in  an  alteration  of  the  form  of  the  lens.  This  view  was  first  expressed 
by  Descartes  (1637),  but  the  first  conclusive  proof  of  it  was  furnished  more 
than  two  hundred  vears  later  by  Max  Langenbeck.  Cramer,  and  Helmholtz 
(1849-1854). 

We  have  already  seen  (page  522)  that  the  radius  of  curvature  of  a  spherical 
refracting  surface  can  be  calculated  from  the  size  of  an  imag^e  reflected  from 


ACCOMMODATIOX 


531 


^y  t^p 


A 


B 


Fig.  22.5. — The  reflected  image  from  the 
cornea  (to  the  left),  that  from  the  an- 
terior surface  of  the  lens  (middle  pic- 
ture), and  that  from  the  posterior  sur- 
face (to  the  right),  after  Helmholtz. 
^4,  as  seen  in  an  eye  adjusted  for 
distant  vision ;  B,  as  seen  in  an  eye 
accommodated  for  near  vision. 


it.     Now  it  has  been  sho\ni  that  in  accommodation  for  near  vision  the  image 

reflected  from  the  cornea  does  not  change,  while  that  from  the  anterior  surface 

of  the  lens,  and  to  a  less  extent  also  that  from  the  posterior  surface,  does. 

That  is  to  say,  the  two  surfaces  of  the 

lens  become  bulged  out  more  in  accom-         a       h     c  a      b       c 

modation.  the  anterior  however  to  a  much 

greater  extent  than  the  posterior. 

In  order  to  observe  these  changes  of 
form,  the  eye  to  be  examined  is  given  two 
definite  points  to  look  at  (/  and  n.  Fig. 
224),  lying  in  the  same  straight  line  di- 
rectly in  front  of  it.  Then  two  slits  of 
light  from  a  large  bright  lamp  ilame  sit- 
uated to  one  side  of  the  line  of  vision  and 
on  the  same  level  with  the  eye  are  thrown 
into  the  eye.  In  Fig.  224  let  A  be  the 
observed  eye  and  C  the  flame,  B  the  eye 
of  the  observer.  If  now  the  observer  move 
his  eye  back  and  forth  in  the  neighbor- 
hood of  B,  so  that  the  angle  B  A  f  is  approximately  equal  to  C  A  f,  he  should 
see  three  pairs  of  images  reflected  from  the  observed  eye,  namely,  a  (Fig.  22-5). 
the  brightest  coming  from  the  cornea,  and  h  and  c  from  the  anterior  and 
posterior  surfaces  of  the  lens.  When  the  eye  is  adjusted  for  distant  vision 
the  images  have  the  appearance  of  Fig.  225,  A;  for  near  vision  (Fig. 
225,  B),  the  image  a  does  not  change,  but  the  image  h  becomes  very  much 
smaller.  By  very  exact  methods  it  can  be  shown  also  that  c  becomes  slightly 
smaller. 

With  these  changes  in  the  form  of  the  lens  the  pressure  in  the  anterior 
chamber  of  the  eye  does  not  increase,  neither  does  the  posterior  surface  of 

the  lens  change  its  position,  hence  the 
lens  as  a  whole  is  not  displaced. 
But  the  anterior  surface  of  the  lens 
presses  forward  and  pushes  the  iris 
before  it.  This  can  be  seen  by  look- 
ing at  the  cornea  of  the  eye  of  an- 
other person  from  the  side  and  a  lit- 
tle to  the  rear  (Fig.  22))).  With 
the  observed  eye  adjusted  for  distant 
vision,  the  observer  should  place  him- 
self so  that  he  can  see  just  a  little 
of  the  black  pupil  projecting  in  front 
of  the  sclerotic.  Then  when  the  eye 
is  accommodated  for  near  vision,  the 
pupil  becomes  much  more  plainly  visible.  We  have  already  called  attention 
to  the  fact  tbat  tbe  pupil  itself  becomes  narrower  in  accommodation. 

According:  to  O.  Weiss,  the  radius  of  curvature  of  the  anterior  surface  of 
the  lens  accommodated  for  a  distance  of  749  mm.,  is  9  mm. ;  for  337  mm.,  8  mm. ; 
and  for  199  mm.,  7  mm. 


Fig.  226. — The  protrusion  of  the  iris  in  accom- 
modation, after  Helmholtz.  .-1,  an  eye  ad- 
justed for  distant  vision;  £,  an  eye  adjusted 
for  near  visioii. 


532 


VISION 


The  whole  anatomical  structure  of  the  eye  indicates  that  the  cUiarjj  muscle 
must  in  some  way  participate  in  jjringing  ahout  the  change  in  the  curvature 
of  the  lens.  But  views  diit'er  considerably  as  to  the  way  in  which  this  takes 
place. 

In  a  meridional  section  of  the  eye.  the  ciUari/  muscle  (Fig.  227)  fills  up 
a  triangular  field  in  the  ciliary  body.  It  constitutes  therefore  in  the  whole 
circumference  of  the  eyeball  a  circular  three-sided,  prismatic  band,  which,  as 


Fig.  227. — Meridional  section  through  the  ciliary  body  of  a  human  eye,  after  Schwalbe.  1,  cor- 
nea :  i",  membrane  of  Descemet ;  -i,  .sclerotic  coat ;  4,  Sclilemm'.s  canal ;  8,  stroma  of  the  iris ;  9, 
pigment  epitlielium  of  the  iris;  10,  inner  connective-tissue  layer  of  the  ciliary  body,  continu- 
ous with  the  connective-tissue  framework  of  the  ciliary  process;  13,  meridional  fibers  of  the 
ciliary  muscles;  14,  radial  fibers  of  the  ciliary  muscle:  l'',  circular  muscle  of  Miiller;  16,  circu- 
lar muscle  fibers  of  the  inner  surface  of  the  ciliary  body;    17,  choroid  coat. 

the  figure  .<hows,  is  often  interlaced  with  strands  of  connective  tissue.  Iwa- 
noflp  distinguishes  three  kinds  of  muscular  fibers  according  to  their  direction, 
namely,  (1)  meridional  fibers  running  from  the  sclerotic  fold,  (3',  Fig.  227) 
backward  to  the  boundary  of  the  true  choroid  coat;  (2)  radial  fibers  extend- 
ing from  the  lamellae  beneath  Schlemm's  canal  to  the  whole  inner  face  of  the 
triangle;  and  (3)  the  circular  fibers,  the  strongest  bundles  of  which  run  along 
the  short  anterior  face  of  the  triangle  and  in  its  inner  anterior  angle  (15,  Fig. 
227).  Besides,  all  the  radial  l)undles  bend  around  on  the  inner  face  of  the 
muscle,  taking  a  circular  direction  and  forming  in  this  way  a  more  or  less 
extensive  circular  layer. 

According  to  Iwanoff  the  ring:  muscle  appears  to  be  developed  to  differ- 
ent degrees  in  eyes  having  different  static  refractive  powers;  thus  in  myopic 
eyes  it  is  almost  entirely  wanting,  while  in  hypermetropic  eyes  it  is  strongly 
developed  and  amounts  to  about  one-third  of  the  whole  ciliary  muscle. 

The  lens  rests  in  a  concavity  in  the  anterior  face  of  the  vitreous  body  and 
is  attached  by  an  anterior  prolongation  of  the  hvaloid  meml^rane  known  as 


ACCOMMODATION 


533 


the  zonule  of  Zinn,  to  the  ciliary  body.  The  zonule  of  Zinn  surrounds  the 
periphery  of  the  lens,  fusing  insensibly  with  its  capsule.  The  greater  part 
of  the  zonule,  from  the  ora  serrata  to  the  tip  of  the  ciliary  process,  is  grown 
fast  to  the  ciliary  body.  But,  since  the  ciliary  processes  do  not  reach  all  the 
way  to  the  lens,  there  is  left  a  small  zone  between  them  and  the  periphery 
of  the  lens,  within  which  the  zonule  is  turned  freely  toward  the  posterior 
chamber.  This  free  part  of  the  zonule  (Fig.  228)  consists  of  several  strands, 
which  may  be  divided,  for  convenience  into  three  groups :  an  anterior,  passing 
to  the  anterior  capsule  of  the  lens  and  called  the  suspensory  ligament ;  a 
middle  group  whose  fibers  are  directed  vertically  to  the  capsule  immediately 
back  of  the  equator  of  the  lens,  and  a  posterior  group  lying  close  to  the 
hyaloid  membrane  and  pass- 
ing over  into  the  posterior  "^^  / 
capsule  of  the  lens.  All  these 
strands  consist  of  parallel  in- 
elastic fibers. 

Among  the  hypotheses 
which  have  l)een  put  forward 
to  explain  the  form  changes 
of  the  lens  in  accommodation, 
the  following  by  Helmholtz  is 
the  one  most  generally  ac- 
cepted at  this  time : 

The  lens  is  an  elastic  body 
which,  Avhile  the  ciliary  mus- 
cle is  inactive,  is  somewhat 
compressed  from  before  back- 
ward by  the  radial  pull  of  the 
zonule  attached  to  its  equator. 
Now  the  zonule  is  firmly  at- 
tached by  its  peripheral  or 
posterior  end  with  the  choroid 
coat  just  at  the  posterior  mar- 
gin of  the  ciliary  processes. 
Consequently  by  contraction 
of  the  meridional  fibers  of  the 
ciliary  muscle  (Fig.  227)  this 
posterior  edge  of  the  zonule 
can  be  drawn  forward,  there- 
by releasing  the  radial  tension 
which  it  exerts  on  the  lens  in 
the  imaccomniodated  condi- 
tion. The  result  is  that  the 
lens  bulges  out  at  its  center 

rendering  both  anterior  and  posterior  surfaces  more  convex.  The  only 
function  of  the  circular  fibers  according  to  this  view  would  be  to  crowd 
the  anterior  part  of  the  ciliary  processes  toward  the  relaxing  lens  and  the 
zonule,  so  as  to  prevent  alike  any  rupture  of  the  tissues  and  any  traction 


Fig.  228. — Zonule  of  Zinn  of  an  adult  man,  meridional 
section,  after  G.  Retzius.  /,  edge  of  the  lens  at  its 
equator;  yl,  vitreous  body;  i,  iris;  a,  short,  strong 
attachment  fibers  of  the  posterior  group;  b,  fibers  of 
the  same  group  springing  from  the  hyaloid  mem- 
brane; c,  the  anterior  group  springing  from  the  ciliary 
process;  d,  fibers  springing  from  the  ciliary  process 
and  connecting  with  other  fibers;  e,  space  between 
the  capsule  of  the  lens  and  the  pericapsular  mem- 
brane. 


534 


VISION 


of  the  anterior  part  of  the  zonule  which  wouUl   antagonize  the  meridional 

fibers. 

Schon  seeks  to  explain  the  change  in  the  form  of  the  lens  in  quite  another 
W9y.  In  his  view  the  circular  libers,  and  to  a  less  extent  the  inner  meridional 
fibers,  of  the  ciliary  muscle  are  the  important  parts.  As  a  consequence  of  their 
contraction  the  ciliary  processes  are  moved  inward  and  somewhat  backward  in 
the  direction  of  the  arrow  (Fig.  229) ;  the  lens,  therefore,  is  pressed  upon  from 
all  sides  and  as  the  schema  in  Fig.  229  shows,  must  bulge  forward. 

Space  Avill  not  permit  us  to  discuss  these  different  hypotheses  more  fully. 
^Ye  would  merely  mention  the  fact  that  Hess  has  brought  forward  a  very  weighty 
argument  in  faVor  of  the  hypothesis  of  Helmholtz.  When  the  mechanism  of 
accommodation  is  stimulated  by  dropping  eserin  in  the  eye,  the  ciliary  proc- 
esses push  forward  toward  the  cornea  and,   at  the  same  time,  inward  toward 

the  edge  of  the  lens,  so  that  the 
ciliary  processes  are  then  found  in 
front  of  the  equator  of  the  lens. 
Again,  in  accommodation  for  near 
vision  the  lens  is  loose  while  in  the 
unaccommodated  eye  it  is  held  firm- 
ly in  place. 

All  authorities  agree,  that  by 
muscular  action  the  eye  can  only 
be  adjusted  for  near  vision  and  not 
for  distant  vision. 

We  have  the  following  state- 
ments from  Hensen  and  Volckers 
with  regard  to  the  innervation  of 
the  ciliary  muscle.  By  stimula- 
tion of  single  ciliary  nerves,  the 
choroid  is  drawn  forward,  its  dis- 
placement at  the  equator  of  the 
eye  being  as  much  as  0.5  mm. ;  the 
anterior  surface  of  the  lens  bulges 
forward  both  in  the  uninjured  eye 
and  after  removal  of  the  cornea 
and  iris ;  and  the  posterior  surface 
of  the  lens  pushes  backward  a  little. 
The  fibers  innervating  the  cili- 
ary muscle  arise  from  the  oculo 
motor.  From  clinical  evidence 
which  has  recently  been  gathered  by  Stuelp  it  appears  that  the  nuclear  center 
for  the  ciliary  muscle  lies  close  to  that  of  the  sphincter  pupillae,  and  that  the 
accommodation  center  lies  in  the  anterior  medial  nucleus  of  the  oculo  motor, 
in  front  of  the  center  for  constriction  of  the  pupil.  [Fig.  230  represents  the 
modern  view  as  to  the  location  of  this  center  (cf.  pages  615,  61G). — Ed.] 

A  convergence  of  the  optical  axes — i.  e.,  a  contraction  of  the  internal  recti 
muscles — takes  place  in  accommodation  even  when  one  eye  is  covered.  But  this 
association  of  convergence  and  accommodation  is  not  an  inseparable  one,  for  a 
person  can  learn  to  converge  the  axes  without  accommodating,  and  vice  versa. 


Fig.  229. — Schema  of  the  mechanism  of  accom- 
modation, after  Schon.  The  form  of  the  lens 
when  the  eye  is  adjusted  for  near  vision  is 
shown  bv  the  dotted  Hne. 


ACCOMMODATION 


535 


viAl'-— Accommodation.. 
fi^-\"- Pupil. 
Convergence. 


Corp.Qvad. 


Fig.  230. — Schematic  representation  of  the  optic  tracts,  modified  from  Fuchs. 

The  field  of  vision  common  to  the  two  ej-es  is  composed  of  a  right  half,  G,  and  a  left  half,  G,.  The 
former  corresponds  to  tlie  left  halves  I  and  /„  of  the  two  retinae,  the  latter  to  the  right  halves 
rand  r,.  The  boundary  between  the  two  halves  of  the  retina  is  formed  by  the  vertical  merid- 
ian. This  passes  through  the  fovea  centralis,  /,  in  which  the  line  of  vision  (F)  drawn  from 
the  point  of  fixation,  F,  impinges  upon  the  retina.  The  optic  nerve  fibers  arising  from  the 
right  halves,  r  and  r,,  of  the  two  retinae  (indicated  by  the  dotted  line)  all  pass  into  the  right 
optic  tract,  T,  while  the  fibers  belonging  to  the  left  halves,  I  and  l„  of  the  two  retinae  pass 
into  the  left  optic  tract,  T,.  The  fibers  of  each  optic  tract  for  the  most  part  pa.<s  to  the  cortex 
of  the  occipital  lobe,  O.C.  ;  the  smaller  portion  of  them,  m,  goes  to  the  oculo  motor  nucleus.  A'. 
This  nucleus  (cf.  page  615)  consists  of  a  series  of  partial  nuclei,  the  most  anterior  of  which 
sends  fibers,  P,  to  the  sphincter  pupillae;  the  next  one  sends  fibers,  ,4,  to  the  muscle  of  accom- 
modation; and  the  third  sends  fibers,  C,  to  the  converging  muscle  (internal  rectus,  »). 


536  VISION 

SECOND    SECTION 

EXCITATION  OF  THE   RETINA  AND  VISUAL  SENSATIONS 

§  1.    LIGHT   RAYS 

Modern  physics  assumes  the  existence  throughout  all  space  of  a  rarefied 
substance,  the  ether,  which,  although  it  has  no  weight,  nevertheless  obeys  in 
general  the  laws  which  govern  the  movements  of  molecules.  The  density  of 
the  ether  is  so  slight  that  it  exercises  no  noticeable  restraint  on  the  movements 
of  the  heavenly  bodies,  with  the  possible  exception  of  the  comets. 

Light  is  regarded  as  extremely  rapid  transverse  (i.  e.,  vertical  to  the 
direction  of  propagation)  vibrations  of  the  ether,  which  are  produced  by  the 
luminous  point  and  are  propagated  through  the  ether  with  very  great  velocity 
(Huygens,  1678;  Euler,  Young,  Fresnel). 

When  sunlight  enters  a  dark  room  through  a  small  slit  and  then  passes 
through  a  glass  prism,  the  small  bundle  of  rays  spreads  out  into  a  broad 
band,  called  the  solar  spectrum,  which  is  not  now  white,  as  the  light  orig- 
inally was,  but  is  of  different  colors  arranged  always  in  the  same  order:  red, 
orange,  yellow,  green,  blue,  indigo,  and  violet.  Sunlight  therefore  consists 
of  rays  which  are  refracted  Ijy  the  spectrum  to  different  degrees,  the  red  rays 
being  refracted  least,  the  violet  rays  most. 

The  difference  in  refrangibility  of  these  rays  is  conditioned  upon  the  dif- 
ference in  the  rate  of  their  propagation  through  solid  and  liquid  media.  They 
are  also  distinguished  by  different  vibration  frequencies  and  consequently  by 
different  wave  lengths.  The  wave  length  (A)  of  extreme  red  rays  is  760 
millionths  of  a  millimeter  (fifi),  and  of  the  extreme  violet  rays  397  /xfj..  But 
the  solar  spectrum  is  not  limited  to  that  which  is  visible  to  human  eyes.  It 
contains  also  rays  of  greater  wave  length  than  760  fifx  (ultra-red  rays)  and 
rays  of  less  wave  length  than  397  /x/x  (ultra-violet  rays).  The  former  are 
characterized  especially  by  their  thermal  effects;  the  latter  by  their  chemical 
effects  on  certain  silver  salts. 

The  tiUra-red  rays  are  not  visible  because,  altliougli  they  are  transmitted 
through  the  media  of  the  eye,  they  do  not  stimulate  the  retina;  while  the 
ultra-violet  rays  are  invisible  for  just  the  opposite  reason — they  are  for  the 
most  part  absorbed  by  the  media  of  the  eye.  When,  as  in  the  operation  for 
cataract,  the  lens  is  removed,  the  visible  spectrum  reaches  down  to  A.  313. 

Different  sources  of  light  contain  the  different  rays  in  different  quantity — 
e.  g..  the  strontium  light  is  red.  the  sodium  light  yellow.  Accordingly,  when 
the  light  from  such  a  flame  is  refracted  by  a  prism  we  get,  not  a  continuous 
spectrum,  but  a  spectrum  which  consists  of  more  or  less  numerous  distinct 
luminous  lines  which  are  characteristic  for  the  different  chemical  elements. 

The  color  of  bodies  which  are  not  self-luminous  depends  upon  the  rays 
which  are  reflected  in  greatest  number  from  them.  or.  if  the  objects  are 
transparent,  upon  the  rays  which  are  transmitted  by  them.  If.  for  example, 
a  surface  is  red,  it  is  due  to  the  fact  that  of  all  the  rays  which  fall  on  that 
surface,  the  red  rays  are  thrown  off  in  greatest  number.     Likewise  a  glass  is 


THE   PHEXOMEXA   OF  EXCITATION  537 

red  because  it  permits  more  of  the  red  rays  than  of  any  other  kind  to  pass 
through  it.  We  must  rememl)er.  however,  that  it  is  only  the  relative  number 
of  rays  reflected  or  transmitted  which  gives  the  color  to  a  nonluminous  object ; 
for  rays  of  other  colors  may  as  a  rule  be  reflected  or  transmitted  at  the  same 
time. 

If  all  the  light  rays  which  fall  upon  a  surface  are  reflected  in  the  same 
relative  numbers  as  they  occur  in  colorless  light  the  surface  appears  white, 
gray  or  black  according  as  the  total  quantity  of  rays  reflected  is  great  or 
small.     The  same  holds  mutatis  mutandis  for  transparent  objects. 

Whether  a  surface  is  colored  or  not  its  brightness  depends  upon  the  quan- 
tity of  reflected  rays:  a  bright  red  surface  reflects  much  light  of  which  a  rela- 
tively large  number  of  the  rays  are  red;  a  dark  red  surface  reflects  the  same 
rays  in  relatively  largest  number,  but  the  total  quantity  of  light  reflected  by 
it  is  relatively  small. 

Two  inferences  which  may  be  drawn  from  the  facts  presented  here  should 
be  kept  steadily  in  view  throughout  the  following  discussion :  that  white  light 
always  consists  of  rays  of  different  wave  lengths 
and  that  the  only  really  pure  colors  are  the  colors 
of  a  pure  spectrum. 

§  2.    THE    PHENOMENA   OF   EXCITATION 

When  light  falls  upon  a  freshly  exposed  retina, 
the  latter  undergoes  a  number  of  changes  which 

are  objectively   demonstrable.      Thus   a  pigment.  Fig.  2.31. — Optogram   formed 

present  in  all  parts  of  the  retina  except  the  vellow  °^  ^'^^  '■'^^'^'^  b>'  a^'tion  of 

,  1        11    1   1  J?  -j^  1        ,1  ■       '7  lisht   on   the    visual    purple, 

spot  and  called  because  of  its  color  the  visual  pur-  ^^^^j.  Kiihne.  The  purple 
pie,  fades  (Fig.  231)  ;  the  coloring  matter  of  the  fades  and  the  image  thus 
pigment  epithelium  (frog's  eye,  Fig.  232)  moves          formed  is  fixed  in  a  solution 

11-  •    1    -"^     ii  •   ^  i    1  of  alum,  after  the  manner  of 

inward,   being  accompanied  m  this  movement  bv          ^  .       '    .  ,    . 

*  1  .  fixmg  the  image  on  a  photo- 

a  shifting  of  the  cone  cells  in  the  same  direction.          graphic  plate. 
and   the   action   current  of   the   retina    (directed 

from  the  inner  surface  toward  the  rods  and  cones)  undergoes  a  positive  varia- 
tion. The  significance  of  the  first  of  these  changes  we  shall  discuss  briefly  on 
page  54:1 ;  of  that  of  the  second  we  know  little  more  than  what  is  contained 
in  the  statement  that  it  furnishes  us  some  external  indication  of  an  excitation 
process ;  the  third  goes  perhaps  a  step  farther  and  brings  the  mode  of  response 
of  the  visual  apparatus  into  line  with  other  forms  of  protoplasmic  activitv. 
But  if  we  wish  to  know  the  course  of  the  excitation  process  we  must  rely  for 
the  most  part  on  our  own  subjective  experiences. 

To  how  great  an  extent  these  subjective  phenomena  are  caused  by  processes 
going  on  in  the  retina  itself,  or  by  changes  in  the  many  other  parts  of  the 
nervous  system  necessary  for  the  production  of  a  conscious  visual  sensation, 
nothing  definite  can  be  said  (except  with  I'egard  to  certain  details).  Unless 
otherwise  expressly  stated  the  facts  and  discussion  in  what  follows  relate  to 
the  entire  nervous  mechanism  concerned  in  visual  sensation. 

When  light  falls  upon  the  retina  the  resulting  sensation  does  not  reach  its 
full  strength  immediately,  and  similarly  vice  versa  when  light  is  suddenly 


538 


VISION 


turned  off  the  sensation  does  not  vanish  instanth,  hut  persists  for  a  meas- 
urahle  time. 

The  latter  statement  is  very  easily  proved.  When  one  looks  for  a  moment 
at  a  bright  lamp  flame,  then  suddenly  closes  the  eyes  and  covers  them  with  the 
hand,  or  looks  at  an  absolutely  dark  background,  he  still  sees  a  l3right  image 
of  the  same  form  as  that  of  the  bright  object  itself.  The  image  gradually 
disappears  and  as  it  does  so  changes  its  color.  This  phenomenon  in  which 
the  bright  parts  of  the  object  remain  bright  and  the  dark  parts  dark  is  called 
a  positive  after-image.  Such  an  after-image  has  at  first  the  proper  color  of 
the  object,  and  very  often  it  reproduces  very  exactly  the  separate  parts  of  the 
object  in  their  proper  form  and  shade. 

Proof  that  the  rise  of  a  visual  sensation  also  requires  a  certain  time  is 
not  much  more  difficult.     We  need  onlv  consider  for  a  moment  the  effect  of 


Fig.  232.— Section  through  the  retina  of  a  frog's  eye,  after  Engelmann.  .4,  after  the  eye  was  kept 
for  from  one  to  two  days  in  complete  darkness;  B,  kept  for  24  hours  in  the  dark,  then  exposed 
for  one-half  hour  to  diffuse  bright  daylight  (cf.  page  537). 


rotating  a  circular  disk  composed  of  black  and  white  sectors  (as  in  Fig.  233) 
to  be  convinced  of  this.  So  long  as  the  rate  of  rotation  is  low.  the  black  and 
white  sectors  remain  perfectly  distinct.  But  as  the  rate  1)ecomes  higher  the 
edges  of  the  sectors  are  obliterated,  and  this  is  true  as  well  of  the  edges  going 
before  as  of  those  coming  after,  whichever  the  direction  of  rotation.  If  the 
excitation  of  the  retina  were  instantaneous,  the  leading  edges  of  the  white 
sectors  ought  to  continue  sharply  defined,  while  from  what  has  just  been 
said  above,  it  is  evident  that  the  edges  coming  after  ought  to  be  indistinct 
(cf.  the  dotted  line  in  Fig.  234). 

With  a  high  rate  of  speed  the  rays  coming  from  the  wliite  sectors  no 
longer  have  sufficient  time  to  produce  the  maximum  excitation  and  on  the 
other  hand  the  light  is  never  completely  shut  out  by  the  black  sectors;  con- 


THE   PHENOMENA   OF   EXCITATION 


539 


sequently  the  brightness  of  the  black  and  white  sectors  oscillate  around   a 
mean  value.     From  a  certain  rate  of  rotation  onward  the  whole  disk  appears 
uniformly    gray,    its    brightness    being    the 
same  as  would  be  obtained  if  all  the  light  re- 
flected by  the  white  sectors  were  distributed 
uniformly  over  the  whole  disk. 

Or  in  the  form  of  a  theorem,  when  a 
point  on  the  retina  is  affected  in  regular 
periodic  succession  for  a  certain  time  a  l>y 
rays  of  a  certain  intensity,  and  is  entirely 
unaffected  for  a  certain  time  h,  if  the  en- 
tire period  a  -\-  h  is  short  enough,  the  sen- 
sation produced  will  be  a  perfectly  continu- 
ous one  and  of  a  strength  which  (within 
certain  limits  at  least)  corresponds  to  that 
obtained  by  continuous  stimulation  with 
light  rays  of  an  intensity  —^  (Talbot's 
proposition).  With  light  of  medium  intensity  the  period  a -\- h  need  not  be 
less  than  0.0-t  second. 


Fig.  233.— After  Helmholtz. 


The  time  required  to  reach  the  maximum  excitation  of  the  stimulus,  what- 
ever the  interval,  is  but  a  fractional  part  of  a  second — e.  g.,  as  shown  graphically 
in  Fig.  235,  about  0.217  second.  Beyond  the  maximal  point,  as  is  evident  from 
the  figure,  the  excitation  gradually  declines  in  intensity  owing  to  the  onset 
of  fatigue. 

The  time  required  to  produce  the  maximal  excitation  is  different  for  the 
different  pure  colors,  being  least  for  the  red  and  greatest  for  the  green  (Kunkel). 

Likewise  the  time  required  for  the 
retinal  excitation  to  wear  off  is  dif- 
ferent for  the  different  colors. 

A.    FATIGUE   AND   RECOVERY 
OF   THE   VISUAL   ORGAN 

When  one  looks  fixedly  for  a 
time  (with  a  light  of  moderate  in- 
tensity, five  to  fifteen  seconds),  at 
a  bright  object,  and  then  directs 
the  gaze  at  a  uniformly  illumi- 
nated surface,  he  perceives  on  the 
latter  an  after-image,  in  which  the 
bright  parts  of  the  object  appear 
dark  and  the  dark  parts  bright. 
That  is.  the  image  is  just  the  re- 
verse of  what  we  have  called  a 
positive  after-image  and  is  de- 
scribed as  a  negative  after-image. 
This  phenomenon  is  due  to  fa- 
tigue of  some  part  of  the  visual  organ,  in  all  probability  of  the  retina  itself. 
The  bright  light  falling  continuously  on  a  certain  point  of  the  retina,  fatigues 


■tn.        -n.              f)           p             cj 

t 

\    /'" 

/' 

1 

! 

\ 
V 

1 
J 

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0          ^ 

'i           ( 

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i 

Fig.  234. — Schema  to  illustrate  the  course  of  ex- 
citation of  the  retina  successively  by  black  and 
white  sectors  (as  in  Fig.  233),  after  Fick.  If 
m-n,  o-p,  etc.,  represent  the  white  sectors,  and 
a-6,  c-d,  etc.,  the  black,  then  the  progress  of 
excitation  is  indicated  by  the  broken  line. 
Starting  at  O,  the  retina  having  just  been  ex- 
posed to  darkness,  the  excitation  rises  suddenly 
at  first  then  more  slowly;  at  n  the  excitation 
ceases  suddenly,  but  requires  some  time  to  fall 
to  the  zero  point,  and  so  on.  The  more  rapid 
the  rotation,  the  more  will  the  broken  line  tend 
to  become  a  horizontal  line. 


540 


VISION 


that  point,  so  that  when  light  from  the  uniformly  illuminated  surface  now 
strikes  the  retina,  that  particular  point  is  incapable  of  being  excited  so  strongly, 
as  the  remaining  relatively  unfatigued  parts;  hence,  the  corresponding  point 
of  the  field  of  vision  appears  dark  in  comparison  with  the  other  parts. 

In  fact  the  sensitiveness  of  the  retina  is  all  the  time  changing  whether  it 
is  being  acted  upon  by  the  light  or  is  protected  from  the  light — in  the  one 
case  becoming  progressively  less  and  in  the  other  progressively  greater.  These 
changes  taken  together  are  described  by  Aubert  as  the  adaptation  of  the  retina. 

For  example,  when  we  pass  from  a  light  room  into  one  very  feebly  lighted 
at  first  we  are  unable  to  see  anything;  gradually,  however,  the  sensitiveness  of 
the  retina  becomes  greater,  until  the  feeble  light  produces  a  plainly  perceptible 

33  40  58      104  166  486 


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8    3749      81       127  359  650 

Fig.  235. — Excitation  of  the  retina  as  a  function  of  the  time  exposed,  after  Exner.     The  abscissa 
represent  the  time  in  thousandths  of  a  second,  the  ordinates  the  strength  of  the  sensations. 

impression ;  in  fact  after  remaining  longer  in  the  dark  room  the  light  can  be 
greatly  reduced  in  intensity  without  passing  below  the  threshold. 

According  to  exact  measurements  on  the  adaptation  of  eyes  to  the  dark  the 
rate  is  about  the  same  for  different  individuals,  but  the  absolute  increase  in 
sensitivity  varies  all  the  way  from  1,400  to  8,000  fold.  With  both  eyes  the 
increase  in  sensitivity  is  1.6-1.7  times  as  great  as  with  only  one  eye.  These 
facts  apply  only  to  the  peripheral  parts  of  the  retina;  for  the  fovea  centralis 
the  adaptation  is  very  much  less  complete,  the  increase  in  sensitivity  being  only 
twentj'  to  thirty  times  the  sensitivity  of  the  eye  adapted  for  light. 

When  we  pass  back  after  complete  adaptation  to  the  dark  into  a  brightly 
illuminated  room,  the  strong  light  at  first  has  a  blinding  effect  upon  the  retina, 
which  has  meantime  become  extremely  sensitive.  But,  after  a  short  time,  its 
sensitiveness  has  so  far  decreased  that  there  is  no  excessive  stimulation.  In 
other  words,  the  eye  adapted  to  the  dark  has  now  become  adapted  to  a  high 
degree  of  illumination.  Another  point  of  evidence  that  the  condition  of  the 
retina  is  adapted  to  the  strength  of  the  light,  is  the  fact  that  the  size  of  the 
pupil  remains  the  same  for  a  rather  wide  range  of  intensity,  changing  only  at 
the  moment  the  intensity  changes. 


SENSATIONS   OF  COLOR  541 

§  3.    SENSATIONS   OF   COLOR 

There  are  three  different  modifications  of  light  which  influence  our  sensa- 
tions of  color:  hrigldness,  which  depends  upon  the  energy  of  the  ether  vibra- 
tions ;  tone,  which  depends  upon  the  wave  length ;  and  saturation,  which  de- 
pends upon  the  purity  of  a  given  wave  length,  or,  in  other  words,  upon  the 
amount  of  white  light  present. 

The  human  eye  can  distinguish  all  of  these  properties.  Indeed,  its  ability 
to  distinguish  differences  of  color  is  very  highly  developed.  Konig  has  esti- 
mated that  in  the  visible  spectrum  there  are  165  different  color  tones,  which 
can  be  distinguished,  and  that  the  total  number  of  different  degrees  of  in- 
tensity perceptible  to  the  human  eye  is  about  660.  When  we  remember  that 
each  tone  can  vary  greatly  in  intensity  and  each  tone  and  intensity  in  turn 
can  have  all  possible  degrees  of  saturation,  we  get  some  idea  of  the  number 
of  possible  color  sensations. 

According  to  Herschel  the  mosaic  workers  in  the  Vatican  can  distinguish 
30,000  different  colors. 

A.    RELATION   OF   THE  PROPERTIES   OF   LIGHT  TO   DIFFERENT 
CONSTITUENTS   OF  THE   RETINA 

Some  color  tones  of  the  spectrum  always  appear  brighter  than  others: 
with  light  of  ordinary  intensity  the  brightest  of  all  is  a  certain  tone  of  yellow 
(535^^).  If  the  different  colors  be  observed  as  the  daylight  fades  it  will 
be  noticed  that  certain  ones  disappear  sooner  than  others — e.  g.,  the  reds 
before  the  blues.  In  a  very  feeble  light  a  weak  spectrum  can  still  be  seen, 
but  only  as  a  band  of  light.  Its  colors  have  disappeared  and  that  part  of 
the  spectrum  which  now  appears  brightest  is  nearer  the  more  refractive  end 
of  the  spectrum  than  it  was  in  broad  daylight.  But  if  only  a  portion  of  the 
weak  spectrum  small  enough  to  be  imaged  on  the  fovea  centralis  be  allowed 
to  enter  the  eye,  its  color  can  be  correctly  perceived  (Konig,  Sherman). 

These  and  other  facts  have  led  to  the  assumption  of  a  functional  differ- 
ence between  the  rods  and  cones.  The  latter,  found  evervwhere  in  the  retina 
and  exclusively  in  the  fovea  centralis,  are  thought  to  be  sensitive  to  light  of 
different  wave  lengths,  but  to  require  rather  a  high  degree  of  illumination. 
The  rods  are  sensitive  to  a  much  feebler  light  but  are  not  sensitive  to  color 
tones  (v.  Kries,  Parinaud  et  ah).  Eyes  which  are  totally  color  blind,  remain- 
ing sensitive  only  to  light  and  darkness,  are  therefore  supposed  to  be  devoid 
of  cones.  Xocturnal  animals  like  the  owl,  bat,  mouse,  cat,  etc.,  are  known  to 
have  relatively  fewer  cones  and  more  rods  than  diurnal  animals  (Max 
Schultze). 

The  visval  purple  (cf.  page  537)  is  also  thought  to  assist  in  vision  by  a 
feeble  light.  In  the  first  place,  it  is  not  found  in  the  cones;  and,  in  the 
second,  there  is  a  close  agreement  between  the  brightness  of  the  different 
wave  lengths  in  a  feeble  light  and  their  action  upon  solutions  of  the  visual 
purple.  Accordingly  it  is  conjectured  that  the  fading  of  the  visual  purple 
is  of  some  service  in  the  stimulation  of  the  rods. 


542  VISION 


B.    SUCCESSIVE   COLOR  INDUCTION 

When  one  looks  fixedly  for  some  seconds  at  a  red  object  on  a  white  frround 
(Fig.  236),  and  then  turns  the  eye  toward  the  white  ground,  he  sees  on  the 
latter  a  distinct  after-image  which  reproduces  the  object  exactly  in  all  re- 
spects but  one — instead  of  being  red  it  is  greenish  blue.  If  the  object  were 
greenish  blue  the  after-image  would  be  red. 

For  every  color  tone  in  the  spectrum  there  is  another,  which  in  exactly 
the  same  wa}'  as  in  this  example  evokes  and  in  turn  is  evoked  by  the  first 
as  an  after-image.  Pure  green,  however,  forms  an  apparent  exception  to  the 
rule.  Its  after-image  is  purple — but  purple  is  a  color 
which  does  not  occur  in  the  spectrum ;  its  relations  thereto 
will  be  mentioned  presently.  Other  pairs  of  colors  which 
are  related  to  each  other  in  this  way  are :  orange  and  l)lue, 
golden  yellow  and  blue,  yellow  and  indigo,  etc. 

„  These   phenomena    show   that   objective   light   can   be 

Fig    236  . 

subjectively  destroyed,  also  that  a  certain  intimate  rela- 
tion exists  between  the  different  colors.  In  order  to  inquire  further  into  these 
facts  which  necessarily  form  the  foundation  stones  for  every  theory  of  color, 
we  must  see  what  results  from  the  mixture  of  colors. 

C.    COLOR  MIXTURE 

By  a  mixture  of  two  or  more  colors  we  mean  that  color  which  is  experi- 
enced when  a  given  point  on  the  retina  is  struck  simultaneously  by  rays  of 
different  wave  lengths.  Every  color  mixture  is  therefore  a  summation  effect 
of  different  light  rays. 

The  best  and  for  many  purposes  the  only  possible  mode  of  procedure  is 
to  mix  pure  spectral  colors.  This  may  l)e  done  by  complicated  apparatus 
which  enables  one  to  isolate  two  spectral  rays  of  different  wave  lengths  and 
to  throw  them  on  the  same  spot  of  a  screen  where  the  mixture  can  be  com- 
pared with  a  reference  color. 

In  this  way  the  different  rays  are  l)rought  into  the  eye  at  the  same  time. 
But  the  experiment  can  be  so  arranged  also  that  the  rays  to  be  tested  will 
fall  successively  on  the  same  spot  of  the  retina.  Then  if  the  sequence  is  rapid 
enough  a  mixture  of  the  two  will  take  place  just  as  in  the  experiment  with 
white  and  black  sectors  (page  539). 

Very  convenient  for  this  purpose  are  Maxwell's  disks.  They  are  circular, 
colored  disks  having  a  radial  slit,  so  that  two  or  more  of  them  can  be  over- 
lapped and  varying  portions  of  each  be  exposed  to  view.  If  the  complex  disk 
thus  composed  of  two  or  more  colored  sectors  is  rotated  rapidly  by  merns  of  a 
clockwork,  the  resulting  mixture  will  depend  upon  the  saturation  of  the  indi- 
vidual colors  employed  and  the  relative  sizes  of  the  different  sectors. 

The  results  of  color  mixture  which  interest  us  most  are  those  obtained  with 
the  above-mentioned  pairs  of  color — red  and  greenish  blue,  yellow  and  indigo, 
etc.  Experiment  has  shown  that  each  of  these  pairs  when  its  components 
are  mixed  at  a  certain  relative  intensity,  produces  the  sensation  of  white  or 
^ay  (which  is  but  a  feeblv  illuminated  white).     Since  each  of  these  colors 


SENSATIONS   OF  COLOR 


543 


complements  tlie  other,  each  one  furnishing  just  what  the  other  lacks  of  being 
white,  they  are  called  compJementary  colors. 

The  sensation  of  white  therefore  can  be  produced  in  very  different  ways, 
namely,  first  by  the  simultaneous  action  of  all  the  rays  contained  in  sunlight, 
when  they  occur  in  the  same  proportion  as  they  are  there  mixed  together, 
and  secondly  by  the  proper  mixture  of  two  complementary  colors.  However 
it  is  impossible  for  the  eye  to  tell  whether  a  given  white  is  composed  of  all 
the  rays  of  the  color  spectrum  or  only  of  red  and  greenish  blue,  orange  and 
blue,  etc.  White  in  other  words  presents  only  quantitative  differences  de- 
pendent upon  different  intensities  of  light,  but  bearing  no  relation  to  the  color 
tones  of  which  it  is  composed.  The  eye  therefore  does  not  analyze:  it  lacks 
entirely  the  ability  so  highly  developed  in  the  ear,  of  resolving  a  given  im- 
pression into  its  separate  components. 

When  two  colors  which  are  not  complementary  are  mixed  together,  instead 
of  white  we  get  a  new  color.  If  red  and  violet,  the  extreme  colors  of  the 
spectrum,  are  mixed  we  get  purple,  the  only  color  tone  which  does  not  occur 
in  the  spectrum.  Purple  is  the  complementary  color  of  green  (see  page  542) 
and  is  in  every  way  different  from  the  colors  the  mixture  of  which  produces  it. 

When  two  simple  colors,  separated  from  each  other  in  the  spectrum  by  less 
distance  than  that  which  separates  com^plementary  colors,  are  mixed,  we  get  a 
color  lying  between  the  two  and  approaching  white  more  the  greater  the  dis- 
tance between  them,  but  becoming  more  nearly  saturated  the  less  the  distance 
between  the  two  components.  When,  on  the  other  hand,  two  colors  separated 
from  each  other  by  a  greater  distance  than  that  which  separates  complementary 
colors  are  mixed,  one  obtains  purple,  or  some  such  color,  which  lies  between  one 
of  the  components  and  the  corresponding  end  of  the  spectrum.  In  this  case 
the  mixture  is  the  more  nearly  saturated  the  greater  the  distance  between  the 
components,  and  approaches  white  more  the  less  the  distance  between  them 
(Helmholtz). 


Violet          Indigo 

1                    1 

Dark  blue  Blue  green  Green         |  ^^y^JJo^^    !  Yellow 

Red 

purple          dark  rose 

light  rose    white           ^^^^^eUow    ^'dlow     '  ^^^^ 

1      •              .     • 

Orange 

dark  rose 

light  rose 

white 

light 
yellow 

yellow          yellow 

Yellow 

light  rose 

white 

light  green 

lightgreen  «-£ 

Greenish 
yellow 

white 

light  green 

light  green  green 

Green 

light  blue 

sea  blue 

blue  green 

Blue 
green 

sea  blue 

sea  blue 

i 

Dark  blue 

indigo 

544  VISION 

III  the  preceding  table  have  been  brought  together  after  Helmholtz  the  results 
of  mixing  different  spectral  colors.  At  the  top  of  the  vertical  columns  and  at 
the  left  are  found  the  simple  colors;  where  the  vertical  and  horizontal  columns 
intersect  are  found  the  colors  resulting  from  the  mixture  of  the  two  simple 
colors  standing  at  the  beginning  of  the  intersecting  columns. 


D.    ON  THE  THEORY   OF   COLOR 

From  the  facts  just  given  it  appears  that  we  can  produce  the  whole  series 
of  different  color  tones  by  appropriate  mixture  of  a  few  simple  colors.  Any 
physiological  theory  of  color  has  therefore  to  show  what  these  simple  colors 
are  and  to  derive  all  color  sensations  from  them. 

There  are  at  this  time  two  principal  opposing  views  as  to  the  production 
of  color,  namely,  the  three-color  theory,  originally  proposed  by  Thomas  Young 


R  O         Y  G  B  V 

Fig.   237. — Excitation  of  the  different  components  of  the  visual  organ  by  Ught  rays  of  different 

wave  lengtlis,  after  Hehnholtz. 

and  later  developed  by  Helmholtz,  and  the  theory  of  antagonistic  colors, 
offered  by  Hering.  Since  an  exhaustive  critical  discussion  of  these  views 
would  call  for  entirely  too  much  room  and  inasmuch  as  it  will  probably  be 
a  long  time  yet  before  the  question  is  finally  settled,  we  shall  limit  the  dis- 
cussion to  a  purely  dogmatic  statement  of  the  essence  of  the  two  theories. 

1.  The  Three-color  Theory. — Young  regarded  red,  green  and  violet  as 
fundamental  or  primary  colors,  because  they  cannot  be  obtained,  at  least  not 
in  complete  saturation,  by  mixture  of  other  colors.  He  supposed  that  in  every 
part  of  the  retina  which  is  capable  of  all  the  color  sensations,  there  are  three 
separate  nerve  elements:  stimulation  of  the  first  produces  the  sensation  of 
red;  stimulation  of  the  second,  that  of  green;  stimulation  of  the  third  the 
sensation  of  violet.  Since  the  action  of  light  on  the  percipient  parts  of 
the  retina  is  in  all  probability  a  chemical  process  in  which  certain  com- 
pounds are  broken  down,  there  would  be  in  the  retina,  according  to  this 
theory,  three  different  visual  substances  corresponding  to  the  three  primary 
colors.  In  order  not  to  commit  ourselves  as  to  the  way  in  which  the  light 
acts  directly,  we  shall  designate  these  percipient  elements  in  general  as  com- 
ponents of  the  visual  organ. 

Light  acts  with  varying  intensity  according  to  its  wave  lengths,  on  the 
three  components.  The  red-perceiving  component  is  excited  most  powerfully 
by  light  of  the  greatest  wave  length ;  the  green-perceiving  component  by 
light  of  medium  wave  length,  and  the  violet-perceiving  by  light  of  the  shortest 
wave  length.  However,  it  is  possible,  and  for  the  explanation  of  certain  phe- 
nomena it  is  necessary,  to  assume  that  each  spectral  color  stimulates  all  the 
components,  one  of  them  feebly,  the  others  powerfully. 


SENSATIONS   OF   COLOR 


545 


In  Fig.  237  the  three  curves  represent  schematically,  according  to  Helm- 
holtz,  the  relative  degree  to  which  each  component  is  stimulated  b}-  the 
different  light  rays  in  the  production  of  their  appropriate  color  sensations, 
thus : 

Simple  red  stimulates  the  red-perceiving  component  strongly,  the  other  two 
feebly;  sensations  of  red. 

Simple  yellow  stimulates  the  red-  and  green-perceiving  components  mod- 
erately, the  violet  feebly;  sensation  yellow. 

Simple  green  stimulates  the  green-perceiving  substance  strongly,  the  other 
two  much  more  feebly;  sensation  green.  Other  effects  can  be  readily  combined 
from  the  figure. 

Stimulation  of  all  components  with  alx)ut  the  same  intensity  gives  the 
sensation  of  white  or  of  whitish  colors. 

According  to  the  three-color  theory,  black  is  only  an  extremely  feeble  white; 
between  the  two  there  is  no  qualitative  difference,  but  only  a  quantitative  one. 

Since  according  to  this  scheme  the  color  system  of  a  man  with  normal 
vision  requires  the  assumption  of  three  primary  colors,  the  eyes  of  this  class 
of  people  are  called  trichromatic. 

Starting  with  the  Young-Helmholtz  theory  Konig  and  Dieterici  have  car- 
ried out  a  very  extensive  series  of  measurements  and  have  calculated  the  form 


^ 


^ 


B 


tft 


6«0        iSO 


Ata      set) 


F 


G 


C  O  £  b  r  G  M 

Fig.  238. — Excitation  of  the  different  components  of  the  visual  organ  by  light  waves  of  different 
wave  length,  after  Konig  and  Dieterici. 


of  their  (ovm)  curves  of  sensation  for  the  three  primary  colors.  They  found 
that  at  the  extreme  red  and  the  extreme  violet  ends  of  the  spectrum  they 
could  distinguish  a  difference  of  brightness,  but  no  difference  of  color  tone, 
hence  these  two  portions  of  the  spectrum,  up  to  Goo  jxix  and  430  ixfx  respectively, 
must  stimulate  only  the  red-  and  the  violet-perceiving  components.  The  re- 
sults which  represent  graphically  the  mean  value  for  the  two  authors  are 
reproduced  in  Fig.  238. 

But  there  are  eyes  with  other  color  systems,  eyes  for  examjde  for  which 


546  VISION 

a  mixture  of  two  definite  rays,  a  long-  and  a  short-waved  one,  can  be  found 
to  match  every  homogeneous  color.  The  color  system  of  such  eyes  is  dichro- 
matic. This  abnormality  is  as  a  rule  inborn  and  is  spoken  of  as  color  hlind- 
ness.  If  the  color  system  of  the  normal  eye  consists  of  three  components, 
that  of  the  dichromatic  eye  might  be  derived  from  it  by  the  absence  of  some 
one  constituent.  According  to  the  Young-Helmholtz  theory  there  would  thus 
be  three  possible  kinds  of  color  blindness :  red  blindness,  green  blindness  and 
violet  blindness.  From  facts  which  will  not  be  given  here  it  appears  that  the 
color  systems  of  the  red  blind  and  the  green  blind  do  correspond  fairly  with 
what  would  be  expected  from  the  theory.  Little  is  knoA^Ti  with  regard  to 
the  third  form. 

How  the  color  blind  actually  experience  colors  can  of  course  only  be  an- 
swered by  persons  in  whom  only  one  eye  has  been  color  blind  from  birth. 
Hippel  and  Holmgren  have  investigated  two  such  cases.  It  must  suffice  here 
to  remark  that  in  one  of  them  mixed  white  light  appeared  the  same — i.  e., 
colorless — to  the  color-blind  as  to  the  normal  eye. 

In  indirect  or  averted  vision  the  ability  to  distinguish  colors  decreases 
gradually  from  the  center  toward  the  periphery  of  the  field  of  vision.  The 
peripheral  limits  for  the  different  colors,  even  for  a  perfectly  normal  eye, 
depend  upon  the  intensity  of  the  light,  the  saturation  of  the  color  and  the 
size  of  the  object.  Thus  Hess  found  that  for  a  definite  shade  of  red  on  a 
grav  backgroimd,  the  limit  was  20°  from  the  axis  of  vision,  provided  the  size 
of  the  object  was  T  mm.  in  diameter ;  with  a  diameter  of  30  mm.  the  same  red 
could  be  recognized  33°  from  the  axis.  According  to  Landolt.  if  the  intensity 
of  light  could  be  made  great  enough  and  the  object  could  be  made  extensive 
enough,  we  would  be  able  to  see  all  colors  at  the  very  periphery  of  the  retina. 

At  all  events  the  capacity  for  color  is  much  less  in  the  peripheral  portions 
of  the  retina  than  in  the  central  portions,  and  with  colored  objects  of  moderate 
size  and  moderate  intensity  of  light  one  may  say  that  a  green  (of  495  ixfx) 
and  a  red  with  a  moderate  admixture  of  blue  disappear  entirely  at  a  relatively 
short  angular  distance  from  the  line  of  vision.  Yellow  and  blue  can  be  recog- 
nized for  some  distance  farther  toward  the  periphery,  in  fact  all  rays  of 
greater  wave  length  than  495  fi/x  are  seen  as  yellow  and  all  of  less  wave  length 
as  blue.  Still  farther  toward  the  periphery  the  sensations  of  yellow  and  blue 
disappear  and  a  zone  which  is  tolerably  color  blind  is  reached  (Hess). 

2.  The  Theory  of  Antagonistic  Colors. — Like  the  three-color  theory,  this 
also  proceeds  on  the  assumption  that  all  our  visual  sensations  are  conditioned 
upon  the  cooperation  of  a  few  components  (visual  substances)  in  the  organ 
of  vision.  According  to  the  former  theory  these  are  present  in  the  retina  itself ; 
but  the  theory  of  antagonistic  colors  leaves  it  undecided  whether  these  substances 
occur  in  the  retina,  optic  nerA^e  or  some  portion  of  the  brain  concerned  in  vision. 

The  three-color  theory,  as  we  have  seen,  explains  the  sensation  of  white 
as  the  result  of  an  equal  excitation  of  the  three  components  and  regards  white 
and  black  as  only  quantitatively  different  sensations.  According  to  Hering's 
theory,  black  and  white  are  qualitatively  different  sensations,  accompanied  by 
opposite  chemical  processes  in  a  special  black-white-perceiving  substance.  The 
sensation  of  white  arises  while  a  process  of  katabolism  is  going  on  in  this 
substance,  that  of  black  during  a  process  of  anabolism.     The  brightness  or 


SENSATIONS   OF   COLOR  547 

darkness  of  any  purely  colorless  sensation,  accordingly,  is  determined  by  the 
ratio  in  which  the  intensity  of  Jcatabolism  stands  to  that  of  anaholism. 

Hering  assumes  four  fundamental  colors:  red,  yellow,  green  and  blue. 
These  colors  are  selected  Ijecause  they  can  occur  without  any  tinge  of  another 
color  occurring  with  them;  or  if  they  do  exhibit  any  evident  inclination 
toward  another  color,  it  is  never  toward  more  than  one  other  at  the  same 
time.  For  example,  yellow  can  merge  into  red  or  into  green,  but  not  into 
blue ;  blue  only  into  red  or  green ;  red  only  into  yellow  or  blue. 

On  the  other  hand,  red  and  green  are  never  clearly  discernible  in  a  color 
at  the  same  time,  nor  yellow  and  blue.  That  is,  the  presence  of  an  evident 
red  sensation  excludes  that  of  an  evident  green;  the  presence  of  blue,  that  of 
yellow,  and  vice  versa;  consequently,  Hering  calls  these  mutually  exclusive 
colors  antagonistic  colors. 

Just  as  the  sensations  of  white  and  black  are  conditioned  upon  opposite 
processes  taking  place  in  the  white  or  black  substance,  the  antagonistic  colors 
are  produced  by  anabolism  or  katabolism,  as  the  case  may  be,  in  two  other 
visual  sul)stances  assumed  by  Hering,  namely,  the  red-green-  and  the  yellow- 
blue-perceiving  substances.  Eed  and  yellow  arise  by  kataljolism,  green  and 
blue  by  anabolism. 

The  main  proposition  of  Hering's  theory  therefore  is  this :  the  fundamental 
sensations  of  the  visual  substances  are  grouped  in  three  pairs :  black  and  white, 
yellow  and  blue,  red  and  green.  For  each  of  these  three  pairs  there  is  a  cor- 
responding anabolic  and  katabolic  process  of  special  quality. 

Since  the  amount  of  anabolism  or  katabolism  caused  by  a  light  stimulus 
in  one  of  the  three  visual  substances  de])ends  not  only  upon  the  intensity  of 
the  stimulus,  but  also  upon  the  excitability  of  the  visual  substance,  the  same 
mixture  of  light  may  appear  l)right  or  dull  colored,  or  colorless,  according  to 
the  physiological  condition  of  the  visual  organ. 

^^^len  the  visual  organ  has  l)een  protected  from  the  light  long  enough  so 
that  a  condition  of  balance  between  the  anabolic  and  the  katabolic  processes 
is  reached,  and  a  colored  light  of  moderate  intensity  is  then  admitted,  the 
excitability  for  that  particular  color  will  decrease  until  it  is  less  than  that 
for  the  antagonistic  color.  Every  mixed  light  which  had  previously  appeared 
colorless  will  now  be  seen  with  a  tint  of  the  antagonistic  color,  or  if  before 
a  mixture  of  fundamental  colors  was  seen,  it  will  now  appear  as  a  mixture 
of  the  two  antagonistic  colors.  Hering's  theory  can  thus  account  for  the 
successive  induction  of  color  or  color  contrast. 

Agreeably  to  his  theory.  Hering  reduces  all  color  blindness  to  red-green 
and  yellow-blue  blindness.  Those  who  are  blind  to  red  and  green  lack  the 
red-green  visual  substance:  everything  which  others  see  as  red  or  green,  they 
see  devoid  of  color ;  in  all  mixed  colors  containing  red  or  green,  they  see  only 
the  yellow  or  blue,  etc. 

E.    SIMULTANEOUS   CONTRAST 

The  idea  of  simultaneous  contrast  can  be  most  simply  presented  by  means 
of  one  or  two  concrete  examples.  If  small  colored  sectors  be  placed  on  a 
white  disk,  as  in  Fig.  239.  and  the  middle  point  of  each  sector  be  interrupted 
by  a  black  and  white  strip,  then  when  the  disk  is  rotated  one  ought  really  to 


548  VISION 

see  a  gray  ring,  corresponding  to  the  black  and  white  strip,  on  a  faintly- 
colored  whitish  ground.  Biit  instead  of  looking  gray,  the  ring  takes  the 
complementary  color  of  the  ground. 

Standing  in  the  moonlight  and  the  gaslight  at  the  same  time,  a  person 
casts  two  shadows — one  from  the  moonlight,  the  other  from  the  gaslight. 
The  ground,  being  illuminated  by  both  the  moon  and  the  yellow-red  light 
of  the  gas  flame,  takes  the  color  of  the  latter.  The  shadow  from  the  moon- 
light is  also  yellow  red,  for  it  is  likewise  illuminated  by  the  gaslight.  The 
other  shadow  which  is  illuminated  by  the  moonlight  ought  to  be  gray,  but 
is  not.  It  has  instead  a  bluish  color — i.  e.",  the  complementary  color  of  the 
ground. 

Simultaneous  contrast  therefore  means  that  an  object  without  color,  in 
the  neighborhood  of  a  colored  one,  takes  on  a  tint  which  is  the  complement 

of  the  color  in  the  object  beside  which 
it  is  placed.  In  the  same  way  a  bright 
object  in  the  neighborhood  of  a  dark  one 
looks  brighter  than  it  really  is. 

We  are  all  the  time  meeting  with  con- 
trast phenomena  which  influence  in  many 
ways  the  impression  we  get  of  color  com- 
positions. If,  for  example,  a  black  design 
be  printed  on  a  red  material,  the  desig-n 
does  not  appear  black,  but  because  of  the 
contrast  greenish  blue.  In  order  to  make 
the  design  actually  appear  black,  it  is 
necessary  to  mix  a  little  of  the  ground 
color  with  the  black — i.  e.,  in  this  case 
the  design  must  be  printed  in  a  very  dark 
Fig.  239.— After  Helmholtz.  red.     The  greenish  blue  produced  by  con- 

trast then  mixes  with  the  red  of  the  de- 
sign, giving  a  faint  white;  hence  the  design  no  longer  appears  gi*eenish  blue, 
but  black  (Chevreul). 

If  on  the  other  hand  the  design  and  ground  work  are  complementary  colors, 
they  intensify  each  other.  A  yellow  design  on  a  blue  material  stands  out  much 
more  prominently  than  it  would  on  any  other  color;  and  the  same  is  true  of 
course  of  black  and  white.  Phenomena  of  this  kind  are  of  no  little  importance 
in  securing  sharpness  of  vision. 

It  is  evident  that  these  contrast  phenomena  are  entirely  of  subjective  origin 
and  cannot  be  caused  by  any  objective  influence  of  the  one  color  on  another. 

According  to  Helmholtz  it  is  all  a  matter  of  judgment.  We  are  accus- 
tomed to  subtract  from  all  colored  surfaces  without  distinction  the  light  by 
which  they  are  illuminated,  so  far  as  that  is  in  the  region  of  their  o^vn  color, 
in  order  to  find  the  body  color  itself.  If  gaslight  and  moonlight  fall  on  the 
same  spot,  the  illumination  of  the  ground  is  a  light  yellow  red.  Now  this 
yellow  red  we  abstract  not  only  from  the  color  of  the  ground,  but  also  from 
that  of  the  shadow,  on  which  no  gaslight  falls;  hence  it  looks  blue  when  it 
is  really  white. 

Hering  on  the  basis  of  a  great  variety  of  experiments  makes  different 
objections  to  this  view,  and  in  many  cases  at  least  has  succeeded  in  showing 


ACTION   OF  THE   EYE   MUSCLES  549 

that  simultaneous  contrast  is  not  a  delusion  of  the  judgment,  hut  rests  upon 
the  action  of  neighhoring  spots  in  the  visual  apparatus.  The  state  of  excita- 
bility of  a  retinal  spot  A,  for  exaimple,  is  always  dependent  upon  the  physio- 
logical condition  of  all  the  rest  of  the  retina,  particularly  of  the  parts  adja- 
cent to  the  spot  A.  Thus,  if  the  spot  A  is  being  constantly  stimulated,  its 
excitability  may  be  raised  or  lowered  merely  by  changing  the  strength  of  the 
light  affecting  other  parts  of  the  retina.  Every  increase  in  the  intensity  of 
the  stimulus  on  other  parts  reduces  the  excitability  of  the  given  spot  A,  so 
that  the  sensation  mediated  by  it  is  less  bright.  Every  decrease  in  the  stimulus 
on  the  rest  of  the  retina  changes  the  condition  of  A  so  that  the  corresponding 
sensation  becomes  brighter.  The  same  laws  apply,  according  to  Hering,  to 
color  contrast.  That  is,  if  the  spot  A  is  exposed  to  white  light  and  the  rest 
of  the  retina  to  yellow-red  light,  the  excitability  of  the  spot  A  for  yellow  red 
is  reduced  and  the  white  field  appears  in  the  complementary  color,  etc.  Hering 
believes  that  the  effects  of  adjacent  retinal  spots  on  one  another  pla}'  an 
essential  part  also  in  the  production  of  positive  and  negative  after-images. 


THIRD    SECTIOX 

MOVEMENTS    OF    THE    EYE    AND    VISUAL    PERCEPTIONS 

§  1.    ACTION   OF   THE   EYE   MUSCLES 

In  discussing  movements  of  the  eye  we  assume  what  is  only  approximately 
true,  namely,  that  they  take  place  about  a  definite  point  called  the  center  of 
rotation,  also  that  when  the  head  is  erect  and  the  gaze  is  directed  straight 
forward  the  two  lines  of  vision  are  horizontal  and  parallel  throughout  (primary 
position). 

Measurements  which  have  been  made  to  determine  the  point  of  origin  and 
the  point  of  insertion  of  the  different  muscles,  with  reference  to  the  center 
of  rotation  and  the  line  of  vision,  as  the  primary  axis,  have  shown  that  the 
three  pairs  of  muscles  are  not  directly  antagonistic.  The  a^xis  of  rotation  of  the 
superior  rectus  muscle  does  not  coincide  with  that  of  the  inferior  rectus,  nor 
does  that  of  the  external  rectus  coincide  with  that  of  the  internal,  nor  that 
of  the  superior  oblique  with  that  of  the  inferior.  For  the  sake  of  simplicity, 
however,  we  shall  neglect  these  differences  and  assume  that  each  pair  of  mus- 
cles rotates  the  eye  about  one  and  the  same  axis  (Volkmann). 

The  positions  of  the  assumed  common  axes  for  the  two  ej^es  are  shown  in 
Fig.  240.  The  line  D-D'  is  the  axis  assumed  to  be  common  to  the  superior 
and  inferior  recti  and  0-0'  that  for  the  two  oblique  muscles.  The  axis  for 
the  external  recti  would  be  vertical  to  the  plane  of  the  paper  at  G.  The 
movement  of  either  eye  in  the  figure  caused  by  the  isolated  action  of  each  of 
these  muscles  may  be  pictured  to  oneself  by  placing  the  book  so  that  one's 
own  line  of  vision  coincides  with  the  axis  of  any  given  muscle,  and  then 
imagining  tlie  eye  in  the  picture  to  rotate  right  or  left  about  the  observer's 
line  of  vision. 

Fig.  241  represents,  according  to  Ilering,  approximately  the  paths  which 


550 


VISION 


the  lino  of  vision  of  the  left  eye  would  describe  on  a  plane  standing  at  right 
angles  to  the  primary  axis  at  the  distance  dJ  from  the  center  of  rotation,  if 
the  eye  were  rotated  about  the  several  axes  as  given  in  Fig.  240.  The  position 
which  the  horizontal  meridian  of  the  eye  would  have  at  the  conclusion  of  the 
movement  is  shown  by  a  short,  heavy  line  at  the  end  of  each  path.  The  length 
of  each  path  corresponds  to  a  rotation  of  about  50°;  the  numbers  mark  the 
successive  positions  of  the  line  of  vision. 

From  this  figure  it  is  clear  that  even  if  the  relations  of  the  axes  were  in 
fact  as  simple  as  we  have  supposed  them  to  be.  it  would  be  possible  to  move 


Fig.  240. — The  extra-ocular  muscles  and  their  axes  of  rotation,  after  Fox.  The  left  eye  is  shown 
with  the  superior  rectus  removed,  r.i.f.,  inferior  rectus;  r.s.,  superior  rectus;  r.e.,  external 
rectus;  r.i.,  internal  rectus;  o.s.,  superior  oblique;  o.i.,  inferior  oblique.  The  line  A  A' 
represents  the  line  of  vision;  T  T',  tlie  transverse  axis  of  tiie  eyeball;  D  D',  the  axis  of  rota- 
tion of  the  superior  and  inferior  rectus  muscles :  this  axis  makes  an  angle  of  63°  with  the  line 
of  vision;  0  0',  the  axis  of  rotation  of  the  inferior  and  superior  oblique  muscles :  this  axis 
makes  an  angle  of  35°  with  the  line  of  vision.  The  axis  for  the  internal  and  external  rectus 
muscles  is  perpendicular  to  the  plane  of  the  paper  at  the  center  of  rotation,  C. 


the  line  of  vision,  etc.,  along  a  vertical  line  only  by  the  proper  cooperation 
of  at  least  two  muscles.  The  movement  directly  upward  involves  the  action 
of  the  superior  rectus  and  the  inferior  oblique;  the  movement  directly  down- 
ward the  action  of  the  inferior  rectus  and  the  superior  oblique.  The  former 
two  assist  each  other  in  the  rotation  upward,  but  the  one  tends  to  roll  the 
eye  outward  and  the  other  inward,  so  that  by  a  compensatory  action  the  rolling 
can  be  prevented  altogether.  Exactly  the  same  is  true  of  the  muscles  which 
rotate  the  eye  downward. 

Knowing  as  we  do  that  the  different  axes  of  the  eye  actually  have  a  less 
simple  arrangement  than  that  here  assumed,  it  is  evident,  as  Volkmann  has 
emphasized,  that  what  are  apparently  the  simplest  movements  of  the  eye 
involve  the  simultaneous  action  of  several  muscles. 


ACTION   OF  THE   EYE   MUSCLES 


551 


A.    LIMITS   OF   THE  EYE    MOVEMENTS 

Helmholtz,  Aubert,  Hering  and  others  have  determined  how  far  the  eye 
can  be  moved  in  the  different  directions  by  means  of  its  muscles,  and  have 
thus  mapped  out  the  limits  of  the  field  of  vision.  With  parallel  lines  of 
vision  the  monocular  fields  of  the  two  eyes,  projected  upon  a  distant  plane, 
have  the  positions  represented  in  Fig.  242.  The  point  m  represents  a  very 
distant  fixation  point.  The  two  monocular  fields  do  not  cover  each  other. 
The  parts  accessible  only  to  the  left  eye  are  ruled  and  are  designated  by  the 
letter  /.  those  accessible^  to  the  right  eye  only  are  horizontally  ruled  and  are 
designated  i)V  the  letter  r. 

However 'it  would  not  be  correct  to  suppose  that  the  unruled  part  of  the 
monocular  field  common  to  the  two  eyes  is  in  fact  the  hinomlar  field.     On 


s  the  result  of  rotation  by  the  separate  ej-e 


Fig    241.— The  paths  described  by  the  hue  of  vision  a 

muscle.*,  after  Hering. 

the  contrarv  the  two  lines  of  vision  cannot  be  directed  at  the  same  time  to 
every  point  in  the  outer  space  to  which  each  line  of  vision  can  be  directed 
alone  The  space  surrounded  by  the  line  a  a  in  Fig.  242  represents  the  binocu- 
lar field  for  distant  vision.  We  see  how  small  is  the  binocular  field  common 
to  the  two  lines  of  vision;  it  is  much  smaller  than  the  field  common  to  both 
visual  axes  also  for  near  vision. 


552 


VISION 


The  two  eyes  are  very  closely  associated  in  their  movements.  Under  normal 
circumstances  the  line  of  vision  of  the  one  cannot  be  directed  to  a  point 
higher  than  that  to  which  the  other  is  directed  at  the  same  time,  and  the  two 
cannot  be  made  to  diverge. 

Theoretically,  by  appropriately  combined  action  of  its  six  muscles,  each  eye 
can  be  turned   in  any  direction   and  rotated  on  any   axis;   but   the   actual 

movements  are  fcAv  in  comparison 
with  those  theoretically  possible.  In 
general  we  may  say  that  only  move- 
ments with  the  lines  of  vision  paral- 
lel or  symmetrically  converged — i.  e., 
directed  toward  a  point  in  the  mid 
line — are  possible.  Convergence  of 
the  lines  of  vision  toward  a  point  not 
in  the  mid  line  is  always  associated 
with  great  effort,  and  as  a  rule  is 
obviated  by  moving  the  head  and 
thus  avoiding,  as  we  are  always  in- 
clined to  do,  extreme  movements  of 
the  eyes. 

This  limitation  of  the  eye  move- 
ments is  of  very  great  importance  for 
visual  perceptions;  for  the  connection 
between  the  retinal  images  and  the  po- 
sition of  the  eyes  is  thereby  rendered 
more  constant  than  would  be  the  case  if  all  theoretically  possible  movements 
were  carried  out. 


Fig.  242. — The  field  of  vision  projected  on  a 
distant  plane  perpendicular  to  the  line  of 
vision,  after  Hering. 


§  2.    SIGNIFICANCE    OF   EYE   MOVEMENTS   FOR   THE    OUTWARD 
PROJECTION   OF   VISUAL    PERCEPTIONS 

It  is  evident  from  the  optical  principles  of  the  eye  that  the  images 
thrown  on  the  retina  by  refraction  of  light  are  always  reversed,  and  yet  we 
always  see  the  objects  to  which  the  images  correspond  right  side  up.  The 
explanation  of  this  phenomenon  has  been  much  discussed,  and  yet  is  all  very 
simple. 

The  newborn  child  sees,  but  understands  nothing  of  what  it  sees.  In- 
cluded in  the  knowledge  which  the  child  gains  by  experience  with  the  sense 
of  sight  is  the  knowledge  of  the  position  of  things.  But  this  knowledge  the 
child  does  not  obtain  by  the  sense  of  sight  alone;  the  bodily  movements  play 
a  determining  part  as  well.  When  the  child  looks  at  its  nurse  the  image  is 
upside  down  on  the  retina.  But  if  it  should  wish  to  touch  the  nurse's  head 
with  its  hand,  it  must  move  its  arm  in  the  right  direction.  In  this  way  a 
definite  connection  is  established  between  the  retinal  image  and  the  move- 
ments, and  the  child  learns  to  project  its  visual  impressions  outward  in  the 
proper  direction. 

The  reason  then  why  we  see  all  objects  right  side  up  is,  that  in  developing 
our  ability  to  recognize  external  objects  and  their  position  in  space,  we  have 


SIGNIFICANCE   OF   EYE   MOVEMENTS 


553 


always  made  use  of  movements  of  the  arm  and  especially  of  the  eyes  them- 
selves, which  have  taught  us  the  proper  direction. 

As  an  illustration  of  the  way  visual  impressions  are  projected  outward  we 
may  take  Scheiner's  (1619)  experiment,  which  at  the  same  time  is  an  interest- 
ing demonstration  of  accommodation.  Two  needles  are  placed  one  behind  the 
other  before  a  bright  background,  the  one  vertical  and  about  18  cm.  from  the 
eye,  and  the  other  horizontal  and  about  60  cm.  from  the  eye.  Then  a  card  con- 
taining two  small  holes,  whose  distance  from  each  other  is  less  than  the  diameter 
of  the  pupil,  is  held  before  the  eye,  and  the  other  eye  is  closed.  If  one  accom- 
modates now  for  one  needle,  while  the  card  is  being  held  so  that  the  line  joining 
the  holes  is  in  the  same  direction  as  the  other  needle,  this  second  needle  will 
appear  double. 

Suppose  the  eye  be  adjusted  for  the  distant  needle,  h  (Fig.  243,  A),  then 
the  image  of  the  near  needle  a  falls  at  a.  Since  each  of  the  two  holes  admits 
a  beam  of  light  from  the  near  needle,  and  these  two  beams  cannot  fall  in  the 
same  place  on  the  retina,  two  faint  images  are  formed  at  the  places  where  they 
cross  the  retina.  In  the  same  way  by  accommodating  for  the  near  needle  a  we 
get  a  double  image  of  h  (Fig.  243,  B),  because  the  rays  from  that  needle  strike 
the  retina  at  two  places.  If  in  the  latter  case  one  hole  in  the  card  is  covered,  the 
image  on  the  same  side  will  disappear;  for  the  image  which  is  formed  by  cross- 
ing (cf.  Fig.  230)  to  the  opposite  side  of  the  retina  has  been  projected  to  this 
side  of  the  field  of  vision — e.  g.,  the  upper  image  at  a  in  the  direction  of  fe'c. 
If,  however,  the  same  hole  c  be  closed  in  the  first  case  (Fig.  243,  A),  the  image 
on  the  opposite  side  disappears;  the  lower  image  at  h'  is  projected  not  in  the 
direction  c,  but  in  the  direction  d. 

Movements  of  the  eye  determine  the  projection  of  our  visual  impressions  in 
other  connections  also.     When  one  looks  through  a  wire  gauze  at  the  window 


Fig.  243. — Scheiner's  experiment. 


the  meshes  appear  largo  and  far  removed  from  the  eye,  but  if  the  eyes  be 
focused  on  a  pencil  point  held  close  to  one's  near  point  of  vision  in  front  of 
the  gauze,  the  meshes  appear  sm.all  and  near — i.  e.,  appear  in  the  plane  of  the 
fixed  point  or  of  the  point  where  the  lines  of  vision  meet.  Although  the  experi- 
ment gives  the  same  result  in  looking  with  one  eye,  the  observer  can  plainly 
feel  that  the  eyes  are  strongly  converged  in  fixing  the  near  object. 
33 


554  VISION 

If,  after  looking  for  a  moment  at  the  sun  until  the  e^^e  is  fatigued,  the 
eyes  be  turned  toward  a  uniformly  lighted  wall,  one  sees  there  an  after-image 
of  the  sun,  the  size  of  which  depends  upon  the  distance  of  the  wall — the  farther 

awav  the  wall  the  larger  the  after-image 
(H."  Merer). 

oooooo  ,  o^  •' 

We  shall   return   again  to   the  condi- 
FiG.  244. — After  Hering.  tions  for  the  perception  of  depth  and  the 

laws  by  which  we  judge  the  apparent  dis- 
tance of  an  ol)jeet.  From  the  facts  just  presented,  which  are  exactly  the 
same  with  and  without  accommodation,  it  follows  that  a  retinal  image  of 
a  given  size  is  projected  in  ditferent  sizes  according  to  the  position  of  the 
visual  lines,  the  object  appearing  smaller  when  they  are  converged,  larger 
when  they  are  parallel. 

The  size  of  the  retinal  image  therefore  is  not  always  the  determining 
factor  in  judging  the  size  of  objects.  The  apparent  size  of  a  well-kno^^oi 
object — e.  g.,  that  of  an  adult  man — does  not  vary  noticeably  when  it  is  seen 
at  ditferent  distances,  although  the  size  of  the  retinal  image  changes  consid- 
erably.    Such  peculiarities   are  the  result 

of    a    gradually    acquired    experience.      A  ^    ^ 

child  relying  on  the  size  of  its  retinal  im-  ^^ 

ages  misjudges  the  size  of   objects  much 
more  than  an  adult.  — 

■  In  forming  judgments  of  linear,  verti-  ::ir: 

cal   and   horizontal    distances,   equally    re-  Fig.  245.— After  Heimholtz. 

moved  from  us,  the  movements  of  our  eyes 

play  a  determining  part  (Wundt).  If  we  compare  a  space  divided  by  points 
or  lines  into  intervals  with  an  equal  space  not  so  divided,  the  former  appears 
greater  than  the  latter  (Hering,  Fig.  244).  Two  squares  of  the  same  size, 
one  ruled  horizontally,  the  other  vertically,  appear  to  be  different  in  both 
breadth  and  height  (Fig.  245).  In  both  these  examples  the  retinal  images 
of  the  two  objects  compared  are  exactly  equal  in  size,  and  the  accommodation 
is  the  same.  The  basis  of  the  phenomenon  appears  to  be  that  it  requires  less 
muscular  effort  to  cast  the  eyes  over  an  empty  space  than  over  one  interrupted 
at  certain  intervals.  It  is  as  if  the  eye  had  to  make  a 
fresh  effort  at  each  point  in  Fig.  244,  and  at  each  line 
in  Fig.  245. 

The  vertical  line  in  Fig.  24()  appears  longer  than 

the  horizontal  one  because  it  requires  greater  muscular 
effort  to  move  the  line  of  vision  up  and  down  than  to 
Fig.  246.  move  it  out  and  in.    For  in  the  movement  of  the  visual 

line  directly  upward  it  is  necessary  that  two  muscles 
cooperate  (cf.  page  550).  One  of  these,  the  superior  rectus,  tends  to  turn 
the  eye  upward  and  inward;  the  other,  the  inferior  oblique,  tends  to  turn  it 
upward  and  outward.  Hence  part  of  the  muscular  force  developed  in  each 
muscle  is  used  in  antagonizing  the  other.  But  in  rotation  of  the  eve  directly 
outward  and  inward  no  such  compensation  is  necessary ;  hence  not  so  much 
muscular  effort  is  required.     The  horizontal  line  therefore  seems  shorter. 


BINOCULAR   VISION 


555 


§  3.    BINOCULAR   VISION 

The  study  of  vision  with  two  eves  is  of  very  great  interest  for  physiological 
psychology,  and  has  been  treated  by  many  excellent  authorities.  Here,  how- 
ever, we  must  limit  ourselves  to  the  most  important  points  and  shall  only 
discuss  the  conditions  of  single  vision  and  the  perception  of  depth. 

A.    CORRESPONDENCE  OF  THE  TWO  RETINA 

It  is  a  matter  of  evervda}^  experience  that  a  distant  object  regarded  with 
both  eyes  in  their  ordinary  position  looks  single,  but  that  if  one  eye  be  pushed 
out  of  line  the  object  then  looks  double.  One  condition  of  single  vision  with 
two  eyes,  therefore,  must  be  that  the  images  fall  on  parts  of  the  two  retinae 
which  exactly  correspond  to  each  other.  Those  points  of  the  retinae  upon 
which  the  same  parts  of  the  two  images  fall  are  called  corresponding  points. 

On  purely  optical  grounds  it  is  evident  that  only  two  points  can  correspond, 
for  with  any  given  position  of  the  eye  a  luminous  point  can  be  pictured  at 


Fig.   247. — The  rivalry  of  the  retinae. 

but  one  definite  spot  in  each  eye.  The  centers  of  the  two  fovae  centrales 
represent  corresponding  points.  The  exact  position  of  others  can  be  deter- 
mined experimentally  by  means  of  an  instrument  kno^^^l  as  the  haploscope 
(Hering).  It  is  evident  on  reflection  that  the  nasal  side  of  one  retina  must 
correspond  to  the  temporal  side  of  the  other,  since  light  from,  say,  the  right 
side  of  the  field  of  vision  must  strike  the  left  side  of  both  retinae  and  vice 
versa. 

B.    SINGLE  VISION   WITH   TWO  EYES 

It  might  be  supposed  in  explanation  of  the  remarkable  fact  of  single  vision 
with  two  eyes,  that  the  optic  nerve  fibers  proceeding  from  corresponding  points 
of  the  two  retina  end  in  the  same  ganglion  cell  of  the  brain.  But  this  is  not 
true,  for  the  independence  of  each  eye  is  much  greater  than  it  would  be  on  this 
hypothesis.  There  is  a  form  of  squint — i.  e..  pathological  deviation  in  the 
positions  of  the  eyes — which  is  due  to  an  abnormal  shortening  of  the  eye 
muscles  (muscular  strabism).  The  line  of  vision  of  the  squinting  eye  devi- 
ates by  a  certain  angle  from  the  proper  position.  Xow  it  happens  that  the 
person  so  affected  sees  single  with  two  eyes  in  which  the  images  do  not  fall 


556 


VISION 


on  symmetrical  points.  If  so,  these  asymmetrical  points  would  nevertheless 
be  corresponding  points.  But  suppose  by  a  slight  operation,  the  squinting 
eye  be  given  its  proper  position;  at  once  double  vision  results,  which  though 
for  a  time  very  disturbing,  gradually  disappears,  either  ])ecause  the  person 
learns  to  disregard  one  image,  or  it  may  be.  by  a  new  arrangement  of  the 
corresponding  points  of  the  two  retinae   (Wundt). 

If  we  take  two  patterns  ruled  in  different  directions  (as  in  Fig.  247)  and 
look  through  cylindrical  tubes  at  one  with  the  left  eye  and  at  the  other  with 
the  right,  Ave  should  expect,  if  the  corresponding  points  of  the  two  eyes  Avere 
connected  Avith  the  same  ganglion  cells,  to  get  a  double  pattern  ruled  both 
ways.     But  instead,  Avhen  the  vertical  lines  of  one  pattern  are  seen  clearly, 

the  horizontal  lines  of  the  other  are  indistinct  and 
vice  versa.  If  the  ca'cs  be  moA'ed  in  the  vertical 
direction,  the  A'ertical  lines  stand  out  more  and 
more  prominenth' — if  in  the  horizontal  direction 
the  horizontal  lines. 

Because  the  two  fields  of  vision  appear  thus 
to  contend  for  the  supremacy,  this  phenomenon 
is  known  as  the  rivalry  of  the  retina. 

The  question  whether  the  correspondence  of  the 
retinae  is  inborn  or  acquired  has  been  ansAvered  in 
very  different  ways.  At  all  events  we  may  be  sure 
that  the  nerve  connections  for  the  movements  of 
the  two  eyes  and  for  keeping  them  in  their  natural 
positions  are  established  before  birth.  For  this 
reason  the  portrayal  of  an  object  on  certain  parts 
of  the  retina  is  especially  favored.  Since  uoaa-  the 
bilateral  connection  of  the  optic  fibers  with  the 
cerebrum  is.  for  the  most  part  at  least,  inborn  also, 
there  must  exist  from  the  earliest  moment  of  extra- 
uterine life  onward  very  favorable  conditions  for 
the  correspondence  of  the  retinae.  Hence  it  will 
be  relatively  easy  for  the  child  in  the  formation 
of  his  visual  sensations  to  relate  the  tAvo  retinal 
images,  together  with  the  tactile  impressions,  to  a 
single  object  and  thus  gradually  to  develop  a  cor- 
respondence of  the  tAvo  retinae. 

C.    PERCEPTION   OF   DEPTH 


Right  Eye 

Fig.  248. — Schema  illustrating 
the  formation  of  images  in 
the  two  ej'es,  of  an  oblique 
line  in  the  median  plane. 


The  principal  significance  of  vision  with  two 

eyes  is  that  it  enables  us  to  estimate  distance  in 

the  sagittal  direction  more  exactly  and  to  obtain 

an  idea  of  the  solidity  of  objects. 

It  is  true  that  one  can  estimate  distances  with  one  eye,  but  he  can  do  so 

much  more  accurately  Avith  two. 

The  factors  A\-hich  figure  in  the  perception  of  depth  ivith  one  eye  are  the 
folloAA'ing:  (1)  A^sual  angle;  (2)  accommodation;  (3)  convergence  of  the 
lines  of  vision. 


BINOCULAR   VISION 


557 


It  is  evident  that  the  visual  angle  can  figure  only  when  we  are  dealing 
with  objects  which  vary  but  slightly  in  size,  and  which  are  well  kno^^Ti  to  us. 
But  under  these  circumstances  and  especially  at  great  distances  where  accom- 
modation and  convergence  can  have  no  part  the 
visual  angle  is  of  very  great  importance. 

As  we  have  already  seen  (page  534),  accom- 
modation and  convergence  are  very  closely  con- 
nected, and  convergence  occurs  in  accommodat- 
ing for  near  vision  even  when  one  eye  is  covered. 
Since  accommodation  is  not  necessary  for  vision 
with  emmetropic  eyes  at  distances  in  the  sagittal 
direction  of  more  than  5  m.,  and  only  becomes 
of  great  importance  at  a  much  smaller  dis- 
tance, it  is  evident  that  these  two  factors  can  only  figure  for  relatively  slight 
distances. 


Left  Eye 


Right  Eye 


Fig.  249. — The  position  of  the  two 
images  (Fig.  248)  on  the  retinae. 


If  a  thread  be  placed  obliquely  in  the  mid  line  of  the  body,  so  that  its  near 
end  (Fig.  248,  a)  is  higher  than  its  farther  end  (&),  one  can  tell  even  with  an 
instantaneous  flash  of  light  from  an  electric  spark — when  the  eyes  have  not 
time  to  move — the  correct  position  of  the  thread,  and  it  never  appears  double 
(Aubert).  And  j-et,  as  Fig.  249  shows,  the  images  of  the  ends  of  the  thread  do 
not  fall  on  corresponding  points  of  the  retina,  and  from,  what  we  have  already 
learned  we  should  suppose  that  the  thread  would  produce  an  impression  of  two 
lines  lying  in  the  same  plane  and  crossing  each  other.    By  looking  very  sharply. 


Fig.  250. 


in  fact,  one  can  get  such  an  impression ;  this  means  that  we  have  here  an  ability 
which  is  not  inborn,  but  is  acquired  by  practice  and  experience. 

It  follows  from  the  experiment  that  the  excitation  of  two  dissimilar 
points  of  the  retina  does  not  always  produce  a  double  image,  but  under  some 
circumstances  gives  the  idea  of  a  single  objective  point.  This  point,  how- 
ever, is  not  in  the  i)lano  of  the  fixed  point,  but  lies  either  in  front  of  or 
behind  it. 

The  accuracy  with  which  we  can  perceive  dilTerences  of  depth  by  vision 
with  dissimilar  points  is  exceedingly  great.  According  to  Heine,  for  per.sons 
endowed  with  extraordinary  acuteness  of  vision  a  displacement  of  the  retinal 
picture  of  only  G  seconds  of  an  arc  (0.000.5  mm.)  is  perceptible.  Thus  at  a 
distance  of  5  m.  a  displacement  in  the  sagittal  direction  of  10  mm.  would 
be  perceptible,  and  at  a  distance  of  100  m.  a  displacement  of  20  m.     Indi- 


558 


VISION 


vidiials  with  normal  acuteness  of  vision  could  perceive  a  displacement  of  about 
twice  this  amount. 

The  above-mentioned  experiment  represents  stereoscopic  vision  in  its  sim- 
plest form.  "When  we  look  at  a  solid  object,  not  too  far  removed,  first  with 
the  right  eye  and  then  with  the  left,  the  picture  we  get  of  the  object  is  not 
exactly  the  same  for  the  two  eyes.  The  right  eye  sees  a  little  more  of  the 
right  side  of  the  object,  the  left  a  little  more  of  the  left  side.  In  Fig.  250 
are  represented  the  images  of  a  truncated  pyramid  as  seen  by  the  two  eyes 

separately.  A  glance  at  the  two  is  suf- 
ficient to  convince  one  that  these  two 
images  could  not  possibly  fall  on  cor- 
responding points  of  the  retinae.  But 
if  these  drawings  be  held  before  the 
eyes  so  that  the  one  may  be  seen  with 
the  right  eye  and  the  other  with  the  left, 
the  two  fuse  together  in  our  minds 
into  a  picture  of  an  actual  pyramid. 

Unless  one  is  accustomed  to  accom- 
modate the  eyes  without  converging  the 
lines  of  vision  this  experiment  is  diffi- 
cult. The  same  result  is  obtained  with- 
out accommodation  if  the  two  pictures 
be  refracted  separately  into  the  two  eyes 
by  means  of  lenses.  This  is  the  princi- 
ple of  the  common  stereoscope  of  which 
Brewster's  form  (Fig.  251)  may  be  taken 

as  an  example.     It  is  apparent  from  the  figure  that  two  pictures  situated  at 

I  and  r  will  be  refracted  so  as  to  be  superimposed  at  o. 

For  stereoscopic  vision  to  be  of  any  importance  the  object  must  not  be  too 
far  removed,  for  then  the  images  belonging  to  the  two  eyes  would  not  be 
noticeably  different.  The  ordinary  stereoscopic  views  of  landscapes  are  photo- 
graphed with  a  double  camera  so  that  the  plates  are  farther  apart  than  the 
distance  between  the  two  eyes.  Consequently  such  photographs  combined 
give  us  an  impression  of  solidity  such  as  natural  vision  does  not  afford. 

References. — Auhert,  "  Physiologische  Optik"  (Graefe-Saemisch's  "  Hand- 
buch  der  Augenheilkunde,"  ii,  2,  Leipzic,  1876). — Fick,  Kiihne  and  Hering, 
"  Gesichtssinn  "  (Hermann's  Handbuch  der  Physiologic,  iii,  1,  Leipzic,  1879). — 
Helmholtz,  "  Handbuch  der  physiologischen  Optik,"  second  edition,  Hamburg 
and  Leipzic,  1886-1896.  The  last  named  cites  a  very  complete  literature  of  the 
subject  of  physiological  optics. — Hering,  "  Zur  Lehre  vom  Lichtsinn,"  Wien, 
1878. — V.  Kries,  several  articles  on  the  "  Physiologic  der  Gesichtsempfindungen," 
Leipzic,  1897-1902. — r.  Kries,  Nagel  and  Schenck,  "Gesichtssinn"  (Handbuch 
der  Pbysiologie,  iii,  1,  Braunschweig,  1904). — Wundt,  "Text-book  of  Physio- 
logical Psychology,"  translated  by  E.  B.  Titchner,  New  York,  1905. 


Fig.  251. — Brewster's  stereoscope. 


CHAPTER    XXII 

THE    PHYSIOLOGY    OF    THE    NERVE    CELL    AND    OF    THE    SPINAL    CORD 

§  1.    GENERAL   CONSIDERATIONS   CONCERNING   THE   FINER 
STRUCTURE    OF   THE    NERVOUS   SYSTEM 

It  has  for  a  long  time  been  custoniarv  to  divide  nerve  tissue  into  two 
elements :  nerve  cells  and  nerve  fibers.  The  nerve  cells  were  first  seen  by 
Ehrenberg  (1833)  in  the  spinal  ganglia.  Romak  (1835)  first  pointed  out 
that  the  processes  of  nerve  cells  are  continued  in  the  sympathetic  nerves  of 
the  verteljrates  as  an  integral  part  of  the  nerve  fibers.  This  was  shown  to  be 
true  also  for  the  invertebrates  by  Helmholtz  and  Hanover  (1842).  Deiters 
(18G3)  demonstrated  that  all  central  nerve  cells  have  two  kinds  of  processes: 
first,  axis-cylinder  processes,  which  connect  with  the  medullated  nerve  fibers 
and  become  directly  continuous  with  this  axis  cylinder;  and  secondly,  proto- 
plasmic processes,  which  break  up  into  very  fine  branches  whose  ultimate  fate 
Deiters  was  unable  to  ascertain. 

By  the  introduction  (1873)  of  Golgi's  method  of  impregnating  the  nerve 
elements  with  silver,  a  fresh  impetus  was  given  to  research  in  the  field  of 
neuro-histology.  With  the  application  of  this  method,  which  has  given  us  such 
a  rich  and  comprehensive  view  of  the  structure  of  the  nervous  system,  are 
associated  preeminently  such  names — apart  from  that  of  Golgi  himself — as 
those  of  Cajal,  Kolliker,  Retzius  and  von  Lenhossek. 

According  to  the  view  represented  by  these  investigators  the  nervous  sys- 
tem is  to  be  regarded  as  made  up  of  genetically  separate  and  distinct  nervous 
units  to  which  the  general  term  neurons  is  now  applied.  The  most  essential 
and  important  part  of  the  neuron  is  the  nerve  cell.  Several  processes  are 
given  off  from  this,  one  or  two  of  which  (from  some  cells  more)  are  con- 
tinued as  the  axis  cylinders  of  nerve  fibers  and  consequently  are  termed  axis- 
cylinder  processes  or  axons.  As  for  the  remaining  processes,  the  so-called 
dendrites  or  protoplasmic  processes  of  Deiters.  they  divide  into  numerous 
branches  which  become  exceedingly  attenuated,  and  in  this  way  greatly  increase 
the  superficies  of  the  nerve  cell. 

The  nerve  process  continues  as  an  integral  part  of  tlie  nerve  fiber  to  its 
final  distribution,  where  it  generally  breaks  up  into  a  small  terminal  arboriza- 
tion. At  different  points  along  the  course  of  the  nerve  fiber  a  variaJjle  number 
of  side  twigs  or  collaterals  are  usually  given  off,  which,  in  turn,  after  a  shorter 
or  longer  course,  like  the  nerve  fibers  themselves,  end  in  delicate  ramifications. 

According  to  the  original  conception  of  the  neuron  theonj  the  individual 
nerve  units  do  not  form  a  continuous  network,  but  are  anatomically  separate 

559 


560       THYSIOLOGY   OF  THE   NERVE   CELL   AND    THE   SPINAL  CORD 


and  distinct,  althougli  both  in  the  central  and  in  the  sympathetic  nervous 
system  the  end  tree  of  one  neuron  may  twine  about  the  cell  body  of  the 
second  so  that  the  latter  is  brought  into  contact  with  the  former  neuron. 
Any  anastomosis  or  actual  structural  continuit}-  of  dendrite  with  end  arbor- 
ization is,  therefore,  emphatically  denied.  Every- 
thing takes  place  b}-  mere  contact. 

In  view  of  the  work  of  Apathy  and  Bethe,  this 
position,  however,  is  no  longer  tenable,  for  it  appears 
to  have  been  definitely  sho^\Ti  that  the  different  nerve 
units  do  unite  by  anastomosis. 

According  to  Apathy's  researches — chiefly  on  inver- 
tebrates— the  nerve  fibers  consist  of  fine  neurofibrils 
which  constitute  independent  morphological  elements. 
Within  the  nerve  fiber  they  preserve  their  individuality 
throughout  and  have  no  connection  whatever  with  one 
another.  In  the  peripheral  end  organs  the  individual 
fibrils  split  up  and  form  an  anastomosing  network. 
Likewise  fn  the  ganglion  cells  the  fibrils  which  enter 
become  branched  and  form  a  network.  But  before 
entering  the  cells  the  delicate  end  twigs  of  the  affer- 
ent fibers  form  a  reticulum  within  the  dense  tangle 
known  as  the  neuropile,  which  occupies  the  center  of 
the  ganglion.  From  this  neuropile  very  delicate  fibrils 
emerge,  penetrate  the  ganglion  cells  and  there  form 
first  a  peripheral  network  (Fig.  252),  from  which  are 
given  off  in  turn  radial  fibrils  that  weave  about  the 
cell  nucleus  a  second  network  of  thicker  fibrils  and  from  this  finally  the  stout 
efferent  fibril  emerges.  The  neurofibrils  therefore  represent  the  conducting  por- 
tion of  the  nervous  system  and  through  them  all  parts  of  the  nervous  system 
are  brought  into  direct  communication  with  one  another  (according  to  Bethe). 
In  certain  invertebrates  at  least  (green  crab,  crawfish),  but  a  small  portion 
of  the  neurofibrils  pass  through  the  nerve  cells.  Here,  then,  the  fibrillar  tran- 
sition from  fiber  to  fiber,  and  their  intermixture  must  take  place,  for  the  most 
part,  in  the  neuropile  and  its  reticulum. 


Fig.  252. — Ganglion  cell  of 
a  leech  {Hirudo),  -with  fine 
peripheral  network  and 
coarse  inner  network. 
From  the  latter  a  stout 
efferent  fibril  is  given  off 
(Bethe). 


Bethe  in  particular  showed  that  the  neurofibrils  are  present  as  conducting 
elements  in  the  nervous  system  of  the  vertebrates  also.  Without  any  inter- 
connection the  fibrils  run  a  separate  and  unbroken  course  to  the  terminal 
arborizations  of  both  the  peripheral  nerve  fibers  and  their  analogues  the 
medullated  fibers  of  the  central  nervous  system.  They  occur  in  the  nerve 
cells  also,  and  almost  every  cell  process  is  connected  with  one  adjacent  to 
it  by  a  bundle  of  fibrils  of  variable  thickness.  In  like  manner  each  dendritic 
process  sends  some  fibrils  into  the  axis-cylinder  process  of  the  cell. 

Covering  the  siirface  of  the  nerve  cells  and  of  their  dendritic  proce^:?  there 
is  found  a  network  with  polygonal  meshes  (Fig.  253),  concerning  whose  real 
nature  different  views  have  been  advanced.  It  was  first  described  by  Golgi. 
According  to  Bethe,  who,  however,  expresses  himself  very  cautiously  in 
this  regard,  this  network  is  of  a  nervous  character,  connecting  on  the  one 
hand  with  the  neurofibrils  of  the  nerve  cells,  and  on  the  other  with  nerve 


THE   FINER  STRUCTURE   OF  THE   NERVOUS  SYSTEM 


561 


fibers  from  without.  Accepting  this  view,  this  pericellular  network  would 
be  analogous  to  the  extracellular  fibrillary  reticulum  in  the  neuropile  of 
the  invertebrates.  In  view  of  the  fact  that  it  is  not  confined  alone  to  the 
surface  of  the  cell,  but  spreads  out  in  three  dimensions  through  the  entire 
gray  matter  of  certain  parts  of  the  nervous  system,  this  network  may  be  looked 
upon  as  constituting  a  new  kind  of  nerve  matter,  probably  corresponding  to 
the  extracellular  '*  gray  "'  whose  existence  Avas  postulated  by  Xissl.  Xissl's 
inference  was  based  on  the  ground  that  even  the  great  num])er  of  nerve  cells, 
dendritic  and  axis-cylinder  processes,  neuroglia  fibers  and  cells,  and  blood 
vessels  taken  collectively,  especially  in  certain  parts  of  the  cerebral  cortex 
but  also  in  other  places,  fall  far  short  of  the  bulk  necessary  to  fill  the  entire 
space. 

What  the  genetic  relationship  is  that  exists  between  the  reticulum  of  the 
invertebrate  g-anglion  or  the  Golgi  network  of  the  vertebrate  nerve  tissue — 
if  indeed  it  be  a  nervous  structure — and  the  nerve  cells  is  still  quite  unknown. 
Even  if  the  pericellular  network  takes  its  origin  from  the  nerve  cells  and  is 
therefore  to  be  regarded  as  a  de- 
rivative of  such  a  structure,  the 
classical  definition  of  the  neuron 
theory  makes  no  provision  or  quali- 
fication for  such  an  additional  ele- 
ment. Moreover,  Bethe  and  others 
have  made  observations  which  pur- 
port to  show  that  the  nerve  fibers 
are  not  produced  as  outgrowths  of 
the  nerve  cells  but  are  laid  down 
separately  by  other  cells.  If  this 
be  true,  the  neuron  theory  cannot 
be  maintained  in  any  form.  But 
since  much  remains  yet  to  be 
cleared  up  in  regard  to  this  ques- 
tion, and  since  different  facts  of  ex- 
perimental physiology  which  Bethe 
has  advanced  in  support  of  his 
view  (cf.  page  575)  really  admit 
of  another  theoretical  construction, 
the  objection  last  urged  against  the 
neuron  theory  can  scarcely  yet  be 
accepted  as  conclusive. 

At  present  we  may  view  the 
structure  of  the  nervous  system 
somewhat  as  follows:  The  nerve 
cells  give  off  several  processes,  one 

or  more  of  which  become  the  axis  cylinders  of  nerve  fibers.  These  consist  of 
fine  fibrils  which  pursue  a  separate  and  unconnected  course  in  the  nerve  fiber, 
oftentimes  penetrate  the  nerve  cell  and  there — in  the  invertebrates,  but  not  in 
the  vertebrates — form  a  real  network.  These  fibrils  anastomose  freely  outside 
the  nerve  cells,  and  al-^o  within  the  cells  in  the  invertebrates,  and  thus  consti- 
tute a  possible  path  for  the  transmission  of  stimuli  from  one  cell  to  the  other. 


Fig.    2.53. — Golpi    network    about    a    cell    of    the 
nucleus  dentatu.s  of  the  dog,  after  Bethe. 


562      PHYSIOLOGY  OF  THE   NERVE   CELL   AND  THE  SPINAL  CORD 

It  must  be  observed,  however,  in  this  connection,  that  our  knowledge  con- 
cerning the  finest  structure  of  the  nervous  system,  especially  in  the  vertebrates, 
is  still  too  meager  to  admit  of  any  one  satisfactory  or  conclusive  view, 

§  2.    THE    STRUCTURE    OF   THE    SPINAL   CORD  i 

A  cross  section  of  the  spinal  cord  (Fig.  254)  shows  the  central  gray  matter 
with  its  contained  nei-ve  cells,  and  surrounding  it  the  white  matter  made  up 
of  nerve  fibers.     The  anterior  longitudinal  or  median  fissure   (a)   and  the  pos- 


r    h 


Fig.  254. — Semidiagrammatic  .section  of  the  spinal  cord,  after  Erb.  a,  anterior  fis.sure;  h,  pos- 
terior septum;  c,  anterior  column;  d,  lateral  column;  c,  posterior  column;  /,  funiculus  gracilis; 
g,  funiculus  cuneatus;  h,  anterior  root;  i,  posterior  root;  A:,  central  canal;  I,  sulcus  inter- 
medius  posterior;  m,  cells  of  the  anterior  horn;  n,  cells  of  the  posterior  horn;  o,  lateral  horn; 
p,  processus  reticularis ;  q,  anterior  commissure ;  r,  posterior  commissure ;  s,  Clark's  column. 

terior  median  septum  (fc)  divide  the  cord  into  two  symmetrical  halves,  con- 
nected by  two  commissures  (q,  r),  the  anterior  white  and  the  posterior  gray 
commissures. 

The  gray  matter,  pierced  in  the  middle  by  the  central  canal  (A;),  has  in 
general  the  appearance  of  the  capital  letter  H,  but  varies  somewhat  in  form 
at  different  levels.  The  roots  of  the  nerves  enter  each  half  of  the  cord  in  sepa- 
rate bundles,  the  posterior  and  the  anterior  spinal  nerve  roots.  These  divide 
the  white  matter  into  three  main  portions:  (1)  the  anterior  columri  lying  between 
the  anterior  longitudinal  fissure  and  the  anterior  nerve  root;  (2)  the  lateral 
column  lying  between  the  anterior  and  posterior  nerve  roots;  (3)  the  posterior 
column  lying  between  the  posterior  nerve  root  and  the  posterior  median  septum. 

*  After  Edinger's  "  Vorlesungen  iiljer  den  Bau  der  Nervosen  Zentralorgane,"  seventh 
edition,  Leipzic,  F.  W.  C.  Vogel,  1904.  Since  the  more  recent  views,  as  set  forth  in 
the  paragraphs  above,  on  the  structure  of  the  nervous  system  are  still  immature,  aiid 
fall  short  of  a  comprehensive  exposition  of  the  structure  of  the  spinal  cord,  in  the  account 
here  and  in  that  which  follows  we  shall  make  use  of  the  anatomical  facts  thus  far  estab- 
lished without  further  reference  to  the  relation  and  connection  which  may  exist  between 
the  individual  cells  and  fibers. 


THE  STRUCTURE  OF  THE  SPINAL  CORD 


563 


The  gray  matter  on  each  side  of  the  cord  is  divided  into  an  anterior  and  a 
posterior  horn.  In  the  lower  cervical  and  in  the  upper  thoracic  regions  of  the 
cord,  as  well  as  in  the  lumbar  region,  the  lateral  portion  of  the  anterior  horn 
becomes  partly  separated  off  as  a  lateral  horn   (o). 

Among  the  nerve  cells  of  the  gray  matter  we  distinguish:  (1)  The  cells 
arranged  in  groups  in  the  anterior  horn;  (2)  the  cells  of  the  so-called  column 
of  Clarke  (s)  situated  at  the  median  side  between  the  anterior  and  posterior 
horns,  and  extending  from  the  end  of  the  cervical  enlargement  to  the  beginning 
of  the  lumbar  cord;  (3)  the  cells  of  the  substantia  gelatinosa  Rolandi  capping 
the  posterior  horn ;  (4)  the  rest  of  the  cells  in  the  posterior  horn. 

The  fibers  of  the  anterior  nerve  roots  are  the  axis-cylinder  processes  of  the 
cells  in  the  anterior  horn  of  the  same  side,  or,  less  frequently,  of  the  opposite 
side,  the  latter  fibers  crossing  via  the  anterior  commissure  before  they  gain  the 
anterior  root.  The  cells  of  the  posterior  horn  on  the  contrary  do  not  connect 
directly  with  fibers  of  the  posterior  root,  since  the  latter  have  their  origin  in 
the  cells  of  the  spinal  ganglia. 

These  cells  of  the  spinal  ganglia,  for  the  most  part,  are  unipolar — i.  e.,  they 
have  but  one  process  which,  however,  after  a  short  course,  splits  into  two 
branches.  One  of  the  two  proceeds  toward  the 
periphery  and  joins  the  anterior  nerve  root  in 
a  mixed  nerve  trunk;  the  other  enters  the  cord 
by  the  posterior  nerve  root.  Practically  all  of 
the  fibers  which  enter  the  cord  divide  into  an 
ascending  and  a  descending  branch,  both  of 
which  give  off  collaterals,  and  sooner  or  later 
end  like  the  collaterals  about  the  cells  of  the 
gray  matter  of  the  cord.  The  peripheral  nerve 
fibers,  therefore,  have  their  origin  either  in  the 
cells  of  the  anterior  horn  or  in  the  cells  of  the 
spinal  ganglia. 

The    nerve    fibers    from    the    anterior    horn 
cells  are  all  efferent  in  function,  and  the  nerve  ^ 
fibers  arising  from  the  cells  in  the  spinal  gan- 
glia are  mainly  afferent  fibers. 

With  regard  to  the  further  connection  of 
the  two  kinds  of  fibers  we  distinguish:  (1)  a 
secondary  efferent  path;  (2)  a  secondary  affer- 
ent path;  and  (3)  the  paths  by  which  afferent 
pass  over  into  efferent  imi)ulses. 

Those  tracts  which  connect  the  nerve  cells 
of  the  anterior  horn  with  the  higher  centers 
we  designate  as  secondary  efferent  paths.  They 
are  the  paths  by  which  impulses  liberated  in  the 
cells  of  the  higher  centers  are  conveyed  to  the 
motor  cells  of  the  anterior  horn. 

The  fibers  entering  the  cord  from  the  spinal 
ganglia   are  brought    into   relation  with   the  cells   of  the  posterior  horn   whose 
axis-cylinder  processes  constitute  the  secondary  afferent  paths.     It  is  by  these 
paths  that   impulses  are  transmitted  to  the  higher  centers. 

The  transition  from  afferent  to  efferent  i)aths  may  occur  in  several  ways. 
The  simplest  instance  is  when  an  afferent  nerve  fiber  or  one  of  its  collaterals 
connects  directly  with  the  motor  cell  of  an  efferent  nerve  fiber  or  with  some  of 
its  processes  by  means  of  fibrils. 


Fig.  2.55. — Schema,  after  Kolliker 
and  Leiihoss6k.  A,  motor  cells 
with  root  fibers;  B,  spinal  ganglion 
cell  with  its  processes;  C,  a  sen- 
sory collateral ;  D,  column  cell  with 
T-shaped  branching  processes;  E, 
collaterals  of  the  same. 


564      PHYSIOLOGY   OF  THE   NERVE  CELL   AND  THE   SPINAL  CORD 

Again  a  nerve  cell  with  its  processes,  etc.,  may  be  intercalated  as  a  new  ele- 
ment between  two  primary  paths,  as  shown  in  the  schema  (Fig.  255)  based  on 
the  neuron  theorj'.  The  terminal  libers  of  an  afferent  nerve  fiber  (B)  or  its 
collaterals  (C)  unite  with  a  nerve  cell  (column  cell)  somewhere  in  the  central 
nervous  system  (D).  This  cell  sends  foi-th  an  axis-cylinder  process  which  has 
several  collaterals  (E)  and  these  in  turn  serve  to  bring  it  into  contact  with 
an  anterior  horn  cell  (A).  By  this  arrangement  it  is  evident  that  an  impulse 
coming  via  a  single  afferent  fiber  is  transmitted  to  a  large  number  of  efferent 
fibers.  If  now  we  imagine  one  or  more  such  cells  interposed  between  the  cell 
(D)  and  the  motor  cell  (A)  the  connection  is  made  still  more  extensive. 

Thus  by  means  of  collaterals  and  intercalated  cells,  and  possibly  through 
the  agency  of  the  pericellular  network,  everj-^  provision  is  made  for  an  afferent 
impulse  to  be  carried  over  at  almost  every  point  of  its  course,  either  directly  or 
indirectly,  to  the  motor  cells  of  efferent  fibers,  and  here  we  have  the  anatomical 
basis  for  facts,  long  since  established  by  physiological  observations,  that  a  given 
afferent  impulse  may  give  rise  to  a  great  variety  of  efferent  effects.  Just  what 
arrangement  obtains  by  which  diffei'ent  paths  have  been  accommodated  to  cer- 
tain special  functions  is  a  question  which  for  the  present  can  scarcely  be  an- 
swered. Only  in  a  general  way  may  we  state  that  between  certain  parts  of  the 
nervous  system  a  connection — be  it  purely  anatomical  or  only  functional — is 
more  easily  established  than  between  other  parts.  This,  however,  is  but  hedging 
the  real  question. 

§  3.    KINDS   OF   NERVES 

A.    CLASSIFICATION   ACCORDING  TO   FUNCTIONS 

Physiologically  nerves  may  be  divided  into  two  large  classes:  afferent  and 
efferent.  The  former  bring  messages  from  all  parts  of  the  body  to  the  central 
nervous  system,  the  latter  convey  impulses  from  the  central  system  to  periph- 
eral organs  in  all  parts  of  the  body. 

The  number  of  fibers  in  the  posterior  root  is  somewhat  larger  than  the  num- 
ber in  the  anterior.  In  two  frogs,  weighing  23  and  6.3  g.  respectively,  Birge 
found  in  the  posterior  roots  3,781  and  5,835  fibers,  and  in  the  anterior  roots 
3,528  and  4,283  respectively.  According  to  counts  made  by  Dale  the  posterior 
roots  of  the  coccygeal  nerves  of  the  cat  always  contain  more  fibers  than  the 
anterior.     Stilling  previously  had  obtained  the  same  result  in  man. 

1.  To  the  efferent  fibers  belong: 

(a)  The  Motor  Nerves — i.  e.,  all  nerves  whose  stimulation  produces  contrac- 
tion of  muscles,  whether  skeletal  muscles,  vascular  muscles,  muscles  of  the  intes- 
tine, glandular  ducts,  bronchioles,  etc. 

(h)  Secretory  Nerves,  page  257  (salivary  glands),  page  263  (gastric 
mucosa),  page  269  (pancreas),  page  396  (sweat  glands). 

(c)  Inhibitory  Nerves — i.  e.,  nerves  which  check  or  stop  any  dissimilatory 
process — e.g.,  the  cardio  inhibitory  in  the  vagus  (page  188),  the  vasodilator 
nerves  (page  234).  the  inhibitory  nerves  of  the  intestine   (page  288). 

Little  is  known  with  regard  to  the  inner  processes  which  result  from  stimu- 
lation of  inhibitory  nerves  in  the  different  organs.  We  have  some  observations 
tending  to  show  that  when  the  vagus  is  stimulated  changes  are  set  up  in  the 
heart  which  antagonize  the  processes  taking  place  during  contraction,  and  from 
these  observations  the  conclusion  has  been  drawn  that  the  vagus  exercises  a 
nutritive  control  over  the  heart.  Other  observations  which  have  been  reported 
at  page  190  show,  however,  that  under  favorable  circumstances  an  animal  with 


KINDS   OF   NERVES  565 

both  vagi   cut   can   live  for   a   long   time   without   exhibiting  any   pathological 
alterations  of  the  heart's  structure.     We  shall  return  in  the  next  section  to  this 
question  of  the  trophic  influence  of  the  nervous  system  on  other  organs. 
2.  The  afferent  nerves  include : 

(a)  All  nerves  which  elicit  conscious  sensations,  namely,  nerves  of  the  higher 
senses,  tactile,  temperature  (and  pain)  nerves  of  the  skin,  and  nerves  of  the 
internal  organs  in  so  far  as  they  mediate  conscious  sensations. 

(b)  Nerves  which  do  not  elicit  conscious  sensations  but  which  acquaint  the 
central  nervous  system  with  the  condition  of  the  different  organs — e.  g.,  the 
depressor  (page  193)  and  the  pulmonary  vagus  (page  327). 

Xo  sharp  line  of  demarcation  can  be  drawn  between  a  and  h,  for  it  is  very 
probable  that  many  nerves  of  the  second  group  mediate  sensations  of  pain  when 
they  are  stimulated  excessively. 


B.    SPECIAL   PROPERTIES   OF   DIFFERENT   KINDS   OF   NERVE   FIBERS 

Histological  studies  have  shown  that  nerve  fibers  differ  in  structure,  and  it 
is  to  be  assumed  a  priori  that  this  difference  is  the  expression  of  a  certain 
physiological  difference.  Our  information  along  this  line,  however,  is  still  very 
inadequate,  and  scarcely  permits  us  to  reach  any  definite  conclusions.  The  fol- 
lowing brief  survey,  mainly  from  the  results  reported  by  Engelmann,  will  serve 
to  indicate  the  present  tendency  of  investigations  along  this  line. 

(1)  When  a  mixed  nerve  is  compressed  the  conductivity  of  its  sensory  fibers 
is  lost  sooner  than  that  of  its  motor  fibers. 

(2)  The  constant  current  acts  on  most  efferent  nerves  only  at  the  instant 
of  closing  and  opening,  but  on  most  afferent  nerves  throughout  the  entire  time 
the  current  is  closed  (cf.  page  421).  The  same  difference  obtains  between  the 
two  groups  of  functionally  different  nerves  with  respect  to  the  tetanizing  action 
of  supranormal  temperatures. 

(3)  The  nerves  of  the  extensor  and  flexor  muscles  in  the  same  animal  are 
unequally'  excited  by  induction  currents.  The  same  is  true  of  those  controlling 
the  adductor  and  abductor  muscles  of  the  crab's  claw;  of  the  nerves  of  the 
extremities  on  the  one  hand  and  the  vagi,  sympathetic,  sweat  nerves  on  the 
other;  the  accelerator  and  inhibitory  fibers  of  the  heart. 

(4)  Many  chemical  agents  have  a  powerful  stimulating  effect  on  motor 
nerves,  but  either  no  action  at  all  or  only  a  very  feeble  one  on  sensory  nerves. 
The  cardio-inhibitory  fibers  are  thrown  out  of  action  by  the  local  effect  of  a 
one-quarter-per-cent  KXO3  solution  applied  to  the  cardiac  branch  of  the  vagus, 
but  the  accelerator  fibers  remain  functional,  etc. 

Several  of  these  differences  may  well  be  due  to  peculiarities  in  the  end  organs, 
but  others  probably  are  dependent  upon  actual  differences  in  the  physiological 
constitution  of  the  nerve  fibers.  This  question  cannot  be  decided  easily  and,  as 
Engelmann  points  out,  one  will  do  well  in  any  case  to  be  cautious  and  not  take 
it  for  granted  that  results  obtained  on  one  species  of  nerve  will  necessarily  hold 
for  all  others. 

C.    MAGENDIE'S   DOCTRINE 

The  famous  anatomist  Willis  surmised  that  the  anterior  roots  of  the  spinal 
nerves  make  connection  with  the  cerebrum,  the  organ  of  sensibility  and  motil- 
ity, and  the  posterior  roots  with  the  basal  parts  of  the  l)rain  presiding  over 
the  vegetative  functions — circulation,  nutrition,  secretion,  etc.  In  1811  Bell 
attempted  to  establish  the  truth  of  this  view  experimentally,  but  when  Magen- 


566       PHYSIOLOGY    OF  THE   NERVE  CELL  AXD  THE   SPINAL   CORD 

die  in  1823  published  the  results  of  his  investigations,  to  be  discussed  imme- 
diateh',  Bell  came  over  to  that  author's  position.  The  law  which  ilagendie 
established  is  often  known  even  yet  as  BcU's  doctrine. 

Magendic's  doctrine  is  that  the  anterior  roots  of  the  spinal  nerve  contain 
only  efferent  fibers,  the  posterior  roots  only  afferent  tibers. 

Originally  the  demonstrations  by  Magendie,  Bell,  Johannes  Miiller  and  their 
followers  only  applied  to  the  motor  nerves  in  the  strict  sense.  But  after  other 
efferent  nerves  had  been  discovered,  proof  was  soon  forthcoming  that  they  also 
make  their  exit  by  the  anterior  roots.  Proof  for  the  vasoconstrictors  was  fur- 
nished by  Pfliiger  and  Claude  Bernard,  for  the  vasodilators  by  Dastre  and  Morat 
also  Gaskell,  and  for  the  sweat  nerves  hy  Luchsinger. 

Several  very  noteworthy  exceptions  to  this  general  law  have  now  to  be  ad- 
mitted. Thus  the  posterior  roots  do  not  contain  afferent  fibers  exclusively,  but 
also  a  few  efferent  fibers.  Strieker  and  his  pupils  find  vasodilator  nerves  for 
the  posterior  extremity  of  the  dog  in  the  posterior  roots  of  the  fourth  and  fifth 
lumbar  nerves,  and  for  the  anterior  extremity  in  the  posterior  roots  of  the 
brachial  plexus  (cf.  page  235).  According  to  Steinach  the  posterior  roots  of 
the  second  to  the  sixth  spinal  nerves  of  the  frog  contain  motor  fibers  for  the 
oesophagus,  stomach,  and  small  intestine — those  of  the  sixth  and  seventh,  motor 
fibers  for  the  rectum  and  those  of  the  seventh  to  the  ninth,  the  same  for  the 
bladder;  but  Dale  was  unable  to  confirm  these  findings.  In  exceptional  cases 
Horton-Smith  and  Dale  found  fibers  for  individual  skeletal  muscles  of  the  frog 
in  the  posterior  roots. 

Bayliss  has  used  the  method  of  degeneration  (cf.  page  567)  for  tracing  out 
the  vasodilators  contained  in  the  posterior  roots  and  has  found  that  they  origi- 
nate in  the  spinal  ganglia.  Hence  they  also  constitute  a  definite  exception  to 
the  rule. 

Still  another  exception,  which,  however,  is  only  apparent,  has  been  observed. 
Magendie  himself  noticed  that  sometimes  the  anterior  roots  were  sensitive. 
Later  he  found  that  this  sensibility  could  only  be  demonstrated  so  long  as  the 
posterior  roots  were  intact.  It  is  now  known  that  this  sensibilitj'  is  to  be  ac- 
counted for  by  the  passing  of  fibers  from  the  posterior  root  along  the  anterior 
root  to  sensorj'  endings  in  the  membranes  of  the  cord.  For  this  reason  the  sen- 
sibility of  the  anterior  root  is  called  recurrent  sensihility. 

It  was  long  supposed  that  the  sensory  fibers  of  a  mixed  nerve  originate  only 
in  the  same  pair  of  roots  as  the  motor  fibers.  Clinical  observation  has  shown, 
however,  that  the  transition  is  much  more  widespread,  since  afferent  nerves  in 
the  peripherj'  of  the  body  often  pass  from  one  nerve  trunk  to  another,  so  that 
within  certain  limits  sensory  transmission  may  take  place  in  both  directions 
within  the  same  nerve  trunk. 

§  4.  FUNCTIONS  OF  THE  NERVE  CELL 

From  the  time  nerve  cells  were  first  discovered  it  has  been  assumed  almost 
universally  that  they  constitute  the  seat  of  the  central  functions  of  the  nervous 
system.  The  most  weighty  support  for  this  view  lay  in  the  constant  difference 
of  behavior  between  the  peripheral  and  central  systems,  the  difference  being 
referred  almost  as  a  matter  of  course  to  the  one  element  which  was  found 
to  be  specific  for  the  central  system.  In  view  of  more  recent  discoveries  on 
the  finer  structure  of  the  central  system,  it  is  not  impossible  that  the  extra- 
cellular net  and  the  connections  between  neurofibrils  play  a  still  more  im- 


FUNCTIONS   OF  THE   NERVE  CELL  567 

portant  role  than  the  nerve  cells  in  the  discharge  of  central  functions.  Al- 
though our  information  is  not  yet  definite  enough  to  warrant  taking  such  a 
position,  it  would  be  well  if  we  had  some  designation  for  those  constituents 
of  the  nervous  system  discharging  these  central  functions,  which  would  not 
prejudice  either  view.  For  simplicity's  sake,  we  shall  retain  the  old  name, 
expressly  remarking  that  the  ol)servations  brought  together  in  this  book  and 
the  conclusions  deducible  therefrom  are  on  the  whole  but  little  affected  by  the 
newer  ideas,  as  to  the  structure  of  the  nervous  system.  Those  ideas  will  only 
become  significant  when  it  has  been  definitely  proved  that  the  functions 
hitherto  ascribed  to  the  nerve  cell  are  exercised  in  greater  or  less  part  by 
extracellular  structures. 


A.    THE  NUTRITIVE   FUNCTIONS   OF   NERVE   CELLS 

In  1852  Waller.  Sr.,  found  when  he  cut  the  posterior  roots  of  the  second 
cervical  nerve  between  the  spinal  ganglia  and  the  spinal  cord  and  killed  the 
animal  (cat  or  dog)  some  time  later,  that  the  peripheral  end  of  the  root  still 
connected  with  the  ganglion  remained  normal,  while  the  central  end  and  its 
continuation  into  the  spinal  cord  degenerated.  When  he  cut  the  nerve  periph- 
erally to  the  ganglion,  the  peripheral  end  degenerated,  while  the  central  end 
and  its  continuation  into  the  spinal  cord  remained  normal.  Finally,  it  was 
shown  that  after  cutting  the  anterior  root  the  peripheral  end  of  the  efferent 
fibers  degenerated  while  the  central  end  remained  normal. 

Before  Waller,  Tiirck  had  found  that  a  partially  transverse  section  of  the 
spinal  cord  produced  degeneration  above  and  below  the  section,  and  that  this 
degeneration  did  not  follow  the  same  columns  continuously. 

Thus  it  was  demonstrated  that  a  nerve  fiber  maintains  its  normal  condi- 
tion only  so  long  as  its  connection  with  the  nerve  cell  is  preserved.  These 
facts  have  been  robbed  of  much  that  was  originally  strange  about  them  by 
the  newer  conceptions  of  the  nerve  fiber  as  a  mere  process  of  the  nerve  cell; 
for  it  is  perfectly  evident  that  a  process  must  degenerate  when  its  connection 
with  the  cell  body  is  lost. 

Wallerian  degeneration  has  been  of  very  great  value  in  tracing  out  the  nerve 
paths  in  the  central  nervous  system  (of.  later),  in  determining  nerve  roots,  and 
in  isolating  physiologically  the  different  kinds  of  fibers  belonging  to  a  given 
nerve  trunk.  The  latter  is  possible  because  the  different  kinds  of  fibers  do  not 
degenerate  at  the  same  rate  after  section. 

But  we  find  it  necessary  to-day  to  amend  the  law  of  Waller  somewhat.  It 
turns  out  that  both  the  stump  of  the  nerve  fiber  left  in  connection  with  the 
nerve  cell  and  the  cell  itself  undergo  secondary  changes  after  section  of  a  nerve. 
The  motor  cells  and  those  of  the  spinal  ganglia  appear  to  behave  somewhat 
differently  in  this  respect.  The  former  exhibit  certain  characteristic  alterations 
of  structure  within  twenty-four  to  forty-eight  hours  after  the  section,  and  within 
fifteen  to  twenty  days  many  of  them  have  gone  to  pieces.  The  remainder,  even 
though  the  end  of  the  nerve  may  not  have  healed  at  all,  become  from  this  time 
on  the  seat  of  r^enerative  changes  and  gradually  recover  their  normal  proper- 
ties. The  same  course  of  events  is  witnessed  in  the  efferent  sympathetic  nerves. 
When  the  cervical  sympathetic  is  cut,  certain  cells  in  the  anterior  horn  of  the 
same  side  become  atrophic;   and   after  section  of   the  fibers  coming  from   the 


568      PHYSIOLOGY   OF  THE   NERVE   CELL   AND   THE   SPINAL   CORD 

first  cervical  ganglion,  the  cells  in  the  ganglion  belonging  to  them  for  the  most 
part  perish. 

The  structural  changes  appearing  in  the  spinal  ganglion  cells  after  section 
of  a  spinal  nerve  lead  to  complete  loss  of  their  integrity  within  about  ninety 
days  (v.  Gehuchten).  In  other  words,  to  continue  in  a  normal  state,  the  spinal 
ganglion  cell  must  receive  its  impulses  from  the  periphery. 

On  the  other  hand,  section  of  the  posterior  root  central  to  the  ganglion  in 
young  animals  does  not  stop  the  development  of  the  ganglion  or  of  the  peripheral 
nerve  fibers  connected  with  it  (Anderson). 

Section  of  afferent  nerves  produces  changes  even  in  certain  nerve  cells  of 
the  spinal  cord,  with  which  they  are  connected  only  secondarily.  In  young  ani- 
mals development  of  the  cells  of  Clark's  column  is  stopped  by  section  of  the 
sciatic  nerve  (Anderson).  In  fact,  even  the  motor  cells  of  the  anterior  horn  as 
well  as  the  anterior  root  fibers  appear  to  be  affected  by  section  of  the  posterior 
roots,  and  especially  if  the  homolateral  half  of  the  spinal  cord  also  is  cut 
through. 

In  view  of  these  results  we  can  readily  understand  how  after  amputation 
of  a  limb  atrophy  will  gradually  extend  to  those  conducting  pathways  and  gray 
masses  of  the  nervous  system  which  were  formerly  in  functional  connection  with 
that  particular  limb.  Such  changes  spread  more  rapidly  in  young  than  in  older 
or  adult  individuals. 

On  the  basis  of  these  facts,  Gudden  has  worked  out  an  experimental  method 
of  tracing  the  conducting  pathways  belonging  to  a  given  organ.  He  merely 
extirpates  the  organ  from  a  young  animal,  keeps  the  animal  alive  for  a  time, 
then  works  out  the  extent  and  localization  of  the  resulting  atrophy. 

The  most  probable  explanation  of  the  atrophy  resulting  from  such  operations 
is,  that  individual  nerve  elements  connected  together  exercise  a  nutritive  influ- 
ence on  one  another  in  virtue  of  the  excitation  processes  which  they  mediate, 
and  that  failure  of  these  excitation  processes  cuts  off  the  nutritive  influence  and 
the  result  is  atrophy.  Thus  when  a  sufficient  number  of  posterior  root  fibers  are 
sectioned,  the  normal  excitation  conveyed  to  the  cells  of  Clark's  column  by  these 
fibers  is  prevented  and  those  cells  atrophy.  The  anterior  horn  cells  robbed  of 
their  peripheral  impulses  by  section  of  the  posterior  roots,  and  robbed  of  most 
of  their  central  impulses  by  hemisection  of  the  cord,  on  the  same  side,  are  thence- 
forth devoid  of  the  proper  nutritive  influence,  and  they  atrophy.  When  a  limb 
is  amputated  the  individual  no  longer  has  any  occasion  for  sending  impulses  to 
the  motor  cells  of  the  lost  member,  and  not  being  used,  nutritive  control  over 
them  is  withdrawn. 

The  nutritive  influence  of  the  nerve  cells  extends  also  to  the  peripheral 
tissues  supplied  by  their  fibers,  for  it  has  long  been  known,  that  the  nutritive 
state  of  many  an  organ  depends  upon  its  connection  with  the  central  nervous 
system.  We  have  already  seen  tliat  a  skeletal  muscle  degenerates  when  its 
motor  nerve  is  cut.  The  submaxillary  gland  decreases  in  size  after  section 
of  its  cerebral  secretory  nerves  (page  25()),  and  undergoes  degeneration  of 
the  true  glandular  substance. 

So  far  as  we  know  yet  muscle  substance  receives  only  a  single  kind  of 
efferent  nerve  fibers.  Consequently  the  very  nerves  which  evoke  the  dissimila- 
tory  processes  of  the  muscle  serve  at  the  same  time  in  some  way  not  yet  under- 
stood to  maintain  the  muscle  in  its  normal  condition  (cf.  page  449),  and 
the  same  may  be  said  of  other  organs. 

Even  afferent  nerves  have  a  nutritive  influence  of  this  kind  on  their  periph- 


FUNCTIONS  OF   THE   NERVE  CELL  569 

eral  end  organs.     For  example,  the  taste  buds  of  the  tongue  degenerate  after 
section  of  the  glosso-pharyngeal  nerve. 

To  sum  up,  we  may  say  that  the  nerve  cells  constitute  the  nutritive  or 
trophic  centers  of  the  nerve  fibers  proceeding  from  them,  and  likewise  of  the 
central  or  peripheral  organs  supplied  hy  the  nerve  fibers. 

In  explaining  certain  phenomena  of  degeneration  the  belief  has  often  been 
expressed  that  there  are  special  nerves  and  centers  whose  sole  function  it  is  to 
maintain  the  normal  state  of  nutrition  in  the  organs  and  tissues,  and  such  nerves 
have  been  designated  as  the  trophic  nerves.  While  we  cannot  regard  the  ques- 
tion of  their  existence  as  finally  disposed  of,  the  results  of  experiments  thus  far 
made  tend  to  discredit  the  whole  conception. 

For  example,  frequent  reference  is  made  to  inflammation  of  the  cornea  after 
section  of  the  trigeminal  nerve  and  to  inflammation  of  the  lungs  after  bilateral 
section  of  the  vagus.  But  as  regards  the  first,  it  is  to  be  observed  that  the 
cornea  is  rendered  insensitive  by  section  of  the  trigeminal ;  consequently  foreign 
particles  which  under  normal  circumstances  would  be  removed  voluntarily  or 
reflexly  by  movements  of  the  eyelids,  are  now  permitted  to  scratch  and  other- 
wise injure  the  cornea,  and  in  this  manner  an  inflammatory  process  can  be  started 
quite  independently  of  any  trophic  influence.  If  the  ear  of  the  animal  be  sewn 
down  over  the  eye  so  as  to  protect  it  from  foreign  particles  no  inflammation 
results  from  section  of  the  trigeminal  (Snellen). 

The  inflammation  of  the  lungs  (vagus  pneumonia)  can  also  be  explained 
without  invoking  a  trophic  nervous  influence.  The  oesophagus  is  paralyzed  as 
the  result  of  the  operation,  and  bits  of  food  remaining  adherent  to  its  walls 
may  very  easily  be  sucked  into  the  lungs  and  there  set  up  the  inflammation 
observed.  Animals  with  an  O'sophageal  fistula  in  the  neck  (cf.  page  246)  undergo 
bilateral  vagotomy  without  any  inflammation  of  the  lungs  (Pawlow),  the  likeli- 
hood of  food  particles  entering  the  lungs  being  very  much  reduced  by  the  fistula. 

Other  experimental  results  which  have  been  brought  forward  in  support  of 
trophic  nerves  are  nothing  more  than  pure  vasomotor  effects. 

Bedsores,  which  frequently  accompany  diseases  of  the  spinal  cord  (myelitis, 
lesions,  compression,  etc.),  are  probably  to  be  explained  rather  as  the  result  of 
a  diminished  vitality  of  the  skin,  which  permits  injury  and  infection,  than  as 
the  specific  result  of  a  loss  of  trophic  influence. 


B.    PHYSIOLOGICAL   STIMULI   OF   NERVE   CELLS 

Under  normal  circumstances  nerve  cells  may  be  roused  to  activity  in  any 
one  of  the  following  different  ways : 

(1)  By  external  stimuli  acting  upon  the  peripheral  end  organs  of  afferent 
nerves.  Afferent  nerves  always  connect  with  a  nerve  cell  of  some  kind,  hence 
any  excitation  of  the  former  must  be  communicated  to  the  latter.  The  cells 
of  the  spinal  ganglia  are  roused  to  activity  by  stimulation  of  the  spinal 
nerves  and  the  nerve  cells  connected  with  the  nerves  of  special  sense  (e.  g., 
the  ganglion  cells  of  the  retina)  are  excited  hy  their  appropriate  stimuli. 

(2)  By  the  action  of  other  nerve  cells.  This  mode  of  excitation  is  very 
common,  for  whenever  an  impulse  is  sent  through  any  length  of  the  nervous 
system  not  covered  ])y  a  single  fiber  it  must  be  transmitted  to  a  fiber  or  fibers 
connected  with  another  cell.  For  examples  of  this  mode,  we  have  only  to 
think  of  the  way  in  which  the  highest  nerve  centers  are  finally  excited  by  a 

34 


570       PHYSIOLOGY   OF   THE   NERVE   CELL   AND  THE   SPLNAL  CORD 

peripheral  stimulus  or  how  the  efferent  motor  cells  in  the  anterior  horn  of  the 
cord  are  excited  through  the  long  cortico-spinal  pathways  by  the  cerebral 
cortex. 

We  must  call  attention  here  to  a  very  noteworthy  difference  in  the  behavior 
of  nerve  cells  of  different  kinds.  When  the  spinal  cord  is  excited — e.  g.,  by 
stimulation  of  the  posterior  spinal  roots — an  action  current  makes  its  appear- 
ance in  the  cord,  just  as  in  the  peripheral  nerves;  but  on  stimulation  of  the 
anterior  roots  no  action  current  is  obtained  in  the  cord — i.-  e.,  the  excitation  can- 
not be  communicated  by  the  motor  cells  to  other  portions  of  the  cord.  And 
yet  an  excitation  started  in  the  cord  by  direct  stimulation  can  be  communicated 
to  the  aiferent  roots.  At  any  rate  in  strychnine  poisoning  when  a  very  strong 
excitation  is  roused  in  the  cord  an  action  current  can  be  demonstrated  in  the 
posterior  roots  (Gotch  and  Horsley). 

(3)  The  reflex  process  represents  an  important  instance  of  transferred 
excitation  within  the  eentral  nervous  system.  This  phenomenon  was  known 
to  Descartes  (1649)  and  later  received  an  essentially  correct  explanation 
through  the  writings  of  Proschaskas  and  of  Marshall  Hall. 

A  reflex  may  be  defined  as  a  physiological  act  in  which  an  afferent  nerve 
excites  an  efferent  nerve  through  the  cooperation  of  the  central  nervous  system, 
but  without  any  participation  on  the  part  of  the  will  or  of  consciousness. 

We  have  already  seen,  in  discussing  the  structure  of  the  central  nervous 
system,  how  this  transfer  of  the  afferent  impulse  to  the  efferent  nerve  may 
take  place  (cf.  page  563  and  Fig.  255). 

(4)  Nerve  cells  may  be  excited  through  the  blood  and  lymph  (automatic 
excitation).  Products  of  decomposition  and  of  internal  secretion  (cf.  page 
356)  are  always  present  in  the  blood  and  lymph  and  are  capable  of  stimulating 
the  nerve  cells  with  which  they  are  brought  in  contact. 

(5)  Xerve  cells  may  be  excited  through  the  inftuence  of  the  will.  When 
we  make  a  muscular  movement  by  direct  effort  of  the  will,  certain  nerve  cells 
are  excited.  The  will  therefore  can  in  some  way  act  upon  nerve  cells,  or, 
more  correctly  stated,  in  those  cerebral  processes  which  represent  the  physical 
correlate  of  our  conscious  volitional  states  certain  nerve  cells  are  active.  How 
this  takes  place  we  cannot  say. 

We  might  conceive  that  these  movements  which  take  place  under  the  influ- 
ence of  the  will  in  reality  represent  a  particular  kind  of  reflexes,  and  in  fact 
one  may  by  introspection  convince  himself  that  what  he  calls  a  voluntary  act 
is  very  often  the  direct  result  of  an  external  stimulus  even  though  it  may  be 
accompanied  by  a  conscious  sensation.  But  it  is  impossible,  for  the  present  at 
least,  to  explain  the  action  of  the  will  in  its  entiretj^  from  this  point  of  view 
and  to  this  question  as  to  that  concerning  the  origin  of  conscious  sensations, 
physiology  is  compelled  to  waive  an  answer. 

C.    MODE   OF  REACTION   OF  NERVE   CELLS  TO   STIMULATION 

Whether  a  nerve  cell  is  stimulated  directly  or  through  the  axis-cylinder 
process  or  other  connection,  it  exhibits  several  characteristics  in  the  mode  of 
its  behavior.  (1)  The  first  of  these  is  its  ahility  to  transform  a  single  momen- 
iarij  stimulus  into  a  long-continned  effect. 


FUNCTIONS   OF  THE   NERVE   CELL  571 

Birge  stimulated  the  spinal  cord  of  the  frog  by  plunging  a  very  fine  needle 
into  it  and  immediately  withdrawing  the  same.  He  recorded  the  muscular 
responses  discharged  by  the  stimulus  and  subsequently  determined  very  accu- 
rately the  portion  of  the  cord  invaded  by  the  needle.  The  result  was  that  stimu- 
lation of  the  white  substance  was  found  to  produce  only  a  single  contraction, 
but  when  the  needle  struck  nerve  cells  in  the  anterior  horn  an  actual  tetanus 
always  appeared — i.  e.,  a  stimulus  occurring  but  once  was  transformed  by  the 
nerve  cells  into  a  stimulus  lasting  for  a  much  longer  time. 

(2)  Another  peculiarity  of  nerve  cells  is  that  they  respond  especially  well 
to  frequent  stimulation,  even  though  the  strength  of  the  stimulus  is  relatively 
very  weak.  This  means  that  nerve  cells  possess  in  a  high  degree  the  propert}' 
of  summation. 

Thus  Kronecker  and  Xikolaides  found  on  stimulating  the  vasomotor  center 
that  single  induction  shocks  of  great  strength  produced  but  slight  effect,  and 


Fig.  2.56. — Reflex  contractions  of  a  fn.g's  leg  to  electrical  stimulation,  after  Stirling.  To  be  read 
from  left  to  right.  The  middle  line  shows  the  time  of  stimulation;  the  lower  hne  is  a  time 
record  in  seconds. 

that  repeated  shocks  of  moderate  strength  and  high  frequency  (optimum  twenty 
to  thirty  per  second)  were  more  efficacious  than  stronger  shocks  at  a  lower 
frequency. 

Exactly  the  same  thing  is  observed  in  reflex  stimulation.  It  is  extremely 
difficult  to  get  any  response  from  a  normal  spinal  cord  with  single  induction 
shocks  (Setschenow).  (Biedermann  obsers^ed,  however,  that  the  responses  are 
easily  obtained,  if  the  spinal  cord  first  be  cooled.)  But  if  the  afferent  nerve  be 
stimulated  with  rapidly  repeated  shocks,  no  difficulty  is  experienced,  and  with 
a  given  strength  of  current  the  muscular  responses  appear  more  promptly  the 
more  frequent  the  stimuli.  This  is  not  because  a  larger  number  of  stimuli  fall 
within  the  latent  period  with  the  higher  frequency;  for  the  absolute  number  of 
stimuli  received  before  the  end  of  the  latent  period  may  be  even  greater  with 
a  low  than  with  a  high  frequency.  Once  an  adequate  frequency  has  been 
reached,  the  length  of  the  latent  period  is,  within  wide  limits,  independent  of 
the  strength  of  the  stimulus  (Stirling). 

The  power  of  the  nerve  cells  to  store  up  stimuli  is  demonstrated  in  the  most 
striking  way  by  the  preliminarri  refexes  observed  by  Sanders-Ezn  after  chemi- 
cal, and  by  Stirling  (Fig.  256)  after  electrical  stimulation.  At  first  after  a 
short  latent  period  several  small  twitches  appear,  then  suddenly,  after  a  long 
latent  period,  a  very  powerful  contraction  is  made.  The  reflex  mechanism  is 
now  exhausted ;  the  preparation  remains  at  rest  notwithstanding  the  continu- 


572      PHYSIOLOGY   OF  THE   NERVE   CELL   AND  THE   SPLNAL  CORD 

ous  stimulation  for  several  seconds,  then  another  powerful  contraction  appears, 
etc.  The  same  thing  has  been  observed  by  Lombard  with  continuous  thermal 
stimulation. 

These  and  similar  facts  teach  us  that  when  the  nerve  cell  has  discharged 
an  unusualh-  strong  impulse  as  the  result  of  summation  of  its  stimuli,  it  is 
to  a  certain  extent  exhausted  and  requires  a  certain  time  to  be  recharged. 
It  is  self-evident  that  the  resistance  of  a  cell  to  stimulation  will  depend  upon 
the  mode,  strength,  and  frequency  of  the  stimulation,  and  we  know  from 
everyday  experience  that  nerve  cells  withstand  the  normal  stimuli  much 
better  than  they  do  our  relatively  crude  artificial  stimuli. 

(3)  Certain  observations  go  to  show  that  nerve  cells.  Just  like  nerve 
fibers  and  muscles  (cf.  page  429),  have  a  refractory  period. 

In  stimulating  the  motor  zone  of  the  cerebral  cortex  Eichet  and  A.  Broca 
observed  that  a  second  stimulus  was  ineffective  if  it  follows  the  first  at  a  shorter 
interv'al  than  0.1  second.  The  reflex  closure  of  the  eyelid  to  a  second  stimulus 
does  not  take  place  if  the  second  stimulus  follows  the  first  at  a  shorter  interval 
than  0.5-1  second  (Zwaardemaker).  According  to  Baglioni,  the  refractory 
period  of  the  sensory  elements  in  the  spinal  cord  of  a  frog  amounts  to  some 
0.25-0.5  second.  The  inability  of  the  normal  spinal  cord  to  mediate  complete 
tetanic  contractions  reflexly  is  to  be  explained  by  this  circumstance. 

(4)  Finally,  artificial  stimulation  of  nerve  cells  teaches  us  that  they  have 
the  ahiJity  to  transmute  the  stimuli  ivhich  they  receive  into  a  perfectly  char- 
act  erist  ic  rh  yth  m . 

Stimulating  the  spinal  cord  of  a  rabbit  with  forty-three  induction  shocks 
per  second,  Kronecker  and  Hall  obtained  muscular  contractions  showing  a 
rhythm  of  twenty  per  second,  whereas  on  stimulating  the  peripheral  nerve  forty- 
three  times  per  second  the  contractions  obtained  had  exactly  the  same  rhythm 
as  the  stimuli.  We  are  not  to  suppose,  however,  that  the  frequency  of  the  im- 
pulses given  off  from  the  central  nervous  system  is  always  the  same.  It  appears 
rather  from  the  experiments  of  Stern  on  the  muscular  sound  produced  by  stimu- 
lation of  different  portions  of  the  nervous  system  with  induction  shocks  of  dif- 
ferent frequency,  that  the  spinal  cord  is  capable  of  discharging  its  impulses  at 
varying  rhythms  up  to  230  per  second,  although  a  number  of  observations  tend 
to  show  (cf.  page  431)  that  the  frequency  at  which  impulses  are  given  off  from 
the  central  nervous  system  is  in  general  very  much  lower  than  this. 


D.  DEPENDENCE  OF  THE  NERVE  CELL  UPON  THE  BLOOD  SUPPLY  AND 
THE  EFFECTS  OF  POISONOUS  SUBSTANCES 

The  nerve  cells  in  the  body  are  intensely  active,  hence  they  require  an 
abundant  supply  of  blood.  In  fact,  it  has  been  observed  that  the  large  gan- 
glion cells  of  the  vagus  and  the  trigeminal  nerves  in  the  bony  fish,  Lophius 
piscatorius,  have  a  small  knot  of  capillaries  of  their  own  penetrating  into  their 
substance  and  so  supplying  them  with  nourishment  (Fritsch). 

When  the  blood  supply  to  the  brain  is  considerably  reduced  by  compression 
of  the  carotids  on  both  sides,  unconsciousness  results,  in  many  cases  at  least, 
because  the  nerve  cells  are  functionally  incapacitated. 


FUNCTIONS   OF  THE   NERVE  CELL 


573 


Stenson's  experiment  of  clamping  the  abdominal  aorta  teaches  us  also  that 
the  nerve  cells  in  the  spinal  cord  very  soon  suffer  from  the  lack  of  blood. 
The  posterior  extremities  become  paralyzed  soon  after  the  aorta  is  closed  off, 
not  because  of  the  absence  of  blood  in  those  parts  but  because  of  its  absence 
from  the  spinal  cord. 

Fredericq  has  investigated  these  phenomena  more  closely  and  has  reached 
the  following  conclusions  for  the  dog:  Some  fifteen  to  twenty  seconds  after  the 
clamp  is  applied  a  temporary  excitation  of  the  motor  cells  begins,  but  within 
thirty  to  forty  seconds  the  motor  paralysis  is  complete.  Up  to  this  time  the 
sensibility  of  the  posterior  parts  is  entirely  unaffected;  but  after  one  and  one- 


Period  of 
Excitation; 
Convulsions 


Period  of 

Respiratory 

Pause 


Final 
Gaspings 


All 

Respirations 

Stopped 


Fig.   257. — The  relative  resistance  of  several  nerve  centers  in  asphyxiation,  schema,  after  Lander- 
gren.    ,  the  vasomotor  center  in  the  medulla;    .  .1 ,  the  cardiac  inhibitory  center; 


-,  the  respiratory  center;     -• 


■,  the  vasomotor  center  in  the  spinal  cord. 


half  minutes  a  hyperaesthesia  sets  in,  followed  by  anaesthesia,  which  is  complete 
at  the  end  of  three  minutes.  If  now  the  clamp  is  removed,  sensibility  returns  in 
five  to  ten  minutes,  but  motility  somewhat  later.  By  continuing  the  occlusion 
long  enough  the  paralysis  and  anaesthesia  become  permanent. 

From  these  facts  we  reach  the  very  ini])ortant  conclusion  that  different 
nerve  cells  have  very  different  powers  of  resistance  to  anaemia. 

Other  observations  go  to  show  that  the  endurance  of  different  nerve  cells 
under  acute  asphyxiation  is  very  different.  The  schema  in  Fig.  257  repre- 
sents, according  to  Landergren,  the  relative  excitability  and  resistance  through- 
out the  different  phases  of  asphyxia  of  the  following  centers :  the  bulbar  vaso- 
motor center,  the  cardiac-inhil)itory  center,  the  respiratory  center,  and  the 
spinal  vasomotor  center  (cf.  page  ^^(S).  The  bulbar  vasomotor  is  first  ex- 
cited and  has  the  least  resistance.  When  the  activity  of  this  center  begins 
to  decline  the  cardio-inhibitory  center  has  reached  the  height  of  its  irrita- 
bility. The  course  which  is  run  by  the  irrital)ility  of  the  respiratory  center 
cannot  be  represented  fully,  owing  to  the  re-^piratory  pause  which  comes  in, 
but  it  seems  to  agree  in  the  main  with  tliat  of  the  vagus  center.     The  spinal 


574      PHYSIOLOGY    OF  THE   NERVE   CELL   AND  THE   SPLNAL  CORD 

vasomotor  centers  are  excited  at  a  rather  late  stage.  Imt  they  continue  active 
at  a  time  when  the  other  centers  are  on  the  wane. 

Although  this  is  not  the  place  for  a  full  discussion  of  the  influence  of  dif- 
ferent poisons  upon  the  nervous  system,  attention  ought  to  be  directed  to  the 
fact  that  certain  observations  have  been  made  which  tend  to  show  that  these 
substances  do  not  act  alike  on  all  nerve  cells.  Thus,  according  to  Baglioni, 
carbolic  acid  in  weak  solution  has  a  heightening  effect  upon  the  irritability  of 
the  motor  mechanisms  in  the  anterior  horn,  while  the  sensory  mechanisms  of 
the  posterior  horn  are  not  perceptibly  affected.  Strychnia  on  the  other  hand 
increases  the  excitability  of  the  sensory  mechanisms  of  the  posterior  horn  and 
leaves  the  motor  mechanisms  of  the  anterior  unaffected.  Immediately  after  its 
application  nicotine  stimulates  the  motor  elements  of  the  medulla  and  spinal 
cord,  also  the  cells  of  the  sympathetic  ganglia,  but  has  no  effect  upon  the  cells 
of  the  spinal  ganglia  (Langley). 

E.  MORPHOLOGICAL  CHANGES  IN  THE  NERVE  CELL.  REPRODUCTION 

AND  REGENERATION 

Within  recent  years  the  structure  of  the  nerve  cell  has  been  made  out  in 
great  detail,  thanks  to  the  great  progress  in  histological  technique,  and  certain 
diffei-ences  have  been  noted  in  the  microscopical  appearance  of  resting  and  of 
active  or  fatigued  cells.  A  full  account  of  this  difference  will  be  found  in  text- 
books of  histology. 

Various  attempts  have  been  made  also  to  demonstrate  that  nerve  cells  or  their 
dendrites  at  least  are  capable  of  ameboid  movements,  and  far-reaching  physio- 
logical and  psychological  hypotheses  have  been  erected  on  the  basis  of  such 
assumptions.  But  these  have  with  justice  been  very  vigorously  contested,  and 
if  the  newer  discoveries  concerning  the  neurofibrils  prove  to  be  true  in  all  respects 
(cf.  page  560),  ameboid  movement  will  have  lost  its  last  vestige  of  support. 

It  is  a  question  of  great  fundamental  importance,  whether  nerve  cells  can 
be  reproduced  in  post-embryonic  life.  Birge  counted  the  motor  cells  in  the  spinal 
cord  and  the  nerve  fibers  in  the  anterior  spinal  roots  in  frogs  of  different  age 
and  convinced  himself  that  both  either  multiply  from  preexisting  nerve  elements 
or  develop  from  other  elements  throughout  life,  for  he  found  an  unmistakable 
relation  between  the  weight  of  the  animal  and  the  number  of  cells  and  fibers. 
For  example,  a  frog  weighing  1^  g.  had  5,984  motor  nerve  fibers,  one  of  OA  g. 
6,481,  one  of  23  g.  7,048,  up  to  a  frog  of  11  g.  with  11,468  fibers.  On  the  average 
for  each  1  g.  increase  in  weight  52  motor  fibers  had  been  added. 

How  long  after  birth  this  new  formation  may  take  place  we  do  not  know. 
In  certain  inflammatory  processes  in  the  brain  mitotic  figures  have  been  seen 
in  the  vicinity  of  nerve  cells,  but  these  facts  teach  us  nothing  with  regard  to 
the  normal  multiplication  of  nerve  cells  in  the  adult  body. 

Most  authors  deny  the  regeneration  of  nerve  tissues  after  extensive  destruc- 
tion of  them  in  the  higher  animals.  But  we  have  two  observations  recorded  in 
the  literature  supporting  such  regenerations :  One  by  Voit  concerns  regeneration 
in  both  hemispheres  of  the  pigeon,  the  other  by  Vitzou  regeneration  of  the 
occipital  lobes  in  the  monkey.  These  are  extremely  important  observations  and 
urgently  demand  confirmation. 

It  has  been  established  by  a  great  many  observations  that  peripheral 
efferent  fibers  regenerate  if  the  nerve  cells  to  which  they  belong  remain 
uninjured. 


REFLEX   PROCESSES  575 

Moreover  the  central  end  of  one  efferent  nerve  can  be  united  with  the 
peripheral  end  of  another.  Two  afferent  nerves  can  likewise  be  crossed  in 
the  same  fashion;  but  it  has  not  yet  been  decided  how  far  afferent  nerves 
mediating  different  kinds  of  sensations  can  be  joined  together.  It  appears 
that  no  union  of  afferent  with  efferent  nerves  is  possible. 

Several  authors  reject  the  view  that  an  actual  regeneration  takes  place  in 
a  nerve  which  has  been  completely  separated  from  the  central  nervous  system, 
and  Bethe  has  reported  a  numljer  of  interesting  experiments  which  tend  to 
discredit  that  view.  Other  authors  have  observed  in  the  peripheral  stump 
of  a  cut  nerve  the  appearance  of  spindle-shaped  cells  lying  in  the  longitudinal 
direction  of  the  nerve.  Should  it  be  shown  beyond  a  douljt  that  axis  cylinders 
develop  within  these  structures  we  could  no  longer  regard  axis  cylinders  as 
processes  of  the  nerve  cells,  and  the  nutritive  influence  over  the  nerve  fibers 
ascribed  to  the  nerve  cell  would  sink  to  a  matter  of  small  importance.  In 
short,  our  whole  conception  of  the  structure  and  functions  of  the  nervous 
S3'stem  would  of  necessity  be  very  profoundly  modified.  Langley.  however, 
on  the  basis  of  some  experiments  of  his  own,  believes  that  the  nerve  fibers 
which  apparently  arise  de  novo  actually  grow  into  the  peripheral  stump  from 
nerves  of  the  surrounding  tissue  and  eventually  trace  back  to  nerve  cells  of 
the  spinal  cord.  It  is  to  be  observed  also  that  Bethe  himself  finds  great  varia- 
tion in  the  number  of  autochthonous  ^  fibers,  since  never  in  his  experiments 
did  all  the  fibers  regenerate  in  this  fashion.  Besides,  this  form  of  regeneration 
appeared  at  its  strongest  only  in  3'oung  animals ;  in  grown  animals  the  fibers 
stopped,  as  Bethe  puts  it.  "  halfway,"  not  l^eing  powerful  enough  of  them- 
selves to  complete  the  regeneration  without  the  help  of  the  spinal  cord.  For 
the  present  the  matter  cannot  be  regarded  as  settled  in  Bethe's  favor. 

Langley  has  contributed  some  very  important  results  on  the  regeneration  of 
sympathetic  nerves,  but  for  several  reasons  it  seems  best  to  discuss  these  in  con- 
nection with  the  subject  of  physiology  of  special  nerves  (Chapter  XXV). 


§  5.    REFLEX   PROCESSES 

A.    SEGMENTATION   IN   THE   CENTRAL   NERVOUS   SYSTEM 

We  learn  from  the  anatomy  of  the  lower  vertebrates  (lamprey,  salaman- 
der) that  the  nerve  fibers  from  the  spinal  roots,  in  certain  sections  at  least, 
run  but  a  short  distance  up  or  down  the  spinal  cord — i.  e.,  that  there  is  here 
an  evident  segmentation  of  the  spinal  cord. 

Likewise  in  the  higher  vertebrates  the  spinal  cord  can  be  regarded  as  to 
a  certain  extent  made  up  of  seriaUy  homologous  parts,  connected  together  in  a 
very  complex  manner.  Each  such  segment  consists  of  a  pair  of  nerve  roots 
together  with  that  portion  of  the  spinal  cord  belonging  to  them  and  consti- 
tutes in  itself  the  simplest  kind  of  a  central  organ. 

Because  of  the  many  short-  and  long-fil)ered  ))atbways  uniting  the  separate 
segments  of  the  spinal  cord  with  each  other  and  with  the  different  portions 
of  the  brain,  impulses  arising  in  the  different  segments  have  so  many  ways 

*  That  is,  originating  in  the  place  where  they  are  found. 


576      PHYSIOLOGY   OF  THE   NERVE  CELL  AND  THE   SPLNAL  CORD 

of  escape  that  the  segmentation  in  the  normal  organism  is  not  apparent. 
That  it  does  exist,  however,  has  been  demonstrated  by  Sherrington's  investi- 
gations on  the  posterior  root  reflexes  in  the  monkey.  It  is  unfortunate  that 
space  will  not  permit  us  to  discuss  these  results  in  detail.  The  following 
concrete  illustration  of  segmental  reflexes  in  the  higher  vertebrates  must 
suffice. 

Goltz  and  Ewald  isolated  the  spinal  cord  of  the  dog  from  the  higher  parts 
of  the  nervous  system  by  a  section  in  the  lower  cervical  or  upper  thoracic  region 
and  then  in  a  second  operation  removed  the  posterior  end  of  the  cord.  There 
remained  only  the  upper  i)art  of  the  thoracic  cord  controlling  what  they  called 
the  "  middle  animal."  When  the  hand  was  rubbed  over  the  right  side  of  the 
thorax  of  such  an  animal,  that  portion  of  the  vertebral  column  containing  the 
remnant  of  the  spinal  cord  was  bent  strongly  to  the  right.  If  a  very  gentle 
stimulus  was  given  distortion  of  the  skin  only  was  observed.  Wetting  the  thorax 
with  water  caused  the  "  middle  animal  "  to  tremble  all  over. 

Sherrington  has  found  that  reflexes  spread  most  readily  to  the  motor  fibers 
of  the  same  pair  of  spinal  nerves,  and  more  readily  to  anterior  roots  near 
the  afferent  path  than  to  those  far  distant.  They  can  also  pass  centrifugally 
as  well  as  centripetally  in  the  cord,  for  stimulation  of  the  fore  leg  will  produce 
a  reflex  contraction  in  the  hind  leg.  Motor  fibers  springing  from  the  same 
segment  of  the  spinal  cord  are  not  all  roused  to  action  with  equal  facility — 
e.  g.,  in  reflex  excitation  of  the  hind  leg  the  flexoTs  of  the  same  side  and  the 
extensors  of  the  opposite  side  are  called  into  play  much  more  easily  than 
the  extensors  of  the  same  and  the  flexors  of  the  opposite  side  (cf.  below, 
page  587). 

B.  GENERAL  FEATURES  OF  REFLEXES 

Although  reflexes  may  be  radiated  very  widely,  as  a  rule,  they  have  a 
rather  limited  distribution,  certain  efferent  nerves  being  set  in  action  by 
definite  afferent  nerves,  whence  the  so-called  regulative  reflexes.  Thus  stimu- 
lation of  the  nerves  of  taste  produces .  a  reflex  secretion  of  saliva  and  of 
gastric  juice;  the  afferent  nerves  of  the  lungs  influence  reflexly  the  respira- 
tory muscles;  the  afferent  nerves  of  the  heart  act  reflexly  upon  the  efferent 
nerves  of  the  heart,  and  upon,  the  vasomotor  nerves;  the  heat  nerves  and 
cold  nerves  produce  reflex  alterations  in  the  secretion  of  sweat  and  in  the 
supply  of  blood  to  the  skin,  etc. 

From  these  examples,  which  represent  but  a  small  number  of  such  reflex 
processes,  we  may  deduce  the  general  rule:  that  the  reflexes  serve  to  regulate 
various  functions  of  the  body,  and  to  adapt  them  to  their  appropriate  ends. 

How  extremely  useful  to  the  body  this  purely  machinelike  regulation  is 
will  be  readily  appreciated,  if  we  but  recall  the  importance  of  the  examples 
just  mentioned  and  try  to  picture  to  our  minds  what  would  happen  in  the 
event  of  their  failure.  How  important  it  is,  too,  that  this  regulation  should 
go  on  independently  of  our  own  wills !  It  has  only  been  by  long  and  toil- 
some investigation  that  scientists  have  learned  the  little  we  know  about  the 
reflex  processes  in  our  bodies.  If  now  our  bodily  functions  could  onlv  be 
carried  out  after  mastering  all  the  details,  how  should  we  ever  learn  them 


REFLEX   PROCESSES  577 

and  how  could  they  be  regulated  meantime?  The  regulative  reflexes  owe 
their  existence  to  the  native  organization  of  the  nervous  system.  Among  the 
many  efferent  nerves  which  ma}'  be  excited  b}'  a  single  afferent  nerve  there 
are  some  to  which  the  impulse  is  transferred  more  readily  than  to  others. 
This  naturally  suggests  that  the  anatomical  connections  in  such  cases  are 
simpler,  possibly  shorter,  than  in  others. 

In  his  researches  on  the  conditions  influencing  secretion  in  certain  digest- 
ive glands  Pawlow's  attention  was  dra-wn  to  one  circumstance  which  is  of 
the  utmost  importance  for  our  comprehension  of  the  reflex  mechanisms.  We 
refer  to  the  psychical  influence  over  certain  glands,  already  mentioned  at 
page  263.  When  the  experiment  animal  had  no  desire  for  food  stimulation 
of  the  mucous  membrane  of  the  mouth  produced  no  secretion  of  gastric  juice. 
The  appetite  therefore  brings  about  a  predisposition  in  certain  portions  of 
the  nervous  system  which  constitutes  an  indispensal)le  condition  for  the  reflex 
outpouring  of  gastric  juice.  In  fact,  appetite  itself,  or  the  mere  sight  of 
food,  can  evoke  the  secretion.  We  meet  with  similar  phenomena  in  other 
portions  of  the  body — e.  g.,  alterations  of  the  heart  beat  under  the  influence 
of  emotions,  blushing,  weeping,  the  involuntary  evacuation  of  urine  and  fseces 
induced  by  certain  psychical  states,  vomiting  caused  by  disagreeable  thoughts, 
and  many  more.  Hence,  while  not  under  the  direct  control  of  the  will  the 
reflex  processes  are  closely  associated  in  manifold  ways  with  states  of  the  mind. 

Many  new  reflexes  are  formed  in  the  course  of  life,  that  is  to  say,  move- 
ments which  originally  were  executed  under  the  control  of  the  will  become 
automatic  by  practice — e.  g.,  standing,  walking,  piano  playing,  and  the  like. 

When  a  person  stumbles  over  a  stone,  the  purposive  movements  by  which 
he  saves  himself  from  a  fall  are  pure  reflexes,  as  we  know  from  the  fact  that 
very  often  the  danger  is  apperceived  only  when  it  is  all  over.  If  in  such 
cases  the  appropriate  movements  had  to  be  made  voluntarily,  very  often  the 
body  would  suffer  injury  before  the  mishap  could  be  prevented.  Another 
purpose  of  reflex  movements  therefore  is  to  protect  the  body  from  external 
injuries. 

Reflexes  play  no  small  part  also  in  personal  culture.  Good  carriag'e  of  the 
body,  for  example,  is  nothing  more  than  the  result  of  practice  of  many  muscular 
movements  originally  performed  painstakingly,  until  they  became  purely  reflex 
in  character.  The  general  conduct  of  a  cultivated  man  in  his  intercourse  with 
his  fellow-men  is  also  largely  a  matter  of  reflex  action.  While  much  in  this 
realm  is  purely  conventional,  even  this  can  only  be  acquired,  so  as  to  be  invari- 
ably performed,  by  practice. 

C.    INHIBITION   OF  REFLEXES 

If  it  is  highly  important  so  to  impress  certain  movements  on  the  nervous 
system  that  they  will  be  performed  more  or  less  reflexly,  it  is  none  the  less 
important  to  suppress  certain  others  which  may  be  unpleasant  or  otherwise 
undesirable.  Many  such  acts  are  pure  reflexes  either  inherited  or  acquired 
by  bad  training.  Such.  e.  g..  are  weeping  and  crying  out  under  pain.  A 
person  can  learn  to  suppress  this  reflex,  just  as  a  child  can  be  taught  not 
to  cry  when  everything  does  not  go  to  its  liking.     Many  facial  expressions 


578      PHYSIOLOGY   OF  THE   NERVE  CELL  AND  THE  SPINAL   CORD 

and  gesticulations  belong  to  the  same  class.     (Recall,  e.  g.,  the  old  story  of 
Demosthenes. ) 

The  suppression  of  reflexes  may  be  explained  as  follows :  When  the  cerebrum 
is  removed  from  an  animal  it  is  observed  that  complex  systemic  reflexes  can  be 
more  readily  and  more  regularly  induced  than  before.  The  cerebrum  has  there- 
fore the  power  either  consciously  or  unconsciously  to  restrain  reflexes,  which  are 
discharged  more  easily  by  lower  centers  working  alone.  It  may  be  supposed  to 
have  the  same  power  over  acts  which  have  come  to  be  easily  performed  because 
certain  pathways  are  strongly  developed  either  by  inheritance  or  as  the  result 
of  habit.  Exercise  of  this  control,  however  small  it  may  be  at  first,  will  accom- 
plish the  suppression  of  such  processes  as  secretion  of  tears  and  the  like. 

But  it  would  be  incorrect  to  suppose  that  reflexes  are  inhibited  only  through 
the  cerebrum.  It  is  not  a  diflScult  matter  to  demonstrate  such  inhibitions  on 
animals  devoid  of  the  cerebrum,  notwithstanding  that  excitability  of  the  reflea 
arc  is  greatly  increased  by  the  operation.  On  the  strength  of  experiments  involv- 
ing chemical  stimulation  of  the  frog's  skin,  Setschenow  taught  that  special 
inhibitorj^  centers  are  to  be  found  in  the  neighborhood  of  the  optic  thalami,  the 
corpora  quadrigemina  and  the  anterior  portion  of  the  medulla  oblongata,  under 
the  influence  of  which  reflexes  from  the  spinal  cord  are  retarded.  These  centers 
can  be  excited  directly  or  by  stimulation  of  afi"erent  nerves,  he  said,  and  are 
always  active  throughout  life.  On  the  other  hand,  there  are  no  inhibitory 
mechanisms  for  reflexes  aroused  by  tactile  stimuli. 

Goltz  demonstrated,  however,  that  reflex  acts  induced  by  all  sorts  of  tactile 
stimuli,  as  mere  contact,  stroking  the  skin,  etc.,  can  under  certain  circum- 
stances be  entirely  suppressed,  and  he  laid  it  down  as  a  general  rule  that 
any  center  mediating  a  definite  reflex  suffers  a  distinct  loss  in  excitability 
whenever  it  is  acted  upon  at  the  same  time  by  any  other  pathway  not  con- 
cerned in  that  particular  reflex. 

Goltz  instanced  the  following  examples  of  inhibitions  of  this  sort.  (1)  The 
heart  may  be  brought  to  a  complete  standstill  by  lightly  tapping  the  abdominal 
viscera  (Klopfversuch).  But  this  otherwise  invariable  result  is  not  obtained  if 
at  the  same  time  a  sensory  nerve  of  one  of  the  legs  is  stimulated  powerfully. 
(2)  If  the  skin  between  the  fore  legs  of  a  male  frog  taken  in  the  breeding  season 
be  stimulated  lightly  with  the  finger  after  the  animal  has  been  beheaded,  the 
finger  will  be  clasped  firmly  by  the  fore  legs  (clasping  reflex).  Ordinarily  this 
reflex  never  fails,  but  if  a  drop  of  acetic  acid  be  applied  to  the  animal  at  the 
same  time  it  very  often  fails.  (3)  If  a  strong  solution  of  common  salt  be 
injected  under  the  dorsal  skin  of  a  frog,  all  reflexes  cease.  The  limbs  hang 
perfectly  limp  and  are  not  drawn  up  even  when  vigorously  scraped  with  a  knife. 
This  condition  lasts  for  some  minutes  and  then  the  reflexes  gradually  return 
(Bethe). 

lieidenhain  and  Bubnoff's  observations  on  morphinized  dogs  furnish  us  fur- 
ther examples  of  inhibitory  processes  in  the  central  nervous  system.  It  is  well 
known  that  muscular  contractions  may  be  induced  by  artificial  stimulation  of 
certain  areas  of  the  cerebral  cortex  (of  which  more  in  Chapter  XXIV).  Such 
contractions  in  morphinized  dogs  are  long  drawn  out,  disappearing  but  gradu- 
all.y  when  the  stimulation  ceases.  But  if,  while  the  after-eifect  is  still  on,  the 
skin  be  stroked  lightly  or  some  other  sensory  stimulus  be  applied,  the  contracted 
muscle  immediately  relaxes;  moreover,  the  same  resuh  is  obtained  if  the  same 
area  of  the  cortex  be  given  another,  this  time   a  weak  or  transitory  stimulus. 


REFLEX   PROCESSES  579 

The  conclusion  is,  that  when  the  cerebral  cortex,  or,  more  correctly,  the  nerve 
cells  of  the  spinal  cord  are  active,  stimulation  of  the  cortex,  imder  certain  cir- 
cumstances, has  an  inhibitory  effect  on  such  activity. 

The  present  status  of  our  information  on  this  subject  may  therefore  be 
summarized  as  follows :  reflex  processes  may  under  certain  circumstances  he 
retarded  or  entirely  stopped  by  stimulation  of  different  portions  of  the  brain- 
stem, of  the  cerebrum  itself,  or  of  afferent  nerves  in  general. 

So  much  is  fact,  but  whether  the  facts  are  to  be  explained  by  postulating 
special  inhibitory  centers  or  in  the  manner  conceived  of  by  Goltz  must  remain 
an  open  question.  It  would  appear,  however,  as  Goltz  observes,  to  require  an 
absolutely  overwhelming  numl^er  of  inhibitory  centers  on  the  former  hypothe- 
sis, to  account  for  all  the  reflex  inhiljitions  with  which  we  are  acquainted. 

But,  as  Biedermann  remarks,  it  is  also  possible  to  explain  the  phenomena 
of  inhibition  in  the  central  nervous  system  on  the  basis  of  special  afferent 
inhibitory  nerves.  If  a  center  momentarily  stimulated  were  to  be  acted  upon 
by  a  nerve  of  this  kind  its  activity  would  be  interrupted  or  diminished — 
i.  e.,  would  be  inhibited.  Biedermann  points  to  the  automatic  regulation  of 
respiration  (cf.  page  328)  and  to  certain  locomotor  reflexes  (cf.  page  587) 
in  the  posterior  extremities  as  examples  of  such  inhibition.  This  inhibition 
of  nerve  cells  in  the  central  system  would  be  entirely  analogous  to  those 
inhibitions  induced  independently  of  the  central  system — e.  g..  on  the  heart 
by  stimulation  of  the  cut  vagus  or  on  the  intestine  by  stimulation  of  the 
cut  splanclmic. 

D.    AUGMENTATION   OF   REFLEXES 

But  the  effect  of  stimulating  two  intersecting  pathways  is  not  always  an 
inhibition;  it  may  be  an  augmentation  of  the  response.  A  stimulus  in  itself 
subminimal  applied  to  the  motor  cortex  (rabbit)  becomes  effective  if  some 
appropriate  reflex  stimulus,  likewise  subminimal,  be  applied  at  the  same  time. 
This  augmentation  of  the  effect  of  one  stimulus  by  the  excitation  of  a  different 
pathway  is  seen  when,  after  removal  of  the  gray  cortex,  the  corona  radiata  is 
stimulated  directly.  The  two  excitations  need  not  be  simultaneous,  the  reen- 
forcement  occurs  just  the  same  if  the  second  stimulus  be  applied  some  tenths 
of  a  second  after  the  end  of  the  first. 

Exner,  who  has  made  a  special  study  of  this  phenomenon,  calls  it  facilita- 
tion ^  (Bahnung)  and  ascribes  to  it  very  great  significance  in  the  functions  of 
the  central  nervous  system. 

Exner  regards  the  case  of  two  central  nuclei  (e.  g.,  the  bilateral  respiratory 
center)  so  closely  connected  that  excitation  of  one  always  or  usually  occurs 
synchronously  with  excitation  of  the  other,  as  a  special  form  of  facilitation. 
When  the  two  are  connected  by  commissural  fibers,  charging  the  one  produces 
a  change  in  the  other  which  renders  it  more  and  more  liable  to  discharge. 

Just  as  self-culture  often  amounts  to  the  suppression  of  unpleasant  or  unde- 
sirable reflexes,  so  its  aim  often  is  to  establish  reflexes  of  a  pleasing  or  desirable 
character,  and  in  this  the  reenforcement  of  one  nerv^ous  pathway  by  another  is  of 
great  service. 

*  Sherrington's  term. 


580      PHYSIOLOGY   OF   THE  NERVE  CELL  AND  THE  SPLNAL  CORD 

E.    REFLEX  RESPONSES  TO   DIFFERENT  STIMULI 

The  kind  of  stimulus  employed  has  much  to  do  with  the  appearance  of 
reflexes.  Not  only  the  end  organs  of  the  nerves  of  special  sense,  but  also 
the  nerves  of  the  internal  organs  (cf,  pages  264,  270)  are  adapted  to  receive 
stimuli  of  certain  special  kinds. 

Since  the  researches  of  Marshall  Hall,  we  have  known  that  in  general  a 
reflex  is  more  easily  discharged  by  stimulation  of  the  peripheral  end  organ 
than  by  stimulation  of  the  corresponding  afferent  nerve  trunk.  The  cause 
of  this  difference  probably  is,  that  peripheral  end  organs  just  because  they 
are  adapted  to  receive  stimuli  of  a  special  kind  react  to  a  stimulus  of  a  definite 
intensity  more  powerfully  than  does  the  nerve  trunk.  For  this  reason  arti- 
ficial stimulation  of  an  afferent  nerve  trunk  never  gives  a  complete  repro- 
duction of  the  reflex  functional  capacity  of  the  nervous  system. 

We  are  compelled  for  want  of  space  to  pass  over  the  observations  which  have 
been  made  with  regard  to  the  different  effects  of  mechanical,  chemical,  thermal 
and  electrical  stimulation  of  the  same  efferent  nerves. 

§6.    AUTOMATIC   EXCITATION 

It  is  impossible  at  present  to  give  an  accurate  estimate  of  the  importance 
of  automatic  excitation,  either  in  the  central  nervous  system  or  in  peripheral 
organs.  The  ease  with  which  reflex  effects  can  be  ascertained  has  probably 
been  the  occasion  of  some  neglect  of  this  question. 

That  this  form  of  excitation  is  extremely  important,  however,  requires  no 
demonstration.  By  special  effort  a  person  can  hold  his  breath,  say,  anywhere 
from  thirty  seconds  to  several  minutes;  but  he  cannot,  even  with  the  utmost 
power  of  his  will,  voluntarily  stop  respiration  altogether.  This  overpowering 
excitation  of  the  respiratory  center  is  the  work  of  accumulated  decomposition 
products  in  the  blood  or  lymph.  We  have  seen  that  the  breath  volume  is 
increased  by  muscular  work.  This  again  is  due  primarily  to  the  stimulating 
effect  of  the  decomposition  products  on  the  respiratory  center,  although  the 
stimulation  of  afferent  nerve  fil)ers  may  play  some  part  also. 

The  attendant  effects  of  asphyxiation  upon  the  circulatory  system  and 
the  skeletal  muscles  are  a  witness  of  how  other  centers  in  the  brain  and  spinal 
cord  may  be  thrown  into  a  state  of  extreme  activity  by  decomposition  products 
present  in  excess. 

Since  we  have  good  reasons  for  thinking  that  the  respiratory  center  is 
stimulated  normally  by  products  of  metabolism,  albeit  its  activity  is  often 
regulated  by  reflexes,  we  may  suppose  that  automatic  excitation  plays  a  con- 
siderable part  in  the  tonic  stimulation  of  other  nerve  centers,  and  that  in 
general  this  is  the  inciting  agency  behind  the  coarser  functions  of  many 
organs,  whereas  their  finer  adjustment  to  the  momentary  needs  is  accomplished 
through  the  various  reflexes  which  play  upon  the  corresponding  centers. 


TONUS  581 

§  7.    TONUS 

By  tonus  we  mean  in  general  a  state  of  continuous  excitation  observable 
in  many  organs,  the  intensity  of  which  may  vary  a  great  deal  according  to 
circumstances.  Recent  contributions  to  the  subject  of  internal  secretion  (cf. 
page  356)  have  resulted  in  showing  that  tonus  is  very  often  caused  by  a 
direct  stimulating  influence  of  substances  formed  in  the  body  upon  the 
peripheral  organs  or  upon  peripheral  or  central  nerve  cells. 

A  very  interesting  example  of  tonus,  which  is  not  dependent  upon  the  central 
nervous  system,  is  furnished  by  the  observation  of  Goltz  and  Ewald  that  a  dog 
gradually  recovers  his  vascular  tonus  after  extirpation  of  a  large  part  of  the 
spinal  cord  (cf.  page  583). 

The  importance  of  direct  excitation  of  peripheral  organs  or  nerve  cells 
for  the  tonus  of  the  diiferent  organs  cannot  be  justly  estimated  at  present, 
for  the  simple  reason  that  our  information  on  the  subject  is  quite  too  limited. 
Nevertheless  we  know  that  many  organs  are  kept  in  a  state  of  tonic  excitation 
through  their  eiferent  nerves,  and  this  is  evidence  that  the  corresponding 
centers  in  the  brain  and  spinal  cord  are  themselves  tonically  stimulated.  The 
cardiac  vagus  and  the  vasoconstrictor  centers  are  notably  of  this  class.  Know- 
ing that  both  these  centers  may  be  stimulated  either  directly  as  in  asphyxiation, 
or  reflexly  by  afferent  nerves,  we  are  driven  to  suppose  that  their  tonus  is  of 
mixed  origin.  Whether  the  automatic  or  the  reflex  factor  is  the  more  im- 
portant we  cannot  decide  at  present. 

Cross-striated  muscles,  particularly  the  sphincters  (sphincters  ani  and 
vesica?),  are  usually  in  a  state  of  tonic  contraction  (cf.  pages  299,  393). 

It  has  been  no  simple  matter  to  demonstrate  tonus  in  cross-striated  muscles. 
The  observation  made  in  amputations  that  on  cutting  through  a  muscle  the 
cut  ends  draw  asunder  leaving  a  gaping  wound  has  no  bearing  on  the  ques- 
tion; for  this  merely  means  that  the  distance  between  the  points  of  origin 
and  insertion  of  a  limb  muscle  is  greater  than  the  natural  length  of  the  muscle 
when  it  is  not  loaded — that  is  to  say,  a  muscle  completely  at  rest  is  stretched 
somewhat  and  when  it  is  cut,  must,  of  course,  gape  open. 

The  following  observation,  however,  makes  it  clear  that  skeletal  muscles 
are  in  a  state  of  tonus.  If  a  decapitated  frog  be  vertically  suspended  with  the 
hind  legs  do^^-nward  and  one,  say  the  right,  sciatic  nerve  be  cut,  the  leg  of 
the  same  side  will  hang  down  more  limply  than  the  other.  This  difference 
can  only  be  due  to  the  fact  that  the  left  leg  is  still  under  the  influence  of  the 
central  nervous  system   ( Brondgeest ) . 

This  form  of  tonus  appears  to  be  of  reflex  origin,  for  when  the  afferent 
spinal  roots  of  the  frog  are  cut  the  gastrocnemius  of  the  same  side  relaxes 
somewhat  (Cyon  and  Steinmann).  Some  muscles,  however,  do  not  elongate 
when  their  efferent  nerves  are  cut ;  which  means  that  some  muscles  are  not 
always  tonically  stimulated  to  the  same  extent  as  some  others. 

Muscular  tonus  may  be,  to  a  certain  extent,  of  peripheral  origin  also.  This 
conclusion  is  drawn  from  the  experiments  by  ^fcade-Smith  cited  on  page  402, 
showing  that  heat  is  formed  in  a  resting  mammalian  muscle  even  when  physio- 
logical connection  with  the  nervous  system  has  been  interrupted  by  ligating 
the  nerve. 


582       PHYSIOElJiGY   OF  THE    NERVE   CELL   AND  THE   SPLNAL  CORD 


§8.    CENTRAL   FUNCTIONS   OF   PERIPHERAL   NERVE    CELLS 

In  discussing  the  innervation  of  the  heart,  digestive  organs,  ureter,  etc., 
we  have  had  occasion  to  mention  the  ganglion  cells  embedded  in  their  muscu- 
latures. According  to  some  authors,  as  we  have  seen,  it  is  to  these  ganglion 
cells  that  the  rhythmical  contractions  of  these  respective  organs  are  due. 
Others  ascribe  to  the  muscles  themselves  an  automatic  property  in  virtue  of 
which  they  are  stimulated  directly  by  the  products  of  metabolism  or  by  the 
normal  variations  in  pressure. 

We  have  no  data  as  yet,  except  perhaps  in  the  case  of  the  intestine  (cf. 
page  288),  which  will  enable  us  to  reach  a  final  decision  as  to  the  significance 
of  these  ganglion  cells.  For  this  reason  we  shall  limit  the  present  discussion 
to  nerve  cells  in  the  sympathetic  ganglia,  in  the  spinal  ganglia,  and  the 
corresponding  ganglia  of  the  cranial  nerves. 

The  first  question  to  engage  our  attention  is  whether  the  nerve  fibers  which 
pass  through  the  sympathetic  ganglia  actually  form  connections  with  the  nerve 
cells  contained  in  them. 

Langley  has  shown  that  nicotine  in  not  over-large  doses  stops  the  propa- 
gation of  impulses  through  the  s}-mpathetic  ganglion  cells,  while  it  leaves 
the  nerve  fibers  and  the  peripheral  nerve  endings  quite  untouched;  and  he 
has  made  extensive  use  of  this  fact  in  answering  the  question  before  us.  It  is 
sufficient  for  the  purpose  merely  to  paint  the  ganglion  with  a  solution  of 
nicotine.  Then  if  stimulation  of  the  nerve  central  to  the  ganglion  has  the 
same  effect  as  before  application  of  the  poison  the  nerve  plainly  does  not 
enter  into  connection  with  the  contained  nerve  cells.  But  if  the  effect  of 
stimulation  is  nullified  by  the  poison,  we  have  evidence  that  the  nerve  cells 
are  intercalated  in  the  conducting  pathway. 

In  this  way  Langley  has  found  that  every  efferent  nerve  fiber  or  collateral 
traversing  the  s3-mpathetic  pathways  is  connected  with  one  peripheral  ganglion 
cell,  and  one  only.  This  relay  station,  as  we  may  call  it,  on  the  way  from 
the  central  system  to  the  periphery  may  be  situated  either  in  a  chain  ganglion 
or  farther  along  toward  the  periphery,  even  as  far  as  the  vicinity  of  the 
peripheral  organ  itself.  The  vasoconstrictor  fibers,  the  secretory  sweat  fibers 
and  the  pilomotor  fibers  of  the  fore  paw  (cat),  all  of  which  connect  with  the 
first  thoracic  ganglion,  may  be  mentioned  as  examples  of  fibers  with  the  former 
mode  of  connection.  But  most  of  the  fibers  of  the  splanchnic  nerve  end  in 
the  ganglia  of  the  solar  plexus ;  and  the  nerves  of  the  external  genital  organs 
likewise  connect  with  nerve  cells  in  the  vicinity  of  the  organs  themselves 
(cf.  Chapter  XXV). 

It  is  no  easy  matter  to  decide  to  what  extent  the  nerve  cells  interpolated 
in  the  course  of  the  sympathetic  nerve  fibers  have  anything  more  than  a 
purely  nutritive  function.  A  priori  the  possibility  is  not  to  be  denied  that 
these  nerve  cells,  like  those  in  the  spinal  cord,  can  exercise  some  central 
functions,  and  certain  observations  which  Goltz  and  Ewald  have  made  on 
dogs  from  which  the  greater  part  of  the  spinal  cord  from  the  lower  cervical 
or  upper  thoracic  region  backward  had  been  removed,  lend  some  support  to 
this  view. 


CENTRAL   FLXCTIOXS   OF   PERIPHERAL   NERVE   CELLS  583 

Once  the  temporary  effects  of  the  operation  had  passed  off,  the  animals 
exhibited  the  following  phenomena.  All  the  cross-striated  muscles  of  the  pos- 
terior parts  degenerated  and  became  transformed  into  connective  tissue.  The 
external  sphincter  of  the  anus  alone  withstood  this  degeneration,  remaining  com- 
pletely functional  as  long  as  the  animal  lived.  The  digestive  processes  went  on 
in  regular  fashion,  just  as  in  the  normal  dog.  The  urine  was  normal  and  was 
normally  voided.  A  pregnant  female  gave  birth  to  five  whelps;  one  of  the 
young,  permitted  to  suckle,  grew  rapidly,  the  milk  being  perfectly  normal.  No 
secretion  of  sweat  could  be  clearly  made  out.  The  blood  vessels  of  the  posterior 
parts  recovered  their  tonus  and  remained  capable  of  reacting  to  a  local  con- 
strictor or  dilator  stimulus.  But  vascular  changes  in  distant  parts  of  the  skin 
could  not  be  induced  nor  could  alterations  in  the  intestinal  movements,  nor 
movements  of  the  sphincter  ani  nor  of  the  bladder  be  induced  by  stimulation 
of  the  hind  paws.  Shedding  of  the  hair  took  place  in  fairly  normal  fashion, 
but  terminated  earlier  on  the  fore  parts  which  were  still  in  connection  with  the 
central  system  than  on  the  hind  parts.  The  bones  took  on  a  peculiar  rotten 
character.  When  the  external  temperature  was  not  too  low,  the  heat  regulation 
was  carried  on  with  adequate  precision. 

It  should  be  mentioned  also  that  certain  poisons,  like  anagyrin  (from  Ana- 
gyris  f(jetida,  Gley),  as  well  as  certain  substances  obtainable  from  various  organs 
of  the  body  (extract  of  the  kidneys  and  adrenals — cf.  page  366),  can  pro- 
duce a  considerable  vasoconstriction  even  when  the  entire  nervous  system  is 
destroyed. 

These  and  otlier  analogous  phenomena  show  beyond  a  doubt  that  many 
functions  of  the  body  can  be  carried  on  independently  of  the  central  nervous 
system.  It  is  probable,  though  not  absolutely  proved,  that  they  take  place 
with  the  help  of  nerve  cells  present  in  the  peripheral  ganglia.  There  remains, 
of  course,  a  possibility  that  these  organs  act  often  quite  automatically. 

But  there  are  some  statements  in  the  literature  which  show  that  reflexes 
can  be  mediated  through  the  sijmpathetic  ganglia,  although  they  teach  us 
nothing  as  to  the  significance  which  these  reflexes  may  have  in  the  normal 
processes  of  the  body.  ' 

Roschansky  destroyed  the  spinal  cord  of  the  cat  below  the  cervical  region 
and  then  stimulated  the  central  end  of  the  splanchnic,  whereupon  the  blood 
pressure  rose  several  millimeters  of  Hg.  The  rise  in  pressure  did  not  appear 
when  the  sympathetic  chain  was  sectioned  between  the  ninth  and  tenth  ganglia; 
hence  it  was  reflexly  produced  through  sympathetic  ganglia  as  a  center. 

Langley  also  has  observed  reflexes  from  sympathetic  ganglia  and  has  given 
an  explanation  of  their  peculiar  mechanism.  After  section  of  all  the  branches 
connecting  the  inferior  mesenteric  ganglion  with  the  central  nervous  system 
(cf.  page  392),  contractions  of  the  bladder  and  of  the  external  anal  sphincter, 
vasoconstrictions  in  the  lower  parts  of  the  rectal  mucosa  and  in  the  mucosa  of 
the  uterus  on  the  opposite  side  can  be  obtained  (best  in  the  cat)  by  electrical  or 
mechanical  stimulation  of  the  central  end  of  one  hypogastric  nerve.  These  effects 
are  dependent  upon  nerve  cells  in  the  ganglion  itself,  for  they  fail  to  appear 
after  nicotine  is  applied  to  that  ganglion.  But  they  are  not  reflexes  in  the  usual 
sense  of  the  word,  for  by  means  of  the  degeneration  method  it  has  been  shown 
that  the  nerve  fibers  carr;s-ing  the  excitation  to  the  ganglion  have  their  trophic 
center  neither  in  the  ganglion  nor  peripheral  thereto,  nor  yet  in  the  spinal 
ganglion.     They  are  therefore  efferent  nerves. 


584       PHYSIOLOGY   OF  THE   NERVE  CELL   AND  THE  SPINAL   CORD 

Langley  would  explain  the  discharge  of  these  reflexes  (axon  reflexes)  in 
the  following  manner.  Nerve  fibers,  as  we  know,  convey  impulses  in  both  direc- 
tions; hence  an  impulse  starting  from  E  (Fig.  258)  is  transmitted  along  the 
efferent  fiber  toward  the  ganglion  (^4).     Here  a  collateral  is  given  off,  and  it  is 


Fig.  258. — Schema  of  an  axon  reflex  through  peripheral  ganglion  cells,  after  Langley. 

this  which  excites  the  nerve  fibers  springing  from  the  cells  of  the  ganglion  and 
proceeding  to  the  bladder  (B). 

.  In  a  similar  manner  Langley  explains  the  fact  that  stimulation  of  the  lum- 
bar sympathetic  causes  an  erection  of  hairs  on  regions  of  the  skin  innervated 
from  the  second,  third,  and  fourth  ganglia  higher  up  (cf.  Fig.  259),  and  similar 
phenomena  from  stimulation  of  the  sympatlietic  in  the  thorax. 

We  must  be  on  our  guard  in  this  matter  of  reflexes  through  peripheral  gan- 
glia lest  we  be  deceived  by  recurrent  fibers.  Suppose,  for  example,  A  (Fig.  260) 
to  be  a  ganglion,  2  and  3,  two  nerve  fibers  passing  from  it.    We  stimulate  2  and 


S'jj.y         Sp.g.  S^.y  Sjj.ff.         Sp.ff. 


Fig.  259. — Schema  of  a  reflex  through  peripheral  ganglion  cells,  after  Langley.  Sp.ij.,  sympa- 
thetic ganglia.  The  arrows  indicate  the  direction  in  which  the  excitation  aroused  by  stimula^ 
tion  of  a  lumbar  sympathetic  nerve  is  propagated. 

get  an  effect  in  the  organ  innervated  by  3.  Such  an  effect  may  be  a  reflex;  but 
it  would  be  obtained  also  if  some  of  the  nerve  fibers  in  2  were  to  turn  back  and 
enter  3,  as  indicated  by  the  dotted  line. 

The  chief  purpose  of  the  spinal  ganglia  consists  in  the  purely  nutritive 
influence  by  which  not  only  their  afferent  nerve  fibers,  but  the  posterior  roots 
and  their  prolongations  and  collaterals  in  the  spinal  cord  as  well,  are  main- 
tained in  normal  condition. 

Since  most  of  the  cells  of  the  spinal  ganglion  give  off  only  one  process  which 
sooner  or  later  splits  into  two  fibers  (the  T-shaped  fibers),  one  going  each  way, 
it  might  be  supposed  that  the  stimuli  coming  from  the  periphery  are  conveyed 
directly  to  the  spinal  cord  without  having  anything  to  do  with  the  gi,nglion  cell. 

This  question  can  be  tested  experimentally  by  determining  whether  a  stimu- 


CENTERS    IN   THE   SPINAL   CORD  585 

lus  is  delayed  by  passing  through  the  ganglion — i.  e.,  whether  a  reflex  response 
evoked  by  stimulation  of  an  afferent  nerve  will  take  place  any  earlier  when  the 
stimulus  is  applied  central  to  the  ganglion  than  when  applied  peripheral  thereto. 
Wundt,  in  fact,  found  a  delay  in  the  reflexes  from  the  spinal  ganglion  of  a  frog 
amounting  to  U.003  second.  Neither  Exner  nor  Moore  and  Reynolds,  however, 
were  able  to  demonstrate  such  a  delay.  Gad  and  Joseph  studied  the  jugular  gan- 
glion of  the  vagus,  which  is  the  homologue  of  the  spinal  ganglia,  and  used  as 
an  indicator  the  change  in  respiratory  movements  produced  by  stimulation.  It 
was  shown  that  as  a  mean  result  of  a  large  number  of  readings  the  reaction 
appeared  0.036  second  earlier  when  the  stimulus  was  applied  central  to  the  gan- 
glion than  when  applied  peripheral  to  it.  If  these  observations  are  confirmed 
we  shall  have  proof  that  in  this  ganglion,  at  least, 
every  impulse  traversing  a  fiber  afferent  to  the  gan- 
glion passes  through  a  nerve  cell. 

But  it  appears  to  be  unnecessary  that  the  im- 
pulse should  pass  through  the  body  of  the  ganglion 
cell.  In  the  crab,  Carcinus  mcenas,  Bethe  observed 
that  the  tonus  of  the  muscles  moving  the  antennte 
persisted  and  reflex  contractions  could  be  induced 
in  them  after  the  mantle  of  solid  ganglion  cells 
inclusive  of  their  nuclei  had  been  pared  off  the 
cerebral  ganglion  which  controls  these  muscles. 
In  this  case  the  excitation  had  been  propagated 
through    the    fibrillary-    reticulum    (cf.    page    560)  ^'^-  2^^- 

still  connected  with  the  nerve  fibers.     Here  we  have 

indubitable  evidence  of  the  importance  of  nerve  fibrils  as  conducting  elements 
in  the  nervous  system.  It  is  true  that  the  phenomenon  could  only  be  observed 
for  some  two  or  three  days  after  the  operation;  but  this  was  to  be  expected,  since 
we  know  that  nonnucleated  cell  fragments  cannot  live  indefinitely. 

Similar  phenomena  have  been  observed  in  the  spinal  ganglia  of  the  verte- 
brates. Langendorff  was  able  to  show  among  other  things  that  the  posterior 
roots  in  the  frog  give  an  action  current  when  stimulated  peripherally  to  the 
ganglion,  as  much  as  twenty-four  hours  after  the  heart  had  been  extirpated — 
i.  e.,  at  a  time  when  reflex  movements  had  long  since  ceased.  Shortly  after  this 
Steinach  demonstrated  for  the  same  animal  that  ganglia  which  had  lain  for 
forty-eight  hours  in  physiological  salt  solution  were  still  permeable  to  the  action 
current.  The  same  thing  took  place  if  a  ganglion  in  the  living  animal  were 
deprived  of  its  blood  supply  for  fourteen  days.  In  both  cases,  to  judge  by  micro- 
scopical appearances,  all  the  ganglion  cells  had  degenerated. 

From  all  this  it  ought  to  be  regarded  as  at  least  probable  that  an  impulse 
can  be  propagated  through  an  afferent  spinal  nerve  without  traversing  the  cell 
body  of  the  corresponding  ganglion  cell. 


§  9.    CENTERS   IN   THE    SPINAL   CORD 

The  spinal  cord  has  a  twofold  function:  it  acts  as  an  independent  central 
organ,  and  serves  as  a  groat  highway  to  connect  the  tributary  afferent  and 
efferent  pathways  with  the  brain. 


35 


586      PHYSIOLOGY   OF  THE  NERVE  CELL   AND  THE  SPINAL  CORD 


A.    CONTROL   OF  SKELETAL  MUSCLES 

The  independent  influence  of  the  spinal  cord  upon  movements  of  the 
skeletal  muscles  is  primarily  of  a  reflex  nature.  Under  suitable  conditions 
all  the  muscles  innervated  from  the  cord  can  be  thrown  into  action  by  stimu- 
lation of  a  single  afferent  nerve,  even  when  the  cord  is  isolated  from  the 
brain.  These  reflexes  are  in  general  well  coordinated,  and,  as  the  examples 
given  below  will  prove,  are  unquestionably  purpusive  in  character.  Be  it 
observed,  however,  that  these  phenomena  are  not  to  be  regarded  as  the  ex- 
pression of  a  "  conscious  "  activity  on  the  part  of  the  cord.  We  ourselves 
often  perform  much  more  complicated  movements  without  being  in  any  wise 
conscious  of  them. 

When  a  drop  of  sulphuric  acid  is  placed  on  the  leg  of  a  decapitated  frog-,  the 
animal  tries  to  remove  the  irritant  with  the  same  leg.  But  if  this  leg  be  held 
fast,  the  other  hind  leg  comes  to  the  help  of  the  first.  When  a  toe  is  pinched 
lightly  the  leg  is  drawn  up  against  the  abdomen.  But  when  the  drop  of  acid 
is  placed  near  the  anus,  both  legs  are  drawn  up  and  are  then  powerfully  extended. 

When  the  foot  sole  of  a  dog,  whose  spinal  cord  has  been  severed,  is  gently 
pressed  against  with  a  broad  surface  the  leg  makes  a  strong  extensor  movement. 
But  if  the  same  foot  sole  be  touched  with  a  sharp  point,  a  flexor  movement 
is  made,  as  if  the  animal  wished  to  withdraw  the  foot  from  a  painful  impulse 
(Sherrington). 

Observations  on  the  ability  of  the  spinal  cord,  isolated  from  the  brain  and 
medulla,  to  regulate  the  muscular  movements  necessary  for  locomotion  are  of 
particular  interest.  An  eel  deprived  of  its  head  immediately  after  the  operation 
swims  about  in  a  basin,  behaving  just  like  a  normal  fish.  It  does  not  merely 
writhe  about  on  the  bottom,  but  swims  up  and  down  and  about  through  the 
water  in  all  directions.  But  the  beheaded  eel  is  not  able  to  maintain  its  normal 
position  in  the  water  and  can  no  longer  swim  backward. 

Schrader  found  that  the  entire  medulla  of  the  frog  as  far  up  as  the  tip  of 
the  calamus  scriptorius  can  be  removed  without  destroying  the  locomotor  reac- 
tion to  reflex  stimuli.  The  movements  were  rather  awkward  but  were  nevertheless 
perfectly  coordinated.  Frog  tadpoles  and  very  young  frogs  exhibit  movements 
of  the  hinder  pajts  without  any  external  stimulus  (Babak). 

It  is  a  very  old  observation  that  decapitated  chickens  can  still  fly.  And 
ducks  with  the  spinal  cord  severed  between  the  fourth  and  fifth  cervical  verte- 
brae make  perfectly  regular  and  very  energetic  swimming  movements  with  their 
feet,  even  when  not  stimulated  externally;  they  make  steering  movements  with 
the  tail  and  flying  movements  with  the  wings,  etc.  But  when  set  down  on  a 
table  they  can  neither  maintain  their  equilibrium  nor  walk  (Tarchanotf). 

So  far  as  is  known  to  the  author  nobody  has  ever  yet  observed  movements  of 
locomotion,  either  spontaneously  or  reflexly  produced,  in  decapitated  mammals. 
We  conclude  that  in  the  lower  vertebrates  at  least  the  spinal  cord  is  of  itself  to 
a  greater  or  less  extent  able  to  regulate  the  muscular  contractions  of  locomotor 
movements. 

The  investigations  of  Sherrington,  Hering,  Jr.,  and  Biedermann  have  given 
us  some  very  important  information  as  to  the  mechanism  concerned  in  these 
reflexes. 

The  first  effect  of  a  brief,  weak  stimulation  of  the  web  of  a  frog's  foot  after 
the  spinal  cord  has  been  isolated,  is  always  a  flexor  movement  on  the  same  side 
or  an  extensor  movement  on  the  other  side,  in  case  the  flexor  movement  is  pre- 


CENTERS   IN  THE   SPINAL  CORD  587 

vented  (cf.  page  576).  Likewise,  one  finds  in  pigeons  with  the  spinal  cord 
cut  that  every  stimulus  applied  to  a  toe  causes  a  reflex  impulse  to  be  sent  to 
the  flexor  muscles  of  the  same  leg  and  at  the  same  time  a  reflex  impulse  to 
the  extensor  muscles  of  the  other  leg  (Singer).  Similar,  though  not  identical, 
results  have  been  obtained  in  the  dog  (Freusberg). 

Unquestionably  these  reflexes  are  components  in  the  mechanism  of  locomo- 
tion, and  hence  we  may  say  that  the  locomotor  movements  observed  in  decapi- 
tated animals  are  conditioned  primarily  upon  this  coincidence  of  flexor  and 
extensor  reflexes  from  the  cord.  In  dogs  and  monkeys  having  the  spinal  cord 
cut  at  the  posterior  end  of  the  thorax.  Heger  has  recently  observed  fairly 
well  coordinated  movements  of  the  hind  parts.  The  animals  were  even  able 
to  walk  and  run  with  the  help  of  the  hind  legs,  although,  as  was  to  be 
expected,  not  with  the  same  precision  as  normal  animals. 

The  same  mechanism  is  probably  operative  also  in  the  uninjured  nervous 
system,  the  motor  impulse  given  out  by  the  brain  being  apportioned  auto- 
matically and  in  the  proper  order  to  the  different  motor  cells  down  the  cord. 

We  have  still  to  mention  the  tendon  reflexes.  When  a  person  crosses  one 
leg  over  the  other,  allowing  the  foot  to  hang  in  an  unrestrained  position,  then 
strikes  the  patellar  tendon  of  this  leg  a  sharp  blow,  the  extensor  cruris  muscle 
contracts  suddenly  giving  the  so-called  "knee  jerk."  Similar  contractions  are 
obtained  by  stimulation  of  other  tendons,  and  by  mechanical  stimulation  of  the 
joints  and  of  the  periosteum.  They  are  wanting  in  tabes — i.  e.,  they  are  wanting 
when  certain  afferent  conducting  pathways  are  disabled. 

In  view  of  this  latter  circumstance,  it  is  natural  to  suppose,  as  Erb  first 
pointed  out,  that  these  contractions  are  pure  reflexes.  But  various  considera- 
tions, especially  the  short  latent  period  of  the  knee  jerk,  made  that  explanation 
very  difficult,  and  Westphal,  the  discoverer  of  such  phenomena,  now  takes  the 
view  that  the  contractions  are  induced  by  the  direct  effect  of  the  mechanical 
shock  upon  the  muscles,  but  only  in  case  the  muscle  has  its  normal  tonus.  This 
condition,  as  we  know  (cf.  page  581),  depends  upon  a  normal  state  of  the 
afferent  nerves. 

Evidence  that  the  tendon  reflexes  are  dependent  upon  the  central  nervous 
system  is  found  in  the  fact  that  their  intensity  varies  directly  with  the  general 
functional  condition  of  the  central  system.  Thus  they  are  weakened  by  fatigue, 
hunger,  and  the  like,  but  are  augmented  by  rest,  food,  etc.  (Lombard). 

B.    INFLUENCE   OF   THE   SPINAL   CORD   ON  THE   VEGETATIVE   FUNCTIONS 

The  above-mentioned  observations  on  the  behavior  of  the  dog  with  a  short- 
ened spinal  cord  (page  583)  call  for  some  revision  of  our  views  as  to  the 
influence  of  the  cord  on  the  vegetative  functions ;  for  several  of  these  functions 
which  from  previous  observations  had  been  regarded  as  totally  dependent  upon 
the  spinal  cord  were  there  seen  to  be  dependent  upon  peripheral  nervous 
mechanisms.  The  urinary  and  sexual  organs,  for  example,  as  well  as  the 
rectum,  remained  perfectly  functional,  even  when  the  entire  lower  part  of 
the  spinal  cord  was  destroyed.  But  these  parts  are  controlled  to  some  extent 
also  by  centers  in  the  central  system,  as  can  be  shown  conclusively  by  stimu- 
lation of  the  appropriate  nerves.  These  centers  are  located  mainly  in  the 
lumbar  region  of  the  cord. 


588      PHYSIOLOGY   OF  THE   NERVE  CELL   AND  THE   SPINAL  CORD 

Goltz  has  made  the  following  observations  on  dogs  with  the  spinal  cord  cut 
between  the  thoracic  and  lumbar  regions.  Erection  of  the  penis  was  induced 
by  mechanical  stimulation  either  of  the  penis  itself  or  of  the  hypogastrium,  by 
pressure  upon  the  bladder,  and  by  excessive  fullness  of  the  bladder  and  of  the 
rectum.  The  bladder  was  emptied  in  perfectly  normal  fashion  as  the  result  of 
mechanical  stimulation  of  the  anus.  Rhythmical  contractions  of  the  anal  sphinc- 
ter, which  could  be  inhibited  by  stimulating  the  sciatic,  were  induced  by  insert- 
ing a  finger  into  the  rectum.  Contractions  of  the  uterus  and  vagina  were  obtained 
by  stimulating  the  sciatic. 

In  the  cat  the  center  for  micturition  is  located  between  the  second  and 
fifth  lumbar  nerves;  that  for  the  anal  sphincter  between  the  sixth  and  seventh 
lumbar.  In  man  the  center  for  the  bladder  is  said  to  lie  at  the  extreme  end  of 
the  spinal  cord  near  the  points  where  the  third  and  fourth  sacral  nerves  make 
their  exit. 

The  spinal  cord  also  contains  centers  for  the  secretion  of  sweat.  When 
the  spinal  cord  of  a  cat  is  severed  below  the  medulla  and  the  animal  is  then 
asphyxiated,  sweat  appears  in  from  two  to  three  minutes.  The  same  is  true 
also  after  cutting  at  the  level  of  the  ninth  thoracic  vertebra. 

The  vasomotor  and  respiratory  nerve  centers  occurring  in  the  spinal  cord 
have  already  been  considered  at  pages  238  and  325  respectively. 

Finally,  mention  should  be  made  again  of  the  cUio-spinal  center  (page 
529)  discovered  by  Budge.  This  center  is  of  special  interest  because,  although 
situated  in  the  cord,  it  presides  over  an  organ  in  the  head. 

§  10.    CONDUCTING   PATHWAYS   IN   THE    SPINAL   CORD 

A.    ELECTRICAL  STIMULATION   OF  THE   CORD 

Before  we  take  up  the  subject  proper,  we  must  dispose  of  one  question 
which  has  been  very  actively  discussed  in  its  time,  namely,  whether  or  not 
the  efferent  fibers  in  the  cord  are  capable  of  being  stimulated  directly  by 
electricity.  All  authors  agree  that  muscular  contractions  can  be  produced 
abundantly  enough  by  electrical  stimulation  of  the  cord;  but  it  has  been 
claimed  by  some  that  these  contractions  either  were  caused  by  direct  stimu- 
lation of  the  root  fibers  or  that  they  were  reflexes  discharged  by  stimulation 
of  the  posterior  columns  and  of  the  afferent  fibers  contained  in  them. 

Biedermann,  however,  among  others,  has  shown  that  the  efferent  pathways 
can  actually  be  stimulated  directly.  He  proceeded  in  the  following  manner. 
The  spinal  cord  of  a  frog  was  first  split  by  a  frontal  section  into  dorsal  and 
ventral  halves.  Since  the  cord  had  also  been  cut  transversely  farther  up, 
there  was  found  in  it,  as  usual,  a  descending  demarcation  current  (cf.  page 
48)  which  increased  its  excitability  for  a  current  in  the  same  direction — 
i.  e.,  for  a  current  whose  cathode  coincided  with  that  of  the  demarcation 
current.  Xow  it  was  shown  that  the  ventral  half  of  the  cord  was  excitable 
at  its  upper  end  for  descending  induction  currents,  while  a  considerably 
stronger  current  was  necessary  to  evoke  a  muscular  contraction  from  a  point 
farther  down.  That  is,  the  current  already  traversing  the  cord  on  account 
of  the  injury  was  reenforced  to  a  sufficient  extent  by  a  weak  induction  shock 
applied  where  the  current  of  injury  was  stronger,  and  by  a  strong  induction 


CONDUCTING   PATHWAYS   IN  THE   SPINAL  CORD 


589 


E. 

-pfif 

-. 

m 

1 

\ 

f 

1^ 

1 

\ 

shock  applied  where  the  current  of  injury  was  weak.     This  relationship  would 
not  hold  if  the  stimulus  were  to  traverse  root  fihers  directly,  and  since  it  could 
not  have  come  by  way  of  the  posterior  columns  or  afferent  fibers,  the  conclu- 
sion is  that  the  stimulus  was  initiated  in  the  efferent 
fibers  of  t4ie  cord  itself.  ^■ 

It  might  be  objected  that  the  effect  in  this  ex- 
periment was  due  to  excitation  of  the  gray  matter. 
But  this  objection  is  met  by  the  circumstance  that  the 
gray  matter  left  in  the  anterior  half  showed  approxi- 
mately the  same  degree  of  excitability  at  whatever  level 
it  was  stimulated. 

Gotch  and  Horsley  have  found  by  stimulation  of 
the  long  efferent  paths  of  the  spinal  cord  that  the  rate 
of  propagation  in  the  cord  is  39.5  m.  per  second. 

B.    METHODS   OF   DETERMINING   THE   CONDUCT- 
ING  PATHWAYS   IN   THE   SPINAL   CORD 

We  have  several  fundamentally  different  meth- 
ods of  determining  the  location  of  the  conduction 
pathways,  which  supplement  each  other  very  nicely. 
They  may  be  summarized  under  the  following  three 
heads : 

A.  Anatomical  Methods. — To  these  belong:  1. 
The  method  first  employed  by  Stilling  of  making 
serial  microscopical  sections  of  the  cord  and  tracing 
out  the  course  of  the  separate  fibers  from  one  section 
to  another.  2.  A  method  first  used  extensively  by 
Flechsig,  which  is  based  upon  the  fact  that  tracts 
having  the  same  function  acquire  their  medullary 
substance  at  about  the  same  time  in  the  embryonic 
or  post-embryonic  development.  Fig.  261  represents 
schematically  the  organization  of  the  cord  as  made 
out  by  this  method. 

B.  Pathologiral-anatoniiral  and  Clinical  Methods. 
— Here  belong:  3.  Observations  on  patients  suffering 
from  diseases  of  the  central  nervous  system,  and  com- 
parison of  these  observations  with  the  post-mortem 
findings.  The  observations  fall  into  two  divisions, 
namely : 

(fl)  Where  the  patient  lives  long  enough  for 
Wallerian  degeneration  to  develop  in  the  tracts  of  the 
cord.  Post-mortem  examination  then  gives  us  the 
same  sort  of  information  as  the  method  based  upon 
development  of  the  medullary  substance.  In  Fig. 
262  is  represented  the  degeneration  in  the  long  motor 
lesion  of  the  cerebral  cortex. 

(&)  Even  if  the  patient  does  not  live  long  enough 
far  advanced,  comparison  of  the  symptoms  with  the  les 


Fig.  261. — Cross -sections 
at  different  levels  of  the 
spinal  cord,  after  Flech- 
sig. /,  at  the  point  of 
exit  of  the  sixth  cervical 
nerve;  //,  at  the  point  of 
exit  of  the  third  thoracic 
nerve;  ///,  level  of  the 
sixth  thoracic;  IV,  of  the 
twelfth  thoracic;  V,  of 
the  fourth  lumbar.  /).<;, 
crossed  pyramiilal  tract ; 
pi',  direct  pyranndal 
tract ;  ks,  lateral  cerebel- 
lar tract;  y,  posterior 
column  of  Goll. 

tracts  following  upon 

for  degeneration  to  be 
ions  found  in  the  cord 


590      PHYSIOLOGY   OF  THE    NERVE   CELL   AND  THE  SPLNAL  CORD 

permit  iis  to  say  on  which  side  of  the  cord  the  pathway  governing  certain 
movements  runs. 

C.  Purely  Physiological  Methods. — Among  these   are   to   be  mentioned: 
4.  Partial  cross  section  of  the  cord  in  live  animals.     The  resulting  functional 


JMlf 


Fig.  262.  '  Fig.  263. 

Fig.   262. Secondary  descending  degeneration  following  a  primary  lesion  of  the  left   cerebral 

hemisphere,  after  Erb. 

Fig.  263. — Arrangement  of  the  experiment  for  study  of  the  conducting  pathways  in  the  spinal 
cord  of  the  monkey  by  the  electrical  method,  after  Gotch  and  Horsley.  The  cord  is  cut  in 
the  middle  of  the  thoracic  region  and  in  the  upper  lumbar  region.  The  stimulus  is  applied  at 
the  upper  section  (£)  and  connection  with  the  galvanometer  (C/)  is  made  from  the  lower  section. 


CONDUCTING  PATHWAYS   IN  THE  SPINAL   CORD 


591 


derangements  give  us  information  similar  in  kind  to  that  obtained  from 
clinical  observations  (3,  b).  The  resulting  degenerations  can  also  be  used 
in  the  same  way  as  corresponding  observations  on  man  (3,  a).  Finally,  after 
partial  section  of  the  cord,  one  can  tell  by  stimulation  of  higher  parts — e.  g., 
the  cerebral  cortex,  whether  certain  efferent  pathways  have  been  interrupted 
or  not.  5.  The  Electrical  Method,  which  has  been  worked  out  especially  by 
Gotch  and  Horsley.  This  is  based  upon  the  fact  that  action  currents  occur 
in  the  central  nervous  system  as  well  as  in  peripheral  nerve  trunks.  Attention 
is  paid  to  the  strength  of  the  action  currents  produced  by  stimulation  of 
different  parts  after  making  various  partial  sections  (cf.  Fig.  263).  6.  Gud- 
den's  Method  (cf.  page  568). 


C.    ANATOMICAL   DATA   CONCERNING   THE   CONDUCTING   PATHWAYS 

OF   THE   CORD 

We  use  the  term  afferent  pathtvays  here  and  in  what  follows  to  designate 
all  those  tracts  which  convey  impulses  from  lower  to  higher  nerve  centers, 
and  the  term  efferent  pathtvays  to  designate  all  those  which  convey  impulses 


A  B 

Fig.  264. — A,  section  through  the  cervical,  and  B,  through  the  lumbar  parts  of  the  cord,  after 
Edinger.  The  approximate  limits  of  the  various  tracts  are  indicated,  la,  crossed  pyramidal 
tracts;  1,  direct  pyramidal  tracts;  2,  anterior  ground  bundle;  3,  ventrolateral  cerebellar  tract 
(or  Gowers's  tract) ;  4,  dorsolateral  cerebellar  tract  (or  Flechsig's  tract) ;  5,  lateral  boundary 
zone  of  the  gray  substance;  6,  Burdach's  column ;  7,  Goll's  column ;  c*,  zone  of  entrance  of  pos- 
terior root  fibers;  9,  ventral  portion  of  the  posterior  column;  10,  border  zone. 


from  higher  to  lower  nerve  centers.  To  the  former  we  shall  add  also  all  the 
paths  which  carry  over  an  afferent  impulse  to  an  efferent  pathway. 

As  we  have  already  seen,  stimulation  of  a  single  afferent  nerve  may  excite 
refiexly  a  great  many  efferent  nerves  even  when  the  spinal  cord  is  isolated 
from  the  brain.  The  connection  of  the  afferent  nerves  with  the  motor  cells 
of  efferent  nerves  must  therefore  be  very  complex.  This  leads  us  to  assume 
that  the  afferent  pathways  in  the  spinal  cord  are  very  much  more  complicated 
than  the  efferent — an  assumption  which  is  sufficiently  borne  out  by  experiment. 

The  nerve  fibers  springing  from  the  nerve  cells  of  the  spinal  ganglia  and 
entering  the  spinal  cord  by  the  posterior  roots  for  the  most  part  divide  imme- 
diately after  their  entrance  into  the  cord,  into  an  ascending  and  a   (.short) 


592       PHYSIOLOGY   OF   THE   NERVE  CELL   AND  THE   SPINAL  CORD 


descending   branch — all  of  which  taken  together  make  up  the  bulk  of  the 

posterior  columns  of  the  cord. 

Some  of  the  fibers  of  the  posterior  roots  pass  into  the  gray  substance  of 

the  spinal  cord,  and  either,  like  their  collaterals,  unite  with  cells  in  the  an- 
terior and  posterior  horns  and  in 
the  substantia  gelatinosa,  or  unite 
with  the  cells  of  Clark's  column. 
The  latter  fibers,  however,  are  re- 
garded by  some  authors  merely 
as  collaterals.  Other  fibers  of 
these  roots  ascend  throughout 
the  whole  length  of  the  spinal 
cord  without  passing  to  the  op- 
posite side.  They  shift  their 
position  somewhat  in  that  they 
come  to  lie  nearer  the  mid  line 
the  higher  they  go,  so  that  the 
median  part  of  the  posterior  col- 
umns in  the  higher  segments  of 
the  cord  contains  the  prolonga- 
tions of  the  posterior  lumbosacral 
and  lower  thoracic  roots,  while 
the  higher  thoracic  root  fibers  lie 
outside  these.  At  the  cephalic 
end  of  the  cord  these  different 
divisions  become  separated  exter- 
nally by  a  strong  connective-tis- 
sue septum ;  the  median  division 
is  then  known  as  Goll's  column, 
the  lateral  as  Burdach's  column. 
The  fibers  of  Goll's  column  end 
in  the  gracilar  nucleus,  those  of 
Burdach's  column  in  the  cuneate 
nucleus.  There  is  authority  also 
for  the  statement  that  fibers  from 
both  columns  pass  directly  to  the 
cerebellum  and  end  there. 

The  secondary  afferent  tracts 
arise  from  the  nerve  cells  with 
which  the  fibers  of  the  posterior 
roots  and  their  collaterals  unite. 
The  following  are  the  better 
known  among  them  :  ( 1 )  Fibers 
from  the  gracilar  and  cuneate 
nuclei  pass  to  the  opposite  side  of 
the  medulla  and  continiie  forward 
in  the  fiUet.  (2)  Long  fibers  arising  from  cells  of  the  posterior  horn  traverse 
the  anterior  and  lateral  columns  of  the  same  and  of  the  opposite  sides  as  the 


Tig.  265. — Diagram  of  the  course  of  the  sensory  con- 
ducting pathways  after  Striimpel.  A,  entrance 
of  the  posterior  sensory  root  fibers  in  tlie  lum- 
bar cord;  gi,  spinal  ganglion;  rp,  posterior  root. 


CONDUCTING   PATHWAYS   IN   THE  SPINAL  CORD  593 

ventrolateral  cerehellar  tract  or  Gowers's  bundle;  in  front  of  the  pons  they 
bend  around  and  enter  the  cerebellum  by  way  of  the  superior  peduncle.  (3) 
Fibers  which  originate  in  the  cells  of  Clarke's .  column  pass  forward  to  the 
cerebellum.  Some  of  these  are  scattered  among  the  fibers  of  other  tracts,  but 
part  of  them  also  form  a  compact  bundle  (Flechsig's  bundle),  which, .from  its 
position  in  the  cord,  is  described  as  the  dorsolateral  cerebellar  tract.  All  these 
fibers  pass  through  the  inferior  peduncle  and  can  be  traced  to  the  superior 
vermis  of  the  cerel)ellum.  . 

The  anterior  roots  are  for  the  most  part  connected  with  nerve  cells  of  the 
anterior  horn  on  the  same  side;  a  few  anterior  root  fibers  spring  from  cells 
of  the  opposite  side. 

Secondary  efferent  pathways  descend  from  the  cerebral  cortex  to  these 
cells,  forming  the  so-called  pyramidal  tracts  (or  the  cortico-spinal  tract). 
Their  mode  of  connection  with  the  anterior  horn  cells,  however,  has  not  been 
definitely  made  out.  In  the  medulla  most  of  these  fibers  cross  (pyramidal 
crossing)  and  continue  downward  in  what  is  known  as  the  lateral  or  crossed 
pyramidal  tract,  which  gives  off  collaterals  to  the  motor  cells  of  the  same  side. 
A  varying  numljer  of  pyramidal  fibers,  however,  do  not  take  part  in  this 
crossing  of  the  pyramid,  but  descend  in  the  anterior  or  direct  pyramidal 
tract,  also  to  a  less  extent  in  the  lateral  pyramidal  tract.  During  their  down- 
ward course  these  direct  tracts  are  all  the  while  giving  off  fibers,  most  of  them 
collaterals,  to  the  opposite  side  of  the  spinal  cord,  so  that  the  crossing  of  the 
cortico-spinal  fibers  becomes  more  and  more  complete  the  farther  we  proceed 
caudalward.  The  result  is  that  the  anterior  pyramidal  tracts  can  be  followed 
only  to  al)out  the  middle  of  the  thoracic  cord,  or,  exceptionally,  to  the  lumbar 
cord.  But  fibers  of  the  direct  pyramidal  tract  are  also  connected  with  anterior 
horn  cells  of  the  same  side. 

Ventral  to  the  crossed  pyramidal  tract  there  runs  another  bundle  of  long 
fibers,  namely,  the  rubrospinal  tract  or  MonaTcow's  bundle,  arising  in  the  red 
nucleus  of  the  tegmentum  and  sending  fibers  to  the  opposite  side  of  the  cord. 
Other  long-fibered  efferent  tracts  are  the  tectospinal  and  the  vestibulospinal. 
The  former  arises  in  the  roof  of  the  mesencephalon  and  runs,  as  a  crossed 
tract  in  the  anterior  column  of  the  spinal  cord,  and  as  an  uncrossed  tract  in 
the  lateral  columns.  The  latter  springs  from  Deiter's  nucleus  in  the  medulla 
oblongata,  where  some  of  the  vestibular  nerve  fibers  have  a  terminal  station, 
and  is  found  in  the  anterior  columns  of  the  cord. 

The  tracts  thus  far  descril)ed — GolVs  and  Burdacli's  columns,  the  dorso- 
and  ventrolateral  cerebellar  tracts,  the  pyramidal  tracts  and  the  efferent  tracts 
just  mentioned — all  represent  connecting  pathways  between  distant  portions 
of  the  central  nervous  system.  Flateau  has  drawn  attention  to  the  fact  that 
they  tend  to  occupy  the  border  zone  of  the  white  columns  in  the  cord;  that 
Avhilo  they  may  at  certain  levels  be  displaced  from  this  zone,  they  always 
return  to  it  at  the  first  opportunity  and  thereafter  keep  their  position  until 
they  turn  into  the  gray  matter. 

The  inner  zones  of  the  white  columns  are  occupied  in  the  main  by  slwrf- 
fibered  tracts  connecting  different  levels  of  the  cord.  Some  of  these  tracts 
arise  from  widely  distributed  multipolar  cells  (column  cells),  which  send  axis 
cylinders  into  the  antero-lateral  column  of  the  same  or  of  the  opposite  side. 


594      PHYSIOLOGY   OF  THE  NERVE  CELL  AND  THE  SPINAL  CORD 

Truf!/(      •^'P      ^nee  ..^  Ankle 


Fig 


MuscI 


CONDUCTING  PATHWAYS   IN  THE  SPINAL  CORD  595 

Here  collaterals  are  given  off  which  again  betake  themselves  to  the  gray 
matter  and  there  end  in  terminal  arborizations  about  other  cells.  Other  fibers 
of  this  class  run  in  the  posterior  columns,  being  found  chiefly  in  the  most 
ventral  section. 

Still  other  cells,  whose  axis  cylinders  break  up  immediately  without  pass- 
ing to  any  well-defined  pathway,  serve  as  connecting  linls  between  different 
elements  at  the  same  level.  Such  cells  are  found  scattered  throughout  every 
cross  section,  but  are  particularly  abundant  in  the  vicinity  of  the  posterior 
horn. 

It  will  be  apparent  from  what  has  gone  before  that  the  antero-lateral  col- 
umns of  the  spinal  cord  are  the  most  important.  In  these  we  have,  besides 
the  particularly  prominent  crossed  and  direct  pyramidal  tracts:  the  dorso- 
and  ventrolateral  cerebellar  tracts,  which  are  among  the  most  important 
afferent  conducting  pathways  to  the  brain;  the  rubrospinal,  the  tectospinal, 
and  the  vestibulospinal  tracts:  and  finally,  the  most  important  commissural 
fibers  binding  together  the  different  levels  of  the  cord. 

D.  EXPERIMENTAL   AND   CLINICAL   OBSERVATIONS    ON   THE    CONDUCTING 
PATHWAYS   IN   THE   SPINAL   CORD 

The  question  which  first  confronts  us  in  experimental  and  clinical  investi- 
gations of  the  pathways  in  the  spinal  cord  is,  whether  or  not  these  pathways 
cross  in  the  cord  itself.  The  second  question  to  be  answered  is,  in  what 
columns  do  they  run. 

^^^len  we  consider  the  difficulties  with  which  investigation  of  this  subject 
is  beset — such,  for  example,  as  the  difficulty  in  animal  experiments  of  making 
just  the  cut  intended,  and  the  uncertainties  attending  the  observatitjn  of 
disturbances  to  sensibility  and  motility  resulting  from  the  operation — we  can 
understand  why  the  statements  of  different  authors  differ  greatly  as  to  the 
results  obtained.  Observations  on  human  patients  are  naturally  well  calcu- 
lated to  supplement  the  observations  on  animals ;  but  here  we  meet  with  the 
difficulty  that  the  lesions  occurring  as  the  result  of  disease  or  accident  are 
seldom  or  never  limited  so  exactly  as  to  give  us  wholly  unequivocal  results. 
The  following  summary  must  be  regarded  as  largely  provisional: 

1.  Efferent  Pathways. — When  a  hemisection  of  the  cord  is  made  in  a  dog, 
immediately  after  the  operation  the  muscles  of  the  same  .side,  whose  nerves  leave 
the  cord  below  the  section,  are  paralyzed,  while  the  muscles  of  the  opposite  side 
remain  entirely  functional.  The  hemisection  seems  thei*efore  to  have  severed  an 
important  pathway  of  the  homonymous  side. 

.  But  this  paralysis  is  not  final.  It  gradually  disappears  more  or  less  com- 
pletely, the  degree  of  recovery  as  well  as  the  extent  of  the  primary  paralysis 
depending  iipon  the  location  of  the  hemisection.  Thus  hemisection  in  the  cer- 
vical cord  produces  a  greater  disturbance  in  the  fore  paw  than  in  the  hind  paw. 
Recovery  is  made  in  both  extremities,  but  it  is  more  complete  in  the  posterior 
than  in  the  anterior.  The  disturbances  to  motility  in  the  jiosterior  extremity 
following  hemisection  of  the  thoracic  cord  last  longer  and  the  recovery  is  less 
perfect  than  after  hemisection  of  the  cervical  cord.  Tlie  more  distally  the  hemi- 
section is  located,  the  more  profound  and  the  more  persistent  are  the  motor  dis- 
turbances which  follow,  and  the  less  perfect  is  the  subsequent  recovery. 


596      PHYSIOLOGY   OF   THE   NERVE  CELL   AND  THE   SPINAL  CORD 

From  these  observations  we  may  conclude  that  in  the  dog  the  motor  path- 
ways follow  tracts  on  both  sides  of  the  cord,  but  that  the  tract  on  the  same  side 
as  the  muscles  to  which  it  conveys  impulses  is  the  more  important.  If  this  tract 
is  suppressed  by  hemisection,  the  one  on  the  opposite  side  takes  up  the  function. 
But  the  nearer  the  hemisection  lies  to  the  point  of  exit  of  any  given  nerve,  the 
more  completely  have  the  fibers  destined  for  that  nerve  already  crossed  from 
the  other  side  of  the  central  system  (see  page  593)  ;  consequently  the  more  pro- 
found is  the  disturbance. 

When  a  hemisection  is  made  in  the  thoracic  cord  of  a  dog,  and  the  resulting 
disturbances  have  disappeared,  a  hemisection  on  the  other  side  higher  up  or  a 
sagittal  section  in  the  mid  line  of  the  cord  will  produce  the  same  eifects  again ; 
in  either  ease  the  operation  has  broken  the  pathways  coming  from  the  heter- 
onymous side. 

But  motility  is  not  permanently  lost  even  after  a  second  hemisection  like 
that  just  described.  In  fact  after  three  alternating  sections  at  different  levels, 
some  motor  fibers  to  the  muscles  of  the  hind  leg  remain  uninterrupted  (Osawa). 
The  alternative  motor  efferent  pathways  therefore  must  be  very  numerous. 

Observations  on  the  motor  effects  of  half-destruction  of  the  spinal  cord  in 
man  may  be  summarized,  after  Kocher,  as  follows :  'Motor  paralysis  on  the 
same  side  appears  immediately  in  a  very  intense  form,  but,  as  a  rule,  it  abates 
in  the  course  of  a  few  days  or  weeks,  and  if  the  anterior  horn  nuclei  are  not 
too  extensively  destroyed,  it  is  so  far  recovered  from  that  only  a  slifi^ht  paresis 
remains.  The  deep  crossing  just  above  the  point  of  exit  of  the  nerves  to  tlie 
extremities  is  of  more  importance  for  the  leg  than  for  the  arm. 

To  judge  by  the  anatomical  facts,  the  motor  paths  destined  for  the  muscles 
of  a  given  extremity  run  in  the  crossed  pyramidal  tracts  and  Monakow's  bundle 
on  the  same  side  of  the  cord  and  in  the  direct  pyramidal  tract  of  the  opposite 
side.  In  accordance  with  this  we  find  it  stated  that  a  section  involving  all 
parts  of  the  cord  except  the  lateral  columns  produces  only  a  slight  reduction 
of  motility,  and  that  it  is  not  finally  abolished  by  section  of  the  lateral  columns 
alone;  in  fact,  the  motility  gradually  returns  and  becomes  fairly  complete 
again.  The  above-mentioned  observations  by  Osawa  show,  however,  that  there 
are  other  efferent  paths  from  the  brain  to  the  spinal  cord  than  these. 

We  have  the  following  statements  concerning  the  course  of  the  conducting 
pathways  for  the  vegetative  functions.  The  vasoconstrictor  nerves  run  in  both 
the  homonymous  and  heteronymous  paths,  the  former  appear  to  be  the  stronger. 
The  tracts  to  the  bladder  and  rectum  are  also  found  on  both  sides;  those  of 
either  side  being  sufficient  to  innervate  the  musculature  of  the  entire  bladder 
and  the  entire  rectum.  The  tract  on  either  side,  therefore,  can  be  injured  with- 
out any  interference  in  the  function  of  the  bladder  or  rectum.  Finally,  the 
sympathetic  fibers  to  the  eye  and  to  the  corresponding  half  of  the  face  descend 
the  whole  length  of  the  cervical  cord  on  the  same  side.  Paralysis  after  destruc- 
tion of  this  tract  appears  to  be  permanent,  although  it  may  decrease  gradually 
in  intensity  (Kocher). 

2.  The  Afferent  Pathways. — Of  these  the  tracts  for  motor  sensations  are 
the  best  known.  It  has  been  known  for  a  long  time  that  in  certain  diseases 
of  the  spinal  cord  in  man  the  sense  of  movement  is  lost  to  a  greater  or  less 
extent  without  any  other  loss  of  sensibility  (ataxia,  cf.  page  472).     Patho- 


CONDUCTING   PATHWAYS   IN   THE  SPINAL  CORD  597 

logical  anatomy  ha?  shoMii  that  the  seat  of  this  disease  is  in  the  posterior 
columns,  exclusive  of  their  ventral  sections.  Hence  we  can  say  that  the  tracts 
for  motor  sensations  in  part,  at  least,  traverse  the  posterior  columns.  These 
tracts  are  on  the  homonymous  side  of  the  cord,  substitution  of  the  other  side 
appearing  very  tardily  if  at  all. 

In  the  dog,  after  section  of  the  posterior  columns,  not  only  does  the  sensa- 
tion of  pain  persist,  but  likewise  the  coarser  sensations  of  touch  and  position  as 
well  as  a  crude  power  of  localization.  There  is  no  apparent  interference  with 
walking  nor  with  finer  isolated  movements  (Borchert). 

How  the  different  sensori/  impressions  received  hy  the  skin  are  propagated 
through  the  spinal  cord  is  a  much  more  difficult  question. 

The  original  doctrine  of  Brown-Sequard  that  these  sensations  traverse 
only  the  heteronymous  side  of  the  cord  has  been  both  confirmed  and  denied 
by  many  authors.  We  shall  limit  ourselves  here  to  the  view  of  Kocher,  who 
has  made  an  exhaustive  study  based  on  abundant  clinical  material  of  his  own. 
'  According  to  this  author,  a  hemilesion  of  the  spinal  cord  produces  on  the 
injured  side  hyperwsthesia  for.  touch  and  pain,  and  in  many  cases  also  for 
heat  and  cold.  Even  the  deeper  parts  are  included  in  this  change,  so  that 
movements  of  the  limbs  become  very  painful.  On  the  opposite  side  there 
is,  as  a  rule,  a  reduction  of  sen.sibility.  But  it  varies  both  as  to  intensity  and 
quality  according  to  the  extent  of  the  injury.  Either  every  kind  of  sensation 
is  lost  altogether  or,  as  is  very  often  the  case,  the  sensation  of  touch  remains 
intact  while  the  others  are  lost,  or,  finally,  the  sensation  of  pain  is  merely 
blunted  and  the  sensations  of  heat  and  cold  are  lost. 

However,  these  disturbances  are  not  final  on  either  side.  The  hyperass- 
thesia  on  the  injured  side  declines  and  the  loss  of  sensation  on  the  opposite 
side  gradually  disappears,  though  for  a  long  time  it  requires  a  stronger  stimu- 
lus to  produce  the  sensation  which  has  been  affected.  The  return  of  pain 
sensations  may  precede  the  revival  of  touch,  the  latter  that  of  heat,  and  heat 
that  of  cold.  These  variations  of  the  symptoms  are  referable  to  differences 
in  the  extent  of  the  lesion. 

After  an  exhaustive  discussion  of  the  clinical  observations,  Petren  has 
reached  the  following  conclusions  with  regard  to  the  tracts  of  the  cord  in 
which  the  different  cutaneous  sensations  are  propagated.  The  pressure  sense 
is  mediated  by  two  different  tracts:  the  one  ascends  in  the  posterior  columns 
of  the  same  side  and  is  the  direct  continuation  of  the  posterior  roots;  the 
other,  after  entering  by  the  posterior  horn,  crosses  entirely  to  the  opposite 
side  and  ascends  probably  as  a  part  of  Gowers's  tract  (cf.  Fig.  264)  in  the 
lateral  column.  The  tracts  for  pain  and  temperature  sensations  follow  this 
second  tract  for  pressure,  hence  run  in  the  cord  only  on  the  opposite  side  from 
the  place  in  the  skin  where  they  originate. 

References. — L.  F.  Barker,  "The  Nervous  System,"  New  York.  1899. — 
IF.  V.  Bechfereiv,  "Die  Leitungsbahnen  im  Gehirn  und  Riickenmark,"  second 
edition,  Leipzie,  1898. — Bethe,  "  Allgemeine  Anatomic  und  Physiologic  des 
Nervensystems,"  Leipzie,  1903. — L.  Edinger,  "  Vorlesungen  iiber  den  Bau  der 
nervosen  Zentralorgane,"  seventh  edition,  Leipzie,  1904. — Exner,  "  Entwurf  zu 


598       PHYSIOLOGY   OF  THE  NERVE  CELL  AND  THE  SPINAL  CORD 

ciner  physiologischen  Erklarungen  der  psychischen  Erschcinungen,"  i,  Leipzig 
and  Wien,  1891. — Van  Gehuchfen,  "  Le  systeme  nerveux  de  I'homme,"  third  edi- 
tion, Lierre,  1901. — Goltz,  "  Beitrage  zur  Lehre  v.  d.  Fiuiktionen  der  Nerven- 
zentren  des  Frosches,"  Berlin,  1869.— 6roZ^2  and  J.  R.  Ewald,  Arch.  f.  d.  ges. 
Physiologie,  Bd.  Ixiii,  1890. — Gotch  and  Ilorsley,  Philosophical  Transactions,  vol. 
cLxxxii,  B,  1891. — Kocher,  "  ^littheilungen  aus  den  Grenzgebieten  der  Medizin 
und  Chirurgie,"  voL  i,  1896. — Langley,  Journal  of  Physiology,  vol.  xvi,  1894. — 
Leyden  and  Goldscheider,  "  Erkrankungen  des  Riickenmarkes  und  der  Medulla 
oblongata."  Wien,  1895;  1897.— Lud wig's  Arbeiten,  1866-1890.— i/.  Redlich, 
"  Die  Pathologie  der  tabischen  Hinterstrangserkrankungen,"  Jena,  1897. — Sher- 
rington, "  The  Spinal  Cord  "  in  Schafer's  "  Text-book  of  Physiology,"  ii,  Edin- 
burgh, London,  and  Xew  York,  1900.^ — Vulpian,  "  Legons  sur  la  Physiologie  du 
systeme  nerveux,"  Paris,  1866. — Th.  Ziehen,  "  Nervensystem,"  i,  1  and  2,  Jena, 
1899-1903. 


CHAPTER    XXIII 

PHYSIOLOGY    OF    THE    BRAIX-STEM 

§  1.    GENERAL   SURVEY 

We  have  seen  in  the  previous  chapter  that  the  spinal  cord  exercises  con- 
trol over  many  different  functions  of  the  hody.  We  have  now  to  learn  that 
an  even  more  complete  control  is  exercised  by  the  highest  parts  of  the  central 
nervous  system,  namely,  the  parts  lodged  in  the  cranium  and  which,  taken 
collectively,  we  call  the  brain.  For,  as  we  shall  see  later,  it  is  no  difficult 
matter  to  demonstrate  that  even  the  cerebral  cortex,  the  highest  part  of  all, 
can  exert  its  influence  over  functions  which  are  quite  independent  of  the  will. 
Experiment  has  shown  that  this  influence  varies  with  different  divisions  of 
the  brain,  and  that  from  the  standpoint  of  the  different  functions  we  must 
for  this  reason  ascribe  to  the  different  parts  a  dignity  of  a  very  different  order. 
For  the  purely  vegetative  functions,  especially  those  which  have  most  to  do 
with  the  mere  maintenance  of  life,  like  the  circulation,  respiration,  digestion, 
etc.,  the  lower  parts  of  the  brain,  particularly  the  medulla,  are  the  most  im- 
portant ;  while  the  cerebrum  is  for  very  good  reasons  regarded  as  the  material 
substratum  of  the  conscious  processes. 

The  extremely  varied  functions  of  the  brain  make  it  necessary  that  the 
nervous  pathways  should  be  connected  with  each  other  in  manifold  ways,  and 
accordingly  we  find  the  structure  of  the  brain  extraordinarily  complex.  This 
circumstance  is,  for  the  physiological  and  clinical  as  well  as  for  the  anatomical 
mode  of  attack,  the  source  of  very  great  difficulties,  which  so  far  have  been 
only  very  imperfectly  surmounted.  Our  knowledge  of  the  functions  of  the 
brain  as  a  whole  and  of  its  different  parts  is  therefore  very  inadequate,  and 
the  data  which  we  have  are  unfortunately  very  contradictory  as  to  many  of 
the  most  important  points. 

A.    METHOD 

The  methods  which  can  be  employed  in  investigating  the  functions  of  the 
brain  are  in  general  similar  to  those  with  which  we  have  already  become  familiar 
in  the  study  of  the  spinal  cord:  anatomical  study  of  its  structure,  artificial  stimu- 
lation, section  or  removal  of  different  parts,  clinical  observations  on  patients 
followed  by  post-mortem  dissection,  etc.  But,  as  will  be  readily  understood,  the 
practical  difficulties  to  be  overcome  here  are  very  much  greater  than  those  met 
with  in  the  study  of  the  cord.  Not  only  is  the  danger  of  disturbance  to  the  cir- 
culation, caused  by  section  or  removal  of  a  part,  as  well  as  the  shock  produced 
by  the  operation,  greater  in  dealing  with  the  brain,  so  that  effects  are  very  often 
much  exaggerated  at  first,  but  in  many  cases  the  function  lost  is  assumed  by 

599 


600 


PHYSIOLOGY   OF  THE   BRAIN-STEM 


Fig.   267. 


-Median  section  through  the  brain  of  an  adult,  after  His. 

below. 


The  figures  refer  to  the  table 


Encephalon  (brain),  I-VI  (Fig.  267) 

Rhombencephalon  (hindbrain),  I-III 
Myeleneephalon   (afterbrain),  I 

Medulla  oblongata  (bulb),  I 
Metencephalon  (secondary  hindbrain),  II 
Pons,  III 
Cerebellum,  II2 
Isthmus  rhombencephali.  III 
Mesencephalon  (midbrain),  IV 
Crura  cerebri,  IVj 
Corpora  quadrigemina,  IV2 
Prosencephalon  (forebrain),  V  and  VI 

Diencephalon   ('tweenbrain  or  interbrain),  V 

Pars  mamillaris  hypothalami  (corpus  mamillare,  etc.),  Vi 
Thalamencephalon,  V2  to  4 
Optic  thalamus,  V2 

Metathalamus  (corpora  geniculata),  V3 
Epithalamus  (pineal  body,  etc.),  V4 
Telencephalon   (endbrain),  VI 

tuber  cinereum  ^ 
Pars  optica  hypothalami 


infundibulum 
pituitary  body 


VIi 


Hemisphferium,  VT2  to  4 
Corpus  striatum,  VI2 

Phinencephalon  (olfactory  lobe,  etc.),  VI3 
Pallium  (cortex  cerebri),  VI4 


GENERAL   SURVEY  601 

some  other  part,  making  the  interpretation  of  results  very  difficult.  Moreover 
this  method  has  to  contend  with  the  difficulty  of  limiting  the  lesion  produced 
exactly  to  the  region  intended. 

In  some  parts  of  the  brain,  as  for  example  the  cerebral  cortex,  it  is  relatively 
easy  to  get  clear  results  with  ordinary  electrical  stimulation,  but  in  others  the 
results  are  too  easily  obscured  by  by-currents  and  in  the  deeper  parts  it  is  prac- 
tically impossible  to  employ  the  method  without  a  serious  operation. 

Comparative  physiology  has  shown  very  conclusively  that  the  importance  of 
different  parts  of  the  brain  is  very  different  in  different  vertebrates.  Hence  one 
cannot  apply  to  man  the  results  obtained  upon  animals  without  some  qualifica- 
tion ;  hence  also  it  is  highly  important  that  analogous  results  should  be  had  upon 
man  himself.  The  great  variety  of  mental  diseases  furnish  us  the  necessary 
material  for  this  purpose,  and  in  many  respects  the  information  obtained  from 
them  supplements  the  information  we  obtain  from  animal  experimentation. 

The  weight  of  the  evidence  accruing  from  such  material  must,  however,  be 
estimated  with  caution  and  only  hy  observance  of  certain  definite  principles. 
Thus  a  tumor  may  be  located  some  place  in  the  brain  and  all  sorts  of  disturb- 
ances may  appear  in  both  the  bodily  and  the  mental  functions  of  the  patient. 
But  one  is  not  justified  in  concluding  from  this  alone  that  all  these  dist\irbances 
result  directly  from  destruction  of  the  part  where  the  tumor  is  located,  for  it 
may  be  that  the  tumor  raises  the  intracranial  pressure  and  has  by  this  means 
disturbed  functions  far  removed  from  the  seat  of  the  lesion.  Again,  a  sudden 
hemorrhage  in  the  brain  occurs ;  the  patient  shows  various  severe  symptoms  and 
dies  within  a  few  hours.  Now  this  is  not  equivalent  to  saying  that  the  different 
disturbances  observed  were  produced  alone  by  paralysis  of  the  part  destroyed  in 
the  hemorrhage ;  they  certainly  were  the  result,  in  part,  at  least,  of  shock,  and 
would  doubtless  have  disappeared  to  a  certain  extent  had  the  patient  lived  longer. 
Only  from  cases  where  there  is  no  rise  of  intracranial  pressure  and  where  the 
patient  lives  some  time  after  the  inception  of  the  lesion  can  conclusions  of  any 
physiological  importance  be  drawn. 

These  preliminary  remarks  with  regard  to  the  principles  which  must  be  borne 
in  mind  in  the  study  of  brain  functions  must  suffice  for  the  present.  As  we 
proceed  with  the  subject  we  shall  have  opportunity  of  discussing  these  funda- 
mental propositions  more  in  detail. 


B.    DIVISIONS   OF  THE   BRAIN 

His  has  divided  the  brain  on  the  basis  of  its  embryological  development 
as  given  in  tlio  tal)le  '  on  opposite  page. 

The  parts  of  the  brain  derived  from  the  first  primary  brain  vesicle  (hind- 
brain)  inclusive  of  the  diencephalon  ("tweenbrain),  were  formerly  described 
collectively  as  the  "  brain-stem  "  in  contradistinction  to  the  endbrain  (telen- 
cephalon). In  presenting  the  subject  of  the  brain  functions  it  seems  advisable 
for  several  reasons  to  continue  as  formerly  the  use  of  this  division  and  to 
apply  the  name  cerebrum  only  to  the  parts  developed  from  the  endbrain. 

*  This  classification  has  been  very  slightly  modified  in  accordance  with  more  modern 
usage  in  English. — Ed. 


602 


PHYSIOLOGY    OF   THE    BRAIX-STEM 


§  2.    THE    MEDULLA    OBLONGATA,    OR   AFTERBRAIN 

The  medulla  oblongata  extends  from  the  upper  end  of  the  spinal  cord  to 
the  lower  edge  of  the  pons,  its  upper  border  being  just  a  little  dorsal  to  the 
lateral  recess  of  the  fourth  ventricle.  Its  length  on  the  ventral  side  is  from 
20  to  24  mm.  and  on  the  dorsal  from  2-i  to  26  mm. 

The  physioJogicnJ  significance  of  the  medulla  consists  chiefly  m  this,  that 
within  its  borders  the  afferent  and  efferent  pathways  of  the  cord  are  brought 


Fig.  268. — Transverse  section  of  the  medulla  oblongata,  after  Edinger. 

into  much  more  intimate  relationships  with  each  other  and  with  the  cranial 
nerves  and  pathways  than  is  the  case  in  the  cord  itself.  By  this  means  the 
efferent  nerves  from  the  cord  can  act  together  for  a  common  purpose  in  a 
much  more  orderly  manner  than  would  be  possible  on  the  basis  of  their 
connections  in  the  spinal  cord  alone,  a  thing  of  profound  importance  for  the 
unity  of  the  bodily  functions. 

The  centers  which  exemplify  this  influence  of  the  medulla  in  the  highest 
degree  are  the  vasomotor  and  respiratory  centers,  the  physiologicaL  purpose 
and  mode  of  action  of  which  have  been  discussed  at  pages  237  and  325. 
Vomiting  may  also  be  mentioned  as  an  instance  of  coordination  of  many 
different  muscles  to  a  common  end,  the  center  for  which  is  probably  situated 
also  in  the  medulla  (cf.  page  286). 

It  is  very  probable  that  the  centers  for  several  other  g'euoral  functions,  which, 
like  vasodilatation,  require  the  harmonious  action  of  many  different  spinal  nerves. 
He  in  the  medulla;  experimental  proof  of  their  presence,  however,  is  w-anting  at 
this  time. 


THE  MEDULLA  OBLONGATA,  OR  AFTERBRAIX 


603 


Puncture  with  a  sharp  instrument  of  a  certain  spot  in  the  medulla  produces 
diabetes  (puncture  diabetes  of  CI.  Bernard)  in  the  animal  suffering  the  opera- 
tion. The  mechanism  concerned  in  this  is  quite  unknown,  but  we  may  conclude 
from  the  observed  fact  at  any  rate  that  in  some  way  the  medulla  plays  an  essen- 
tial part  in  the  regulation  of  carbohydrate  metabolism  (cf.  page  375). 

Although  the  medulla  of  the  higher  vertebrates  cannot  alone  effect  the  coor- 
dination of  skeletal  muscles  necessary  for  locomotor  movements,  nevertheless 
extensive  motor  effects,  both  reflex  and  automatic,  appear  more  readily  with  the 
medulla  intact  than  when  it  is  removed ;  and  we  may  imagine  at  least  that  this 
influence  of  the  medvdla  over  the  skeletal  muscles  is  not  without  its  significance 
for  their  function  as  heat  producers. 

Edinger  oliserves  that  the  centers  which  preside  over  the  above-named  and 
other  similar  associations  are  probably  to  be  sought  among  the  multipolar 
cells  distributed  through  the  substantia  reticularis  of  the  medulla,  and  de- 
scribed by  Bechterew  as  the  nucleus  reticularis  tegmenti  (Fig.  268). 

The  medulla  assumes  a  still  higher  dignity  physiologically  when  we  realize 
that  it  contains  the  nuclei  of  origin  of  many  efferent  cranial  nerves  as  well 
as  the  nuclei  around  which  the  central  endings  of  many  afferent  cranial  nerves 
split  up.  Xamed  from  below  upward,  these  nerves  are  the  hi/poglossal.  the 
spinal  accessory,  the  vagus,  the  auditory,  the  facial  and  the  trigeminal  (Fig. 
269),  although  the  last  three  and  their  nuclei  do  not  belong  exclusively  to 
the  medulla. 

The  efferent  fibers  contained  in  the-e  nerves  supply  the  most  widely  dif- 
ferent organs,  but  especially  those  which  are  most  important  for  the  vegetative 
processes  of  the  body ;  such.  e.  g.,  as  the  tongue,  the  salivary  glands,  the  phar- 


Hai.asc.  cffmm. 


Jlad-turterjeret 


Fig.  269. — Pasition  of  the  nuclei  of  the  cranial  nerves,  after  Edinger.  The  medulla  and  pons  are 
supposed  to  be  transparent.  The  cells  of  origin  of  the  efferent  nerves  are  black,  the  end- 
nuclei  of  the  afferent  nerves  red. 


ynx,  oesophagus,  stomach  and  intestine;  the  larynx,  air  passages  and  lungs; 
the  heart  and  blood  vessels.  The  corresponding  afferent  fibers  convey  im- 
pulses to  the  medulla  from  the  internal  car ;  the  skin  of  the  face ;  the  mucous 
membrane  of  the  mouth  inclusive  of  the  tongue,  the  pharynx,  oesophagus, 
stomach  and  intestine;  the  larynx,  air  passages  and  lungs;  the  heart,  etc.; 


604  PHYSIOLOGY   OF   THE   BRAIN-STEM 

and  these  impulses  have  a  large  part  in  the  regulation  of  the  important  proc- 
esses going  on  in  these  and  other  organs. 

It  follows  that  the  medulla  exercises  a  determining  influence  on  the  fol- 
lowing functions :  secretion  of  saliva,  movements  of  the  tongue,  swallowing, 
movements  of  the  stomach  and  intestine,  vomiting,  secretion  of  the  gastric 
and  pancreatic  juices ;  force  and  frequency  of  the  heart  beat,  vascular  tonus, 
and  regulation  of  the  blood  flow ;  respiratory  movements  and  movements  of 
the  larynx ;  also,  to  a  certain  extent,  at  least,  the  heat  regulation  of  the  body 
both  through  the  blood  vessels  and  the  skeletal  muscles.  In  short,  digestion, 
circulation,  respiration  and  heat  regulation  are  all  to  a  considerable  extent 
dependent  upon  the  medulla. 

Some  of  these  functions  are,  it  is  true,  relatively  simple;  for  example,  the 
reflex  secretion  of  saliva  is  on  a  plane  with  the  simpler  reflexes  from  the 
spinal  cord.  But  others,  and,  in  fact,  most  of  them,  are  very  complicated,  as 
a  critical  study  of  the  processes  of  swallowing,  breathing,  and  distribution  of 
blood  to  the  different  organs  will  readily  convince  one. 

Moreover,  experiment  has  shown  that  the  different  nerves  act  not  only  upon 
the  efferent  nerves  belonging'  to  the  same  organ,  or  organ  system,  but  that  their 
influence  extends  to  other  organ  systems.  Thus,  e.  g.,  by  swallowing  repeatedly 
the  heart  beats  are  at  first  quickened,  but  subsequently  are  lowered  to  a  rate  below 
the  original;  the  vascular  tonus  decreases;  the  expiratory  phases  of  respiration 
last  longer;  labor  pains  become  weak  or  cease  altogether;  hiccoughing  may  be 
stopped  by  repeated  swallowing,  etc.  (Kronecker  and  Meltzer). 

When  we  remember  that  in  addition  to  exercising  this  multifarious  con- 
trol over  the  functions  enumerated  above,  the  medulla  is  the  afferent  pathway 
of  impulses  from  the  cord  to  the  higher  parts  of  the  brain,  and  of  efferent 
impulses  from  the  latter  to  the  former,  it  is  apparent  at  once  that  it  con- 
stitutes an  organ  absolutely  {ndispensahle  to  life.  The  immediate  cause  of 
death  by  destruction  of  the  medulla  is  stoppage  of  the  respiration,  and  by 
keeping  up  this  function  artificially,  life  can  be  prolonged  somewhat.  But 
this  is  not  sufficient  to  maintain  life  indefinitely,  for  other  disturbances,  espe- 
cially that  of  the  heat  regulation,  are  enough  to  bring  on  death  within  a 
relatively  short  time. 

On  the  other  hand,  it  can  be  sho^vTi  that  even  a  mammal  can  survive 
section  of  the  brain  at  the  upper  edge  of  the  medulla,  provided  its  continuity 
with  the  spinal  cord  be  not  interrupted,  without  immediate  danger  to  life  and 
without  resort  to  artificial  respiration  or  anything  of  the  kind.  Since,  how- 
ever, such  an  animal  cannot  move  about  or  take  nourishment,  it  is  of  course 
impossible  to  keep  it  alive  very  long. 

Frogs,  which  because  of  the  much  lower  intensity  of  their  metabolism 
require  very  little  food  and  hence  can  go  a  long  time  without  any  food,  live 
much  longer  when  deprived  of  the  brain  above  the  medulla.  In  fact,  Shrader 
succeeded  in  removing  from  frogs  everything  down  to  the  medulla  inclusive 
of  the  cerebellum  and  the  most  anterior  part  of  the  medulla  itself,  and  in 
keeping  them  alive  for  four  months.  The  most  striking  thing  about  the 
behavior  of  these  animals  was  an  apparently  irresistible  impulse  to  be  con- 
stantly moving. 


THE  CEREBELLUM  605 


§  3.    THE    CEREBELLUM 

The  cerebellum  is  connected  by  means  of  its  peduncles  on  the  one  hand 
with  the  spinal  cord  and  on  the  other  with  the  higher  parts  of  the  brain. 
Impulses  to  and  from  the  cerebellum  are  conveyed  over  pathways  contained 
in  these  peduncles. 

Many  nerve  cells  are  found  both  in  the  gray  cortex  of  the  cerebellum  and 
in  the  gray  nuclei  located  in  its  interior.  The  various  nuclei  are  connected 
by  means  of  association  fibers  with  the  cerebellar  cortex,  and  the  different 
subdivisions  of  the  latter  are  connected  with  each  other  in  numerous  ways 
by  means  of  other  association  fibers. 

In  animals  deprived  of  the  cerebellum,  and  also  in  men  suffering  from 
extensive  destruction  of  this  organ,  various  characteristic  symptoms  are  ob- 
served. But  among  them  we  do  not  find  either  motor  or  sensory  paralysis 
of  any  Icind.  Hence  we  may  conclude,  what  is  borne  out  also  by  anatomical 
connections,  that  the  cerebellum  is  not  in  the  direct  line  of  connection  between 
the  higher  parts  of  the  brain  and  the  medulla  or  the  spinal  cord,  but  that  it 
constitutes  a  system  in  itself  branching  off  to  one  side,  which  both  acts  upon 
and  is  acted  upon  by  the  other  parts  of  the  central  nervous  system. 

Removal  of  the  cerebellum  does  not  of  itself  endanger  life;  it  is  therefore 
not  an  indispensable  organ,  although  it  does  exert  a  profound  influence  over 
certain  functions  of  the  body. 

According  to  Steiner,  artificial  stimulation  of  the  cerebellum  in  fish  has  no 
effect. — By  mechanical  stimulation  with  a  fine  needle  Xothnagel  observed  in  the 
rabbit  that  the  head  was  turned  to  the  opposite  side  and  the  vertebral  column 
was  curved  so  as  to  become  concave  toward  the  opposite  side. — Electrical  stimu- 
lation between  the  left  hemisphere  and  the  vermis  of  a  dog  moving  freely  about 
the  laboratory  produced,  in  experiments  by  Lewandowsky,  forced  flexion  toward 
the  same  side,  so  that  the  vertebral  column  became  bent  convexly  to  the  right ; 
idtimately  the  animal  fell  over  to  the  right  or  went  off  in  circular  movements 
in  the  same  direction. — On  the  other  hand  the  tonic  contraction  of  the  skeletal 
muscles  is  inhibited  by  stimulation  of  the  surface  of  the  cerebellum  (Sherring- 
ton). But  from  such  observations  as  these  we  can  only  conclude  that  the  cere- 
bellum is  in  some  way  related  to  the  bodily  movements.  For  more  exact  infor- 
mation as  to  what  that  relation  is,  we  must  direct  our  attention  to  the  study  of 
the  symptoms  attending  lesions  of  the  cerebellum. 

In  certain  fishes  where  the  cerebellum  is  higlily  developed,  it  can  be 
removed  without  producing  any  apparent  disturbance  either  to  the  bodily 
movements  or  to  equilibrium ;  the  animals  merely  wabble  slightly  sidewise 
while  swimming.  The  cleaner  cut'  the  operation,  the  less  marked  are  these 
wabblings.  and  within  a  day  or  so  they  practically  disappear.  Likewise  after 
unilateral  ablation  of  the  cerebellum  there  is  no  disturbance  in  locomotion 
(Steiner). 

In  frogs,  where  the  cerebellum  is  very  slightly  developed,  the  posture  of 
the  body  and  the  leaping  movements  after  extirpation  are  not  to  be  distin- 
guished from  those  of  the  normal  animal.  When  the  animal  is  placed  in 
water,  it  swims  and  behaves  otherwise  quite  normally.  But  when  it  leaps 
36 


606 


PHYSIOLOGY   OF  THE   BRAIN-STEM 


upon  the  edge  of  the  basin,  one  observes  that  very  often  it  leaps  too  far  or 
not  quite  far  enough.  Again,  when  it  does  succeed  in  reaching  the  bank  it 
often  settles  down  with  a  portion  of  the  body  projecting  over  the  edge,  whereas 
a  normal  frog  is  never  content  until  it  has  a  solid  footing  under  the  whole 
body.  The  symptoms  attending  ablation  of  the  cerebellum  are  therefore  not 
at  all  striking  (Steiner). 

Removal  of  the  cerebellum  from  the  green  lizard  and  the  turtle  produces 
no  perceptible  effect   (Steiner,  Bickel). 

In  operations  similar  to  these  on  the  higher  vertebrates,  it  has  been  noted 
that  no  pain  is  produced  unless  the  medulla  or  pons  is  injured. 

Rolando,  Magendie  and  Flourens  long  ago  observed  irregularities  in  the 
bodily  movements  following  operations  on  the  cerebellum,  but  they  explained 

them  in  very  different  ways.  By  many 
researches  which  have  been  made  on 
this  subject  since  that  time,  these  dis- 
turbances have  been  confirmed  and 
their  cause  more  closely  analyzed. 

We  cannot  discuss  all  of  these  in- 
vestigations here,  but  must  be  content 
to  consider  some  of  the  leading  facts 
l)rought  out  by  work  done  within  recent 
years. 

In  order  to  make  the  phenomena 
following  extirpation  of  the  cerebellum 
more  intelligible,  we  shall  recite,  after 
Luciani,  the  clinical  history  of  a  dog 
in  which,  as  was  ascertained  subse- 
quently by  dissection,  all  but  the  lower 
outer  portion  of  the  cerebellum  had 
l^een  removed  on  the  left  side,  while 
only  a  small,  unimportant  fragment  had  been  left  on  the  right  (Fig.  270). 
There  were  three  successive  operations,  but  the  following  description  relates 
only  to  the  phenomena  which  appeared  after  the  last,  performed  on  the  13  th  of 
August,  1883. 

For  some  time  after  the  operation  the  animal  was  unable  to  right  himself, 
but  lay  on  his  back,  the  vertebral  column  bent  strongly  to  the  left  and  the  fore 
limbs  powerfully  extended.  This  contracture  increased  and  spread  to  the  hind 
limbs  when  the  animal  tried  to  place  his  four  feet  straight  on  the  floor.  The 
animal  ate  and  drank  without  help  when  the  head  was  supported  against  the 
wall.  Thrown  into  a  tank  of  water  he  reared  up  suddenly  with  head  out  of 
the  water  and  fell  over  backward.  But  he  soon  recovered  his  eciuilihrium  and 
swam  in  the  normal  fashion,  his  head  out  of  the  water.  Coming  to  the  edge 
of  the  tank  and  attempting  to  climb  out,  he  again  fell  over  backward  but  soon 
righted  himself  in  the  water.  Now  and  then  in  turning  round  the  head  went 
under,  but  it  was  quickly  lifted  out  and  the  equilibrium  recovered. 

About  the  second  week  these  symptoms  began  to  abate  somewhat.  "When  the 
animal  was  placed  in  a  standing  posture  with  the  four  legs  abducted  so  that  he 
was  well  supported,  and  was  left  to  himself,  he  stood  for  some  seconds  swaying 
backward  and  forward,  but  the  swayings  rapidly  became  too  extensive  and  he  fell 


Fig.    270. — Almost  complete  extirpation  of 
the  cerebellum  of  a  dog,  after  Luciani. 


THE  CEREBELLUM  607 

over  backward  to  the  left. — The  contracture  mentioned  above  gradually  dimin- 
ished, but  the  animal  was  still  able  to  lift  himself  only  by  his  fore  legs,  i/ws- 
cular  iveakness,  particularly  in  the  hind  limbs,  was  very  marked. 

Gradually,  however,  this  weakness  passed  off  and  by  the  24:th  of  September 
the  animal  began  to  stand  on  all  fours  and  to  take  steps,  supported  against  the 
wall.  Some  ten  days  later  he  took  his  first  steps  unsupported,  and  from  this  on 
his  ability  to  walk  steadily  improved.  On  the  31st  of  October  the  following 
description  was  written  concerning  his  gait :  "  quick,  almost  twitchlike  move- 
ments, the  head  lowered,  the  back  slightly  convex,  very  pronounced  lateral  move- 
ments of  the  spinal  column,  abnormal  elevation  and  abduction  of  the  fore  leg, 
movements  of  the  hind  legs  not  in  accord  with  those  of  the  fore  legs,  often  fall- 
ing on  a  smooth  floor,  seldom  on  a  rough  one."  Particularly  noticeable  was  the 
extreme  effort  with  which  the  dog  walked,  and  which  was  expressed  in  the  dysp- 
noea, lolling  of  the  tongue  and  need  of  rest  at  short  intei-vals.  Thrown  into  a 
tank,  he  was  now  able  to  swim  powerfully  and  well,  getting  his  equilibrium 
very  promptly. 

On  the  11th  of  January,  1884,  it  was  noted,  among  other  things,  that  the 
animal  could  not  stand  perfectly  still  even  for  a  moment.  The  most  he  could 
do  was  to  stand  for  a  few  minutes  with  the  legs  wide  apart,  swaying  back  and 
forth  until  he  decided  either  to  walk  or  to  lie  down.  When  the  animal  walked 
he  presented  a  most  perfect  picture  of  ataxia.  Coordination  of  his  movements 
was  frequently  quite  normal,  but  whenever  the  regular  rhythm  was  interrupted, 
as  in  turning  or  attempting  to  walk  rapidly,  or  if  one  leg  slipped  causing  the 
body  to  fall  down  behind  thereby  impeding  his  progress,  coordination  between  the 
fore  and  hind  legs  was  lost  for  the  time.  It  was  noted  also  that  the  legs  were 
lifted  abnormally  high  in  walking  and  that  the  spinal  column  undulated  slightly 
up  and  down.  Luring  the  animal  on  with  food  only  aggravated  his  symptoms 
without  improving  his  speed.  On  the  whole  the  gait  was  much  slower  and  the 
loss  of  strength  by  exercise  much  greater  than  in  a  normal  animal,  leading  to 
extreme  fatigue  in  a  verj'  short  time. 

We  see  that  the  effects  of  removing  the  cerebellum  wear  off  to  a  certain 
extent  with  time,  and  only  those  which  remain  after  several  months  can 
be  described  as  the  final  effects.  The  latter  Liiciani  summarizes  as  follows : 
asthenia,  or  loss  of  strength;  atonia,  or  loss  of  tonus  in  resting  muscles;  and 
astasia,  or  loss  of  steadiness  in  all  kinds  of  movements. 

Several  authors  have  reported  that  while  lesion  on  one  side  of  the  cere- 
bellum caused  motor  disorders,  two  symmetrical  lesions  on  the  opposite  sides, 
whether  large  or  small,  either  produced  no  effect  at  all  or  only  slight  ones. 
In  Luciani's  experience  this  was  not  the  case.  When  the  middle  lobe  or 
vermis  was  extirpated  more  or  less  completely,  immediately  after  the  opera- 
tion tonic  contraction  of  the  fore  leg  or  neck  muscles  came  on  whenever  the 
animal  attempted  to  do  anything  voluntarily.  But  these  effects  passed  off 
in  a  few  days,  and  whatever  permanent  effects  then  remained  stood  out  very 
clearly,  although  naturally  less  pronounced  than  after  practically  complete 
removal  as  above  described.  These  disorders  probably  appeared  in  all  muscles, 
but  were  more  sharply  defined  in  certain  definite  groups — e.  g..  those  of  the 
hind  limbs.  In  animals  from  which  the  vermis  was  removed  to  the  same 
extent  on  both  sides  permanent  effects  were  equally  distributed  to  the  two 
halves  of  the  body,  whereas  when  the  removal  was  more  extensive  on  one  side 
than  the  other,  the  effects  were  more  strongly  marked  on  the  one  side. 


608  PHYSIOLOGY   OF  THE   BRAIN-STEM 

These  effects  gradual!}^  became  compensated  more  or  less  completely,  and 
in  certain  cases  to  such  an  extent  that  one  could  scarcely  distinguish  the 
animal  from  a  normal  one.  We  shall  discuss  this  form  of  compensation 
presentl}'. 

Mere  division  of  the  cerebellum  into  a  right  and  left  half  by  a  median  longi- 
tudinal section  is  entirely  without  effect  (Russell). 

Complete  removal  of,  say,  the  right  side  of  the  cerebellum  produces,  imme- 
diately after  the  operation,  rotation  about  the  long  axis  of  the  animal  from 
left  to  right  (seen  from  the  dog's  back),  squinting  of  the  eyes  to  the  left, 
nystagmus  (to-and-fro  movements  of  Ijoth  eyes  from  side  to  side),  spiral 
twisting  of  the  spinal  column  or  at  least  of  the  neck  region,  curvature  of  the 
spine  with  concavity  to  the  right,  tonic  extension  of  the  fore  leg  and  at  times 
of  the  hind  leg  on  the  same  side. 

\Mien  these  effects  have  passed  off,  we  ol)serve  again,  as  the  permanent 
effects,  the  complex  of  s}Tnptoms  described  as  asthenia,  atonia  and  astasia. 
The  muscles  of  the  operated  side  are  the  ones  chiefly  affected,  and  the  dis- 
turbance is  so  great  that  for  more  than  a  month  animals  can  neither  stand 
up  nor  walk  without  support.  Later  compensation  develops  so  that  the  equi- 
librium is  preserved  both  in  walking  and  in  swimming.  And  yet  for  some 
months  after  the  operation  numerous  effects  due  directly  to  the  absence  of 
the  part  removed  are  clearly  perceptible. 

In  man  many  cases  of  rather  extensive  destruction  of  the  cerebellum  have 
been  descriljed  in  wliich  no  permanent  effects  were  to  be  oI)served.  This 
agrees  very  well  with  the  observation  made  on  animals,  that  one  part  of  the 
cerebellum  can  take  over  the  work  of  another  part  removed. 

When  the  defect  is  more  extensive  the  most  prominent  symptoms  are  simi- 
lar to  those  observed  in  animal  experiments,  namely,  incoordination  of  loco- 
motor movements',  such  as:  unsteadiness  of  gait,  loss  of  equilibrium,  swaying 
movements,  etc.  In  light  cases  the  patient  may  manage  to  stand,  with  the 
legs  wide  apart,  quite  steadily,  but  in  severe  cases  the  body  sways  in  spite 
of  strong  abduction.  With  the  feet  and  legs  close  together,  flexor  and  extensor 
movements  of  the  metatarsi  and  of  the  toes  are  kept  up,  the  whole  body  sway- 
ing to  and  fro  until  the  patient  may  lose  his  balance  entirely  and  fall  over. 
When  he  walks  he  keeps  his  legs  wide  apart  and  his  toes  first  flexed  and  then 
extended;  sometimes  he  walks  on  his  heels,  sometimes  tips  forward  on  his 
toes ;  he  sometimes  bends  his  knees,  sometimes  presses  them  far  back  or  keeps 
them  straight ;  the  feet  are  only  slightly  lifted  from  the  ground ;  the  body 
totters  and  reels  from  one  side  to  the  other — in  short,  the  patient  walks  like 
a  drunken  person  and  not  infrequently  falls  to  the  ground.  In  some  cases 
the  patient  cannot  even  walk  with  support,  whereas  lying  on  his  back  he  can 
move  his  legs  perfectly  and  can  tell  exactly,  without  looking,  where  a  leg  is — 
can  in  fact  place  one  leg  in  a  position  exactly  like  that  in  which  the  other 
has  been  placed  for  him;  hence  his  motor  sense  is  not  impaired.  In  many 
cases  the  anterior  extremities  are  entirely  unaffected,  so  that  the  patient  can 
make  the  most  precise  movements  with  his  hands. 

Another  very  frequent  symptom  in  diseases  of  the  cerebellum  is  vertigo, 
which  however   may  be   entirely  wanting   when  the   incoordination   is  very 


THE  CEREBELLUM  609 

marked,  or  may  be  present  when  there  is  no  derangement  of  the  movements. 
These  two  symptoms  are  therefore  entirely  independent  of  each  other.  Ver- 
tigo is  distinguished  by  its  great  intensity  and  is  ahnost  continuously  per- 
manent. Sometimes  it  is  present  while  the  patient  is  lying  down,  but  as  a 
rule  only  when  he  sits  up.  Sometimes  it  seems  to  the  patient  as  if  the  objects 
all  about  him  were  moving,  but  as  a  rule  he  imagines  himself  to  be  moving, 
that  everything  supporting  him  has  fallen  away  and  that  his  body  assumes 
all  sorts  of  impossible  positions. 

When  we  have  added  that  the  patient  often  suffers  pain  ui  tJie  head,  which 
is  commonly  localized  just  above  the  neck  on  the  same  side,  we  have  enumer- 
ated all  the  symptoms  of  a  cerebellar  lesion,  so  far  as  it  is  recognizable  at  all 
by  external  symptoms. 

Individuals  suffering  from  extensive  or  complete  congenital  defect  of  the 
cerebellum  are  observed  to  be  considerably  defective  in  intelligence  also.  But 
we  cannot  conclude  from  this  that  the  cerebellum  is  of  any  direct  significance  as 
the  seat  of  the  psychical  activities,  for  it  is  almost  self-evident  that  the  causes 
which  operate  to  inhibit  development  of  the  cerebellum  would  have  an  inhibiting 
influence  on  other  parts  of  the  brain.  Besides,  we  find  in  the  literature  cases 
of  very  extensive  destruction  of  the  cerebellum  not  accompanied  by  any  notice- 
able effect  on  the  intelligence. 

From  these  experimental  and  clinical  results  Luciani  concludes  that  the 
cerebellum  both  histologically  and  physiologically  is  a  hilateral  organ,  but  that 
its  influence  is  rather  direct  than  crossed ;  whereas  the  influence  of  the  cere- 
brum, also  a  bilateral  organ,  is  mainly  crossed.  While  the  influence  of  the 
cerebellum  however  is  not  limited  to  the  muscles  active  in  locomotion,  but 
extends  to  the  entire  voluntary  musculature,  its  chief  influence  is  over  the 
muscles  of  the  posterior  extremities  and  the  extensor  muscles  of  the  spinal 
colunm. 

In  general  all  regions  of  the  cerebellum  would,  in  Luciani's  view,  appear 
to  have  the  same  function,  so  that  the  permanent  effects  of  removal  of  the  dif- 
ferent parts  would  differ  not  in  kind,  but  merely  in  extent,  duration  and  intensity, 
and  also  as  to  predominance  on  the  one  side  of  the  body  or  the  other.  The  cere- 
bellum therefore  would  not  be  a  collection  of  several  functionally  different  parts, 
each  having  a  direct  relation  to  a  special  group  of  muscles;  but  on  the  contrary 
a  functionally  homogenous  organ,  the  different  parts  of  which  have  the  same 
general  purpose  as  the  whole  and  are  mutually  replaceable  so  long  as  their  natural 
connections  are  not  disturbed. 

This  conception  cannot  at  present  be  so  definitely  maintained,  for  we  have 
some  observations  which  show  pretty  positively  the  presence  of  a  functional 
localization  in  individual  lobes  of  the  cerebellum.  Thus  Thomas  observes  that 
destruction  of  the  vermis  disturbs  more  especially  the  movements  of  the  poste- 
rior extremities;  and,  according  to  v.  Rynberk,  destruction  of  the  middl(>  half 
of  the  vermis  affects  the  neck  muscles,  while  sharply  circumscribed  destruction 
of  that  part  of  the  hemisphere  just  lateral  to  this  middle  region  affects  the 
movements  of  the  anterior  extremity  (dog). 

Impulses  are  conveyed  to  the  cerebellum  by  many  different  pathways  (Fig. 
271).  We  shall  consider  first  of  all  those  which  connect  with  the  vestibular 
nerve  and  those  traversing  the  lateral  cerebellar  tract  of  the  cord  (cf.  Fig.  26-4 


610 


PHYSIOLOGY   OF  THE   BRAIN-STEM 


and  page  593),  because  the  anatomical  relationships  mark  them  as  of  special 
importance,  and  because  we  have  such  evidence  also  from  physiological 
experiments. 

As  Stefani  especially  has  pointed  out,  the  symptoms  following  ablation  of 
the  cerebellum  present  in  many  respects  a  striking   agreement  with   those 


^^ 


Fig.  271. — Diagram  showing  paths  connecting  the  cerebellum  and  pons  with  the  cerebrum,  after 
Barker.  /,  fibers  of  frontal  cerebro-cortico-pontal  path  derived  from  pyramidal  cells  in  the 
cortex  of  the  frontal  lobe.  1,  Frontal  cerebro-cortico-pontal  path  forming  a  medial  bundle  of 
white  fibers  on  the  ventral  side  of  the  superior  peduncle;  2,  bundle  of  fibers  connecting  the 
temporal  or  temporal  and  occipital  lobes  with  the  cerebellum;  3,  cell  body  in  the  pons  giving 
off  a  fiber  to  terminate  in  the  opposite  cerebellar  hemisphere;  4,  cell  body  connected  with  the 
temporal  cerebro-cortico-pontal  path  giving  off  a  fiber  to  the  opposite  hemisphere  of  the 
cerebellum;  5  and  6,  Purkinje  cells  in  the  cerebellar  cortex  giving  off  fibers  to  the  nuclei 
pontis;  7  and  8,  cell  bodies  in  the  nuclei  pontis  sending  fibers  toward  the  cerebrum. 


THE  CEREBELLUM  611 

which  follow  extirpation  of  the  membranous  lab}Tinth  of  the  internal  ear 
(cf.  page  4TG).  and  the  inference  seems  not  too  far  drawn  that  the  business 
of  the  cerebellum  consists  in  part  in  the  physiological  elaboration  of  impulses 
contributed  to  it  by  the  vestibular  nerve. 

In  so  saying  we  do  not  wish  to  assert  that  the  labyrinth  acts  exclusively  on 
the  cerebellum,  or  that  the  cerebellum  receives  impulses  only  from  the  labyrinth, 
for  other  observations  make  such  a  view  quite  untenable. 

Recently  Marburg  has  cut  the  lateral  cerebellar  tract  in  the  cord  of  a  dog 
at  the  level  of  the  second  cervical  segment.  After  a  bilateral  operation,  sway- 
ing movements  appeared  l)oth  in  walking  and  in  standing,  the  legs  were  placed 
and  held  in  abnormal  positions,  the  pelvis  was  abnormally  inclined  and  the  spine 
abnormally  curved.  Voluntary  movements,  tonus  of  the  muscles,  sensibility  of 
the  skin  and  the  general  strength  of  the  animal  appeared  to  be  unaffected. 

These  disorders  are  doubtless  due  to  the  absence  of  certain  afferent  im- 
pulses coming  from  the  locomotor  organs,  and  the  idea  of  Lussana,  recently 
taken  up  and  developed  by  Lewandowsky,  that  the  symptoms  following  in- 
juries to  the  cerebellum  are  really  to  be  interpreted  as  a  derangement  of  the 
muscular  sense,  might  not  be  so  far  amiss  as  Luciani  supposes. 

No  claim  is  made  that  the  cerebellum  constitutes  the  only  center  of  the 
muscular  sense,  nor  is  there  anything  to  prove  that  the  conscious  processes 
depend  upon  it,  for  plenty  of  other  facts  show  with  perfect  clearness  that  the 
sensations  of  motion  and  position  are  present  after  the  cerebellum  has  been 
removed,  also  that  they  are  profoundly  influenced  by  destruction  of  certain  parts 
of  the  cerebral  cortex  when  the  cerebellum  is  uninjured. 

The  impulses  brought  to  the  cerebellum  by  the  above-named  pathways  and 
by  other  fibers  are  elaborated  in  that  organ  by  some  process  which,  so  far  as 
we  know,  is  independent  of  consciousness.  At  any  rate  the  fibers  leaving  the 
cerebellum  are  the  medium  of  some  influence  which  increases  the  potential 
energy  (sthenic  activity)  of  the  neuromuscular  mechanisms,  and  the  degree 
of  their  tonus  (tonic  activity)  during  functional  pauses.  It  also  quickens  the 
rhythm  of  the  impulses  while  the  mechanisms  are  active  and  causes  these 
impulses  to  be  so  fused  and  regulated  that  they  eventuate  in  harmonious  move- 
ments of  the  proper  extent,  intensity,  etc.   (static  activity). 

Against  this  formulation  of  the  cerebellar  functions,  which  Luciani  makes 
in  summing  up  the  effects  of  extirpation,  different  objections  have  been  urged 
by  certain  authors,  who  wish  to  regard  the  cerebellum  as  the  seat  of  the  muscular 
sense,  the  organ  for  the  maintenance  of  equilibrium,  or  for  the  coordination  of 
certain  muscular  movements.  Since  these  views  are  not  out  of  harmony  with 
the  facts,  it  seems  to  the  author  that  they  arc  not  inconsistent  with  Luciani's 
position,  but  that  they  differ  from  his  view  rather  in  the  mode  of  expression  than 
on  fundamental  grounds. 

Thomas,  who  has  attempted  to  analyze  the  regulating  influence  of  the  cere- 
bellum still  more  closely,  gives,  among  others,  the  following  example  of  its  action. 
When  the  fore  foot  is  lifted  voluntarily  from  the  ground,  the  impidse  from  the 
motor  cortex  of  the  cerebrum  extends  not  only  to  the  necessary  muscles,  but  by 
a  special  pathway  it  excites  also  the  cerebellum  to  send  o\it  impulses  which 
increase  the  tonus  of  the  adductor  and  trunk  muscles  uf  the  same  side.     But 


612  PHYSIOLOGY   OF  THE   BRAIN-STEM 

this  increase  of  tonus  \vould  be  of  no  use  if  the  point  of  insertion  of  these  mus- 
cles were  not  fixed,  hence  there  must  be  also  an  increase  in  the  tonus  of  the 
trunk  muscles  on  the  opposite  side.  The  cerebellum  exercises  this  regulating 
influence  by  means  of  the  various  pathway's  proceeding  from  it  to  the  motor 
nuclei  in  the  spinal  cord  and  to  the  motor  cortex  in  the  cerebrum  (cf.  Fig.  271). 

It  is  likely  that  the  compensation  which  gradual!}^  appears  after  extensive 
injury  to  the  cerebellum  is  the  work  of  the  cerebrum,  particularly  of  the 
motor  regions  (cf.  Chapter  XXIV).  The  following  observations  by  Luciani 
speak  for  such  an  explanation : 

Three  operations  were  performed  on  the  same  dog :  in  the  tirst  the  right 
half  of  the  cerebellum  was  removed ;  in  the  second  the  motor  regions  of  the  cor- 
tex were  destroyed  in  both  cerebral  hemispheres ;  and  in  the  third  the  remainder 
of  the  cerebellum  was  taken  away.  The  animal  remained  alive  for  eleven  months 
after  the  operation  and  was  then  killed.  During  these  eleven  months  he  could 
neither  hold  himself  up  nor  walk  without  support.  In  none  of  the  animals 
obsei-ved  by  Luciani  in  which  the  cerebellum  alone  was  destroyed,  did  anything 
like  this  occur.  The  difference  was  due,  as  Luciani  observes,  not  to  the  mere 
extirpation  of  the  cerebral  cortex,  for  this  operation  of  itself  produces  only 
transitory  symptoms.  It  appears  rather  that  destruction  of  the  motor  cortex 
removed  just  those  conditions  which  made  it  possible  for  the  animal  without  a 
cerebellum  to  find  the  necessary  compensatory  movements.  It  is  especially 
worthy  of  remark  that  swimming  movements,  which  do  not  require  to  be  coiirdi- 
nated  so  finely  as  walking  movements,  could  be  performed  by  this  animal  per- 
fectly well. 

The  motor  disturljances  which  appear  immcdintphj  after  the  operation  on 
the  cerel)ellum,  the  peduncles,  or  the  pons  are  particularly  severe  and  should 
be  given  special  mention.  The  animal  sometimes  gets  into  certain  attitudes 
called  forced  positions,  which  it  seems  unable  to  get  out  of,  returning  inevita- 
bly to  the  same  posture  every  time  it  is  compelled  to  take  another;  or  it 
performs  what  are  called  forced  movements,  rolling  over  and  over  around  the 
long  axis  of  the  body,  or  running  around  in  a  circle  like  a  circus  animal,  or 
describing  cranklike  movements  around  its  anterior  end  as  a  pivot — in  all 
of  these  being  quite  unable  to  prevent  the  movement,  or,  to  put  it  differently, 
apparently  striving  all  the  while  for  a  state  of  equilibrium  which  it  is  unable 
to  find. 

The  motor  disturbances  appearing  after  unilateral  extirpation  of  the  cere- 
bellum at  their  period  of  greatest  intensity  are :  agitation,  restlessness,  ofttimes 
whining  or  groaning,  curvature  of  the  spine  with  concavity  toward  the  oper- 
ated side,  accompanied  by  tonic  extension  of  the  anterior  extremity  of  the 
same  side  and  spasmodic  movements  of  the  three  other  extremities;  spiral 
rotation  of  the  head  and  neck  toward  the  sound  side  accompanied  by  strabis- 
mus and  nystagmus  of  one  side,  and  often  by  deviation  of  the  eye  on  the 
operated  side  inward  and  downward,  of  the  other  eye  outward  and  up- 
ward ;  a  tendency  to  roll  over  about  the  long  axis  of  the  body  in  the  direction 
of  the  twisting  and  of  the  strabismus — i.  e.,  as  seen  from  the  hack  of  the 
animal,  from  the  sound  toward  the  injured  side. 

Whether  these  phenomena  are  caused  by  the  excessive  irritation  on  the 
cut  side,  or  by  the  predominance  of  the  sound  side  over  the  injured  one. 


THE  MESENCEPHAI^ON   OR   MIDBRAIN  613 

cannot  be  decided  at  present.  Luciani,  who  formerly  regarded  the  movements 
as  the  effect  of  overstimulation  on  the  peripheral  stump  of  the  peduncle  left 
by  the  wound,  no  longer  expresses  himself  so  positively. 


§  4.    THE  MESENCEPHALON  OR  MIDBRAIN 

The  upper  part  of  the  midbrain  is  composed  of  the  corpora  quadrigemina 
and  the  pineal  body,  which  is  now  regarded  as  a  remnant  of  an  ancestral 
eye ;  the  lower  part  consists  of  the  crura  cerebri.  Both  parts  stand  in  intimate 
relation  to  the  visual  organ,  the  former  constituting  a  relay  station  in  the 
optic  nerve,  the  latter  containing  nuclei  for  the  most  important  intrinsic 
and  extrinsic  muscles  of  the  eye.  In  addition  the  midbrain,  like  all  other 
divisions  of  the  brain  except  the  cerebellum,  is  a  conducting  pathway. 


A.    THE   CORPORA   QUADRIGEMINA 

When  the  optic  lobes,  which,  in  the  lower  vertebrates,  correspond  to  the  cor- 
pora quadrigemina  of  the  higher,  are  removed  from  fishes  (Steiner),  or  from 
the  frog  (Beehterew),  the  one  prominent  symptom  is  blindness.  According  to 
Flourens  the  same  thing  is  true  in  birds;  but  from  more  recent  investigations 
it  appears  that  after  unilateral  destruction  the  power  of  vision  in  the  opposite 
eye  is  only  reduced,  not  totally  destroyed  (Stefani). 

In  dogs  Beehterew  found  after  destruction  of  one  anterior  body  that  the 
homolateral  halves  of  the  two  retinae  became  blind,  although  the  defect  in  the 
opposite  eye  was  the  more  extensive.  By  more  complete  removal  of  both  anterior 
bodies  almost  total  blindness  was  produced.  The  reaction  of  the  pupil  to  light, 
however,  was  very  little  affected,  which  is  the  case  also  after  the  same  operation 
in  birds. 

Destruction  of  one  posterior  body  produced  disturbances  to  vision  in  the 
median  part  of  the  opposite  retina. 

In  view  of  these  observations,  that  in  the  mammals  as  well  as  in  the  lower 
vertebrates  the  corpora  quadrigemina  are  included  in  the  optic  tract,  it  is 
the  more  remarkable  that  in  men  suffering  from  disease  of  the  anterior  bodies 
no  considerable  derangement  of  vision  has  with  certainty  been  established. 
Suppression  of  one  entire  anterior  quadrigeminal  body  occasions  only  a  mod- 
crate  reduction  of  the  visual  power  and  leaves  the  color  sense  quite  intact. 
Likewise  in  the  monkey,  destruction  of  the  anterior  bodies  produces  no  demon- 
strable effect  on  vision  (Bernheimer). 

Since  now  we  know  from  anatomical  discoveries  that  in  both  men  and 
monkeys  the  anterior  body  receives  fibers  from  the  optic  nerve  of  the  same 
and  of  the  opposite  sides,  and  gives  off  fibers  which  can  l)e  followed  to  the  visual 
area  of  the  cortex,  we  conclude,  supposing  the  observations  just  mentioned 
to  be  correct,  that  the  bundle  of  fibers  running  between  the  visual  area  and 
the  anterior  quadrigeminal  l)ody  is  of  no  direct  importance  for  the  act  of 
vision.  There  is  evidence  that  this  tract  is  concerned  rather  with  certain 
nwfor  impulses  discharged  from  the  visual  area,  such  for  example  as  the 
influence  of  visual  impressions  upon  the  movements  of  the  eye  and  of  the 
body. 


614  PHYSIOLOGY   OF   THE   BRAIN-STEM 

Besides,  it  is  very  probable  that  the  optic-nerve  fibers  entering  tlie  anterior 
corpora  quadrigeniina  play  a  considerable  part  in  the  reflex  excitation  of  the 
nuclei  of  the  eye  muscles  located  along  the  floor  of  the  aqueduct  of  Sylvius. 
The  fact  that  in  the  monkey,  at  least,  these  fibers  end  in  large  numl^ers  under 
and  about  the  aqueduct,  and  the  results  of  electrical  stimulation  both  favor 
this  view.  By  stimulating  the  anterior  body  of  the  dog,  Adamuk  obtained 
the  following  movements  of  the  eyes :  stimulating  on  the  right  side  of  one 
body,  movement  of  both  eyes  to  the  left;  stimulating  in  the  midline,  parallel 
movement  of  both  e3^es  directly  upward;  stimulating  the  posterior  side,  simul- 
taneous movements  downward  and  inward.  Movements  of  the  iris  were  also 
observed.  After  a  sagittal  section  in  the  median  plane,  only  the  eye  on  the 
same  side  was  moved.  Ferrier  has  made  observations  similar  to  these  on 
the  monkey. 

Some  clinical  observations  indicate  that  the  posterior  corpora  quadrigemina 
are  concerned  in  the  propagation  of  auditory  impressions,  the  hearing  in  the 
opposite  ear  being  affected  in  cases  where  this  part  is  diseased.  Bechterew 
and  Flechsig  assert,  in  agreement  with  this  view,  that  the  ganglion  of  the 
posterior  Iwdy  receives  fibers  by  way  of  the  lateral  fillet,  from  the  cochlear 
nerve,  and  v.  Monakow  has  shown  that  the  internal  geniculate  body  is  abun- 
dantly connected  with  the  posterior  quadrigeminal  body  and  sends  fibers  to  the 
cortex  of  the  temporal  lobe.  The  statements  that  stimulation  of  the  posterior 
body  in  dogs  and  monkeys  evokes  a  cry  from  the  aniiiuil.  and  that  production 
of  voice  is  stopped  by  section  of  that  liody,  lend  some  weight  also. 

B.    THE   CRURA   CEREBRI 

The  crura  cerebri,  or  more  correctly  the  gray  matter  which  forms  the  wall 
of  the  aqueduct  of  Sylvius,  is  of  special  interest  mainly  because  the  nuclei 
of  the  oculo  motor  and  trochlear  nerves  are  found  there. 

Fig.  272  represents  in  a  frontal  section  the  nuclei  of  the  oculo  motor  as  made 
out  by  Bernheimer.  It  is  evident  that  this  nucleus  consists  of  several  parts, 
namely,  a  lateral  chief  nucleus,  a  median  nucleus  with  small  cells  {Ke  M)  and 
an  unpaired  median  nucleus  with  large  cells  (Gr  Mk).  It  is  evident  from  the 
figure  also  that  the  nerve  roots  connected  with  the  nucleus  are  in  part  crossed. 

By  successive  and  complete  removal  of  the  extrinsic  and  intrinsic  eye  mus- 
cles innervated  by  the  oculo  motor,  and  by  a  study  of  the  resulting  changes  in 
the  nucleus,  Bernheimer  has  reached  the  following  conclusions  with  regard  to 
the  function  of  its  different  parts  (Fig.  273)  :  The  extrinsic  muscles  are  inner- 
vated by  the  lateral  chief  nucleus,  but  its  cells  are  not  grouped  into  sharply 
divided  individual  nuclei.  The  small-celled  median  niiclei  (Ke  M,  Fig. 
272)  supply  the  intrinsic  muscles  of  the  homolateral  eye,  and  the  large-celled 
median  nucleus  (Gr  Mk,  Fig.  272)  belongs  to  the  intrinsic  muscles  of  both 
eyes. 

v.  Monakow  has  made  some  clinical  ol)servations  as  to  the  relations  of 
these  parts  in  man.  but  at  present  the  only  conclusions  that  can  be  drawn 
are  that  the  intrinsic  muscles  (ciliary  muscle  and  the  muscles  of  the  iris) 
are  represented  in  the  extreme  anterior  end  of  the  nucleus,  and  the  extrinsic 
muscles  in  the  remaining  divisions. 


THE   MESENCEPHALON   OR   MIDBRAIN 


615 


Before  this  Hensen  and  Volckers  had  observed,  in  substantial  agreement 
with  the  findings  of  v.  Monakow,  that  stimulation  at  the  posterior  end  of 
the  floor  of  the  third  ventricle  gave  movements  of  accommodation,  and  at  a 

/CeM 


arMK 


^^M-^'-  m^^.m^■'yy 
'     M\0r■ 
v-^^^v.,  ■!     ..    ,>;'>;■/: ^■■■.■.- 


Vhff  F 


\ 


■  •■-  V 


/^  f 


CF 


Fig.  272. — Frontal  section  through  the  anterior  tiuadrigeniinal  body  of  a  32-34  weeks'  human 
fetus,  after  Bernheinier.  The  section  passes  througli  the  lateral  chief  nucleus,  the  small- 
celled  medial  nucleus  (KeM),  tlie  large-celled  median  nucleus  (dr.MK),  the  extra-nuclear 
cour.se  of  the  medial  and  lateral  fibers  (Uikj  F,  and  Uy.  F)  of  the  third ner\e,  and  the  last  bit 
of  tlie  extra-nuclear  course  of  the  crossed  lateral  fibers  (GF).  QGF,  trans\erse  sections  of 
crossed  fibers  arising  from  behind  and  above. 


616 


PHYSIOLOGY   OF  THE   BRAIN-STEM 


point  somewhat  farther  back  gave  contraction  of  the  pupil  (cf.  Fig.  230). 
Stimuhition  at  the  anterior  border  of  the  aqueduct  of  Sylvius  gave  contraction 
of  the  internal  rectus,  and  stimulation  somewhat  farther  back  gave  in  serial 
order  contraction  of  the  superior  rectus,  levator  palpebrae  superioris.  inferior 
rectus,  and  finally  of  the  inferior  oblique.  When  the  stimulus  was  applied 
to  the  lateral  surface  or  the  deeper  parts  of  the  corpora  quadrigemina,  or  to 
the  cut  surface  of  the  transverse  section  in  the  optic  thalamus,  the  pupil 
became  dilated. 

Bernheimer  employed  a  similar  method  on  monkeys.  The  two  halves  of 
the  oeulo  motor  nucleus  were  separated  by  a  median  sagittal  section  and  weak 

electrical  stimuli  were  applied 
at  different  points.  The  results 
were  isolated  movements  of 
the  diiferent  eye  muscles  inner- 
vated from  the  side  stimulated 
and  contraction  of  the  pupil  on 
the  side  stimulated.  The  lat- 
ter effect  was  obtained  only 
when  the  stimulus  was  applied 
somewhat  internal  to  the  me- 
dian cut  surface  below  the 
aqueduct  and  in  the  anterior 
third  of  the  region  occupied 
by  the  anterior  quadrigeminal 
body — i.  e..  in  the  region  of  the 
small-celled  median  nucleus 
{Ke  M,  Fig.  2:2). 

Special  observations  as  to  the 
connections  of  the  two  sides  of 
the  oculo  motor  nucleus  afford 
some  grounds  for  believing  that 
the  nuclei  of  the  two  sphincters 
(pupil  and  accommodation)  as 
well  as  the  nuclei  of  those  ex- 
trinsic muscles  which  take  part 
in  synergic  movements  of  the 
eyes,  are  united.  The  latter  is 
shown  by  the  fact  that  synergic 

movements  cease  when  the  paired  nuclear  region  is  split  in  two  by  a  median 

sagittal  section. 

Complete  division  of  the  brain  at  the  anterior  end  of  the  midbrain  pro- 
duces a  remarkable  state  of  inertness  in  the  muscles,  which  is  described  by 
Sherrington  under  the  name  of  acerebraJ  rigidity.  It  is  recognized  by  the 
fact  that  certain  muscles  become  stiff:  the  elbows  and  knees,  for  example, 
are  rigidly  extended,  the  tail  is  inflexible,  etc.  This  condition  appears  to  be 
due  to  the  influence  of  the  afferent  nerves  from  the  regions  affected,  for  the 
stiffness  in  the  arm  muscles,  for  example,  entirely  disappears  after  section 
of  the  posterior  roots  for  the  arm. 


Fig.  273. — Schematic  representation  of  the  nucleus  of 
oculo  motor  nerves,  after  Bernheimer.  Tlie  red  lines 
indicate  the  direct,  and  the  black  the  crossed  root 
fibers.  B.M.,  intrinsic  muscles  of  the  ej'e;  Lev., 
levator  palpebrse  sup.;  R.s.,  superior  rectus;  R.int., 
internal  rectus;  Obl.inj.,  inferior  obliquus;  R.inf., 
inferior  rectus;  Tr.,  superior  oblique. 


THE   DIEXCEPHALON   OR    'TWEENBRAIN  617 

Reflex  stimulation  of  an  animal  in  this  condition  produces  certain  coor- 
dinated movements  which  are  unmistakably  related  to  the  movements  of  loco- 
motion. For  example,  the  left  anterior  and  the  right  posterior  extremities 
become  flexed,  while  the  right  anterior  and  the  left  posterior  are  extended 
at  the  same  time,  and  vice  versa.  Xot  infrequently  these  reflexes  alternate, 
beginning  regularly  with  flexion  of  the  extremity  directly  stimulated.  At 
the  same  time  the  head  and  neck  are  twisted  toward  the  stimulated  side ;  the 
mouth  is  opened,  the  lips  and  the  tongue  are  retracted,  the  eyelids  opened,  the 
pupil  is  dilated ;  the  animal  utters  cries  or  groans,  etc.  These  reactions,  which 
when  the  cerebrum  is  intact  usually  accompany  painful  sensations,  sometimes 
appear  singly,  sometimes  in  certain  combinations. 

Rigidity  of  the  triceps  muscle  can  be  intermitted  by  stimulation  of  the  white 
matter  between  the  anterior  and  the  lateral  columns  or  by  stimulation  of  cer- 
tain peripheral  nerves  of  the  posterior  extremity.  The  effect  is  felt  chiefly  on 
the  homolateral  side,  but  to  a  less  extent  on  the  heterolateral  side  also. 


§  5.    THE    DIENCEPHALON   OR    TWEENBRAIN 

The  many  connections  of  the  'tweenbrain  with  the  gray  matter  of  the 
cerelirum  on  the  one  hand  and  with  the  afferent  nerve  tracts  on  the  other 
speak  in  most  eloquent  terms  for  the  great  physiological  importance  of  this 
division  of  the  brain.  In  fact,  all  the  tracts  in  which  we  should  expect  to 
find  prolongations  of  the  posterior  root  fibers  (the  main  part  of  the  fillet 
layer,  the  superior  peduncle  of  the  cerebellum,  the  longitudinal  bundle  of 
the  formatio  reticularis),  and  the  fibers  of  the  optic  tract — all  enter  the 
'tweenbrain,  from  which  in  turn  they  are  continued  to  the  cerebral  cortex. 
The  latter  also  sends  out  fibers  to  the  'tweenbrain,  from  which  further  efferent 
tracts  are  given  off  ( Flechsig ) . 

It  is  possible  that  the  external  geniculate  body  is  the  point  of  origin  of  the 
efferent  optic  fibers,  and  that  the  reflexes  discharged  by  optic  stimuli  are  here 
carried  over  to  them. 

The  experimental  and  clinical  observations  on  the  'tweenbrain  are  not  of 
such  a  kind  as  to  give  us  even  a  crude  notion  of  its  actual  physiological  pur- 
pose in  the  normal  l)rain.  We  can  only  say  that  it  appears  from  clinical 
observations  and  from  the  anatomical  facts  that  the  different  nuclei  in  this 
portion  of  the  brain  have  different  functions,  and  that  as  a  result  we  have 
here  a  fairly  sharp  localization  of  different  paths  and  their  connections. 
Hence  when  the  optic  thalamus  contains  a  sharply  circumscribed  lesion,  cer- 
tain afferent  impulses  are  wanting,  and  for  this  reason,  as  v.  Monakow  ob- 
serves, many  complicated  movements  are  deficient ;  many  others  are  abnornmlly 
performed,  certain  components  being  overstimulated,  certain  others  inhibited. 

On  the  otlier  hand  the  conditions  appear  to  be  very  favorable  for  substitu- 
tion of  functions  in  the  optic  thalamus,  so  that  when  lesions  are  not  too 
extensive  the  effects  are  only  temporary  or  may  be  entirely  wanting.  This 
is  probal)ly  to  be  explained  in  part  by  a  bilateral  influence  of  the  thalami 
in  which  the  conmiissura  mollis  connecting  them  together  assumes  a  certain 
significance. 


618 


PHYSIOLOGY   OF   THE   BRAIN-STEM 


§  6.    FUNCTIONS   OF   THE   BRAIN-STEM   AS   A   WHOLE 

While  it  is  not  possible  as  3'et  to  name  the  exact  functions  of  the  separate 
centers  in  the  corpora  quadrigemina,  the  optic  thalami  and  certain  other 
parts  of  the  brain-stem,  we  have  some  observations  on  decerebrated  animals 
which  should  afford  us  some  light  as  to  the  functions  of  the  hindbrain,  'tween- 
brain  and  midbrain  taken  together.  What  the  central  nervous  S3^stem  is 
capable  of  without  the  cerebrum,  considered  in  connection  with  the  functions 
remaining  after  removal  of  all  the  parts  anterior  to  the  medulla,  should  give 
us  a  general  idea  of  the  total  powers  of  the  brain-stem. 


The  lowest  vertebrate,  Amphioxus,  has  no  true  encephalon :  its  brain  consists 
only  of  a  slight  enlargement  at  the  anterior  end  of  the  spinal  cord.  Anteriorly 
and  laterally  this  enlargrenient  embraces  a  ventricle  which  is  continuous  poste- 
riorly with  the  central  canal  of  the  spinal  cord.  This  "  brain  "  contains  internally 
a  ganglionic  mass  and  externally  a  mass  of  nerve  fibers.  The  former  consists 
mainly  of  multipolar  cells,  whose  fibers  pass  over  into  the  fibers  of  the  outer  layer 
running  longitudinally  of  the  animal. 

Steiner  divided  this  "  fish  "  into  two  pieces,  a  head  and  a  tail  piece.  After 
some  minutes  both  parts  responded  to  mechanical  stimulation  by  making  per- 
fectly regular  locomotor  movements,  at   the  same  time  preserving  equilibrium 

and    swimming   with    the    anterior   end    of   the 
piece  fons^ard.     They  fell  over  on  their  broad 
side  however  as  soon  as  the  movement  ceased. 
The   animals   could  even  be   cut   into   three  or 
four  pieces,  and  under  the  circumstances  named 
each    part    could    still   make    locomotor    move- 
ments.    Steiner's  conclusion   is  that   the  body 
of  Amphioxus  consists  of  perfectly  equivalent 
metameres  and  has  in  general  no  motor  center. 
Danilewsky  obtained  results  of  very  differ- 
ent purport.     After  division  of  the  animal  into 
an  anterior  and  a  posterior  half,  he  noticed  in 
the  piece  containing  the  brain  occasional  "  vol- 
untary "  movements  apparently  independent  of 
any  external  stimulus;  while  the  posterior  half 
remained    perfectly    motionless.      By    artificial 
stimulation  movements  could  be  obtained  in  the  anterior  half  more  easily  than 
in  the  posterior.     They  continued  for  from  fifteen  to  thirty  seconds  after  stimu- 
lation and  consisted  of  a  series  of  bending  and  stretching  movements. 

When  the  head  was  cut  off,  the  above-mentioned  voluntary  movements  ceased. 
The  animal  then  lay  for  one  to  two  days  without  spontaneously  changing  its 
position  in  any  wise,  when  care  was  taken  to  remove  all  external  stimuli.  The 
reflex  movements  to  artificial  stimuli  were  perfectly  normal,  but  were  not  abun- 
dant, and  the  irritability  of  the  headless  animal  was  considerably  less  than  that 
of  the  isolated  anterior  half. 

Danilewsky  concludes  from  these  and  other  observations  that  the  so-called 
brain  of  the  Amphioxus  contains  the  centers  for  voluntary  motions;  destruction 
or  separation  of  these  from  the  rest  of  the  cerebral  nervous  system  results  in 
loss  of  motility,  providing  no  external  stimulus  of  sufficient  strength  acts  upon 
the  animal. 


Olfactory  nerve 

Forebrain 

(hemispheres) 
Midbrain 

(optic  lobes) 

Hindbrain 
(cerebellum) 

Afterbrain 
(medulla 
oblongata) 


Fig.    274. — The  brain    of    Squalius 
cephalus,  a  bony  fish,  after  Steiner. 


FUNCTIONS   OF   THE   BRAIX-STEM   AS   A   WHOLE 


619 


In  the  true  fishes  the  cerebrum  is  but  slightly  developed,  and  in  the  lampreys 
and  bony  fishes  the  cortex  consists  of  only  a  simple  layer  of  epithelial  cells. 

After  extirpation  of  the  cerebrum  from  a  bony  fish  (Squalius  cephalus,  Fig. 
274)  the  animal  moves  exactly  like  a  noiTQal  animal,  and,  according  to  Steiner, 
it  is  quite  impossible  to  discover  anything  anomalous  in  its  movements.  When 
an  earthworm  is  thrown  to  the  fish,  it  makes  a  rush  for  the  booty,  seizes  it  while 
it  is  still  falling  and  devours  it.  A  cord  of  about  the  same  dimensions  thrown 
into  the  water  may  or  may  not  be  seized,  but  is  never  eaten.  A  decerebrated 
fish  may  be  even  fastidious  about  its  food ;  spurning  fish  worms  but  taking 
crumbs  of  bread  from  the  surface  of  the  water.  When  one  red  wafer  and  four 
white  ones   are  thrown  to   it,  the         ^^^  _ 


Nasal  capsules 


Olfactory  bulb 

Forebrain 

(hemispheres) 
"Tweenbrain 

Midbrain 
(optic  lobes) 

Hindbrain 
(cerebellum) 

Afterbrain 

I  medulla  oblongata) 
Vagus  nerve 


Fig.   275. — The  brain  of  Scyllium  canicula,  a  dog- 
shark,  after  Steiner. 


fish  regularly  chooses  first  the  red 
and  then  the  white  ones.  It  does 
not  move  to  take  the  food  from  the 
observer's  hand,  but  will  take  it 
from  a  long  string.  Finally,  the 
decerebrated  fish  wall  exchange  ca- 
resses with  its  uninjured  compan- 
ions. From  these  observations  we 
may  conclude  that  suppressipn  of 
the  cerebrum  in  this  genus  is  of 
no  particular  consequence — that  to 
judge  from  the  behavior  of  the 
animal  after  the  operation,  the 
parts  remaining  are  suflficient  for 
the  discharge  of  all  the  central 
functions. 

We  have  no  experiments  which 
give  us  any  clew  as  to  the  impor- 
tance of  the  'tweenbrain  in  the  bony  fish.  But  Steiner  has  reported  some  in  which 
he  removed  both  the  midbrain  and  the  'tweenbrain  along  with  the  cerebrum. 
Following  this  operation  the  animal  would  lie  entirely  motionless  on  its  side  or 
on  its  back,  with  the  fins  hanging  perfectly  limp.  Hence  we  can  say  that  the 
higher  functions  of  the  central  nervous  system  are  dependent  upon  the  'tween- 
brain and  the  midbrain,  but  just  what  share  each  one  takes  we  do  not  yet  know. 

The  selanchians  also  (dog  shark,  Scyllium  canicula,  Fig.  275)  withstand 
removal  of  the  cerebrum  without  suppression  of  their  movements.  After  a  few 
rounds  about  the  tank  the  animal  lies  quietly  on  the  bottom  of  the  tank  for 
many  hours  or  even  days  at  a  time,  Steiner  having  scarcely  ever  seen  one  in 
motion  when  it  was  not  excited  by  some  external  stimulus.  Besides,  the  animal 
does  not  spontaneously  take  food,  but  its  inability  to  do  so  is  not  the  result  of 
loss  of  the  cerebrum  icself,  but  is  rather  due  to  the  functional  loss  of  its  olfactory 
lobes,^  which  of  course  is  a  necessary  consequence  of  the  operation.  Careful 
investigation  of  the  normal  dogfish  confirms  this  indication  that  it  seeks  food 
entirely  by  the  sense  of  smell. 

Simultaneous  removal  of  both  the  'tweenbrain  and  the  cerebrum  likewise 
produces  only  insignificant  effects.  Since  this  operation  involves  destruction  of 
the  optic  ner%'es,  such  animals  are  of  course  blind;  and  yet  they  can  swim  in  a 
perfectly  normal  manner.  One  observes,  however,  that  after  some  time,  which 
appears  to  be  shorter  after  removal  of  the  forebrain  alone,  the  animal  clings  to 


'  The  olfactorj'  lobe  consists  of  the  olfactory  bulb  and  the  olfactory  tract. — Ed. 


620 


PHYSIOLOGY   OF   THE   BRAIX-STEM 


some  corner  or  wall  and,  at  least  so  far  as  observed,  never  leaves  its  retreat  except 
when  disturbed. 

After  removal  of  the  forebrain,  'tweenbrain  and  hindbrain  the  dogfish  never 
spontaneously  makes  any  movements.  Roused  artificially,  its  movements  are 
effective  and  perfectly  regular,  and,  so  long  as  it  does  not  leave  the  normal  plane 
with  reference  to  the  direction  of  gravity,  it  keeps  its  balance  properly.  But  let 
it  once  get  out  of  the  normal  position  in  the  water,  and  its  equilibrium  is  easily 

lost.  It  may  even  come  to  rest 
lying  on  its  back.  When  the  ani- 
mal is  suddenly  and  forcibly  placed 
on  its  back  it  makes  very  evident 
efforts  to  regain  its  normal  posi- 
tion, but  does  not  always  succeed. 
Hence  in  the  dogfish  also  the 
so  -  called  spontaneous  movements 
and  the  finer  coordination  of  move- 
ments appear  to  be  bound  up  with 
the  'tweenbrain  and  the  midbrain. 
The  lower  parts  of  the  brain,  how- 
ever, are  alone  sufficient  to  carry 
out  fairly  well  coordinated  move- 
ments started  by  artificial  means. 
Schrader  also  removed  the 
cerebrum  from  frogs  (Fig.  276) 
without  injuring  the  'tweenbrain. 
There  was  no  noticeable  effect : 
the  frogs  moved  about  "  sponta- 
neously "  from  one  place  to  an- 
other, they  swam  like  perfectly 
normal  animals;  at  the  approach 
of  cold  weather  they  burrowed  into 
the  mud  or  under  stones ;  or,  pass- 


Olfactory  nerve 


Olfactory  lobe 


Forebrain 
(hemispheres) 


'Tweenbrain 


Midbrain 
(optic  lobes) 

Hindbrain 

(cerebellum) 
Afterbrain 

(medulla  oblongata) 


Fig.   276. — The  brain  of  a  frog,  after  Steiner. 


ing  the  winter  in  the  open,  they  adapted  themselves  to  external  conditions  and 
with  the  same  results  as  did  their  normal  companions.  At  the  end  of  the 
hibernating  season,  or  in  summer  some  months  after  the  wound  was  perfectly 
healed,  the  animals  operated  upon,  just  like  the  normal  ones,  caught  all  the  flies 
in  the  cage,  and  so  on. 

But  when  the  'tweenbrain  was  injured  along  with  the  cerebrum,  the  same 
condition  appeared  as  had  formerly  been  described  by  Goltz  as  the  consequence 
of  removing  the  cerebrum  alone.  There  were  no  motor  effects  strictly  speaking, 
but  the  animals  had  lost  all  their  spontaneity.  When  a  frog  in  this  condition 
was  not  roused  by  some  external  stimulus,  it  would  sit  perfectly  still,  until  it 
dried  up  to  a  mummy ;  it  never  tried  to  catch  flies,  no  difference  how  many  were 
in  the  cage — it  starved  to  death  in  the  midst  of  plenty,  unless  it  was  artificially 
fed.  Its  movements  were  just  like  those  of  a  normal  frog  except  that  they  were 
perfectly  machinelike — a  given  stimulus  always  giving  the  same  response.  Since 
the  optic  nerves  were  left  uninjured  by  the  operation,  the  animal  was  influenced 
by  visual  impressions,  avoiding  obstacles  by  going  round  them  or  jumping 
over  them.  When  it  was  lowered  into  and  under  the  water  very  gradually, 
by  means  of  a  mechanism  driven  by  a  screw,  the  stimulus  of  the  change  of 
medium  was  not  suflicient  to  cause  the  frog  to  move.  It  simply  remained  sus- 
pended in  the  water  at  a  depth  determined  only  by  the  amount  of  air  in  the 
lungs. 


FUNCTIONS   OF   THE   BRAIN-STEM   AS   A   WHOLE 


621 


We  may  conclude  that  in  fishes  and  frogs  the  central  nervous  system  up 
to  and  including  the  "tweenbrain  is  sufficient  to  regulate  all  the  animal's 
functions  (with  the  exception,  of  course,  of  those  directed  by  the  sense  of 
smell)  just  as  in  the  normal  animal.  Xoticeable  changes  are  produced  in 
the  behavior  of  the  dogfish  after  removal  of  the  'tweenbrain  and  the  midbrain, 
in  the  frog  only  after  injury  to  the  "tweenbrain. 


After  taking  out  the  cerebrum  of  a  lizard  (Fig.  277),  Steiner  observed  no 
other  result  than  loss  of  spontaneous  ingestion  of  food  and  of  voluntary  move- 
ments.    When   stimulated   the    animal  moved   in   a  perfectly   normal   manner, 
avoided   obstacles,   climbed   up   the  wall   of 
the   cage,   exhibited   no   disturbance   of   the 
muscular  sense,  etc.     On  the  other  hand  it 
would  no  longer  try  to  escape  when  threat- 
ened.    Likewise,  when  the  cerebrum  and  the 
'tweenbrain  both  are  removed,  the  lizard  can 
still   make  perfectly  normal  movements  in- 
cluding leaps  of  large  size.    It  appears,  how- 
ever,   to    become    quiescent    sooner    and    its 
movements  in  climbing  seem  less  accurately 
regnilated  than  in  the  animal  with  the  'tween- 
brain intact. 

The  turtle  without  a  cerebrum  differs 
only  a  little  from  the  normal  animal.  It 
makes  spontaneous  movements,  reacts  like  a 
normal  animal  to  light  rays  and  is  able  to 
estimate  visual  impressions  properly  for  its 
own  advantage.  It  is  uncertain,  however, 
whether  such  an  animal  takes  food  sponta- 
neously. One  such  animal,  it  was  observed, 
left  tadpoles  placed  in  its  cage  untouched 
for  as  long  as  three  days.  Since,  however, 
an  animal  whose  olfactory  nerves  only  were 
cut  did  the  same  thing,  it  is  possible  that 
here  as  with  the  dogfish  the  determining 
factor  is  the  sense  of  smell. 

In  extirpating  the  'tweenbrain  from  the 
turtle,  it  is  necessary  to  destroy  the  optic 
nerves;  hence  the  result  of  the  operation  is 
blindness.  Nevertheless  the  animal  is  able 
to  orient  itself  in  space  excellently,  and, 
although  it  seldom  does  so,  to  move  spon- 
taneously. Some  slight  abnormalities  also 
are  exhibited  in  its  gait  and  in  the  manner 
of  its  carriage. 

Finally,  when  the  midbrain  in  addition 
to  the  cerebrum  and  'tweenbrain  are  re- 
moved, a  remarkable  phenomenon,  first  observed  by  Fano,  ensues — namely,  an 
uncontrollable  impulse  to  move  about  (cf.  the  similar  behavior  of  the  frog,  page 
604).  The  animal  creeps  incessantly  in  an  aimless  way;  goes  back  and  forth 
from  land  to  water  and  from  water  to  land  apparently  without  ever  finding  a 
comfortable  place.    There  are,  however,  unmistakable  abnormalities  in  its  move- 


Fore  brain 

(hemispheres) 


Pineal  liody 
(part  of 
'tweenbrain! 

Midbrain 
(optic  lobes) 


Hindbrain 
(cerebellum  1 


Afterbrain 
(medulla 
oblongata) 


m^m- 


FiG.  277. — Tlie  brain  of  a  lizard  {Hatteria 
punctata),  after  Wiederslieim.  The 
cranial  nerves  are  indicated  by 
Roman  numerals. 


622 


PHYSIOLOGY   OF   THE   BRAIN-STEM 


ments :  in  walking-  the  limbs  are  lifted  too  high,  extended  too  far  and  sometimes 
are  set  down  too  far  to  one  side  or  the  other;  the  result  is  that  the  carapace 
wabbles  from  side  to  side  and  strikes  the  floor  first  with  one  corner,  then  with 
the  other. 

The  chief  difference  between  the  lizard  and  the  turtle  and  ihe  lower  verte- 
brates after  removal  of  the  cerel)rum,  it  would  seem,  is  that  they  do  not 
spontaneously  take  food,  while  the  lizard  also  does  not  move  at  all  spontane- 


Olfactory  lobe 


Forebrain 
(hemispheres) 


Midbrain 

(optic  lobes) 
Hindbrain 

(cerebellum) 


Fig.  278. — Brain  of  a  pigeon,  after  Wipilcrshpim.     The  cranial  nerves  are  numbered. 


ously.  It  is  likely  therefore  that  the  cerebrum  is  not  of  the  same  importance 
in  animals  of  this  grade  as  it  is  in  the  higher  vertebrates  such  as  birds  and 
mammals.  But  even  in  the  latter  it  can  be  demonstrated  that  the  lower  parts 
of  the  central  nervous  system  can  maintain  a  high  degree  of  activity. 

Of  the  numerous  observations  on  birds  which  have  been  made  since  the  time 
of  Rolando,  we  shall  cite  only  those  of  Schrader  on  pigeons.  These  animals  in 
Schrader's  hands  survived  the  operation  of  removing  the  cerebrum  (Fig.  278) 
for  four  to  five  weeks  and  died  then  as  the  result  of  progressive  general  weakness 
which  began  about  the  fourth  week. 

Diiring  the  first  three  or  four  days  they  remained  in  a  sleepy  condition, 
standing  with  feathers  ruffled,  head  drawn  in,  eyes  closed  (and  often  on  one  leg), 
just  where  they  were  placed.  Now  and  then  they  would  shake  themselves,  smooth 
out  their  feathers  with  the  beak,  stretch  themselves  as  if  drowsy  and,  if  desiring 
to  defecate,  would  take  a  few  steps.  When  thrown  up  into  the  air,  they  made 
flying  movements  but  came  obliquely  downward,  striking  the  wall  or  other  obsta- 
cles and  rather  falling  to  the  floor  than  reaching  it  by  "lighting";  then  they 
once  more  sank  into  a  stupor.  In  short,  the  animals  appeared  bereft  of  all 
initiative,  and  one  would  be  inclined  to  declare  them  blind  and  deaf  and  to  doubt 


FUNCTIONS   OF   THE   BRAIN-STEM   AS  A  WHOLE  623 

whether  even  the  sense  of  touch  were  intact.  But  if  they  came  through  the  first 
few  days,  they  presented  quite  a  different  picture. 

They  now  began  to  wander  about  and  to  keep  up  a  tireless  march  about  the 
cage.  The  cadence  was  a  moderately  quick  step,  but  frequently  as  the  movement 
went  on  it  increased  in  frequency  until  it  became  a  run,  which  then  tapered  off 
to  the  usual  cadence  again,  or  was  sometimes  suddenly  interrupted  and  the  ani- 
mal settled  down  to  sleep.  It  appears  that  these  restless  movements  were  not 
the  result  of  any  abnormal  state  of  excitation,  for  the  same  animals  which  wan- 
dered about  tirelessly  all  day  spent  the  night  quietly  in  one  spot. 

These  movements  from  the  first  are  controlled  by  sight,  for  the  animal  always 
avoids  obstacles  about  the  same  as  a  normal  pigeon.  They  are  also  regulated  by 
the  sense  of  touch  and  any  temporary  disturbance  of  the  equilibrium  is  regu- 
hirly  compensated  by  the  proper  motions. 

Only  one  reaction  to  auditory  impressions  was  observed,  namely  that  the 
l)igeon  drew  back  at  the  crack  of  a  match.  Various  and  sundry  tones  and  noises 
were  tried  but  without  any  api^arent  effect. 

But  the  movements  of  a  decerebrated  pigeon  are  readily  interrupted  by  other 
means :  one  has  only  to  touch  the  animal  lightly  or  to  lift  it  and  set  it  down 
again,  and  it  immediately  draws  in  the  head,  ruffles  up  its  feathers  and  falls 
asleep. 

By  specially  devised  experiments  it  is  possible  to  show  that  the  pigeon  is 
able  to  coordinate   its  movements  to  a  definite  end.     When,  for  example,   one 


Olfactory  bulb 


Median  lougitudiiial  fissure - 

/  \  \ 

Forebrain  (hemispheres) 


Midbrain  (corpora  quadrigemina) 

V         A      -'  '  / 

Pineal  bod\  _ 

Hindbrain  (cerebellum) 

Lateral  lobe 
and 
Vermis  of  cerebellum 

Afterbrain  (medulla  oblongata) - 

Fig.  279. — Brain  of  rabbit,  after  Wietlerslieim. 

was  placed  four  or  five  feet  from  the  floor  on  a  small  flat  surface  and  a  jicreh 
was  pla('(>d  one  or  two  yards  distant  from  it,  the  pigeon  flew  to  the  perch  and 
grasped  it  firmly  with  its  feet.  Moreover,  when  the  j)igeon  was  given  a  choice 
between  flying  to  the  perch  and  flying  to  a  table  some  yards  farther  away,  it 
very  decidedly  preferred  the  latter. 

But  it  never  flew  up  spontaneously  from  the  floor.     And  it  could  not  be  ascer- 
tained positively  that  the  decerebrated  pigeon  ate  of  its  own  accord. 
37 


624 


PHYSIOLOGY   OF  THE    BRAIX-STEM 


Briefly  stated,  every  action  of  the  pigeon  without  a  cerebrum  gives  the 
observer  a  peculiar  but  perfectly  unmistakable  impression  of  an  automaton. 
Its  actions  are  very  diverse  and  very  complicated,  but  under  given  circum- 
stances can  be  very  definitely  predicted  with  a  high  degree  of  certainty.  The 
decerebrated  bird  moves  therefore  in  a  world  of  objects,  the  position  in  space, 
size,  configuration  of  which  determine  the  character  of  its  movements,  but 
which  are  otherwise  entirely  without  meaning  to  the  bird.  One  thing  like 
another  is  a  mere  space-filling  mass:  it  avoids  or  pushes  aside  another  pigeon 
as  it  would  a  stone.     A  cat  or  a  dog  means  no  more  than  an  inanimate  object. 

A  decerebrated  male  coos  like  a 
normal  male  and  exhibits  evi- 
dence of  sexual  desire — but  his 
affections  are  entirely  objectless. 
It  appears  to  be  a  matter  of  in- 
difference to  him  whether  a  fe- 
male is  present  or  not.  In  the 
same  way  a  female  shows  no  in- 
terest in  her  young.  If  full- 
fledged,  they  follow  the  mother, 
screaming  incessantly  for  food; 
but  they  might  as  well  address 
their  entreaties  to  a  stone. 

The  functions  left,  however, 
are  very  important  ones.  To 
what  extent  they  depend  upon 
the  "tweenbrain  cannot,  for  want 
of  critical  attention  to  this 
point,  be  definitely  stated.  But 
fj'om  Schrader's  observation  that  animals  in  which  the  optic  thalami  were  in- 
jured extensively  in  removing  the  cerebrum  stumbled  over  very  slight  o1)stacles 
and  did  not  correct  the  positions  of  their  limbs  immediately  when  they  were 
displaced,  it  seems  probable  that  the  'tweenbrain  plays  an  important  role  in  all 
these  functions. 

Among  mammals  we  have  observations  on  the  complete  removal  of  the 
cerebrum  from  rahhits  and  dogs  (Figs.  279  and  280). 


Fig.  280. — Lateral  view  of  the  dog's  brain,  showing 
the  different  lobes  of  the  cerebrum,  after  Ellen- 
berger  and  Baum.  1,  Olfactory  lobe;  2,  bound- 
ary between  the  olfactory  and  frontal  lobes;  3, 
boundary  between  the  frontal  and  parietal  lobes 
(cruciate  fissure);  4,  olfactory  tract;  5,  piriform 
lobe;  6,  frontal  lobe;  7,  parietal  lobe;  8,  temporal 
lobe;  9,  occipital  lobe;  10,  cerebellum;  11, 
boundary  between  the  parietal  and  temporal 
lobes  (fissure  of  Sj'lvius) ;  12,  medulla  oblongata. 


According  to  Christiani,  rabbits  with  the  cerebrum  removed  sat  immedi- 
ately after  the  operation  just  as  normal  animals  are  careful  to  sit,  and  when 
attempts  were  made  to  catch  them  by  the  hind  leg-  they  ran.  Spontaneous  move- 
ments were  also  occasionally  made.  But  when  they  were  not  disturbed  in  any 
way  and  were  protected  from  powerful  stimuli,  they  easily  fell  asleep.  They 
woke  from  this  sleep  without  being  roused  externally.  They  walked  about  for  a 
long  time  but  finally  came  to  rest  and  went  to  sleep  again.  There  was  nothing 
abnormal  in  any  of  these  movements :  the  animals  avoided  obstacles  without 
touching  them;  they  made  stops  in  the  midst  of  their  wanderings;  they  climbed 
and  sprang  upon  objects;  etc. 

The  rabbit  therefore  can  also  regulate  its  movements  quite  normally  with- 
out a  cerebrum  and  can  use  its  visual  sense  for  this  purpose.     We  have  no 


FUNCTIONS   OF  THE   BRAIN-STEM   AS   A   WHOLE 


625 


more  exact  observations  on  their  behavior,  as  the  animals  in  these  experiments 
were  not  observed  for  more  than  twelve  hours  after  the  operation- 
It  api^ears  from  Cbristiani's  observations  that  this  regulation  is  the  work  of 
the  'twcenbrain,  for  in  rabbits  deprived  of  this  part,  or  in  which  it  was  exten- 
sively injured,  the  coordination  necessary  for  locomotion  and  for  maintaining 
the  equilibrium  in  sitting  and  standing  was  entirely  lost. 

Much  more  significant  than  these  observations  are  those  of  Goltz  on  a  de- 
cerebrated dog  which  survived  the  operation  for  a  long  time.  In  this  dog, 
whose  history  we  shall  now  relate,  not  only  was  practically  all  the  cerebrum 
destroyed,  but  the  'tweenbrain  and  to  a  large  extent  the  corpora  quadrigemina  on 
the  left  side  as  well.  The  functions  carried  out 
by  this  dog  were  therefore  probably  less  extensive 
than  would  be  possible  if  the  cerebrum  ordy  were 
extirpated.  Since  this  experiment  is  of  the  ut- 
most importance  for  a  proper  conception  of  the 
functions  of  the  central  nervous  system,  we  shall 
report   it  somewhat  extensively. 

The  left  hemisphere  of  this  dog  was  removed 
in  two  operations  on  the  27th  of  June  and  the 
23d  of  November,  1889,  the  entire  right  hemi- 
sphere was  removed  in  one  operation  on  the  17th 
of  June,  1890.  The  dog  lived  until  December  31, 
1891,  when  he  was  killed  by  bleeding,  and  was 
therefore  under  observation  for  a  year  and  a  half 
after  the  last  operation.  Fig.  281  is  a  picture  of 
the  brain  as  it  ajjpeared  at  autopsy. 

On  the  third  day  after  the  last  operation 
(June  20,  1890)  the  animal  walked  about  the 
room  without  falling.  From  this  time  on  his 
strength  increased  so  rapidly  that  on  the  22d  of 
July  he  easily  climbed  up  an  inclined  plane  of 
twenty  degrees.  The  ability  to  perform  crude 
muscular  movements  was  therefore  perfect. 

After  some  months  considerable  disturbance 
in  nutrifion  made  its  appearance,  the  hind  parts 
becoming  more  and  more  emaciated.  By  feeding 
the  animal  heavily  this  progressive  emaciation 
was  finally  overcome,  but  the  certainty  of  the 
dog's  movements,  which  was  so  plain  a  feature 
for  a  few  weeks  after  the  operation,  did  not  re- 
turn. In  spite  of  this  until  a  few  days  before  his 
death  he  was  able  to  raise  himself  on  his  hind  legs 
and  to  place  his  paws  on  the  grating  of  his  cage. 
According  to  Goltz  himself  the  cause  of  this 
emaciation  lay  partly  in  the  fact  that  the  animal 

continually  moved  about  in  his  cage  and  that  he  never  rested  nor  slept  so  long 
as  a  normal  animal.  It  is  probable  also  that  it  was  due  to  imperfect  heat  regu- 
lation, since  the  heat  loss  was  greater  than  normal.  At  any  rate  it  is  stated 
that  the  skin  was  noticeably  warm.  Otherwise,  judging  by  nothing  more  than 
the  fact  that  the  animal  lived  so  long,  the  heat  regulation  nnist  have  been  fairly 
good.  When  the  dog  slcj)!,  he  curled  up  as  normal  dogs  do;  in  a  warm  room  he 
panted  and  stretched  out  his  tongue;  and  in  a  cold  room  he  shivered. 


Fig.  281. — The  remainder  of  the 
brain  of  Goltz's  dog,  after  re- 
moval of  the  cerebral  hemi- 
spheres. The  medulla,  pons, 
cerebellum  and  the  roots  of 
all  the  cranial  nerves  con- 
nected with  the  medulla  and 
pons  were  perfectly  normal. 
The  corpora  quadrigemina 
were  somewhat  degenerated. 
All  tliat  was  left  of  the  cere- 
bral cortex  was  a  small  portion 
of  the  temporal  lobe  on  each 
side. 


626  PHYSIOLOGY  OF  THE   BRAIN -STEM 

Digestion  went  on  normally:  the  tongue  and  the  teeth  were  normally  pre- 
served; there  was  no  foul  odor  from  the  mouth;  the  faeces  were  of  normal  color 
and  consistency.  Xo  observations  were  made  as  to  the  utilization  of  foodstuffs. 
The  urine  contained  no  proteid  nor  sugai-.  The  animal  (a  male)  gave  no  evi- 
dence of  sexual  heat. 

The  cruder  movements,  such  as  locomotion,  were  fairly  normal  and  the  gait 
on  a  rough  floor  was  tolerably  good.  On  a  smooth  floor  the  animal  slipped  very 
easily,  but  recovered  his  feet  without  help.  He  never  walked  on  the  backs  of 
his  feet;  and  immediately  straightened  them  M'hen  his  toes  were  forcibly  turned 
under. 

Placed  on  a  table  with  one  foot  over  a  trapdoor,  the  dog  allowed  the  foot  to 
follow  the  trap  for  a  distance  as  it  fell,  but  did  not  lose  his  equilibrium. 

It  happened  once  that  the  dog  had  one  hind  paw  injured.  Until  the  paw 
was  completely  healed  he  hopped  about  on  three  legs,  keeping  the  injured  mem- 
ber voluntarily  lifted  from  the  floor. 

Hence  the  bodily  movements  were  regulated  in  many  different  ways.  And 
yet  his  movements  were  not  very  precise,  for  when  he  was  pinched  he  corild  not 
purposely  reach  the  place.  If  for  example  he  was  pinched  on  the  left  hind  foot, 
he  would  snap  to  the  left,  but  seldom  caught  the  offender's  hand. 

The  sense  of  touch  was  noticeably  dull.  When  by  means  of  a  fine  tube  air 
was  blown  between  the  hairs  on  the  back  of  his  foot,  he  did  not  move;  he  was 
likewise  insensitive  to  blasts  on  his  nose.  But  certain  parts  of  the  skin,  as  for 
example,  the  interior  of  the  ear,  proved  to  be  extremely  sensitive.  He  responded 
promptly  to  stronger  cutaneous  stimuli  and  could  be  awakened  from  his  sleep  in 
this  way.  If  while  he  was  walking  about  he  was  pinched  anjT^'here,  he  gave 
evidence  of  his  displeasure  by  various  expressions  of  the  voice,  or  even  snapped. 

In  order  to  test  the  sense  of  taste,  Goltz  made  the  following  experiment. 
He  placed  some  horse  meat  in  each  of  two  dishes.  To  the  one  he  added  milk, 
the  other  he  covered  with  an  extremely  bitter  solution  of  quinine.  He  fed  the 
dog  several  pieces  of  the  meat  wet  with  milk,  one  after  the  other,  by  simply 
holding  them  close  to  his  nose.  They  were  seized,  chewed  and  swallowed.  Sud- 
denly he  offered  him  a  piece  from  the  quinine  dish.  It  also  was  seized  and 
chewed  once;  then  the  dog  made  a  wry  face  and  spat  it  out. 

The  sense  of  smell  was  of  course  lost.  It  was  only  by  stimulation  of  the 
branches  of  the  trigeminal  nerve  that  pungent  odors  had  any  effect  on  the  animal. 

Auditory  sensations  were  very  much  blunted,  although  it  was  possible  to 
rouse  the  animal  from  sleep  by  a  purely  auditory  stimulus. 

The  sense  of  sight  was  practically  lost.  The  pupils  of  both  eyes  contracted 
when  light  was  thrown  into  them,  and  the  eyes  were  closed  when  a  dazzlingly 
bright  light  from  a  bull's-eye  lantern  was  thrown  in  the  dog's  face.  In  rare 
cases  he  turned  his  head  to  one  side.  That  was  all.  He  was  unable  with  the 
aid  of  vision  to  avoid  obstacles  placed  in  his  way;  and  the  blank,  idiotic  ex- 
pression of  his  eyes  never  changed  in  the  least  when  threatening  gestures  were 
made  or  a  strange  dog  was  held  so  that  the  images  must  have  been  formed  on 
the  retina. 

The  animal's  intelligence  was  very  much  reduced.  He  was  so  stupid  that 
on  the  last  day  of  his  life  he  raised  a  howl  when  he  was  lifted  out  of  the  cage  to 
be  fed,  just  as  he  had  done  for  months.  He  never  gave  any  expression  of  joy 
and  only  showed  displeasure  when  he  was  pinched  or  handled  roughly.  Once 
when  he  had  gone  without  food  for  a  longer  time  than  usual,  he  made  sounds 
indicating  his  impatience.  He  also  ate  more  voraciously  than  usual.  But 
when  he  had  eaten  his  fill,  he  stopped  and  lay  down  to  rest  or  to  sleep. 

He  never  learned  to  lick  himself  dry  when  he  became  wet,  so  that  he  shiv- 


FUNCTIONS   OF   THE   BRAIN-STEM   AS  A   WHOLE  627 

ered  much  from  cold  at  times.  He  likewise  never  tried  to  hold  a  bone  with  his 
fore  paws. 

In  view  of  this  it  is  the  more  remarkable  that  the  animal  again  acquired  the 
ability  to  eat  and  to  drink.  For  a  long  time  it  was  necessary  to  push  the  food 
far  back  in  the  animal's  throat,  for  when  it  was  merely  laid  on  the  front  end  of 
his  tongue  it  was  neither  chewed  nor  swallowed.  On  the  twenty-third  day  after 
the  last  operation  it  became  unnecessary  to  push  the  food  so  deep  into  the  mouth. 
It  was  seized  by  the  tongue  and  carried  back  when  placed  pretty  well  forward 
in  the  mouth.  Gradually  the  dog  got  better  control  of  his  jaws,  and  finally  had 
made  such  progress  that  he  could  drink  a  large  bowl  of  milk  when  his  snout 
was  held  close  in  it,  and  could  eat  meat  when  the  dish  was  placed  so  that  his  snout 
touched  the  food.  The  reason  for  touching  the  food  will  be  apparent  when  we 
remember  that  the  sense  of  smell  was  entirely  lost  and  the  sense  of  sight  reduced 
to  almost  nothing. 

The  following  experiment  shows  that  the  animal  could  do  a  rather  more 
difficult  task.  A  small  blind  alley  was  made  by  means  of  two  boards  placed 
endwise  against  the  wall.  When  the  dog  was  let  into  ,this  alley,  which  was  so 
narrow  that  he  could  not  turn  round  in  it,  he  walked  to  the  end  and  reached 
up  on  the  wall,  "  trying  "  in  vain  to  get  out.  Finally  he  began  to  walk  back- 
ward, and  after  about  twenty  minutes  managed  to  back  all  the  way  out,  although 
the  length  of  the  alley  was  only  about  twice  the  length  of  the  animal. 

It  follows  from  these  observations  that  a  dog  without  his  cerebrum  is 
al)le  to  carry  out  all  of  the  functions  necessary  to  life,  if  only  his  food  be 
placed  immediately  in  front  of  his  nose;  that  he  is  still  able  to  perform 
locomotor  movements  satisfactorily;  that  these  movements  are  influenced  and 
regulated  by  the  muscular  and  tactile  senses;  also  that  the  sense  of  hearing 
and  the  sense  of  sight,  although  in  a  very  slight  degree,  can  influence  his 
movements.  Finally,  his  behavior  during  hunger  and  after  taking  food  teach 
us  that  the  bodily  desires  are  still  "  felt."  The  cerebrum  we  must  conclude 
is  not  necessary  for  any  of  these  functions,  nor  for  passing  from  the  sleeping 
to  the  waking  condition  and  vice  versa. 

Flechsig  was  able  to  determine  on  a  human  monster,  in  which  only  the 
lower  parts  of  the  brain  up  to  and  including  the  posterior  corpora  quadrigemina 
were  developed,  that  these  findings  for  the  dog  apply  at  least  in  part  to  man. 
The  child  lived  for  a  day  and  a  half  and  during  this  time  gave  various  signs  of 
discontent.  It  whimpered  occasionally  and  its  whimperings  became  more  vig- 
orous and  various  movements  of  its  limbs  became  more  active  when  its  skin  was 
pinched. 

The  observations  here  brought  together  on  the  effects  of  removing  the 
cerebrum  from  different  vertebrates  may  be  summarized  briefly  as  follows: 
these  effects  are  very  slight  or  even  unnnticeahle  in  the  lowest  vertebrates, 
hut  the  higher  we  ascend  the  scale  of  animal  life,  the  more  pronounced  and 
extensive  thej/  become.  But  even  in  the  highest  of  the  lower  animals  studied 
(dog),  the  functions  of  the  central  nervous  system  which  remain  are  sufficient 
to  maintain  all  the  vital  processes  necessary  for  life,  with  the  single  exception 
of  seeking  food.  The  effects  are  chiefly  upon  the  highest  powers  of  the 
nervous  system,  especially  upon  those  which  we  comprehend  as  belonging  to 
consciousness.     For  these  powers  the  cerebrum  in  the  highest  vertebrates  at 


62$  PHYSIOLOGY   OF   THE    BRAIN-STEM 

least  plays  the  determining  part,  and  cannot  1)G  replaced  Ijy  the  lower  nerve 
centers.  With  regard  to  the  state  of  consciousness  in  decerebrated  animals, 
it  is  evident  that  no  proposition  can  be  laid  down  which  is  entirely  free  from 
objection,  and  there  is  no  occasion  here  to  discuss  the  hypotheses  bearing 
on  the  subject  which  have  been  put  forward. 

References.— Go?<z,  Arcbiv.  f.  d.  ges.  Physiol,  Bd.  li,  1892.— L.  Liiciani, 
"Das  Kleinhirn,"  Leipzic,  1893. — v.  Monakow,  "  Gehirnpatholog:ie,"  Wien,  1897. 
— Nothnagel,  "  Topische  Diagnostik  der  Gehirnkrankheiten,"  Berlin,  1879. — 
Schrader,  Arcbiv.  f.  d.  ges.  Physiol.,  Bd.  xli,  xliv,  1887,  1889.— -S^^ner,  "Die 
Funktionen  des  Zentralnervensystem  und  ibre  Pbylogenese,"  1-4,  Braunschweig, 
1885-1900.— /I.  Thomas,  "  Le  cervelet,"  Paris,  1897. 


CHAPTER    XXIV 

PHYSIOLOGY    OF    THE    CEREBRUM 

It  has  long  been  assumed  that  the  brain  represents  the,  material  substratum 
of  the  psychical  activities.  Descartes  regarded  the  pineal  gland  as  the  seat  of 
the  mind;  Willis  located  perception  in  the  corpora  striata,  imagination  in  the 
corpus  callosum,  and  memory  in  the  convolutions;  and  Cabanis  expounded  his 
doctrine  that  the  brain  secretes  thought  in  the  same  way  as  the  liver  secretes  bile. 

Gall  was  the  first  to  get  a  deeper  insight  into  the  signiificance  of  the  brain 
as  the  substratum  of  the  psychical  life  of  man,  and  he  undertook  to  prove  this 
doctrine  by  actual  observation.  As  Flourens,  the  most  positive  opponent  of  Gall, 
put  it,  this  doctrine  existed  in  science  before  Gall,  but  after  him  it  ruled  there. 
Investigating  each  sense  by  itself,  Gall  excluded  all  of  them,  one  after  the  other, 
from  any  direct  participation  in  the  powers  of  intelligence.  So  far  from  being 
developed  in  proportion  to  the  intelligence,  most  of  the  senses  he  saw  are  devel- 
oped exactly  in  inverse  proportion  thereto.  Taste  and  smell  are  sharper  in  the 
mammals  than  in  man,  sight  and  hearing  are  more  keenly  developed  in  the  birds 
than  in  manunals;  but  the  brain  is  everywhere  developed  in  direct  proportion 
to  intelligence.  Intelligence  remains  after  loss  of  sight  and  of  hearing  and 
would  probably  survive  all  the  senses. 

The  brain  therefore  is  the  only  organ  of  the  mind.  It  consists  however  of 
many  different  parts,  and  the  question  naturally  arises  Avhether  all  of  these  parts 
are  of  the  same  importance  for  the  psychical  activities.  Gall  and  his  pupils  had 
the  idea  that  only  the  cerebral  hemispheres  represent  the  substratum  of  the 
mind,  and  from  what  we  have  learned  in  the  preceding  chapter,  and  as  we  shall 
prove  more  fully  in  this  one,  we  can  now  make  this  affirmation  with  much 
greater  definitcncss.  The  lower  parts  of  the  brain  probably  have  no  direct  sig- 
nificance for  the  psychical  functions.  As  has  been  observed  in  the  preceding 
chapter,  their  purpose  seems  to  be  rather  to  regulate  quite  independently  of  the 
consciousness  and  of  the  will  a  number  of  the  purely  vegetative  functions  and 
to  connect  the  cerebral  hemispheres  with  the  remainder  of  the  nervous  system. 

Gall  however  was  not  satisfied  merely  to  have  demonstrated  the  importance 
of  the  brain  for  the  psychical  life,  but  proceeded  to  work  out  a  detailed  psychology 
which  he  endeavored  to  bring  into  line  with  his  ideas  concerning  the  functions 
of  the  brain. 

Gall's  psychology  subdivided  the  intelligence  into  a  number  of  diflferent  fac- 
ulties entirely  indei)endent  of  one  another,  each  of  which  had  its  own  power  of 
perception,  memory,  judgment,  imagination,  etc. 

The  most  positive  objections  can  be  raised  against  this  conception  of  the 
mental  personality  of  man  as  an  aggregate  of  arbitrarily  chosen  and  independent 
faculties.  This  was  early  realized  by  Flourens  who,  in  direct  opposition  to  Gall, 
laid  great  emphasis  on  the  unity  of  the  ego.  Moreover,  the  faculties  which 
Gall  postulated  were  not  coordinated  with  each  other,  but  were  of  all  possible 
and  impossible  kinds.  Some  were  partly  metaphysical,  some  related  to  the  emo- 
tions and  some  stood  in  direct  connection  with  the  sensations. 

629 


630  PHYSIOLOGY   OF   THE  CEREBRUM 

It  is  practically  certain  that  Gall's  psychology  would  never  have  attracted 
any  further  notice  if  he  had  not  attempted  also  to  locate  the  organs  for  the 
different  faculties  in  different  parts  of  the  brain. 

His  point  of  departure  was  an  observation  which  he  had  made  as  a  student. 
He  thought  he  had  discovered  that  those  of  his  fellows  who  had  a  good  memory 
for  words  had  prominent  eyes.  Hence  the  organ  for  this  faculty  must  be  situated 
above  and  behind  the  eye  sockets.  He  conceived  that  the  organs  of  the  different 
faculties  lay  only  on  the  surface  of  the  brain,  also  that  wherever  a  certain  organ 
was  especially  well  developed  the  skull  at  that  point  was  bulged  out. 

Hence  if  one  were  to  observe  the  most  characteristic  peculiarities  in  the 
traits  and  the  character  of  many  different  individuals  and  were  to  study  their 
skulls,  one  could  determine  the  exact  location  of  the  separate  organs.  Then 
nothing  would  be  simpler  than  to  determine  a  person's  character  and  the  quality 
of  his  endowments  by  examining  his  skull.  What  a  broad  and  extremely  inter- 
esting perspective  this  simple  and  (in  the  fullest  meaning  of  the  word)  palpable 
doctrine  opened  up !  And  how-  extraordinarily  useful  phrenology,  as  the  new 
science  was  called  by  its  disciples,  would  be  in  education  and  in  the  choice  of 
a  life  work! 

Gall  was  unquestionably  a  good  observer,  and  in  many  points  the  funda- 
mental principles  of  his  method  were  not  far  wrong.  But  this  did  not  prevent 
him  from  losing  all  critical  sense  and  discretion  when  it  came  to  determining 
empirically  the  location  of  his  "  organs."  Gall's  own  writings  and  those  of  his 
followers  furnish  the  most  flagrant  examples  of  this ;  nevertheless  his  doctrines 
were  for  a  long  time  espoused  in  certain  qviarters  with  the  greatest  confidence. 

In  science  phrenology  soon  had  its  day,  and  since  Flourens  published  his 
researches  on  the  functions  of  the  brain  (1S22),  it  has  belonged  among  the  curi- 
osities of  the  scientific  lumber  room. 

Flourens'  works  declared  that  only  the  cerebral  hemispheres  were  of  any 
direct  importance  for  intelligence.  He  laid  down  the  following  propositions, 
which  are  given  here  in  his  own  words:  (1)  One  can  cut  away  from  the  front, 
the  back,  the  top  and  from  the  sides,  a  fairly  large  part  of  the  cerebral  hemi- 
spheres without  destroying  the  intelligence.  Hence  a  rather  limited  portion  of 
the  brain  is  sufficient  for  the  exercise  of  its  mental  functions.  (2)  The  more  one 
removes  of  the  brain  substance  the  more  is  the  intelligence  weakened,  and  its 
powers  proportionally  restricted.  When  a  certain  limit  is  passed  the  intelligence 
vanishes  altogether.  For  the  complete  development  of  the  mental  powers  there- 
fore all  the  different  parts  of  the  cerebrum  work  together.  (3)  When  one  par- 
ticular function  is  lost,  all  are  lost ;  when  one  faculty  vanishes,  all  vanish.  There 
are  no  different  organs  for  the  different  faculties  or  sensations.  The  ability  to 
perceive,  judge,  or  will  one  thing-  has  its  seat  in  the  same  point  as  the  ability 
to  perceive,  judge,  or  will  another.  This  ability,  which  in  its  essence  is  one  and 
indivisible,  has  its  seat  in  a  single  organ. 

For  more  than  a  decade  the  conception  expressed  in  the  propositions  above, 
partly  owing  to  the  reaction  against  phrenology,  partly  owing  to  the  weight  of 
Flourens'  investigations  on  the  physiology  of  the  nervous  system,  was  regarded 
as  the  last  word  of  science  with  regard  to  the  relation  of  the  mind  to  the  brain. 
This  is  not,  however,  the  modern  conception. 

There  was  indeed  a  modicum  of  truth  in  phrenology.  iSTot  that  its  positing 
the  different  intellectual  qualities  in  definite  regions  of  the  brain  was  correct, 
nor  that  its  postulate  that  the  form  of  the  skull,  its  curvatures  and  prominences, 
gives  expression  to  the  functional  capabilities  of  the  underlying  parts,  has  been 
found  to  accord  with  fact.  In  this  respect  phrenology  has  been  relegated  far 
to  the  rear,  we  hope  for  once  and  all.     But  further  research  has  demonstrated 


PHYSIOLOGY   OF  THE  CEREBRUM  631 

•that  the  cerebral  hemispheres  have  not  one  and  the  same  function  in  all  of  their 
parts;  it  has  shown  that  in  the  production  and  elaboration  of  the  different  kinds 
of  sensations  as  well  as  in  the  influence  of  the  cerebrum  on  the  functions  of  the 
body,  entirely  different  areas  of  the  hemispheres  are  active. 

We  may  go  farther  and  say  that  we  have  certain  grounds  for  believing  that 
different  sections  of  the  cerebrum  participate  in  the  different  mental  processes; 
yet  the  modern  doctrine  of  cerebral  localization  is  at  bottom  something  quite 
different  from  the  old  phrenology.  Phrenology  assumed  that  there  were  a  num- 
ber of  different  organs  in  the  brain,  each  specifically  set  aside  for  some  complex 
function,  although  that  function  was  sometimes  purely  metaphysical.  The  new 
doctrine  has  been  content  to  establish  first  of  all  the  importance  of  the  different 
parts  of  the  brain  for  the  functions  of  the  body  and  for  the  sensations  produced 
by  stimulation  of  the  afferent  nerves.  It  has,  it  is  true,  ventured  a  step  farther 
and  has  sought  to  bring  the  activity  of  the  mind  under  physiological  investiga- 
tion. But  these  investigations  aim  to  discover  how  the  psychical  functions  can 
be  carried  out  by  the  cooperation  of  the  various  parts  of  the  brain — exactly  the 
reverse  process,  therefore,  of  the  phrenology  of  Gall.  Finally,  the  spirit  of  mod- 
em research  is  poles  asunder  from  the  spirit  of  phrenology:  it  will  not  forcibly 
warp  the  facts  into  line  with  preconceived  ideas  and  arbitrary  hypotheses;  but 
it  seeks  to  be  entirely  fcee  from  bias,  and  in  this  spirit  to  determine  by  observa- 
tion and  experiment  the  facts  which  may  be  able  to  help  us  on  toward  a  deeper 
theoretical  comprehension  of  the  cerebral  functions. 

As  early  as  1825,  Bouillaud  tried  to  show  that  lesions  of  the  cerebral  hemi- 
spheres involved  loss  of  the  coordinated  movements  necessary  for  speech  only 
when  the  most  anterior  divisions  of  the  brain,  the  frontal  lobes,  were  affected. 
Somewhat  later  (1836)  Marc  Dax  stated  that  articulate  speech  was  controlled 
by  a  place  in  the  left  half  of  the  brain.  But  his  ideas  received  no  encourage- 
ment— in  fact  they  were  described  as  pseudo-scientific.  In  1861,  however,  Broca 
made  definite  observations  on  some  diseased  cases  and  was  able  to  establish  the 
fact  that  (in  right-handed  persons)  destruction  of  the  third  frontal  convolution 
of  the  left  hemisphere  abolishes  the  power  of  speech. 

These  statements  were  soon  corroborated  by  observations  on  similar  cases  by 
other  authors,  and  thus,  contrary  to  Flourens'  doctrine,  a  functional  differentia- 
tion of  the  cortex  into  different  regions  was  demonstrated.  But  there  was  con- 
siderable hesitation  about  giving  up  the  doctrine  of  the  unity  of  the  brain,  and 
it  was  not  until  investigations  had  been  carried  much  further  that  it  was  finally 
overthrown. 

On  purely  anatomical  grounds  Meynert  concluded  that  the  anterior  part  of 
the  cerebral  hemispheres  was  more  closely  related  to  motion  and  the  posterior 
part  to  sensation.  Then  came  (1870)  the  work  of  Fritsch  and  Hitzig  by  which 
it  was  established  for  all  time  that  different  parts  of  the  hemispheres  actually 
have  different  functions. 

Among  the  many  articles  of  faith  which  had  long  been  held  with  regard  to 
the  brain,  was  the  belief  that  the  cerebral  cortex  was  nonexcitable  electrically — 
i.  e.,  that  no  visible  effect  could  be  produced  by  application  of  the  electric  current 
to  the  cortex.  Fritsch  and  Hitzig  showed  that  this  idea  was  wholly  erroneous 
and  demonstrated  that  by  electrical  stimulation  of  the  cortex  muscular  move- 
ments could  be  obtained;  but  that  they  could  only  be  obtained  when  the  current 
was  applied  to  certain  definite  portions.  The  resulting  movements  appeared  in 
various  groups  of  muscles — those  of  the  face,  the  fore  or  the  hind  leg,  etc. — ac- 
cording to  the  exact  point,  within  the  general  area,  which  was  stimulated.  From 
other  portions  of  the  cortex  the  current  produced  no  visible  effect. 

These  discoveries  excited  the  greatest  interest  and  led  to  many  now  researches 


632 


PHYSIOLOGY   OF  THE  CEREBRUM 


of  various  kinds  which  both  served  to  establish  the  doctrine  of  different  physio- 
logical functions  for  different  cortical  regions,  and  at  the  same  time  to  greatly 
broaden  and  deepen  our  knowledge  of  the  cerebral  functions. 

Since  very  little  is  known  with  regard  to  the  physiological  purposes  of  the 
basal  ganglion  (e.  g.,  the  nucleus  candatus.  nucleus  lentiformis.  the  gray  masses 
of  the  claustrum,  etc.)  belonging  properly  to  the  cerebrum,  we  shall  pass  over 
them  here  and  in  this  chapter  shall  consider  first  the  motor  and  sensory  areas  of 
the  cortex,  and  then  take  up  the  psycho-physical  functions  of  the  cerebrum. 


FIRST    SECTION 
THE   MOTOR   AND   SENSORY   AREAS   OF  THE   CORTEX 


g  1.    THE   MOTOR   AREAS 


A.    GENERAL   SURVEY 


-4SG 


COR 


The  results  of  Fritsch  and  Hitzig  to  which  we  liaA-e  referred  on  the  pre- 
ceding page  were  as  follows:   Xo  movements  were  obtained  by  stimulation 

of  the  posterior  part  of  the  cere- 
bral cortex  with  weak  electric  cur- 
rents. But  when  the  current  was 
applied  to  the  anterior  part,  move- 
ments appeared  on  the  opposite  side 
of  the  body.  With  a  weak  stimulus 
the  effect  was  confined  to  certain 
sharply  defined  groujis  of  muscles. 
With  a  stronger  stimulus  the  move- 
ments appeared  also  in  other  groups 
on  the  same  side   (cf.  Fig.  282). 

With  rapidly  repeated  induction 
shocks  applied  to  the  different 
points,  the  appropriate  muscles 
could  be  thrown  into  tetanus.  Con- 
tinued for  several  seconds,  this  form 
of  stimulus  produced  a  persistent 
tetanus  w-hich  might  spread  to  all 
parts  of  the  body  (cortical  epilepsy, 
cf.  below,  page  641). 

Tlie  first  question  suggested  by 
these  ol)servations  is,  what  part  of' 
tlie  cerebrum  is  the  part  primarily 
stimulated  by  the  current — the  cor- 
tex, the  underlying  white  matter,  or 


Fig.  282. — Dorsal  surface  of  the  dog's  brain, 
with  the  excitation  points  indicated  according 
to  Fritsch  and  Hitzig.  a,  neck  muscles;  +, 
extensors  and  adductors  of  the  foreleg;  +, 
flexion  and  rotation  of  the  foreleg;  -,  hindleg; 
O,  face;  Scr,  sulcus  cruciatus;  ASG,  anterior 
sigmoid  gyrus;  PSG,  posterior  sigmoid  gyrus; 
COR,  coronary  gyrus;  cor,  coronary  fissure; 
/,  //,  ///,  IV,  first  to  fourth  external  con- 
volutions. 


the  deeper  parts  of  the  brain? 
The  answer  is  unanimous,  that  the  cortex  represents  the  immediate  point 
of  attack.     The  following  are  among  the  most  important  experimental  proofs 
of  this  proposition: 


THE  MOTOR   AREAS 


633 


In  the  first  place  it  may  be  observed,  that  if  the  current  took  effect  on  the 
lower  parts  of  the  cerebrum,  muscular  movements  should  be  obtained  by  appli- 
cation of  the  current  to  widely  different  regions  of  the  cortex.  Since  this  is  not 
the  case,  it  is  merely  a  question  between  the  cortex  and  the  subjacent  white  mat- 
ter. The  following  facts  speak  against 
the  latter  possibility : 

(1)  Under  certain  circumstances  it  is 
possible  to  stimulate  the  cortex  mechan- 
ically, but  the  white  matter  cannot  be 
so  stimulated  (Luciani  and  Tamburini). 
(2)  It  requires  a  stronger  current  to  stimu- 
late the  corona  radiata  electrically  than  to 
stimulate  the  cortex.  (3)  On  the  other 
hand  a  muscular  contraction  caused  by 
continuous  stimulation  of  the  cortex  ceases 
decidedly  sooner  than  after  stimulation  of 
the  corona  (Levy).  (4)  After  poisoning 
with  chloral  (Franck  and  Pitres),  the  cor- 
tex becomes  inexcitable,  but  movements  can 
still  be  obtained  from  the  corona.  Like- 
wise the  cortex  is  rendered  inexcitable  to 
a  depth  of  2-3  mm.  by  painting  it  with 
cocain  (Carvalho). 

Again  when  a  certain  muscular  con- 
traction is  aroused  first  from  the  cortex 
and  then  from  the  corona  and  the  first 
two  responses  are  recorded,  it  is  found 
that  the  latent  period  of  the  first  is  con- 
siderably longer  than  that  of  the  second 
— e.  g.,  cortex,  0.065  second ;  corona,  0.045 
second   (Franck).     The  difference  of  0.02 

second  is  doubtless  due  to  a  delay  in  the  excitation  process  occasioned  by  the 
nerve  cells  (Fig.  283).  The  facts  also  that  the  contraction  curve  following  cor- 
tical stimulation  rises  more  slowly  and  is  not  so  regular  as  that  following  stimu- 
lation of  the  corona,  and  that  cortical  stimulation  is  accompanied  by  a  clonic  ' 
contraction,  while  stimulation  of  the  corona  is  not,  are  probably  to  be  explained 
by  the  presence  of  nerve  cells. 

Hence  it  is  conceivable  that  the  electrical  stimulus  acts  directly  on  the  large 
pyramidal  cells  of  the  cortex  (cf.  Fig.  284,  right  side  Nos.  4,  5,  6)  although  this 
would  not  mean  that  there  might  not  be  other  points  of  attack,  as,  c.  g.,  the  end 
arborizations  of  the  afferent  nerves  as  well. 

These  things  ])einfj  so,  we  may  say  that  certain  definite  regions  of  the 
cortex  stand  in  a  more  definite  relation  to  the  movements  of  the  body  than 
do  other  ])arts  of  the  brain.  These  regions  are  described  as  the  motor  cortical 
area^  of  the  cerebrum. 

B.    STIMULATION    OF   THE   MOTOR    CORTICAL   AREAS   IN    DIFFERENT 

MAMMALS 

It  would  lead  us  too  far  afield  to  descril)e  here  in  detail  all  the  results 
obtained  by  electrical  stimulation  of  the  cortex  in  the  different  mammals. 


Fig.  283. — Latent  period  of  muscular  con- 
traction induced  by  stimulation  of  the 
cortex  (upper  tracing),  and  bj-  stimula- 
tion of  the  underlying  white  substance 
(lower  tracing),  after  Franck.  The 
time  record  in  each  ca.se  is  in  l-l()Oths 
of  a  second.  The  instant  of  stimulation 
is  indicated  by  the  vertical  line  to  the 
left,  the  beginning  of  the  contraction 
by  the  vertical  line  to  the  right. 


'  By  clonic  contraction  is  meant  one  whose  strength  is  continually  changing  (cf.  Fig.  291). 


634 


PHYSIOLOGY   OF  THE  CEREBRUM 


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9-  f\    I  ■*■*,    ii 


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But  there  is  one  result  which  stands 
out  very  prominently :  the  higher  the 
rank  of  the  animal  in  the  scale,  the 
greater  is  the  variety  of  isolated  move- 
ments which  can  be  obtained  by 
sliarply  localized  stimulation — i.  e., 
the  greater  is  the  number  of  excitable 
points  and  hence  the  higher  is  the  de- 
gree of  localization.  This  fact  to- 
gether with  the  close  similarity  of 
structure  l)etween  the  simian  brain 
and  the  human  brain  makes  the  results 
on  monkeys  of  the  utmost  importance 
from  the  standpoint  of  human  physi- 
ology; consequently  we  shall  describe 
the  experiments  on  these  animals, 
Avhich  we  owe  to  Beevor,  Horsley, 
Schafer  and  Sherrington,  somewhat 
fully. 

The  arrangement  of  the  fissures 
and  convolutions  in  the  monkey's 
brain  corresponds  exactly  to  that  of 
the  human  brain,  or,  more  correctly 
speaking,  it  can  be  regarded  as  a  sim- 
plified schema  of  the  human  brain. 
Eeference  to  Figs.  285  and  286  will 
make  this  fact  apparent  without  fur- 
ther description. 

The  motor  cortical  zone  of  the 
monkey's  l)rain  extends  over  parts  of 
Ijoth  the  median  and  convex  surfaces 
of  the  hemisphere.  On  the  convex 
siirface  it  consists  of  the  two  central 
convolutions  and  of  the  immediately 
adjacent  parts  of  the  frontal  convolu- 
tions. On  the  medial  side  the  greater 
part  of  the  g3'rus  marginalis  belongs 
to  this  zone. 

Within  this  great  motor  zone  can 
be  distinguished  areas  for  the  larger 
divisions    of    the    bodv    musculature: 


Fig.  284. — Structure  of  the  cortex  of  the  con- 
volutions bordering  on  the  fissure  of  Rolando, 
after  Cajal.  The  figure  to  the  right  represents 
the  structure  of  the  anterior  central  con- 
volution, that  to  the  left  the  structure  of  the 
posterior  central.  1,  Plexiforin  layer;  2,  small  pyramidal  cells;  .3,  medium-sized  pyramidal 
cells;  4,  large  superficial  pyramidal  pells;  5,  small  star-shaped  cells;  6,  large,  deep  pyramidal 
cells;  7,  layer  of  spindle-shaped  and  triangular  cells. 


THE  MOTOR  AREAS 


635 


^ 


Fig.  285. — Motor  cerebral   localization   in   the   monkey   (Macacus  sin^cus),   a£ter   Horsley  and 
Schafer.     Outer  surface  of  left  hemisphere. 


Fig.  286. — Motor  cerebral  localization  in   the   monkey   (Macacus  sinicus),  after   Horsley  and 
Schiifer.     Inner  surface  of  the  left  hemisphere. 


636  PHYSIOLOGY   OF  THE   CEREBRUM 

tlius  the  lower  part  of  the  two  central  convolutions  is  related  to  the  muscnla- 
ture  of  the  face,  the  niiddle  part  to  that  of  the  anterior  extremity,  and  the 
upper  part  to  the  muscles  of  the  posterior  extremity.  On  the  very  edge  of  the 
liemisphere  is  an  area  for  the  movements  of  the  trunk.  That  portion  of  the 
motor  zone  lying  immediately  in  front  of  the  anterior  central  convolution  is 
adapted  for  movements  of  the  head  and  eyes.^ 

In  the  gyrus  marginalis  on  the  medial  surface  of  the  hemisphere  we  find 
in  serial  order  from  anterior  to  posterior  areas  for  the  head,  the  antcrwr 
extremity,  the  trunk-  and  the  posterior  extremity. 

On  closer  investigation  of  the  suhject  we  find  that  within  each  of  the 
cortical  areas  for  the  greater  divisions  of  the  musculature,  a  specialization 
like  that  shown  diagrammatically  in  Fig.  287  ^  can  be  demonstrated. 

The  movements  obtained  by  cortical  stimulation  are  in  many  respects 
similar  to  voluntary  movements.  x\s  a  rule  they  represent  the  combined 
action  of  several  groups  of  muscles;  they  are  seldom  performed  by  a  single 
group  and  never  by  a  single  muscle. 

In  stimulating  the  cerebral  cortex  of  the  monkey  Sherrington  observed 
that  simultaneously  with  the  contraction  of  certain  eye  muscles,  the  tonus 
of  the  antagonistic  muscles  decreased  (cf.  page  G40).  This  is  by  no  means 
an  isolated  phenomenon,  for  according  to  further  observations  by  Hering,  Jr., 
and  Sherrington,  it  appears  to  be  a  general  rule  that  on  stimulation  of  a 
definite  point  in  the  cortex,  contraction  of  the  appropriate  muscle  is  accom- 
panied by  relaxation  of  its  antagonist.  For  example,  on  stimulation  of  the 
point  in  the  cortex  for  extension  of  the  elbow,  one  gets  contraction  of  the 
triceps  group  and  at  the  same  time  relaxation  of  the  biceps,  or  on  stimulation 
of  the  point  for  extension  of  the  fingers,  one  gets  contraction  of  the  extensores 
and  relaxation  of  the  flexores  digitorum,  etc.  These  authors  declare  that  in 
the  monkey  they  never  observed  simultaneous  contraction  of  true  antagonists, 
such  as  the  extensor  and  flexor  of  the  elbow.  The  simultaneous  contractions 
of  antagonistic  muscles  described  by  other  authors  might  have  been  due  among 
other  things  to  diffusion  of  the  stimulus  from  one  cortical  field  to  another 
lying  near  it. 

When  a  stimulus  applied  to  a  given  field  in  the  cortex  produces  movements 
in  other  muscles  than  those  corresponding  strictly  to  that  field,  it  is  observed 
that  the  movement  always  spreads  first  to  other  muscles  of  the  same  member — 
e.  g.,  contractions  of  the  shoulder  muscle  are  accompanied  by  movements  in 
all  the  muscles  of  the  anterior  extremity  even  down  to  the  fingers.  If  the 
initial  contraction  be  in  the  muscles  of  the  thumb,  the  movements  spread 
farther  and  farther  up  the  arm  to  the  wrist,  elbow  and  shoulder. 

The  contributions  of  Beevor  and  Horsley  on  the  motor  zone  of  the  orang- 

'  According  to  Bechterew,  contractions  of  the  brow,  closure  of  the  lids,  and  movements 
of  the  ear  are  also  obtained  from  this  part  of  the  cortex. 

*  According  to  H.  Munk,  the  cortical  area  for  the  musculature  of  the  trunk  lies  in  the 
frontal  lobe. 

^  For  the  sake  of  simplicity,  the  different  fields  in  this  figure  have  been  represented  as 
if  they  were  sharply  distinct  from  one  another,  whereas  in  reality  tiiere  are  no  sharp 
boundaries  demonstrable,  either  between  the  smaller  areas  or  the  larger  areas.  One  field 
always  passes  gradually  into  the  other. 


THE   MOTOR   AREAS 


637 


outang,  and  those  of  Sherrington  and  Greenl)auni  on  the  orang-outang,  gorilla 
and  the  chimpanzee,  are  of  very  great  interest  partly  hecause  these  anthropoid 
apes  stand  closest  in  the  scale  to  man  himself,  and  partly  for  the  special 
reason  that  a  further  progressive  development  of  this  zone  from  the  monkeys 
to  the  highest  apes  is  therein  unmistakably  demonstrated.  The  fact  of  this 
development  teaches  us  in  the  clearest  possible  manner  how  careful  we  must 
be  in  applying  the  results  obtained  from  other  animals  to  man  himself. 

The  general  division  of  the  motor  zone  as  it  has  been  made  out  in  the 
monkeys  is  the  same  in  its  larger  features  for  the  apes.     There  are  however 


55  >» 


a 


^ J 


Arrangement  of  excitable  fibtrs  in  the  internal  capsule. 
Fig.   287. — Motor  cortical  areas  in  the  monkey  (.Macacus  xinicus),  after  Bcevor  and  IIorslej\ 


several  very  iiolcworthy  (litl'cicnccs  hctwccii  the  two  groups.  In  the  monkeys 
(cf.  Fig.  285)  we  liiul  on  the  convex  surfaces.  l)olh  on  the  central  and  the 
frontal  convolutions,  single  excitable  regions  from  which  several  kinds  of 
inoveincnts  can  be  discharged.  In  the  apes  (cf.  Fig.  288)  the  region  on  the 
frontal  convolutions  contains  but  one  field  from  which  only  movements  of 
the  eyes  can  be  induced.  The  posterior  central  convolution  is  entirely  or  in 
verv  huge  part  inexcitable.  the  motor  cortical  areas  being  for  the  most  part 
gathered  together  in  the  anterior  central  convolution.  Again,  wliereas  in  the 
monkeys  there  are  no  sliarp  demarcations  between  the  cortical  areas  for 
different  groups  of  muscles,  in  the  orang-outang  the  cortical  areas  for  the 
main  divisions  of  the  body  are  separated  by  regions  which  are  inexcitable. 


638 


PHYSIOLOGY  OF  THE  CEREBRUM 


While  the  isolation  of  smaller  areas  within  any  larger  area,  as  of  the  arm  or 
the  leg.  is  not  so  marked  as  this  localization  of  group  areas,  it  is  nevertheless 
much  sharper  than  it  is  in  the  monkeys ;  for  when  contraction  is  induced  by 
stimulation  of  a  definite  point,  it  is  as  a  rule  confined  to  one  definite  group 
of  muscles  and  does  not  spread  as  in  the  monkeys  to  all  or  most  of  the  muscles 
of  the  same  member. 

For  purposes  of  diagnosis  the  exposed  cerebral  cortex  of  man  (Figs.  289 
and  290)  has  in  rare  cases  been  stimulated  electrically,  and  results  have  been 
obtained  which  in  general  agree  with  observations  based  on  cortical  lesions, 
as  well  as  Avith  the  above-described  results  on  the  manlike  apes.     The  motor 


Toes^ 
Ankle 


Anus  &  Vagina 
Sulcus 


Abdomen 


centralis 


Thorax 


Shoulder  - 
Elbow 
Wrist 

Finger  & 
Thumb 

Eyes    ■' 


Sulcus  centralis 


Nose' 
Closing  mouth 


Opening  j         Mastication 

.,  l^ocal  cords 

mouth 

Pig.  288. — The  motor  cortical  areas  of  the  chimpanzee,  after  Sherrington  and  Greenbaum.  The 
extent  of  the  motor  zone  is  indicated  in  black.  The  red  arrows  indicate  the  region  in  which 
the  special  areas  are  to  be  found. 


cortical  zone  of  man  probal)]y  consists  therefore  of  the  anterior  central  con- 
volution, the  posterior  part  of  the  frontal  convolutions  and  the  paracentral 
lohule.  Within  this  zone  the  areas  for  lateral  movements  of  the  head  and 
eyes  are  located  in  the  posterior  part  of  the  second  frontal  convolution ;  the 
face  musculature  is  represented  in  the  lower  part  of  the  anterior  central  eon- 
volution,  the  muscles  of  the  upper  extremity  in  the  middle  part,  and  those 
of  the  lower  extremity  in  the  upper  part.  The  paracentral  lobule  in  each 
hemisphere  (Fig.  290)  seems  to  be  associated  with  both  opposite  extremities. 
Above  the  cortical  area  for  the  upper  extremity  is  found  the  area  for  the 
musculature  of  the  trunk. 

It  is  probably  not  too  much  to  suppose  that  the  smaller  areas  within  each 
of  these  larger  areas  have  the  same  general  arrangement  as  have  those  of 
the  apes. 


THE  MOTOR   AREAS 


639 


Moreover,  it  is  found  in  these  stimulation  experiments  on  man  that,  just 
as  in  the  manlike  apes,  the  locolization  is  very  sharp,  that  the  movements 
indeed  are  confined  to  single  groups  of  muscles,  and  that  l)etween  the  excitable 
points  are  regions  which  are  inexcitable. 


Fig.  289. — Diagram  of  the  external  surface  of  the  left  cerebral  hemisphere  of  man,  after  Ecker. 


Teniyor°' 
Fig.  290. — Diagram  of  the  internal  surface  of  the  right  cerebral  hemisphere  of  man,  after  Ecker. 


640  PHYSIOLOGY  OF  THE  CEREBRUM 

C.    DIRECT   AND   CROSSED  EFFECTS   OF   STIMULATION   OF  THE  MOTOR 

CORTICAL  AREAS 

As  already  noted  at  page  632,  the  movements  induced  by  stimulation  of 
the  cerebral  cortex  occur  mainly  in  the  opposite  half  of  the  body.  But  move- 
ments can  be  obtained  also  in  the  muscles  of  the  same  side.  Of  these  hilateral 
movements  some  can  be  obtained  even  with  a  very  weak  stimulus.  With  the 
great  majority  of  muscle  groups,  however,  the  movements  on  the  same  side 
can  only  be  induced  with  relatively  strong  stimuli. 

The  eye  movements  are  to  be  classed  as  bilateral  movements  since  stimula- 
tion of  one  hemisphere  causes  both  eyes  to  be  rotated  toward  the  opjiosite 
side.  But  the  bilaterality  in  this  case  is  only  an  apparent  one ;  for  the  internal 
rectus  of  one  eye  contracts  at  the  same  time  as  the  external  rectus  of  the 
other.  Inhibition  of  the  antagonistic  muscle  is  also  an  important  factor. 
When  all  the  nerves  except  the  abducens  to  the  eye  muscles  of  one  side,  say 
the  left,  are  cut  in  the  monkey,  the  left  eye  naturally  is  deflected  to  the  left, 
because  the  tonus  has  been  destroyed  in  all  but  the  external  rectus  muscle. 
But  if  movement  of  the  eves  to  the  right  is  then  induced  by  appropriate 
stimulation  of  the  cerebral  cortex,  the  left  eye  will  turn  back  to  the  right 
as  far  as  the  median  line  even  though  the  internal  rectus  has  been  paralyzed. 
That  is,  the  stimulation  has  caused  the  tonus  of  the  left  external  rectus  to 
be  intermitted.  Since  this  experiment  succeeds  also  when  the  corona  radiata, 
the  internal  capsule,  etc.,  are  stimulated,  the  inhibition  in  question  must  be 
started  from  some  center  below  the  cortex  (Sherrington,  cf.  page  636). 

The  action  induced  in  the  face  muscles  is  really  bilateral,  although  those  of 
the  opposite  side  contract  the  more  powerfully.  This  is  true  of  the  buccinator 
as  well  as  of  the  muscles  of  the  tongue  and  vocal  cords. 

With  regard  to  other  muscular  contractions  induced  from  the  same  side  of 
the  brain,  it  is  to  be  remarked:  (1)  that  their  latent  period  is  longer  than  that 
of  muscles  on  the  opposite  side  (Franck  and  Pitres)  ;  (2)  that  they  require  a 
stronger  stimulus;  and  (3)  that  the  muscles  of  the  same  side  of  the  body  never 
make  coordinated  movem.ents  as  do  those  of  the  opposite  side,  but  show  instead  a 
tonic  contraction  more  or  less  like  an  extended  tetanus. 

We  see  therefore  that  considerable  differences  exist  between  the  movements 
of  the  same  and  of  the  opposite  side,  and,  as  Gotch  and  Horsley  especially 
have  emphasized,  it  is  probably  to  he  assumed  that  the  muscles  of  the  same 
side  are  not  so  immediately  dependent  upon  the  cortical  areas  as  are  those 
of  the  opposite  side. 

It  is  conceivable  that  the  excitation  is  conveyed  to  the  muscles  of  the  same 
side  by  first  crossing  in  the  brain  to  the  corresponding  motor  areas  of  the  oppo- 
site hemisphere.  But  if  this  be  the  case,  it  is  not  the  only  course  the  excitation 
can  take,  for  contractions  on  the  same  side  have  been  obtained  by  a  number  of 
authors  even  after  the  removal  of  these  opposite  areas,  or  of  the  entire  opposite 
hemisphere. 

The  crossing  therefore  must  take  place  in  the  lower  centers.  Lewaschew 
obtained  movements  in  the  left  hind  leg  by  stimulating  the  left  hemisphere 
after  hemisection  of  the  spinal  cord  on  the  left  side.  In  this  case  the  excita- 
tion had  crossed  to  the  right  side  of  the  cord  and  had  crossed  back  again 
below  the  level  of  the  section  (twelfth  thoracic  segment)  to  the  left  half.     But 


THE   MOTOR   AREAS  641 

this  does  not  teach  us  anything  definite  as  to  the  part  of  the  central  nervous 
system  in  which  the  stimulus  branches  oft"  from  Lne  main  path  to  reach  muscles 
of  the  same  side.  It  is  probable  that  this  place  is  to  be  sought  among  the  gray 
masses  of  the  brain-stem.  As  Gotch  and  Horsley  suggest,  the  cerebellum  might 
have  a  large  share  in  this  distribution  of  impulses  from  the  cerebrum. 

D.    THE  COMMISSURES   BETWEEN  THE  CORTICAL  AREAS  OF  THE  TWO 

HEMISPHERES 

One  would  suppose  a  priori  that  the  corpus  callosum,  the  great  commissure 
binding  together  the  two  hemisplieres,  must  be  of  very  great  physiological 
importance;  and,  in  fact,  the  most  far-reaching  hypotheses  have  been  erected 
on  this  supposition.  But  the  results  of  actual  experiments  designed  to  throw 
light  on  the  purpose  of  this  part  are  very  meager.  Several  authors  (Longet, 
Magendie.  Flourens,  Franek.  Ferrier,  Koranyi  and  others)  have  found  that 
separation  of  the  two  hemispheres  by  a  complete  sagittal  section  through  the 
corpus  callosum  produces  no  effect  on  the  behavior  of  the  animal  (rabbit, 
dog)  provided  the  hemispheres  be  left  entirely  uninjured.  Lesions  of  the 
corpus  callosum  also  produce  no  permanent  effect  (Wernicke).  The  neces- 
sary cooperation  between  the  two  hemispheres  in  the  functions  of  the  brain 
is  therefore  not  brought  about  by  the  corpus  callosum. 

The  fibers  running  in  the  corpus  callosum  from  one  motor  zone  to  the 
other  when  stimtilated  from  the  upper  surface  of  that  body  (except  rostrum 
and  tlie  splenium)  produce  bilateral  muscular  movements.  Applying  the 
stimulus  just  behind  the  anterior  genu  gives  movement  of  the  head  and  eyes; 
applying  it  farther  posteriorly  we  get  in  serial  order:  movements  of  the  two 
arms  at  the  shoulder  joints,  and  of  the  upper  half  of  the  trunk;  movements 
of  the  forearm,  hands  and  fingers;  movements  of  the  posterior  half  of  the 
trunk  and  of  the  tail ;  movements  of  the  posterior  extremities.  Xo  move- 
ments of  the  face  muscles  have  been  obtained.  It  was  only  very  rarely  that 
the  movements  were  so  isolated  and  so  sharply  localized  as  with  stimulation 
of  the  cortex. 

After  extirpation  of  the  motor  zone  on  one  side,  the  movements  are  uni- 
lateral ;  they  are  induced  therefore  with  the  help  of  the  motor  zone.  When 
the  corpus  callosum  is  stimulated  after  sagittal  section  and  after  extirpation 
of  one  hemisphere,  unilateral  movements  are  obtained  on  the  side  from  which 
the  hemisphere  has  been  removed.  The  excitation  aroused  by  stimulating 
the  fibers  of  the  corpus  callosum  passes  therefore  to  both  motor  regions  and 
thence  is  propagated  in  the  usual  way  to  the  nuclei  of  the  motor  nerves 
(Mott  and  Schiifer). 

For  the  effects  of  sectioning  the  corpus  callosum  in  cases  of  lesion  of  the 
cerebral  cortex,  see  page  660. 

E.    CORTICAL  EPILEPSY 

It  was  observed  ])y  Fritscli  and  Hitzig  in  their  early  work  on  this  sub- 
ject that  by  continuous  stimulation  of  the  cerebral  cortex  of  maiinnals,  cramp- 
like  contractions  can  be  produced  which  do  not  remain  confined  to  the  set 
of  muscles  associated  with  the  area  stimulated,  ])ut  may  extend  to  all  the 


642 


PHYSIOLOGY  OF  THE  CEREBRUM 


muscles  of  the  body.     P'lirther  investigations  along  this  line  have  given  us 
the  following  results : 

The  spasm  begins  always  in  the  group  of  muscles  whose  cortical  area  is 
stimulated,  and  from  there  spreads  in  a  perfectly  regular  manner  to  the  other 

muscles.  If.  for  example  in  the  dog, 
the  left  cortical  area  for  movements  of 
the  eyelids  is  stimulated,  the  attack 
begins  in  the  eyelids  of  the  opposite 
side,  and  from  there  passes  to  the 
face  muscles.  As  a  result  the  head 
is  turned  to  the  right,  whereupon  the 
spasm  extends  to  the  right  anterior, 
and  then  to  the  right  posterior  ex- 
tremity. Then  for  the  first  the  mus- 
cles of  the  left  side  are  affected  and 
the  spasm  spreads  in  reverse  order 
from  below  upward,  sweeping  over 
the  muscles  of  the  posterior,  then 
of  the  anterior  extremity,  and  so  on 
until,  last  of  all,  the  muscles  of  the 
eyelids  on  the  left  are  reached. 

Fig.  291  may  be  cited  as  showing 
the  characteristics  of  the  cramplike 
contractions.  As  will  be  seen,  it  is 
at  first  tonic,  later  becoming  clonic 
in  character.  A  sleepy  condition  or 
a  condition  of  great  agitation  may 
ensue  as  an  after-effect. 

The  attacks  appear  on  prolonged 
stimulation,  sometimes  while  the 
stimulation  is  in  progress  and  some- 
times after  it  has  ceased.  They  may 
appear  also  "  spontaneously  "  when 
superficial  lesions  are  made  within 
the  motor  zone  and  the  animal  is 
kept  alive ;  after  the  wound  is  healed 
the  epileptic  attacks  come  on  without 
stimulation. 

Likewise  in  man  cortical  epilepsy 
occurs  as  the  result  of  irritative  le- 
sions of  the  motor  zone,  and  on  the 
whole    is    of    about    the   same   char- 
actor    as     tliat     following     artificial 
stimulation  in  animals.     This  is  dis- 
tinguished from  the  usual   form   of 
epilepsy,  by  the  retention  of  consciousness  at  least  at  the  beginning  of  the  at- 
tack, and  sometimes  throughout  its  whole  course.    The  patient  feels  the  attack 
approaching,  and  can  protect  himself  from  injuries  while  it  is  on. 


THE   MOTOR  AREAS  643 

Since  the  excitation  in  cortical  epilepsy  spreads  to  different  muscle  groups 
just  the  same  after  extirpation  of  the  motor  zone  on  the  opposite  side  from  the 
one  stimulated,  and  since  a  single  group  of  muscles  is  not  absolved  from  the  effect 
by  extirpation  of  its  own  particular  field  in  the  cortex  when  the  stimulus  is  applied 
to  another,  it  is  probable  that  the  actual  irradiation  takes  place  through  the 
mediation  of  subcortical  centers.  This  is  borne  out  also  by  the  fact  that  once  an 
attack  is  well  advanced  extirpation  of  the  motor  zone  does  not  stop  it. 

F.    SUPPRESSION   OF  THE  MOTOR   CORTICAL   FIELDS 

As  the  observations  given  in  the  preceding  chapter  have  shown,  the  entire 
cerebrum  can  be  removed  not  only  from  the  lower  vertebrates  but  from  the 
rabbit  and  dog  as  well,  without  destroying  the  ability  of  the  animal  to  carry 
out  coordinated  movements  of  locomotion.  This  proves  at  once  that  in  these 
animals  the  motor  regions  of  the  cerebral  cortex  are  not  indispensable  for 
movements  of  this  kind.  However,  in  the  decerebrated  dog  there  were  notice- 
able disturbances  in  motion,  which  might  not  have  been  caused  by  removal 
of  the  motor  region  alone  but  also  by  the  absence  of  other  parts  of  the  cere- 
brum. In  order  to  establish  the  phi/siologiral  importance  of  the  motor  areas, 
it  is  necessar}-  therefore  to  study  the  behavior  of  animals  from  which  these 
fields  only  have  been  extirpated. 

WHien  the  motor  fields  of  one  hemisphere  have  been  completely  or  mainly 
removed  from  a  dog.  for  a  time  immediately  following  the  operation  there 
is  a  more  or  less  profound  disturbance  in  the  movements  of  the  opposite  side ; 
but  this  effect  is  only  temporary.  The  animal  gradually  recovers  its  ability 
to  move  the  opposite  muscles,  and  after  some  time  the  motor  defects  become 
quite  minimal.  A  dog  from  which  Goltz  removed  the  left  hemisphere  became 
"silly";  he  was  not  so  lively  as  before;  did  not  play  with  other  dogs,  etc. 
But  none  of  his  muscles  were  entirely  paralyzed.  When  he  was  called  he 
came  wagging  his  tail  and  let  himself  be  stroked.  When  one  started  to  go 
the  dog  followed.  He  fouglit  off  other  dogs  that  displeased  him.  He  held 
a  piece  of  bread  just  as  skillfully  as  a  normal  dog,  but  did  not  hold  a  bone 
so  well  with  the  opposite  foot  (the  right)  as  with  the  other.  He  could  stand 
\\\)  on  liis  hind  legs,  although  the  right  leg  was  somewhat  weak.  He  ran 
here  and  there  of  his  own  accord,  but  turned  oftener  to  the  left  than  to  the 
right.     He  could  turn  to  the  right,  though  less  skillfully  and  less  quickly. 

It  is  therefore  unquestionably  true  that  a  dog  which  has  lost  the  motor 
zone  of  one  side  can  still  move  those  muscles  which  respond  to  stimulation 
of  that  cortical  zone.  It  has  been  supposed  that  such  an  animal  could  not 
perform  intentional  movements  with  these  muscles.  But  this  view  is  con- 
troverted by  the  following  observations  on  a  dog  whose  entire  cerebral  cortex 
on  the  left  side  had  been  removed. 

A  bowl  was  placed  before  the  animal  containing  bits  of  meat  scattered  in 
some  coarse  gravel.  In  scratching  for  the  meat  he  used  his  left  fore  paw.  But 
when  this  one  was  held  fast  he  immediately  made  the  same  movement  with  the 
right  fore  paw  (Goltz). 

In  a  well-trained  dog  Gaule  trimmed  off  on  both  sides  all  the  cortex  which 
could  be  visibly  excited  with  a  weak  constant  current.  After  the  usual  phenom- 
ena of  paralysis  had  passed  off,  Gaule  trained  the  dog  again  and  was  able  to 
38 


644  PHYrilOLOGY   OF  THE  CEREBRUM 

teach  him  a  whole  series  of  complicated  movements  which  gave  evidence  of  his 
intelligence.  However,  he  showed  also  a  considerable  number  of  disturbances 
of  the  motor  mechanisms,  among  which  may  be  mentioned  especially  his  in- 
ability to  perform  isolated  movements  with  only  one  extremity.  Besides,  his 
movements  were  excessive  and  were  done  with  a  waste  of  energy;  and  there  was 
no  proper  gradation  of  them — e.  g.,  in  order  to  extend  his  paw,  he  was  compelled 
first  to  sit  upright  and  then  to  give  both  paws  at  the  same  time  in  a  rather 
sudden  and  explosive  manner. 

From  these  and  other  experiments  of  the  kind  it  appears  that  the  move- 
ments of  the  dog.  including  those  which  must  be  regarded  as  intentional  and 
conscious,  can  be  carried  out  without  the  cooperation  of  the  motor  areas; 
but  that  on  the  other  hand,  the  finer  regulation  of  these  movements  is  for 
the  most  part  destroyed  by  extirpation  of  the  corresponding  areas.  It  would 
follow  that  in  the  dog  the  motor  cortical  areas  are  really  necessary  only  for 
the  nicer  regulation  of  movements. 

Horsley  and  Schafer  observed  the  following  phenomena  after  extirpation 
of  the  cortical  areas  from  the  monkey  (Macacus).  If  the  whole  excitable 
region  on  the  convex  side  of  the  hemisphere  were  extirpated  and  only  the 
median  cortical  region  left,  there  was  exhibited  an  almost  complete  paralysis 
of  the  opposite  arm,  paralysis  of  the  facial  muscles,  weakness  in  the  muscles 
of  the  posterior  extremities,  and  a  greater  or  less  difficulty  in  moving  the 
head  toward  the  opposite  side.  The  muscles  of  the  trunk  were  iniaffected, 
and  the  weakness  in  the  posterior  extremity  was  not  so  great  that  the  animal 
could  not  use  it  in  walking  and  climbing. 

When  only  a  part  of  the  excitable  region  on  the  convex  surface  of  the 
hemisphere  was  destroyed — e.  g..  the  field  for  the  wrist  and  fingers — a  perma- 
nent weakness  appeared  in  these  muscles  while  the  other  muscles  were  mov- 
able in  a  perfectly  normal  fashion.  In  the  same  way  destruction  of  the 
cortical  field  of  the  arm  produced  paralysis  of  the  arm  without  any  disturb- 
ance in  the  movements  of  the  face,  head,  trunk  or  posterior  extremity.  When 
the  destruction  of  the  field  was  complete,  paralysis  of  the  corresponding 
muscles  appeared  to  be  permanent.  But  when  a  part  of  the  field  was  left 
behind  the  ability  to  move  the  parts  returned  to  a  certain  extent. 

The  consequences  of  destroying  the  motor  region  on  the  medial  side  are 
worthy  of  note.  Following  bilateral  destruction  of  this  region  there  was 
complete  paralysis  of  the  muscles  of  the  trunk,  a  certain  weakness  in  those 
of  the  arms  and  a  very  extensive  paralysis  in  the  muscles  of  the  posterior 
extremities.  The  weakness  in  the  arms  involved  mainly  certain  shoulder 
muscles,  especially  those  which  draw  the  shoulder  blade  upward  and  back- 
ward ;  it  was  less  marked  in  the  muscles  of  the  arm  and  forearm,  and  scarcely 
or  not  at  all  noticeable  in  the  finger  muscles.  Paralysis  of  the  posterior 
extremities  extended  to  almost  all  the  muscles,  only  a  few  flexors  of  the  hip 
joint  being  exempt. 

By  practice  the  monkey,  like  the  dog,  can  acquire  the  use  of  muscles 
corresponding  to  the  extirpated  cortical  fields;  can  learn,  in  other  words, 
to  execute  intentional  movements  with  them. 

Hering,  Jr.,  found  that  the  cortical  fields,  electrical  stimulation  of  which 
gave  movements  of  the  forearm,  including  grasping  movements,  could  be  entirely 


THE   MOTOR   AREAS  645 

removed  without  destroying  the  animal's  ability  to  close  the  fist  on  the  opposite 
side  or  to  use  the  hand  in  grasping  objects. — Sherrington  has  made  similar  obser- 
vations on  the  anthropoid  apes. 

Goltz  had  the  opportunity  of  observing  for  more  than  ten  years  a  monkey  in 
which  the  greater  part  of  the  frontal  and  parietal  lobes  on  the  left  side  had  been 
destroyed.  Thus  the  motor  region  of  the  left  hemisphere  was  entirely  or  almost 
entirely  thrown  out  of  function.  Xevertheless,  by  practice  the  monkey  succeeded 
in  recovering  his  ability  to  use  the  right  arm  and  right  hand  for  definite  pur- 
poses. He  learned  to  grasp  fruits  with  the  right  hand  and  to  offer  it  in  greet- 
ing, etc.  He  could  move  all  of  the  muscles  directly  under  control  of  the  will,  but 
the  movements  of  the  right  limbs  remained  incomplete,  cumbrous  and  awkward. 

After  these  observations  it  scarcely  oiifrlit  to  be  loniror  assumed  tliat  the 
motor  region  in  the  monkey  is  of  much  greater  importance  than  it  is  in 
the  dog.  It  is  indeed  very  probable  that  there  is  a  difference  in  degree  be- 
tween the  two.  but  certainly  not  a  difference  in  kind. 

Horsley  and  Schiifer's  observations  point  to  the  interesting  fact  that  in 
the  monkey  the  motor  cortical  areas  on  the  upper  medial  surface  of  the  hemi- 
spheres are  concerned  mainly  with  what  we  may  call  the  coarser  movements, 
those  by  which  the  body  is  kept  in  its  natural  position  and  moves  itself  from 
place  to  place.  The  cortical  areas  on  the  convex  surfaces  of  the  hemisphere 
are  of  decidedly  greater  importance  for  the  more  refined  movements,  e.g., 
those  wliich  are  executed  by  the  muscles  of  the  head,  face  and  arms. 

In  order  to  establish  the  location  and  influence  of  the  motor  cortical  areas 
in  the  human  hrain,  we  have  recourse  either  to  excitation  experiments  or  to 
clinical  and  pathological  observations.  The  former  evidently  can  never  be 
very  numerous,  and  our  knowledge  of  the  functions  of  the  human  motor  cortex 
rests  mainly  on  clinical  observations  of  the  effects  of  lesions  in  the  cerebrum. 

It  not  infrequently  happens  that  in  post-mortem  examinations  very  ex- 
tensive lesions  of  the  cerebral  cortex  are  found,  which  were  not  accompanied 
in  life  by  an}^  observable  disorder.  Compilations  of  such  cases,  which  we 
owe  to  Cliarcot  and  Pitres,  Jvxner,  Xothnagel  and  others  show  that  these 
cortical  fields  which  have  no  direct  significance  for  the  bodily  movements 
embrace  all  parts  of  the  cortex  with  the  exception  of  the  anterior  central 
convolution  inclusive  of  the  operculum,  the  paracentral  lol)ule.  and  the  pos- 
terior part  of  the  frontal  convolutions.  But  if  the  lesions  are  found  within 
the  portions  ju.st  named,  a  more  or  less  extensive  disturbance  in  the  move- 
ments of  the  opposite  half  of  the  l)ody  is  sure  to  have  been  observed.  Hence 
we  can  say  that  the  motor  cortical  field  in  man  has  on  the  whole  the  same 
extent  as  the  cortical  zone  in  the  anthropoid  apes,  and  that  this  covers  the 
anterior  central  convolution  inclusive  of  the  paracentral  lobule,  and  the  foot 
of  the  frontal  convolutions. 

For  working  out  the  cerebral  localization  in  detail  the  very  small  cortical 
lesions  are  of  course  the  important  ones.  The  more  restricted  the  lesion,  the 
more  limited  will  he  the  disturbance  of  function,  and  of  course  the  more 
definitely  can  the  location  of  a  particular  field  be  decided  upon.  Such  lesions 
have  yielded  results  which  agree  essentially  with  the  corresj)onding  observa- 
tions on  the  brain  of  the  anthropoid  apes,  and  with  the  excitation  experi- 
ments on  the  human  brain  itself. 


646  PHYSIOLOGY   OF  THE  CEREBRUM 

The  distiirl)ancc  in  function  which  makes  its  appearance  after  a  lesion 
in  the  motor  region  is  as  a  rule  greater  at  first  than  later,  owing  no  doubt 
to  some  interference  with  the  circulation  and  to  shock.  After  this  remote 
effect  of  the  lesion  has  passed  away,  as  it  does  within  a  few  days,  the  primary 
loss  of  function  comes  more  prominently  to  the  front.  Movements  of  parts 
connected  with  the  cortical  area  destroyed  can  no  longer  be  executed  as  be- 
fore, and  in  adults  they  are  either  finally  lost  or  are  always  thereafter  executed 
with  abnormal  weakness.  It  is  to  be  observed,  however,  that  even  such  move- 
ments can  continue  to  he  performed  in  association  with  others.  When,  for 
example,  the  cortical  field  for  the  extension  of  the  right  thumb  is  entirely 
destroyed,  the  ability  to  make  sure,  strong  and  precise  extensor  and  abductor 
movements  with  that  thumb  is  lost ;  but  in  connection  with  the  fingers  it  can 
still  be  used  very  skillfully  in  various  kinds  of  complicated  movements  (v. 
Monakow). 

The  influence  of  the  cerebral  cortex  in  man  on  the  movements  of  his  body 
appears  very  clearly  from  the  following  observation.  A  patient  was  born  with 
hemiplegia  on  the  left  side.  When  he  was  taken  to  the  hospital  at  the  age  of 
twenty-nine,  his  left  limbs  were  very  much  stunted.  He  could  walk  with  the 
help  of  crutches,  but  could  not  lift  his  left  leg  from  the  floor.  On  opening  the 
skull  it  was  found  that  the  whole  right  hemisphere  of  the  cerebrum  had  disap- 
peared and  was  replaced  by  fluid  (L'Allemand). 

In  considering,  the  recovery  of  the  muscular  functions,  we  must  bear  in 
mind  that  the  extremities  are  represented  not  only  on  the  convex  surface  of 
the  cerebrum,  but  also  on  the  medial  side ;  also  that  according  to  observations 
on  monkeys,  it  is  only  the  coarser  movements  that  are  dependent  on  the  latter 
region.  When  therefore  the  lesion  occurs  only  on  the  outer  convex  portion 
of  the  cortex,  it  is  still  possible  for  the  medial  portion  to  direct  the  coarser 
movements  of  the  extremities. 

With  lesions  acquired  very  early  in  life,  a  very  considerable  degree  of  resti- 
tution is  possible.  In  one  case  of  defect  of  the  two  right  central  convolutions 
observed  by  v.  Monakow,  the  patient  at  ten  was  al)le  to  use  his  left  arm 
(atrophied  though  it  was)  in  the  proper  way,  in  all  possible  sorts  of  manipula- 
tions— e.  g.,  in  playing  ball ;  some  considerable  clumsiness  was  apparent  how- 
ever in  the  use  of  the  left  hand  and  fingers. 

After  a  cortical  lesion  controcfurcs — i.  e.,  abnormal,  persistent  contrac- 
tions— gradually  make  their  appearance  in  the  muscles  of  the  paralyzed  limbs. 
Different  hypotheses  have  been  put  forward  concerning  the  cause  of  these, 
but  their  discussion  here  would  lead  us  too  far  afield.  It  must  suffice  to 
observe  only  that,  according  to  H.  Munk,  contractures  in  the  monkey  can 
be  prevented,  if,  as  soon  as  the  limbs  affected  begin  to  offer  some  resistance 
to  passive  movements,  they  be  stretched  as  far  as  possible  for  a  few  minutes 
every  day.  The  contractures  are  brought  on  by  the  loss  of  motility.  Hence 
they  do  not  occur  in  the  case  of  animals  which  move  about  spontaneously 
after  the  operation,  for  the  paralyzed  extremity  can  be  used  in  connection 
with  the  other  extremities  in  walking  even  though  isolated  movements  can- 
not be  executed. 


THE  MOTOR   AREAS 


647 


G.    THE    COURSE    OF   THE    CONDUCTING    PATHWAYS    FROM    THE    MOTOR 
CORTICAL  FIELDS   TO   THE   NUCLEI   OF   THE   MOTOR   NERVES 

The  nerve  paths  wliich  originate  in  the  great  p3Tamidal  cells  of  the  cerebral 
cortex  proceed  tlirough  the  corona  radiata  to  the  internal  capsule,  through  this 
to  the  crus  cereliri  and  then  continue  distalward  to  the  nuclei  of  origin  of  the 
motor  nerves,  with  which  they  are  connected.  The  pyramidal  pathways  are 
connected  with  motor  nerves  of  the  opposite  side.  The  fibers  belonging  to 
the  cranial  motor  nerves  pass  to  the  opposite  side  in  different  parts  of  the 
brain-stem,  while  the  pyramidal  fibers  which  reach  the  spinal  cord  cross  for 
the  most  part  in  the  medulla  (crossed  pyramidal  tracts),  but  in  part  also  in 
the  spinal  cord  itself  (direct  p}Tamidal  tracts).  All  these  paths  degenerate 
after  destruction  of  the  cerebral  cortex  (see  Fig.  262,  page  590). 

Clinical  evidence  has  shown  that  these  paths  pass  through  the  corona  radiata, 
forming,  as  we  might  expect,  a  pretty  compact  bundle.     Lesions  in  the  corona 


Fifi.  292. — The  motor  tract  (dark)  at  various  levels  of  the  internal  capsule,  after  Beevor  and 
Horsley.  L,  lenticular  nucleus;  T,  optic  thalamus;  C,  caudate  nucleus;  a,  anterior  commis- 
sure; F,  point  of  junction  of  the  lenticular  and  caudate  nuclei. 


produce  isolated  paralyses  of  the  face,  arm  or  leg  musculature,  showing  that  the 
paths  proceeding  from  the  motor  cortical  areas  are  distinct  from  one  another  also 
in  their  further  course. 

In  the  internal  capsule  the  pyramidal  paths  are  drawn  closer  together,  the 
deeper  they  go.  According  to  Beevor  and  Horsley,  at  a  high  level  they  fill  the 
entire  cross  section  of  the  capsule  with  the  exception  of  its  most  anterior  and 
most  posterior  sections.  Further  down  they  are  restricted  more  and  more  to  the 
posterior  limb  of  the  capsule,  as  may  be  seen  from  Fig.  292. 

The  separate  tracts  can  be  fairly  well  stimulated  in  the  internal  capsule. 
Some  responses  are  bilateral  just  as  in  the  case  of  not  overstrong  stimulation  of 
the  cortex ;  but  most  are  unilateral.  The  bilateral  responses  are :  eversion  of  the 
lips,  movements  of  mastication,  swallowing,  adduction  of  the  vocal  cords — all  of 
them  equally  strong  on  both  sides;  opening  and  closing  of  the  eyelids,  protrusion 
of  the  lips,  retraction  of  the  angle  of  the  mouth — all  stronger  on  the  opposite 
side ;  the  rest  are  strictly  unilateral. 

Beginning  at  the  most  anterior  part  of  the  capsule  which  can  be  stimulated, 
and  moving  the  electrodes  gradually  backward,  the  following  responses  in  the 
order  named  are  obtained  in  the  monkeys  (Beevor  and  Horsley)  :  opening  of 
the  eyelids,  turning  the  eyes  to  the  opposite  side,  opening  of  the  angle  of  the 
mouth,  rotation  of  the  head  and  eyes  to  the  opposite  side,  rotation  of  the  head 
alone  to  the  opposite  side,  movements  of  the  tongue,  of  the  angle  of  the  mouth. 


648  PHYSIOLOGY  OF  THE  CEREBRUM 

shoulder,  elbow,  wrist  and  fingers,  thumb,  trunk,  hip,  foot,  knee,  great  toe  and 
smaller  toes  (cf.  Fig.  287).  The  points  corresponding  to  the  movements  within 
any  given  cross  section,  however,  are  not  sharply  delimited,  but  overlap  each 
other. 

But  the  pyramidal  tracts  are  not  tlie  only  motor  pathways  from  the  cere- 
bral cortex.  According  to  Kothman.  al>lation  of  the  pyramidal  paths  alone 
in  the  dog  causes  no  essential  change  in  the  electrical  stimulation  of  the 
motor  region :  the  motor  impulses  are  then  conveyed  by  MonaJcow's  bundle 
(see  page  59fi).  In  monkeys  however  the  latter  plays  but  an  unimportant 
role  in  this  respect,  for  after  section  of  the  pyramidal  paths,  only  movements 
of  the  hand,  fingers  and  toes  could  be  obtained  l)y  electrical  stimulation  of 
the  cortex. 

Even  after  complete  suppression  of  all  those  pathways  in  the  monkey, 
and  notwithstanding  the  failure  of  subsequent  stimulation  of  the  motor  region, 
the  motor  functions  of  the  limbs  were  not  permanently  abolished.  Impulses 
which  reach  the  cord  in  other  ways  can  always  produce  slight  isolated  move- 
ments of  the  fingers;  indeed,  after  complete  severance  of  all  the  paths  of  the 
lateral  and  anterior  columns  of  the  cord  on  one  side,  a  restitution  takes  place 
which,  while  very  incomplete,  makes  possible  not  only  associated  but  isolated 
movements  as  well.  Tliere  are  therefore  several  patliways  by  which  the  cere- 
bral cortex  may  influence  the  movements  of  the  l)ody. 


H.  DEVELOPMENT  OF  THE  MOTOR  AREAS  OF  THE  CORTEX 

The  investigations  of  Flechsig  on  the  formation  of  the  medullary  substance 
in  the  nerve  paths  of  the  central  nervous  system,  have  brought  to  light  the 
fact  that  the  pyramidal  paths  in  man  receive  their  medullary  substance  only 
at  the  very  end  of  intrauterine  life.  In  the  dog  these  same  paths  are  not 
provided  with  their  medullary  substance  until  after  birth. 

In  accordance  with  this  fact  the  excitability  of  the  motor  region  in  newborn 
dogs  is  but  slight,  so  much  so  that  it  has  been  stated  by  some  authors  to  be  alto- 
gether wanting  until  the  tenth  day.  This  appears  certainly  to  be  incorrect, 
for  Paneth  has  found,  for  example,  that  responsive  movements  can  be  obtained 
by  stimulation  of  the  cerebral  cortex  in  dogs  only  one  to  two  days  after  birth. 

According  to  Bary,  the  first  movements  obtainable  exhibit  various  noteworthy 
differences  from  those  of  somewhat  older  animals.  They  are  not  confined  to 
separate  groups  of  muscles  as  are  the  latter,  but  involve  the  whole  anterior  or 
posterior  extremity  of  the  opposite  side ;  the  duration  of  the  contraction  and  the 
latent  period  are  also  much  longer.  Moreover,  in  very  young  animals  the  excita- 
bility of  the  cortex  is  easily  destroyed  by  all  sorts  of  injuries,  narcosis,  cooling, 
exposure,  etc. 

From  about  the  tenth  day  onward  special  areas  for  the  separate  groups  of 
muscles  develop  on  the  cortex,  and  pari  passu  with  this  development,  the  dura- 
tion of  the  contraction  and  the  length  of  the  latent  period  become  shorter,  and 
the  resistance  of  the  cortex  to  fatigue  also  greater. 

On  the  other  hand  it  should  be  observed  that  in  the  guinea  pig,  in  which  the 
pyramidal  paths  receive  their  medullary  substance  in  utero,  the  cortex  is  ex- 
citable before  birth. 

Of  great  interest  also  is  the  observation  made  by  Herzen   and  others  that 


THE  VEGETATIVE  PROCESSES  OF  THE  BODY         649 

newborn  puppies  from  which  the  motor  region  was  extirpated  suffered  no  sort 
of  motor  disturbance,  even  immediately  after  the  operation.  This  observation 
teaches  us  that  at  a  time  when  the  pyramidal  paths  are  not  complete  anatomically, 
the  motor  region  is  incapable  of  any  apparent  physiological  function,  which  is 
borne  out  also  by  the  fact  that  puppies  begin  to  support  themselves  on  their  feet 
only  after  the  pyramidal  paths  have  received  their  medullary  substance, 

§  2.  INFLUENCE  OF  THE  CEREBRAL  CORTEX  ON  THE 
VEGETATIVE  PROCESSES  OF  THE  BODY 

In  discussing  the  innervation  of  the  different  vegetative  organs  we  have 
from  time  to  time  called  attention  to  the  influence  of  the  cerebral  cortex 
on  their  functions.  In  order  to  obtain  a  satisfactory  conception  of  the  cortical 
functions,  it  will  l)e  necessary  to  summarize  briefly  these  and  other  similar 
phenomena  in  this  connection. 

Artificial  stimulation  of  the  cerebrum,  as  we  have  seen,  produces  an  epileptic 
attack  all  too  easily ;  and  the  excitation  in  such  an  attack  is  spread  through  the 
subcortical  centers  to  all  the  cross-striated  muscles.  At  the  same  time  the  res- 
piratory, cardiac  and  vasomotor  centers,  the  centers  controlling  the  digestive 
apparatus  and  those  of  the  iris,  are  also  excited.  But  while  this  is  of  great 
interest,  it  gives  us  no  definite  information  with  regard  to  the  probable  normal 
influence  of  the  cerebral  cortex  itself  on  these  organs  and  their  functions. 

In  similar  experiments  on  curarized  animals,  the  epileptic  attack  is  masked 
because  of  the  paralysis  of  the  skeletal  muscles,  nevertheless  the  accompanying 
phenomena  in  the  vegetative  organs  make  their  appearance  as  usual.  But  these 
experiments  on  curarized  animals  must  not  be  trusted  too  far  (Franck).  It 
appears  that  the  influence  which  is  exercised  by  the  cerebral  cortex  on  the  vege- 
tative processes  proceeds  in  general  from  the  motor  region  and  its  immediate 
neighborhood.  Indeed,  Franck  asserts  that  the  effects  which  he  has  observed  on 
respiration,  the  heart,  blood  vessels  and  salivary  secretion  in  the  dog  after  stimu- 
lation of  the  cerebral  cortex  can  be  obtained  from  almost  the  entire  motor  region, 
but  from  no  other  points  on  the  cortex.  Respiration  is  accelerated  or  slowed 
according  to  the  strength  of  the  excitation,  just  as  in  stimulation  of  the  periph- 
eral sensorj'  nerves,  and  the  depth  of  respiration  is  likewise  affected.  The  glottis 
becomes  narrow  with  the  tendency  to  expiration  and  becomes  wider  with  the 
tendency  to  inspiration,  etc. — With  weak  stimulation  the  pulse  rate  as  a  rule  is 
accelerated,  with  strong  stimulation  it  is  retarded.  The  blood  vessels  constrict. 
We  know  also  that  salivary  secretion  and  contractions  of  the  urinary  bladder  are 
influenced  from  the  motor  region  (see  page  239). 

Other  authors,  however,  have  reached  different  conclusions.  According  to 
Horslcy  and  Semon,  the  muscles  of  the  vocal  cords  and  of  the  larynx  in  the 
monkey  have  their  cortical  area  in  the  lowermost  part  of  the  central  convolu- 
tions and  within  this  region  the  following  definite  movements  can  be  localized : 
(1)  bilateral  adduction  of  the  vocal  cords;  (2)  the  same  movement,  plus  move- 
ments of  the  pharynx;  (3)  elevation  of  the  larynx,  accompanied  by  movements 
of  the  face,  the  jaws  and  the  tongue;  (4)  depression  of  the  larynx. 

Spencer  has  obtained  the  following  effects  on  the  respiratory  movements  by 
stimulation  of  the  cerebral  cortex  in  several  different  species  of  animals  (mon- 
key, dog.  cat,  rabbit)  :  slowing  and  stoppage  of  respiration  by  stimulation  of 
the  border  of  the  temporal-sphenoidal  lobe  lateral  to  the  base  of  the  olfactory 
tract;  acceleration  of  respiration  by  stimulation  of  the  convex  upper  surface  in 


650  PHYSIOLOGY   OF  THE  CEREBRUM 

the  region  of  the  motor  areas;  clonic  inspiratory  spasm  (snuffing)  by  stimula- 
tion of  the  border  of  the  olfactory  bulb  and  tract,  also  on  the  uncinate  gyrus. 

Bechterew  and  Mislawsky  make  mention  of  a  vasoconstriction  from  stimu- 
lating certain  parts  of  the  motor  region,  and  a  vasodilatation  from  other  parts/ 

From  these  observations  it  nia}^  be  gathered  that  the  cerebral  cortex,  espe- 
cially the  motor  zone  and  its  immediate  neighborhood,  exercises  an  unmis- 
takable influence  on  the  vegetative  processes  of  the  body. 

Doubtless  this  influence  is  greater  over  some  organs  than  over  others. 
Movements  like  those  of  the  larynx  and  to  a  certain  extent  also  those  of  the 
thorax,  which  can  be  very  exactly  and  very  delicately  graduated,  especially  after 
long  practice,  must  naturally  be  very  intimately  dependent  upon  the  cerebral 
cortex,  even  though  the  coarser  movements  of  the  same  anatomical  parts,  such 
as  are  necessary  for  the  mere  ventilation  of  the  lungs,  are  independent  of 
the  cerebrum.  Quite  different  effects  have  been  obtained  from  the  cerebral 
cortex  on  the  heart,  blood  vessels,  etc.  These  effects,  as  has  been  repeatedly 
observed,  are  most  correctly  regarded  as  reflexes  similar  to  those  which  are 
discharged  by  all  kinds  of  afferent  nerves.  Most  of  them  are  accessory  to  the 
muscular  movements  controlled  by  the  cortex,  and  some  at  least,  like  the 
acceleration  of  the  heart  and  vasoconstriction,  accompany  every  voluntary 
movement.  The  chief  significance  of  this  cortical  influence  on  the  circu- 
latory organs  is  that  they  can  be  thereby  adapted  to  the  different  requirements 
placed  upon  them.  The  effects  of  psychical  states  on  the  vegetative  functions 
of  the  body,  Avhich  have  been  discussed  at  page  577,  are  in  all  probability 
mediated  by  the  cerebral  cortex. 

Finally,  there  are  certain  observations  which  indicate  that  different  por- 
tions of  the  cerebrum  have  a  different  influence  on  the  general  state  of  nutri- 
tion of  the  body.  Thus,  if  a  large  part  of  the  most  anterior  portion  of  the 
dog's  cerebrum  be  extirpated  on  both  sides,  the  animal  always  exhibits  a 
tendency  to  become  lean  and  to  remain  so;  he  suffers  very  extensively  also 
from  a  persistent  inflammatory  skin  disease  which  is  associated  with  great 
redness  and  itching.  On  the  other  hand,  a  dog  deprived  of  its  occipital  lobe 
on  both  sides  regularly  becomes  fat.  It  sometimes  happens  in  this  case  that 
the  dog  acquires  an  eczema  also,  but  it  is  much  more  easily  held  in  check 
and  much  more  easily  cured  (Goltz). 

§  .3.    THE    SENSORY   CORTICAL   AREAS 

The  first  method  which  we  naturally  think  of  in  attempting  to  determine  the 
significance  of  the  cerebral  cortex  for  sensation,  is  the  investigation  of  effects 
upon  the  different  sensations  in  man  and  animals  which  result  from  lesion, 
destruction  or  extirpation  of  different  portions  of  the  cortex.  In  experiments 
on  animals,  however,  we  meet  at  once  with  an  ol)stacle  in  the  fact  that  we 
can  only  judge  of  the  probable  loss  of  sensation  by  the  movements  and  general 
behavior  of  the  animal.  Our  conclusions  are  therefore  very  uncertain,  espe- 
cially in  cases  where  the  intelligence  of  the  animal  is  greatly  reduced.  Since 
it  is  just  such  cases  which  ought  to  be  most  decisive  for  the  purpose  in  hand, 

^  For  the  effects  of  the  cerebral  cortex  on  the  digestive  organs,  see  pages  261,  264,  284. 


THE   SENSORY   CORTICAL  ARE.\S  651 

we  are  often  forced  to  be  content  merely  with  finding  that  tlie  animal's  move- 
ments are  infiuenced  by  some  sensory  stimulus,  without  l)eing  able  definitely 
to  say  how  far  the  action  may  be  regarded  as  the  expression  of  a  conscious 
sensation,  or  whether  it  is  not  rather  purely  reflex.  Our  safest  and  most 
important  conclusions,  therefore,  we  get  from  observations  on  man. 

Wo  can  obtain  valuable  information  also  by  excitation  experiments  (of  which 
more  further  along),  by  the  action  current,  and  especially  by  anatomical  study 
of  the  afferent  conducting  pathways.  In  this  section  we  shall  linait  ourselves 
to  the  study  of  regions  where  the  sensory  paths  end.  These  regions  are  known  as 
the  sensory  areas — tactile  area,  olfactory  area,  auditory  area,  visual  area,  etc. 

A.  AREA  OF  GENERAL  SENSATION  AND  TOUCH 

Since,  as  we  have  seen,  even  the  complete  removal  of  a  whole  hemisphere 
from  a  dog  does  not  greatly  inconvenience  the  animal,  the  locomotor  movements 
being  surprisingly  little  affected,  it  follows  that  the  regulation  of  the  coarser 
movements  which  goes  on  under  the  influence  of  the  afferent  nerves  can  be 
accomplished  independently  of  the  cortex.  On  the  other  hand,  observations 
by  Goltz,  H.  ^Iimk,  and  others  show  that  in  the  dog  extirpation  of  the  motor 
region  and  of  the  cortical  areas  lying  immediately  adjacent  thereto  causes  all 
sorts  of  derangements  of  the  tactile  and  the  motor  senses.  It  follows  that 
the  afferent  pathways  from  all  parts  of  the  body  serving  the  tactile  and  motor 
senses  enter  these  regions.  Similar  sensory  disturbances  have  been  observed 
in  the  monkey  also  after  extirpation  of  tlie  motor  region. 

When  the  entire  cortical  area  for  the  hinder  extremity  is  removed,  and  as  a 
consequence  the  muscles  of  the  opposite  leg  can  no  longer  execute  finely  graded 
movements,  for  some  days  after  the  operation  there  is  complete  insensibility  in 
this  extremity,  and  a  certain  bluntness  of  sensibility  becomes  permanent. 

With  still  more  extensive  destruction,  the  finer  movements  of  the  hand  and 
foot  are  permanently  arrested,  and  for  some  time  after  the  operation  the  sensi- 
tiveness of  the  paws  is  very  much  reduced,  so  that  the  animal  reacts  only  to 
very  painful  stimuli.  In  fact  the  sensitiveness  of  the  hand  and  foot  becomes 
permanently  so  slight  that  a  severe  pinch  produces  no  reaction  at  all  (Mott).  On 
the  other  hand,  Schiifer  has  found  that  a  monkey  which  does  not  react  at  all  to 
a  painful  pinch  immediately  notices  a  very  light  tactile  stimulus  applied  to  the 
paralyzed  extremity. 

The  monkey  (page  645)  from  which  Goltz  had  removed  the  entire  motor 
region  of  the  left  hemisphere,  took  no  notice  of  the  gentle  tactile  stimuli  applied 
to  the  right  extremity.  Stronger  pressure  stimuli,  however,  were  always  felt. 
The  motor  sensations  were  also  somewhat  diminished. 

Although  the  observations  made  on  man  difTer  from  one  anothiM-  in  niany 
points,  on  one  point  there  is  positive  agreement,  namely,  that  the  motor  region 
and  its  immediate  neighborhood  is  the  cortical  area  for  the  sense  of  touch. 
It  is  noteworthy  that  the  motor  and  sensory  disorders  are  not  as  a  rule 
coterminous.  In  some  cases  the  paralysis  involves  most  of  the  muscles  of 
the  opposite  side,  wliereas  the  disturliance  in  sensation  going  with  it  is  of 
but  slight  extent :  in  other  cases  with  a  sharply  circumscribed  motor  paralysis, 
there  goes  a  reduction  of  sensibility  covering  a  very  considerable  area. 


652  PHYSIOLOGY   OF   THE   CEREBRUM 

From  the  summaries  of  clinical  cases  of  this  character  it  appears  with 
perfect  definiteness,  however,  that  so  far  as  these  particular  disorders  are 
concerned,  lesions  of  the  occipital,  temporal,  and  the  greater  part  of  the  frontal 
lobes  are  of  no  consequence;  that  therefore  the  cortical  field,  lesion  of  which 
is  accompanied  l)y  loss  of  general  sensation  and  touch  embraces  the  central 
and  parietal  convolutions,  the  paracentral  lobule  and  possibly  the  posterior 
part  of  the  frontal  convolutions. 

More  detailed  study  of  cases  appertaining  to  this  subject  appears  to  show 
further  that  the  anterior  central  convolution,  the  importance  of  which  as  a 
place  of  origin  for  the  long-fibered  efferent  tracts  was  discussed  at  page  633, 
can  be  tlirown  out  of  function  without  entailing  any  loss  of  general  sensa- 
tion, that  therefore  the  sensory  cortical  area  consists  for  the  most  part  of  the 
posterior  central  and  the  parietal  convolutions.  The  disturbances  to  the  dif- 
ferent modalities  of  sensation  resulting  from  lesions  within  these  parts  of  the 
cortex  appear  to  be  rather  different  in  degree.  The  pain  sensations  suffer 
least;  the  pressure  and  temperature  sensations  are  said  to  be  somewhat  re- 
duced, but  are  not  by  any  means  always  abolished.  The  power  of  localization 
is  very  profoundly  affected  and  the  patients  make  very  great  mistakes  when 
tested  for  this  sense.  The  motor  sensations  are  likewise  much  disturbed ; 
patients  can  neither  recognize  the  exact  position  of  their  limbs  nor  tell  when 
they  are  moved  passively.  Whether  there  is  any  dependence  of  the  modality 
affected  upon  the  exact  place  of  the  lesion  within  the  general  region,  we  can- 
not say  definitely  at  present. 

Further  proof  of  the  functional  relations  here  indicated  is  found  in  the 
anatomical  discoveries  concerning  the  convergence  of  the  conducting  path- 
ways of  the  tactile  and  other  general  sensory  nerves  into  the  cerebral  cortex. 
As  Flechsig  has  pointed  out,  these  for  the  most  part  enter  the  posterior  central 
convolution  and  only  a  small  fractional  ])art  of  them  reaches  the  anterior 
central.  Besides,  the  paracentral  lobule,  the  first  frontal  convolution  and  the 
g^Tus  fornicatus  also  receive  such  fibers.  But,  on  the  other  hand,  the  origin 
of  the  pyramidal  pathways  is  found  chiefly  in  the  paracentral  lobule,  in  the 
whole  anterior  central  convolution  and  in  the  posterior  part  of  the  first  frontal 
convolution.  It  is  significant  also  in  view  of  this  arrangement  that  the  an- 
terior central  convolution,  as  well  as  the  posterior  part  of  the  first  and  second 
frontal  convolutions,  has  a  different  structure  from  that  of  the  other  cortical 
regions  and  that  of  the  posterior  central  convolutions.  The  chief  difference 
consists  in  the  enormous  thickness  in  the  former  of  the  layers  of  the  middle- 
sized  and  the  superficial  giant  pyramidal  cells  (Cajal,  see  Fig.  2^4).  From 
these  relations  we  can  understand  how  it  is  that  motor  paralysis  of  cortical 
origin  is  not  necessarily  accompanied  by  loss  of  sensibility. 

It  is  also  possible  to  convince  oneself  by  stimulation  that  the  region  under 
consideration  is  in  fact  a  terminus  of  sensory  nerves.  If  the  central  convolu- 
tions of  an  una?sthetized  man  be  stimulated  electrically,  while  lie  feels  no 
pain  there  is  at  first  an  itchy,  prickling  sensation  in  that  part  of  the  body 
whose  muscles  contract  to  the  stimulus — an  observation  which  agrees  with  the 
statements  of  patients  suffering  from  cortical  epilepsy  regarding  the  premoni- 
tory symptoms  of  epileptic  attacks. 

In  short,  from  the  clinical  evidence  obtained  on  men  and  from  experiments 


THE   SENSORY  CORTICAL   AREAS  653 

on  animals  it  appears  that  the  cortical  area  of  the  general  sensory  and  tactile 
nerves  is  very  closely  related  to  the  motor  cortical  field  in  a  spatial  sense 
as  well  as  in  a  functional  sense,  but  that  in  man  it  lies,  at  least  for  the  most 
part,  outside  the  motor  cortical  field  (Fig.  293). 

B.  THE  CORTICAL  AREAS  OF  TASTE  AND  SMELL 

The  parts  of  the  brain  directly  connected  with  the  olfactorj-  organ  are  very 
differently  developed  in  different  genera  of  animals.  In  man,  as  we  have  already 
seen  (page  486),  this  sense  is  but  slightly  developed. 

Our  knowledge  of  the  cortical  areas  of  the  olfactory  nerves  is  ba^ed  almost 
exclusively  on  anatomical  evidence.  Judging  by  this,  the  olfactory  area  in 
man  embraces  the  whole  posterior  edge  of  the  base  of  the  frontal  lobe  and 
the  basal  part  of  the  gyrus  fornicatus  on  the  one  hand  and  the  uncus  and  a 
part  of  the  neighboring  inner  apex  of  the  temporal  lobe  on  the  other.  These 
two  areas  are  connected  at  the  base  of  the  insula  (Fig.  29-1). 

Speaking  of  the  cortical  area  for  the  gustatory  nerve.  Bechterew  states 
that  in  the  dog  bilateral  destruction  of  a  region  corres])onding  to  the  anterior 
lower  portion  of  the  third  and  fourth  external  convolutions  (Fig.  282)  oblit- 
erates the  sense  of  taste  entirely;  with  unilateral  destruction  there  is  total 
loss  of  taste  on  the  opposite  side  and  a  slight  weakening  on  the  same  side 
as  the  lesion.  Following  only  slight  injuries,  an  improvement  is  noticeable 
within  a  few  days,  while  after  more  extensive  lesions  the  defect  continues  for 
months.  Stimulating  these  portions  of  the  cortex,  Bechterew  noted  contrac- 
tion of  the  lips  on  the  opposite  side,  movements  of  the  tongue,  movements 
of  mastication  and  swallowing. 

C.    THE  AUDITORY  AREA 

H.  Munk  finds  that  removal  of  the  temporal  lobes  on  both  sides  produces 
complete  deafness,  but  no  other  disturbance.  Extirpation  of  one  temporal 
lobe  makes  the  animal  deaf  in  the  opposite  ear.  Stimulation  of  the  temporal 
convolutions  produces  movements  of  the  external  ear  which  are  probably  con- 
nected in  some  way  with  auditory  impressions. 

Similar  results  have  been  observed  by  other  authors,  but  we  find  it  stated  by 
still  others  that  bilateral  extirpation  of  these  parts  produces  only  temporar%-  deaf- 
ness or  no  evident  sign  of  it  at  all.  Brown  and  Schafer  completely  removed  both 
temporal  lobes  from  a  monkey.  Immediately  after  the  operation  the  animal's 
intelligence  was  very  much  affected,  but  this  condition  gradually  passed  away  so 
that  the  animal  once  more  became  very  intelligent.  The  authors  themselves  and 
several  other  physiologists  and  physicians  tried  numerous  experiments  with  the 
animal  and  came  to  the  conclusion  that  all  its  senses  including  hearing  were  per- 
fectly acute.  Moreover,  there  was  no  chance  for  the  claim  that  the  reactions  of 
this  animal  to  auditory  stimuli  were  really  due  to  excitation  of  the  cutaneous 
nerves.  From  these  observations  it  appears  therefore  that  the  auditory  pathways 
do  not  end  in  the  temporal  lobes  alone,  although  they  may  be  most  concentrated 
there. 

The  course  of  the  fibers  of  the  cochlear  nerve  inside  the  cerebrum  leaves 
no  doubt  that  the  temporal  lobes  in  man  stand  in  very  intimate  relation  with 


654 


PHYSIOLOGY   OF  THE  CEREBRUM 


Vision 


Fig.  29.3. — Right  cerebral  hemisphere  seen  from  the  outside,  after  Flechsig.  In  this  and  the 
following  figure  the  sensory  areas  are  indicated  with  red  dots.  The  region  where  the  dots  are 
thickest  is  the  region  where  most  of  the  sensory  pathways  end. 


General  Sensation 


Vision 


Smell 


Fig.   294. — The  inner  surface  of  the  left  cerebral  hemisphere,  after  Fleclisig. 


THE   SExNSORY   CORTICAL   AREAS  655 

the  auditory  nerves.  The  fibers  of  this  nerve  leaving  the  ganglion  cells  of  the 
cochlear  nucleus  are  carried  by  the  lateral  fillet  to  the  posterior  quadrigeminal 
body  (Flechsig  and  Bechterew).  This  is  abundantly  connected  with  the  in- 
ternal corpus  geniculatum,  which  in  turn  is  connected  exclusively  with  the 
cortex  of  the  temporal  lobe  (v.  Monakow).  According  to  Flechsig,  the  two 
transverse  convolutions  of  this  lobe  represent  the  substations  of  the  auditory 
nerve. 

These  convolutions  lie  deep  in  the  fissure  of  Sylvius,  where  they  push  in 
between  the  posterior  border  of  the  island  of  Reil  and  the  outer  free  surface 
of  the  first  temporal  convolution.  The  fact  that  in  all  cases  of  total  deafness 
as  the  result  of  bilateral  destruction  of  the  human  cortex  thus  far  known, 
this  region  of  the  two  transverse  convolutions  was  affected,  speaks  strongly 
for  its  importance  as  an  auditory  cortical  area.  Cases  of  deafness  or  of  dull 
hearing  on  one  side  following  injury  to  this  region,  or  to  its  coronal  radiation 
or  to  its  fibers  in  the  internal  capsule,  furnish  evidence  to  the  same  effect. 


D.    THE   VISUAL  AREA 

Experimental  as  well  as  clinical  and  anatomical  evidence  indicates  that  the 
cortical  area  for  the  optic  nerve  is  to  be  sought  chiefly  in  the  occipital  lobe. 
Statements  differ  a  great  deal  as  to  the  exact  boundaries  of  this  area,  owing 
in  part  at  least  to  the  fact  that  in  some  animals  the  localization  is  sharper 
than  in  others. 

In  the  dog.  according  to  H.  Munk,  the  two  retinae  are  projected  upon  the 
occipital  lobes  in  the  following  manner.  The  extreme  lateral  part  of  each 
retina  is  represented  by  the  extreme  lateral  surface  of  the  occipital  lobe  on 
the  same  side.  But  by  far  the  greater  part  of  each  retina  is  represented  by  the 
remaining  greater  part  of  the  occipital  lobe  on  the  opposite  side,  the  inner 
edge  of  the  retina  corresponding  to  the  median  edge  of  the  occipital  lobe, 
the  upper  edge  of  the  retina  to  the  anterior  edge  of  the  lobe,  and  the  lower 
edge  to  the  posterior  edge. 

As  opposed  to  this  Goltz,  among  others,  has  observed  after  bilateral  extir- 
pation of  the  occipital  lobe,  that  while  a  great  reduction  of  the  visual  power 
and  a  very  considerable  loss  of  intelligence  may  result,  the  animal  still  cannot 
be  called  totally  blind.  For,  although  he  may  not  respond  to  a  threat  with  the 
hand  or  with  a  light,  he  still  is  able  to  avoid  obstacles  fairly  well  without 
being  guided  in  any  way  by  the  sense  of  toiich.  These  observations  show  that 
the  animal  in  this  very  low  mental  condition  either  receives  visual  sensations 
through  the  remaining  parts  of  the  cortex,  or  tliat  the  movements  can  be 
regulated  by  retinal  impulses  with  the  help  of  the  subcortical  centers. 

Several  authors,  however,  have  observed  that  in  the  dog  a  temporary  reduc- 
tion of  the  visual  power  on  the  corresponding  halves  of  the  two  eyes  (homolateral 
hemiamblyopia)  may  result  from  the  removal  of  other  cortical  regions  (e.  g.,  the 
motor  zone).  One  would  be  inclined  to  conclude  from  this  that  while  most  of 
the  fibers  from  the  optic  tracts  reach  the  occipital  lobe,  some  of  them  have  ter- 
mini in  other  parts  of  the  cortex.  But  the  following  observations  by  Hitzig, 
which  have  recently  been  confirmed  in  their  entirety  by  Exner  and  Tmamura, 
prove  that  the  relationship  is  still  more  complex.    If  a  part  of  the  occipital  cortex 


656 


PHYSIOLOGY  OF  THE  CEREBRUM 


be  removed  from  a  dog,  and  then  after  the  heniiamblyopia  has  disappeared  the 
motor  zone  also  be  removed,  no  additional  effects  on  vision  are  produced.  But 
the  remarkable  thing  is  that  the  same  is  true  if  the  operations  be  performed  in 


Accommodaiion. 

Pupil. 

Convergence. 


Corp.  Quad. 


Fig.  295. — Schematic  representation  of  the  optic  triicts,  modified  from  Fuchs. 

Division  of  tlie  optic  tract  at  yg,  or  cc,  or  removal  of  tlie  left  occipital  lobe  produces  right  liemi- 
anopia.  In  the  first  case  there  would  be  no  reaction  of  the  pupil  to  light  on  illuminating  the 
left  half  of  either  retina.  Division  of  the  chiasm  at  ss  protluces  temporal  hemianopia. 
Division  of  the  fibers  at  m  abolishes  the  reaction  of  the  pupil  to  light.  The  fibers  connecting 
the  optical  cortex  (O.C.)  with  the  midbrain  (cf.  page  657)  and  with  other  portions  of  the 
cortex  (Assoc.)  (page  660)  are  shown.     O.R.,  optical  radiation;  O.c,  oculo  motor  nerve. 


reverse  order.  After  the  heniiamblyopia  resulting  from  removal  of  the  motor 
zone  has  passed  off,  an  extirpation  within  the  occipital  lobe  is  entirely  without 
effect.     We  shall  discuss  the  significance  of  these  facts  further  along  (page  6tj0). 


THE  SENSORY  CORTICAL   AREAS  657 

In  the  monl-cij  the  observations  of  H.  Mimk,  Brown  and  Schafer  and  others 
agree  in  showing  that  extirpation  of  one  whole  occipital  lobe  results  in  loss 
of  vision  on  the  corresponding  halves  of  the  two  retinae  (homolateral  herai- 
anopia.  Fig.  295),  and  bilateral  extirpation  in  total  blindness.  According  to 
H.  Munk,  there  should  be  a  projection  of  the  retina  upon  the  occipital  lobes 
of  the  monkey  like  that  described  above  for  the  dog.  But  Brown  and  Schafer 
have  not  obtained  any  positive  results  in  this  direction  by  partial  removal  of 
the  occipital  lobes. 

The  clinical  evidence  is  perfectly  clear  that  in  man  the  cortical  area  for 
the  optic  nerve  is  situated  in  the  occipital  lobes.  A  sufficiently  extensive  lesion 
of  the  occipital  cortex  is  followed  just  as  in  the  monkey  by  homolateral  hemi- 
anopia  on  both  sides.  As  a  rule,  this  is  not  complete,  for  the  line  of  separation 
leaves  the  central  part  of  the  visual  field  intact.  In  certain  individual  cases 
of  bilateral  hemianopia  accompanying  lesions  of  both  occipital  lobes,  the 
portion  corresponding  to  the  yellow  spot  may  remain  entirely  free. 

Opinions  differ  considerably  as  to  the  exact  location  of  the  visual  area 
in  the  occipital  lobe.  According  to  Xothnagel,  it  is  coterminous  with  the 
cuneus  and  the  first  occipital  convolution ;  according  to  Yialet,  with  the  whole 
median  surface  of  the  occipital  lobe.  Still  others  extend  it  further,  to  the 
first  and  third  occipital  convolutions,  or  even  to  the  angular  gA^us,  which 
latter,  according  to  Ferrier,  is  the  region  for  distinct  vision.  As  opposed  to 
these,  and  on  the  strength  of  some  very  convincing  cases,  Henschen  in  par- 
ticular advocates  the  view  that  only  the  cortex  along  the  calcarine  fissure  is 
to  be  regarded  as  the  area  of  vision. 

Flechsig,  on  the  basis  of  his  embryological  studies,  takes  very  much  the 
same  view.  Most  of  the  optic  fibers  end  in  the  wall  of  the  calcarine  fissure, 
and  those  regions  of  the  visual  area  situated  outside  of  this  limited  tract  have 
but  a  limited  share  in  the  true  visual  process. 

The  visual  conducting  paths,  according  to  most  investigators,  take  the 
following  course  to  the  occipital  cortex.  The  optic  fibers  springing  from  the 
ganglion  cell  layer  of  the  retina  pass  to  the  chiasm;  those  corresponding  to 
the  outer  lateral  parts  of  the  retina  remain  uncrossed;  the  remainder  cross. 
With  their  end  arborizations  some  come  into  relation  with  the  ganglion  cells 
of  the  anterior  quadrigcminal  body;  many  more,  and  among  them  the  fibers 
from  the  macula,  with  the  cells  of  the  external  corpus;  and  a  smaller  number 
with  cells  in  the  pulvinar.  New  pathways  spring  from  these  various  cells 
and  make  their  way  to  the  occipital  lobes. 

In  the  opinion  of  v.  Monakow,  the  reason  the  macula  region  so  often 
remains  intact  in  cerebral  lesions  is  that  it  is  probably  represented  throughout 
by  a  rather  extensive  cortical  zone;  the  macula  fibers  then  would  be  connected 
witli  practically  all  parts  of  the  corpus  geniculatum  ext. ;  consequently,  if  the 
lesion  left  any  fibers  to  the  cortex  intact,  impulses  from  the  macula  could 
still  be  transmitted. 

According:  to  Flcehsipr,  efferent  fibers  pass  out  from  the  occipital  lobes,  and 
convey  impulses  from  the  cortex  to  the  optic  thalamus  and  the  anterior  corpus 
quadripeiium  by  way  of  which  impulses  can  be  conveyed  from  the  optic  lobes 
to  various  muscles  and  other  peripheral  organs. 


658  PHYSIOLOGY   OF  THE  CEREBRUM 

Artificial  stimulation  of  the  cortex  l^ack  of  the  angular  gyrxia  in  the 
monkey  ( H.  Munk,  Schafer)  gives  conjugate  movements  of  the  eyes  toward 
the  opposite  side,  the  plane  of  vision  being  at  the  same  time  directed  upward, 
downward  or  horizontally,  according  as  different  points  of  this  region  are 
stimulated.  The  latent  period  of  these  movements  is  longer  than  that  of 
corresponding  eye  movements  which  appear  on  stimulation  of  the  frontal  lobe, 
they  are  also  obtained  after  removal  of  the  frontal  lobe;  hence  are  probably 
evoked  through  the  above-mentioned  subcortical  centers.  The  same  move- 
ments occur  when  the  occipital  cortex  and  the  eye  region  of  the  opposite 
frontal  lobe  are  stimulated  simultaneously. 

Movements  of  the  iris  also  can  be  aroused  by  stimulation  of  the  cerebral 
cortex.  Dilatation  of  the  pupil  is  most  easily  obtained  in  the  monkey  by  stimu- 
lation of  the  motor  region  for  the  eye  muscles  and  of  the  o(Mpital  lobe.  This 
dilatation  appears  when  the  cervical  sympathetics  are  cut,  and  probably  must  be 
regarded  as  at  least  partly  due  to  an  inhibition  of  the  sphincter  muscle.  Con- 
striction of  the  pupil  seems  to  be  obtained  only  as  an  exceptional  result  of  corti- 
cal stimulation, 

E.    RECAPITULATION 

From  the  facts  which  have  just  been  brought  forward  with  regard  to  the 
cortical  areas  of  the  nerves  of  special  sense,  it  appears  probalile  that  they, 
like  the  motor  areas,  become  more  sharply  concentrated  the  higher  we  ascend 
in  the  scale  of  mammals;  also  that  their  importance  for  special  sensations 
becomes  greater  and  greater.  Moreover,  it  is  evident  that,  as  a  general  rule, 
efferent  paths  from  all  the  sensory  cortical  areas  are  so  arranged  as  to  convey 
impulses  to  just  those  muscles  which  are  of  the  most  service  to  the  particular 
senses.  Thus,  the  cortical  field  for  the  sensory  nerves  of  the  skin,  of  the 
muscles  and  the  joints  lies  in  the  immediate  vicinity  of  the  great  motor  cor- 
tical area  or  practically  coincides  with  it ;  we  get  movements  of  the  ears  from 
the  temporal  lol)es  where  lie  the  auditory  areas,  and  movements  of  the  eyes 
from  the  occipital  region.  We  shall  discuss  the  deeper  physiological  and 
psychological  significance  of  these  cortical  areas  in  the  following  section. 


SECOND    SECTIOX 

THE   PSYCHO-PHYSICAL   FUNCTIONS   OF   THE 
CEREBRUM 

While  an  exhaustive  discussion  of  the  psychical  activities  of  man  is  plainly 
out  of  the  question  in  this  book,  a  brief  summary  of  the  most  important  facts 
of  modern  physiological  psychology  seems  called  for  here,  because,  quite  inde- 
pendently of  any  particular  psychological  system,  or  of  any  spiritualistic  or 
materialistic  point  of  view,  these  facts  may  of  themselves  afford  us  valuable 
insight  into  the  complex  mechanism  of  cerebral  activity.  We  designate  these 
functions  psycho-physical  in  order  to  expressly  indicate  that  we  shall  discuss 
them  not  from  the  standpoint  of  metaphysics,  but  solely  from  the  standpoint 
of  physiology,  and  without  wishing  to  take  any  position  with  reference  to 
spiritualism  or  materialism. 


THE   MOTOR  AND  SEXSORY   CORTICAL  AREAS  659 

§  1.    THE    SIGNIFICANCE    OF    THE    MOTOR   AND    SENSORY 
CORTICAL   AREAS 

We  liave  seen  that  the  motor  cortical  areas  constitute  the  place  of  origin 
of  the  long-fibered  motor  pathways,  and  that  the  sensory  pathways  terminate 
in  different  cortical  areas.  WTiat  then  is  the  physiological  and  psychological 
significance  of  these  areas? 

Theoretically,  the  simplest  psychical  events  probably  take  place  in  the 
cortical  areas  of  the  higher  senses,  for  in  such  events  the  bodily  movements 
phiy  l)ut  a  relatively  sul)ordinate  part,  or  at  least  do  not  occupy  so  prominent 
a  phice  in  consciousness  as  do  the  sensory  components  of  our  experiences.  We 
shall  therefore  begin  with  the  sensory  areas. 

The  conceptiM^most  widely  held  at  present  is,  that  the  excitation  of  these 
cortical  fields  itsen  produces  the  appropriate  simple,  special  sensations ;  that 
the  simple  visual  sensations,  for  example,  arise  in  the  visual  area  of  the 
occipital  lobe;  the  simple  auditory  sensations  in  the  auditory  area  of  the 
temporal  lobe,  etc. 

But  this  cannot  be  looked  upon  as  actually  proved.  If,  for  example,  we 
follow  in  our  imagination  the  conducting  pathway  of  optical  impressions  froim 
the  periphery  to  the  cerebral  cortex  it  is  evident  at  once  that  any  complete 
interruption  of  that  pathway,  no  matter  where  it  might  occur,  would  cause 
total  blindness;  also  that  any  partial  interruption,  wherever  it  might  occur, 
would  necessarily  produce  partial  Ijlindness.  From  this  point  of  view  it  is 
a  matter  of  indifference  whether  the  interruption  take  place  by  a  peripheral 
lesion  or  l)y  a  lesion  in  the  corresponding  part  of  the  optical  cortex.  If  only  we 
can  assume  that  the  activity  of  any  part  of  the  cerebrum,  be  it  never  so  small, 
will  occasion  a  conscious  process,  then  one  can  say  that  the  simplest  visual 
impression  is  produced  by  excitation  of  the  optical  area  in  the  cortex.  But 
this  is  only  an  unproved  postulate. 

Moreover,  our  simplest  conscious  states  are  always  very  complicated.  Witti 
the  sim))k'st  optical  impression — that,  for  example,  of  a  luminous  point — we 
observe  not  only  the  strength  of  the  light  and  the  color,  l)ut  its  position  in*the 
field  of  vision,  its  apparent  distance  from  the  eye,  its  apparent  size.  All  this 
is  given  at  the  first  glance,  and  it  is  at  least  very  difficult  to  suppose  that  all 
this  can  come  into  consciousness  by  the  activity  of  the  optical  cortex  alone. 

It  would  appear  to  l)e  justifial)le  therefore  to  assume  that  pathways  pass 
out  from  the  optical  cortex  and  connect  this  fiekl  with  others,  and  that  even 
the  simplest  visual  sensations  require  the  cooperation  of  several  different 
cortical  regions.  The  excitation  furnished  the  optical  cortical  area  is  of 
course  an  important,  perhaps  the  most  important,  component  of  tlie  whole 
process.  And  with  Flechsig  we  would  especially  emphasize  the  point  that 
what  gives  the  sensation  its  active  character,  Avhat  makes  it  essentially  clear 
and  distinct,  is  brought  about  by  this  very  component. 

The  manifold  ways  in  which  the  different  sensorjf  area.^  are  connected 
together  and  the  great  importance  of  such  connection  for  the  olijective  valua- 
tion of  our  sense  impressions  are  beautifully  illustrated  by  the  following 
observation  on  successfully  operated  patients  born  blind.  Such  iiersons  learn 
to  recognize  an  external  object  presented  to  them  by  feeling  it  with  the  fingers 


660  PHYSIOLOCY  OF  THE  CEREBRUM 

— i.  e.,  the  visual  impression  gets  its  proper  interpretation  through  the  idea 
already  gained  by  touch.  But  if  the  patient  has  seen  in  this  way  an  object 
a  single  time,  he  is  able  to  recognize  it  immediately  with  the  eye  the  next 
time.  The  connections  of  the  optical  center  with  the  other  parts  of  the 
cerebral  cortex  were  therefore  already  present,  and  it  was  only  necessary  for 
the  patient  to  compare  the  visual  impression  with  the  tactile  impression  a 
single  time  in  order  to  fix  the  memory  picture  of  the  object  permanently. 
It  can  scarcely  be«  maintained  therefore  that  the  optical  memory  pictures  are, 
as  has  so  often  been  a,ssumed,  so  to  speak  imprinted  on  the  optical  cortex, 
for  in  cases  like  these  just  described  there  would  not  be  time  enough  to  form 
such  an  imprint. 

The  exhaustive  analysis  which  Exner  has  made  of  the  visual  disorders  ob- 
served by  Hitzig-  following  lesions  of  the  motor  cortex  in  th^log-  (of.  page  655) 
shows  that  different  cortical  fields  participate  in  the  perception  of  things  visuallj. 
When  the  cortex  within  the  motor  region  is  destroyed,  many  fibers  which  connect 
the  occipital  lobe  with  this  region  are  severed.  Hence  the  perception  aroused  by 
appropriate  stimulation  of  the  optic  nerve  will  be  wanting  in  those  components 
which  relate  to  motility.  Consequently  the  elaboration  of  the  visual  impression 
after  the  operation  becomes  deficient  and  hemiamblyopia  sets  in,  notwithstand- 
ing that  the  optical  cortex  is  intact.  Recovery  from  the  visual  disorder  is  pos- 
sible because  the  hemisphere  of  the  opposite  side  takes  up  the  functions  of  the 
injured  side,  connections  being  gradually  established  which  lead  ultimately  to 
complete  restitution  of  function.  Extirpation  within  the  occipital  lobe  of  the 
injured  hemisphere  now  is  without  effect  because  this  hemisphere  has  no  fur- 
ther part  to  play  in  the  elaboration  of  visual  impressions. 

This  interpretation  receives  substantial  support  from  the  fact  that  section 
of  the  corpus  callosum — which  in  an  injured  animal  is  without  demonstrable 
effect  (see  page  641)- — in  a  dog  which  has  already  lost  the  motor  zone  and  has 
recovered  from  the  resulting  hemiamblyopia,  immediately  produces  this  disor- 
der again  and  leaves  no  possibility  of  recovery.  Likewise  the  hemiamblyopia 
continues  permanently  if  one  removes  a  piece  of  the  cortex  and  at  the  same 
time  sections  the  corpus  callosum. 

What  has  here  been  said  of  the  visual  area  is  of  course  true  for  the  cortical 
areas  of  the  other  higher  senses,  and  for  those  of  general  cutaneous  sensation, 
touch,  etc. ;  the  excitation  immediately  aroused  is  conveyed  by  means  of  new 
pathways  to  other  parts  of  the  brain,  and  by  the  cooperation  of  several  different 
cortical  fields  the  conscious  process  associated  with  those  particular  senses  is 
aroused. 

From  all  that  we  know  of  the  central  organs  of  the  nervous  S3'stem.  it 
appears  very  probable  that  the  motor  cortical  fields  do  not  of  themselves 
originate  the  impulses  which  they  send  to  the  muscles  of  the  body,  but  that 
they  must  first  be  acted  upon  by  other  cortical  regions.  We  naturally  think 
first  of  the  closely  associated  sensory  cortical  region  as  a  source  of  such 
excitation,  and  it  cannot  be  denied  on  purely  a  priori  ground  that  in  very 
many  simple  movements  aroused  b}'^  the  cortex,  the  efferent  impulse  is  dis- 
charged by  an  afferent  impulse  very  much  after  the  manner  of  a  reflex.  Here 
belongs  the  touch  reflex,  for  example,  described  by  H.  ]\runk,  which  consists 
of  a  feeble  flexion  of  the  toes  and  the  foot,  when  the  hairs  on  the  back  of  the 
foot  are  lightly  stroked  the  wrong  way,  and  which  is  permanently  lost  after 


LANGUAGE   FACULTIES  661 

extirpation  of  the  cortical  region  corresponding  to  the  extremities.  This 
mechanism,  however,  does  not  suffice  for  complicated  movements,  and  still 
less  for  learning  new  movements.  In  such  cases  several  other  portions  of  the 
cortex  must  be  called  into  play  and  it  is  these  which  finally  stimulate  the 
discharging  cells  of  the  motor  pathways. 

This  conclusion  is  supported  by  the  circumstance  that  in  localized  artificial 
stimulation  within  the  motor  cortex  (provided  no  epileptic  attack  is  induced) 
the  movements  obtained  are  always  relatively  simple,  being  confined  to  a  few 
groups  of  muscles.  They  almost  always  lack  the  orderly  coordination  of 
several  different  groups  which  characterize  the  voluntary  movements,  and  even 
appear  in  certain  reflexes  from  the  spinal  cord  (see  page  587). 

The  following  observation  may  be  cited  as  still  further  support  for  this 
conception.  If  the  cortical  area  of  a  definite  part  of  the  body  be  sought  out 
by  electrical  stimulation,  and  it  be  then  isolated  from  the  rest  of  the  cortex  by 
a  circular  cut,  the  effect  is  just  the  same  as  if  it  were  extirpated  in  toto, 
although  the  blood  supply  may  not  have  been  disturbed  by  the  process  of  cutting 
(Marique,  Exner,  and  Paneth). 

The  following  experiment  by  J.  R.  Ewald  likewise  speaks  against  the  idea 
that  the  voluntary  motor  impulses  originate  in  the  motor  cortical  areas.  A 
small  hole  is  made  in  the  skull  of  a  dog  and  after  opening  the  dura  mater,  elec- 
trodes are  fastened  in  in  such  a  way  that  the  cortex  can  be  stimulated  as  the 
animal  moves  freely  about.  Different  movements  can  then  be  induced  accord- 
ing as  one  or  the  other  of  the  cortical  fields  is  stimulated ;  but  the  animal  takes 
no  notice  of  them,  even  when  just  in  the  act  of  making  a  voluntary  movement. 
It  is  clear  that  such  a  stimulus  does  not  interfere  with  the  normal  stimulus, 
which,  it  would  seem,  therefore,  must  originate  elsewhere. 


§  2.    LANGUAGE   FACULTIES 

The  ability  to  use  language,  as  even  a  cursory  survey  of  the  way  in  which 
we  acquire  the  power  of  speech  will  show,  requires  the  cooperation  of  a  number 
of  different  parts  of  the  cerebral  cortex.  Lesions  in  different  parts  of  the 
cortex  and  of  the  corona  radiata  produce  various  disorders  in  the  language 
powers,  the  study  of  which  will  give  us  further  insight  into  the  mechanism 
concerned  in  psychophysical  processes.  What  follows  is  based  mainly  on  the 
ideas  of  v.  Monakow. 

A  child  is  born  with  the  ability  to  move  all  his  muscles;  he  sees  and  hears. 
But  he  lacks  for  the  most  part  the  power  to  coordinate  his  movements  to  any 
purpose:  he  does  not  understand  what  he  sees,  he  does  not  comprehend  what  he 
hears;  he  has  "  no  language  but  a  cry."  But  his  power  to  see  and  to  hear  begins 
to  be  exercised.  He  gradually  learns  to  recognize  people  and  the  commonest 
objects  about  him,  he  hears  the  names  by  which  these  people  and  things  are 
called  and  learns  little  by  little  to  recognize  them.  Finally,  he  begins  to  imi- 
tate these  sounds  and  after  many  fruitless  attempts  succeeds  at  last  in  com- 
passing the  first  intelligible  and  orderly  articulate  sound.  This  is  usually  the 
name  of  his  mother. 

And  so  it  goes  on.  The  child  gains  wider  knowledge  from  the  appearance 
of  different  objects,  learns  their  names  and  practices  them — i.  e.,  learns  to  make 
the  necessary  movements  of  his  organs  of  speech. 


662 


PHYSIOLOGY   OF  THE  CEREBRUM 


Soon  the  ability  to  form  ideas  is  developed,  by  which  we  mean  that  the 
child  learns  to  include  the  single  concrete  objects  of  the  same  kind  under  a 
common  designation.  And  as  his  mental  powers  develop  still  further,  he  comes 
to  incorporate  into  his  circle  of  ideas  notions  concerning  the  relations  of  objects 
to  one  another,  notions  of  their  properties,  their  position  in  time  and  space, 
etc.  Finally,  the  abstract  ideas  also  begin  to  be  more  than  mere  words  for  the 
child,  and  a  view  of  the  world,  as  yet  of  course  very  vague  and  indefinite, 
becomes  his  own. 

In  all  this  course  of  development  of  the  mental  powers,  speech  plays  a 
determining  part  and  this  part  becomes  more  significant  the  more  the  child 
comes  to  rely  upon  abstract  ideas.  He  requires  no  great  store  of  words  to  rep- 
resent objects  themselves  and  their  simplest  relations  to  each  other,  for  direct 
contemplation  will  serve  him  here.     But  when  it   comes  to  more  complicated 


Fig.  296. — Diagram  of  the  speech  tract  together  with  the  various  centers  of  the  cerebral  cortex 
concerned  in  speech.  L,  area  of  the  image  of  speech  movements;  A,  area  of  word-sound 
memory;  O,  area  of  memory  for  the  optic  images  of  writing;  Occ.I.,  O.II.,  O.III.,  first  to 
third  occipital  convolutions;  i^  7. ,  F  II.,  finst  and  second  frontal  convolutions;  F  III.,  third 
frontal  convolution  (Broca's  area);  T  I.,  T  II.,  T  III.,  first  to  third  temporal  convolutions; 
Cj}.,  posterior  central  convolution;  Pi.,  inferior  parietal  gyrus;  Ins.,  island  of  Reil;  ai,  asso- 
ciation tracts  between  L  and  the  central  portions  of  the  association  areas;  Li.,  motor  speech 
tract. 


relations   of  concrete   objects,   and  especially  to   abstract   ideas,   a  satisfactory 
conception  can  only  be  gained  through  the  medium  of  language. 

The  names  of  concrete  objects  have  therefore  much  less  significance  for 
our  mental  operations  than  the  words  by  which  we  designate  abstract  ideas, 
and  we  may  conclude  from  this  that  the  latter  require  a  more  complex  order  of 
activity  on  the  part  of  the  brain  than  the  former.  Accordingly  we  find  in 
certain  disorders  of  speech  resulting  from  injuries  in  the  brain — e.  g.,  in  lighter 
forms  of  the  so-called  amnestic  aphasia — that  the  patients  forget  proper  names 
and  the  names  of  things,  while  abstract  substantives,  verbs,  adjectives,  conjunc- 
tions, etc.,  are  retained. 


LANGUAGE   FACULTIES  663 

The  language  faculties  make  a  distinct  advance  when  the  child  learns  to 
read  and  write.  The  symbols  of  spoken  words  used  in  written  language — 
words  and  the  letters  of  which  they  are  composed — are  inculcated  in  the  same 
way  as  spoken  words,  and  at  the  same  time  the  ability  is  acquired  to  reproduce 
these  symbols  in  writing.  The  movements  used  in  writing,  just  like  other  move- 
ments, are  controlled  by  various  afferent  impulses. 

Our  powers  of  language  are  made  up  therefore  of  the  following  compo- 
nents: (1)  Memory  pictures  of  the  written  and  spoken  words;  (2)  the  ability 
to  make  the  coordinated  movements  necessary  in  speech  and  writing;  (3) 
constant  control  of  this  al)ility  through  various  afferent  pathways. 

Lesions  in  certain  regions  of  the  cortex  or  in  the  corona  radiata  produce 
disturbances  of  greater  or  less  extent  in  these  delicate  mechanisms,  which  are 
comprehended  under  the  name  of  aphasia,  and  differ  in  kind  and  extent 
according  to  the  place  of  lesion. 

One  of  the  simplest  forms  of  aphasia  is  that  of  alexia,  or  word  blindness, 
which  is  characterized  by  the  inability  to  recognize  written  or  printed  letters 
or  to  compose  words  of  them.  This  disorder  (in  right-handed  people)  follows 
injury  to  the  white  matter  of  the  left  angular  gyms  and  of  the  second  occipital 
convolution,  the  corresponding  cortex  remaining  uninjured.  Simple  alexia 
would  thus  be  produced  by  interruption  of  the  association  fibers  connecting 
the  visual  cortical  area  with  other  cortical  regions  which  are  active  in  the 
use  of  language.  When  the  cortex  alone  of  the  angular  gyrus  is  affected, 
alexia  does  not  ensue,  and  this  may  be  taken  as  a  proof  that  that  portion  of  the 
cortex  is  not,  as  has  been  supposed  by  many  authors,  the  "  center  "  for  reading. 

Alexia  may  occur  without  affecting  the  ability  to  speak,  and  this  is  readily 
understood  when  we  remember  that  aside  from  writing  reading  is  the  latest 
acciuirement  in  the  development  of  the  language  powers,  and  might  well  exer- 
cise but  a  slight  influence  on  the  speech  mechanism  pure  and  simple. 

It  is  possible  for  the  patient  to  be  able  to  write  even  when  he  cannot  read, 
and  this  is  explained  by  supposing  that  the  association  pathways  which  are 
active  in  writing  have  escaped  the  lesion.  Such  a  patient  may  even  succeed 
in  deciphering  script  or  printing  by  executing  the  appropriate  movements  for 
making  the  letters  which  he  sees,  but  would  not  otherwise  comprehend.  In 
this  case  he  reads  by  using  the  memorj^  pictures  of  these  movements  and  by 
bringing  them  through  association  fibers  into  connection  with  the  cortical  areas 
which  mediate  the  necessary  movements  of  the  organ  of  speech. 

Other  disorders  of  the  language  powers  are  produced  by  lesions  within  the 
red  area  in  Fig.  29(5,  and  the  white  matter  lying  immediately  under  it.  In 
right-handed  people  it  is  always  the  left  hemisphere  which  is  affected.  These 
disorders  differ  both  in  kind  and  extent,  and  can  be  divided  into  two  groups 
— motor  and  sensory  aphasia — according  as  the  expressive  or  the  perceptive 
phase  of  language  is  the  more  affected.  Between  the  two  are  various  inter- 
mediate modifications. 

Motor  aphasia,  which  tlirough  the  work  of  Broca  has  been  of  so  much 

importance  for  the  development  of  our  views  concerning  the  functions  of  the 

•  cerebrum   (see  page  031),  appears  in  its  purest  and  simplest  form  when  only 

the  special  motor  functions  of  speech  are  arrested.     In  this  case  the  person 
39 


664  PHYSIOLOGY  OF  THE  CEREBRUM 

affected  can  write  and  can  understand  written  or  spoken  words  normally,  but 
cannot  speak  or  read  aloud  either  voluntarily  or  after  another  person.  The 
part  affected  is  only  the  subcortical  portion  beneath  the  posterior  third  of 
the  third  frontal  convolution.  The  lesion  interrupts  only  the  conducting 
pathways  serving  the  organs  of  speech,  on  their  way  to  the  internal  cajisule. 

But  if  the  cortex  of  the  posterior  part  of  the  third  frontal  convolution 
(Broca's  convolution)  is  injured,  other  disorders  appear  even  though  the 
lesion  be  a  ver}-  slight  one.  The  patient  now  loses,  besides  the  power  of  speak- 
ing, the  power  of  writing  spontaneously,  although  he  may  acquire  it  again. 
The  ability  to  write  by  dictation  is  always  partially  destroyed  soon  after  the 
lesion  makes  its  appearance. 

More  profound  still  are  the  disorders  when  the  third  left  frontal  convolu- 
tion is  somewhat  more  extensively  injured.  Writing  spontaneously  and  by 
dictation  becomes  very  difficult,  although  the  defect  is  not  duo  to  any  motor 
effects  on  the  right  arm.  It  is  difficult  for  the  patient  to  understand  written  or 
printed  words  even  though  he  may  recognize  them  perfectly;  he  quickly  tires 
of  reading,  and  cannot  compose  words  when  the  proper  letters  are  shown  him 
one  after  the  other,  cannot  recognize  words  when  the  letters  are  placed  verti- 
cally instead  of  horizontally,  etc.  On  the  other  hand,  the  ability  to  understand 
spoken  words  and  to  copy  words  in  writing  is  generally  unimpaired. 

When  the  superior  temporal  convolution  is  injured  somewhat  extensively, 
the  other  typical  form  of  aphasia  appears.  This  is  called,  from  its  most 
prominent  symptom,  word  deafness  or,  after  Wernicke  who  first  described  it, 
sensory  aphasia. 

This  form  of  aphasia  may  also  be  very  simple  in  character;  the  patient 
can  speak,  read  and  write ;  his  comprehension  of  language  is  undisturbed,  but 
he  cannot  understand  spoken  words,  whereas  he  can  not  only  hear  but  also 
correctly  interpret  every  other  kind  of  noise  and  sound.  He,  lacks  the  ability 
to  interpret  the  sounds  of  letters ;  and  this  is  probably  due  to  the  interruption 
of  certain  association  pathways,  the  elements  serving  other  language  faculties 
remaining  unimpaired. 

As  a  rule,  however,  word  deafness  is  closely  associated  with  much  more 
serious  disorders.  This  is  what  we  should  exjiect,  if  we  rememJier  how  great 
is  the  influence  of  spoken  words  on  the  total  language  powers,  and  how 
numerous  are  the  connections  of  the  auditory  association  pathways  with  other 
parts  of  the  brain.  Any  cortical  lesion  in  the  temporal  lobe  must  therefore 
necessarily  involve  many  different  bundles  of  association  fibers;  consequently 
word  deafness  is  accompanied  by  many  different  effects  on  the  general  lan- 
guage powers. 

Clinical  ohservaiions  have  given  us  the  following  facts  with  respect  to  this 
form  of  aphasia.  With  lesions  in  the  posterior  part  of  the  first  temporal 
convolution,  voluntary  speech  appears  on  superficial  examination  not  to  be 
particularly  affected,  but  in  reality  it  is  always  paraphasic — i.  e.,  the  person 
shows  an  inclination  to  confuse  words  and  to  talk  gil)l)erish ;  and  since  the 
auditory  control  is  largely  impaired  he  makes  all  sorts  of  errors  in  enuncia- 
tion without  being  aware  of  them.  Repeating  words  after  another  person  is 
for  the  most  part  impossi])le,  because  the  sounds  of  words  are  not  retained 
long  enough  in  the  memory  to  be  understood.     Reading  aloud  is  out  of  the 


THE   ASSOCIATION  CENTERS   OF   FLECHSIG  665 

question,  because,  while  the  letters  are  seen,  they  are  not  ahva3's  recognized 
as  signs  of  certain  definite  sounds.  The  ability  to  write  spontaneously  or 
after  dictation  is  very  profoundly  affected  and  the  ability  to  copy  is  often 
somewhat  reduced.  We  find  likewise  when  the  destruction  is  somewhat  more 
extensive  that  it  is  always  difficult  and  sometimes  impossible  for  the  patient 
to  understand  writing. 

The  disorders  which  are  produced  by  lesions  of  the  first  temporal  convolu- 
tion may  vary  also  according  to  the  mental  and  literary  culture  of  the  indi- 
vidual. Highly  educated  persons  suffer  less  in  their  ability  to  understand 
written  or  spoken  words  or  in  their  ability  to  write  than  do  the  uneducated. 

Recovery  of  language  powers  lost  by  these  various  lesions  is  to  a  greater 
or  less  extent  possible.  This  is  explained  in  part  by  the  assumption  of  the  lost 
functions  by  the  right  hemisphere,  and  in  part  possibly  by  the  establishment 
of  new  associations  by  means  of  collateral  and  other  connections  which  have 
been  left  unharmed. 

When  the  language  powers  are  destroyed  to  any  great  extent,  the  mental 
powers  must  naturally  suffer.  Here  again  the  extent  and  duration  of  the  dis- 
order will  depend  upon  the  position  and  extent  of  the  lesion  as  well  as  upon 
the  relative  importance  of  the  different  components  in  the  person's  particular 
language  mechanism.  If,  as  is  usually  the  case,  the  individual  is  influenced 
most  by  the  sound  images  of  words,  word  deafness  would  naturally  produce  a 
greater  reduction  in  his  intelligence  than  if  he  relied  mainly  upon  memory 
pictures  of  printed  or  written  words. 

Closely  related  I)ut  not  idt'iitical  with  the  language  faculties  are  the  musical 
facilities.  !Music  constitutes  a  language  of  its  own,  the  finer  nuances  of  which 
are  intelligilde  only  to  a  relatively  few  favored  individuals.  Clinical  observa- 
tions made  within  recent  years  have  shown  that  brain  diseases  ma}'^  cause 
disorders  in  these  powers  exactly  similar  to  those  affecting  the  ordinary  lan- 
guage faculties.  Thus  we  find  loss  of  the  ability  to  sing  (vocal  motor 
a})hasia),  note  blindness,  loss  of  the  ability  to  write  musical  notes  (musical 
agraphia),  tone  deafness,  etc.,  all  of  which  are  comprehended  under  the 
general  term  amusia.  There  is  also  a  certain  degree  of  independence 
both  in  the  relation  of  these  to  one  another  and  in  their  relations  to  aphasia. 
For  example,  a  person  may  be  able  to  sing  and  not  to  speak,  or  to  speak  and 
not  to  sing.  It  is  probable  that  at  least  certain  of  the  special  clinical  forms 
of  amusia  are  anatomically  inde])endcnt.  and  that  they  are  caused  by  lesions 
in  the  vicinity  of  those  which  produce  the  different  forms  of  aphasia.  The 
localization  for  that  special  form  of  amusia  known  as  tone  deafness,  which  is 
characterized  hy  loss  of  the  ability  to  recognize  musical  sounds  as  such,  is 
probal)ly  in  the  first  or  first  and  second  convolutions  of  the  left  temporal  lobe 
in  front  of  the  region  the  destruction  of  which  causes  word  deafness  (Edgren). 


§  3.    THE   ASSOCIATION   CENTERS    OF    FLECHSIG 

The  discnssion  in  the  pn^eding  ])aragraphs  has  taught  us  that  the  higher 
functions  of  the  l)rain  which  are  in  the  imnuvliate  service  of  the  mental  facul- 
ties are  carried  out  under  the  cooperation  of  several  cortical  regions.     Brain 


666 


PHYSIOLOGY   OF  THE  CEREBRUM 


anatomy  lias  long  since  dcinonstrated  various  systems  of  fibers  by  which  the 
two  hemispheres  and  ditferent  regions  of  the  same  hemisphere  are  joined 
together.  And  quite  recently  our  knowledge  of  the  subject  has  been  enriched 
so  materially  by  the  investigations  of  Flechsig  that  future  researches  in  this 
field  will  have  a  much  safer  point  of  departure  than  hitherto. 

A.    ANATOMICAL 

Froni  what  we  have  learned  in  preceding  sections  we  know  that  only  about 
one  third  of  the  entire  surface  of  the  cerebrum  is  in  direct  connection  with 
tracts  which  mediate  sensory  impressions  and  arouse  mental  mechanisms. 
We  know,  moreover,  both  from  the  anatomical  structure  of  the  brain  and 
from  the  fairly  certain  localization  of  cortical  motor  and  sensory  areas,  that 
the  remaining  parts  of  the  cerebral  cortex  have  nothing  whatever  to  do  with 
afferent  or  efferent  tracts.  They  serve  to  connect  and  associate  the  impulses 
delivered  by  the  sensory  nerves,  to  originate  the  resulting  motor  impulses,  and 


Fig.   297. — The  myelogcnetic  areas  of  the  human  brain,  outer  surface,  after  Flechsig. 

to  elaborate  perceptions  into  higher  mental  processes;  in  short,  these  parts  are 
to  be  regarded  as  the  organs  of  our  purely  psychical  activities.  We  shall  speak 
of  them  in  the  following  pages  as  the  association  centers. 

We  find  sufficient  grounds  for  this  view  both  in  the  clinical  observations 
which  have  been  made  and  in  the  results  of  anatomical  investigation.  The 
microscopical  structure  of  these  parts  of  the  cortex  alone  indicates  that  they 
are  of  different  character  from  the  other  cortical  areas.  While  the  cortical 
areas  of  the  nerves  of  special  sense  possess  in  each  case  something  which 
clearly  recalls  the  distribution  of  nerves,  in  the  particular  peripheral  organ  to 
which  each  corresponds,  the  association  centers  have  more  in  common.    Although 


THE  ASSOCIATION  CENTERS  OF   FLECHSIG 


667 


they  are  scattered  widely  over  the  surface  of  the  cerebrum,  the  microscopical 
structure  is  much  the  same  type  in  all  of  them. 

The  same  thing  is  taught  by  the  mode  of  development  of  the  myelin  sub- 
stance in  the  white  matter  of  the  brain.  It  is  well  known,  through  the  work  of 
Flechsig,  that  the  fibers  running  to  certain  areas  of  the  cortex  receive  their 
medullary  sheaths  much  earlier  than  those  running  to  other  areas.  In  fact,  at 
a  time  when  the  myelin  substance  in  some  convolutions  is  almost  entirely  com- 
plete, in  others  it  is  just  beginning,  and  in  still  others  has  reached  a  medium 
stage  of  development.     At  certain  stages,  therefore,  we  can  distinguish  medul- 


FiG.  298. — Myelogenetic  areas  of  the  luiman  brain,  inner  surface,  after  Flechsig. 


lated,  nonmedullated  and  half-medullated  convolutions  which  present  uniform 
structures  throughout,  and  in  all  individuals  of  appi'oximately  the  same  age 
have  practically  the  same  relative  position.  Flechsig  distinguishes  thirty-six 
such  "  myelogenetic  "  areas.  They  are  numbered  according  to  the  order  in  which 
they  receive  their  myelin  substance,  and  are  divided  chronologically  into  three 
groui)s. 

Those  areas  which  are  mostly  myelinated  at  birth  at  term  are  called  by 
Flechsig  primordial  regions :  here  belong  Xos.  1  to  10,  Figs.  297  and  298. 
Anatomically  they  are  distinguished  mainly  by  their  great  richness  in  paths  to 
and  from  the  subcortical  centers  (projection  fibers).  By  comparison  of  Figs. 
297  and  29S  with  Figs.  293  and  294,  it  may  be  seen  that  these  areas  embrace  the 
points  of  entrance  into  the  cortex  of  all  sensory  pathways  as  well  as  the  points 
of  exit  of  all  the  motor  pathways.  It  is  not  known  at  present  whether  certain 
of  these  primordial  regions  (for  example.  No.  10,  Fig.  297)  are  connected  with 
perii)heral  end  organs  or  not. 

The  second  group  of  cortical  areas  includes  the  intermoditirji  rcjiions  (Nos. 
11  to  30)  ill  which  the  myeliiiation  begins  before  the  end  of  the  first  month 
after  birth.  Tt.  the  third  group,  the  ierminal  regions,  belong  those  areas  which 
are  myelinated  after  tlie  first  month  (31  to  36).     In  these  as  well  as  the  most 


66S  PHYSIOLOGY  OF  THE  CEREBRUM 

intermediary  regions  there  are  fewer  projection  fibers  than  in  the  primordial 
regions.  Individual  fibers  indeed  are  to  be  demonstrated,  but  thej-  are  very 
scarce  as  compared  with  those  in  other  tracts. 

The  terminal  regions,  on  the  other  hand,  are  richest  in  association  fibers, 
that  is,  in  fibers  running  from  one  region  of  the  cortex  to  the  other;  in  fact 
they  may  be  said  to  constitute  the  nodal  points  of  the  long  association  systems. 
But  there  are  no  long  systems  to  be  found  which  can  be  said  to  unite  any  two 
primordial  regions  regarded  as  sensory  centers.  A  visual  and  an  auditory  im- 
pression, for  example,  could  not  meet  in  a  primordial  center:  this  could  only 
happen  in  one  of  the  intermediary  or  terminal  regions. 

The  last  named  therefore  constitute  association  centers.  Three  reo^ions 
in  each  hemisphere  are  embraced  by  them,  namely,  a  frontal  or  anterior,  an 
insular  or  middle,  and  a  parieto-occipito-temporal  or  posterior  region.  There 
is  no  reason  to  believe  that  these  three  are  of  equal  importance  for  the 
psychical  functions;  in  fact  their  positions  with  reference  to  the  different 
sensory  areas  would  seem  to  indicate  that  they  have  special  functions.  The 
posterior  association  center  is  intercalated  between  the  visual,  the  auditory 
and  the  tactile  areas;  the  anterior  between  the  tactile  and  the  olfactory — 
probably  also  the  gustatory — areas :  the  middle  between  the  auditory,  the 
olfactory  and  the  tactile  areas. 

The  anterior  center  is  formed  by  the  anterior  half  of  the  first  and  the 
greater  part  of  the  second  convolutions.  On  the  basal  side  of  the  frontal  lobe 
the  gyrus  rectus  particularly  Ijelongs  to  this  center.  The  middle  center  covers 
the  insula.  The  posterior  center  embraces  the  precuneus,  the  parietal  con- 
vohitions.  parts  of  the  lingual  gyrus,  the  fusiform  gyrus,  the  .second  and 
third  temporal  and  the  anterior  portions  of  all  three  occipital  convolutions 
(see  Figs.  293  and  29-i). 


B.    THE   ANTERIOR   ASSOCIATION   CENTER 

We  have  already  learned  from  observations  on  animals  that  extirpation  of 
the  frontal  lobes  produces  noteworthy  alterations  in  the  intelligence  and  char- 
acter of  the  animal.  After  removal  of  the  most  anterior  portion  of  the  brain, 
dogs  become  exceedingly  irritable.  Harmless,  good-natured  animals  become 
fierce  and  malicious,  so  that  after  the  operation  they  will  not  even  allow  them- 
selves to  be  touched.  The  animal's  movements  are  exceedingly  cumbrous  and 
awkward.  He  cannot  hold  a  bone  firmly,  his  whole  carriage  of  himself  is  un- 
steady, he  stumbles  easily  and  on  a  slippery  floor  at  once  loses  his  footing  (Goltz). 

In  line  with  this,  Bianchi  has  observed  that  the  intelligence  with  which  a 
monkey  performs  complicated  acts  is  often  greatly  affected  hy  the  removal  of 
both  frontal  lobes. 

Similar  changes  in  character  have  not  infrequently  lieen  observed  in  men 
with  lesions  of  the  frontal  convolutions.  Persons,  who  before  were  well  dis- 
posed and  orderly,  became  foolish,  impatient  and  headstrong,  and  at  the  same 
time  changeable  and  fickle.  Xeither  sensory  nor  motor  disorders  of  any  kind 
can  l)e  demonstrated  on  them  (Welt). 

Flechsig  has  given  the  following  description  of  the  effects  of  lesion-;  in 
the  frontal  association  centers  observed  on  men.    The  patient  sometimes  loses 


THE  ASSOCIATION  CENTERS   OF   FLECHSIG  669 

all  sense  of  his  actual  relations  to  the  world,  imagining  himself  possessed  of 
great  wealth,  or  the  recipient  of  high  honors;  sometimes  he  confuses  per- 
ceptions of  external  objects  with  the  inner  consciousness  of  his  own  person, 
or  vice  versa,  his  consciousness  of  himself  with  impressions  of  the  outer  world, 
so  that  he  either  forgets  that  he  exists  or  takes  no  notice  of  his  surroundings. 
There  need  be  no  confusion  of  ideas  in  the  strict  sense  of  the  term.  He  may 
speak  rationally  and  in  a  perfectl}'  orderly  way  about  various  subjects  within 
his  mental  grasp,  but  he  is  unable  to  distinguish  between  the  true  and  the 
false,  the  imaginary  and  the  real,  the  possible  and  the  impossible;  and  along 
with  this  defect  of  the  logical  sense  there  goes  a  loss  of  the  ethical  and  esthetic 
judgments,  so  that  he  does  things  which  are  utterly  irreconcilable  with  his 
former  character.  The  patient  thus  loses  his  composure,  and  this  to  a  greater 
degree  the  more  he  is  actuated  by  stronsj  feeling  or  is  under  the  influence  of 
passion.  When  once  he  becomes  angered,  a  fit  of  rage  comes  over  him  like  an 
avalanche.  A  stage  is  finally  reached  where  all  self-control  is  lost  and  he  is 
ruled  in  everything  merely  by  the  logic  of  madness.  Whatever  is  uppermost 
in  his  mind  he  does  without  regard  to  his  surroundings  or  to  good  taste.  At 
last  imbecility  sets  in  and  the  personality  is  lost  entirely. 

C.    THE  POSTERIOR  ASSOCIATION   CENTER 

Goltz  observed  the  following  effects  of  removing  the  occipital  lobes  from 
dogs.  The  tactile  sense  was  undisturbed,  the  animal  was  not  merely  able  to 
move  all  the  muscles  of  his  body  voluntarily,  but  could  perform  all  kinds  of 
movements  with  almost  as  much  facility  as  a  normal  animal.  He  had  no  trouble 
in  eating  and  could  hold  a  bone  between  the  paws,  etc. 

H  the  animal  were  vicious  before  the  operation,  removal  of  the  occipital 
lobes  made  him  docile.  Nothing  then  served  to  exeite  him;  he  was  always  calm 
and  deliberate.  But  his  perceptive  faculties  suffered  considerable  diminution 
and  his  intelligence  sank  to  a  low  level. 

In  man  lesions  within  the  posterior  association  center  have  been  observed 
to  ))roduce  alexia  (cf.  page  (>();>),  and  a  more  or  less  distinctive  loss  of  the 
power  to  interpret  visual  impressions  of  other  kinds.  All  such  disorders, 
whatever  their  extent,  are  included  under  the  term  "  mind  blindness  "  given 
by  H.  Munk. 

Typieal  mind  blindness  in  man  is  characterized  by  v.  Monakow  in  the  fol- 
lowing manner:  The  person  affected  has  impressions  and  sensations  of  light  but 
can  no  longer  recognize  the  objects  of  his  surroundings.  This  is  not  because 
his  memory  pictures  of  the  objects  are  gone,  but  bcx-ause  the  associations  neces- 
sary for  understanding  them  are  no  longer  possible,  that  is,  the  memory  pic- 
tures cannot  be  called  up  by  the  retinal  stimulus,  although  they  may  be  aroused 
by  another  sense,  or  quite  spontaneously.  Among  other  things  a  person  can  tell 
one  color  from  another  but  cannot  find  the  right  names  for  the  colors.  He 
cannot  tell  just  the  quality  of  the  color  of  the  sky,  or  of  leaves,  or  of  blood,  etc. 

While  the  memory  for  many  different  forms  of  visual  impressions  may  be 
just  as  good  as  ever,  it  appears  as  a  rule  to  be  considerably  impaired  for  recent 
impressions.  vSueh  patients  are  unable  to  describe  the  forms  of  objects  pre- 
sented to  them  just  a  moment  before,  while  they  have  a  perfectly  clear  picture 
of  objects  with  which  they  are  familiar,  such  as  a  knife  or  a  watch,  and  can 


670  PHYSIOLOGY  OF  THE  CEREBRUM 

describe  them.  They  can  also  acquire  new  optical  images,  but  it  is  much  more 
diflScult  than  formerly.  Sometimes  the  memory  for  old  and  familiar  objects 
as  well  as  for  less  familiar  ones  is  affected  and  the  person  cannot  describe  well- 
known  buildings  and  streets  of  his  own  town  so  as  to  direct  another  person 
how  to  go  from  one  point  to  another.  In  severe  forms  of  mind  blindness  all 
objects  and  persons  alike  appear  strange,  and  may  not  be  recognized  even  in 
their  general  relations. 

What  the  patient  is  unable  to  recognize  by  optical  impressions  alone,  he 
can,  however,  properly  orient  by  means  of  other  impressions — for  example,  audi- 
tory impressions.  Thus  a  patient  who  fails  to  recognize  his  own  friends  by 
sight  may  recognize  them  by  their  voices,  etc. 

Mind  hUtidness  comes  on  if  the  lesion  extends  to  the  white  matter  of  the 
occipital  lobe,  and  in  all  probability  is  caused  by  the  interruption  of  the  asso- 
ciation pathways  and  by  injury  to  the  association  areas.  It  is  not  referable 
to  any  definite  locality,  but  can  be  produced  by  abscesses  in  different  parts  of 
the  lobe.  In  the  great  majority  of  cases  thus  far  observed,  the  abscesses  are 
situated  in  both  hemispheres.  ]\rind  blindness  has  not  yet  been  observed  as 
the  result  of  disease  on  the  right  side  alone. 

The  phenomena  of  mind  blindness  undoubtedly  show  that  the  occipital  lobes 
play  a  determining  part  in  the  proper  evaluation  of  optical  impressions.  Ob- 
servations on  more  extensive  lesions  of  the  posterior  association  center,  in 
Flechsig's  sense,  teach  us  also  that  mental  disorders  of  a  more  serious  nature 
may  result  from  the  loss  of  its  function. 

The  first  symptom  of  a  diseased  condition  involving  a  large  part  of  this 
center  is  incoherence  of  ideas,  that  is,  a  primary  intellectual  deficiency  and 
something  quite  independent  of  the  effects  which  follow  purely  and  simply 
as  the  result  of  a  loss  of  ordinary  associative  connection  of  external  impres- 
sions. Many  of  these  patients  exhibit  no  lack  of  clearness  as  to  their  own 
person,  evince  no  lack  of  composure  in  their  conduct,  no  deep  perversion  of 
their  feelings  or  desires;  but  they  do  not  correctly  interpret  external  objects, 
and  consequently  misuse  them.  They  mistake  one  person  for  another,  and  lose 
their  bearings  both  spatially  and  temporally.  The  mental  images  of  what  goes 
on  outside  are  lost,  consequently  a  clear  understanding  of  the  external  world 
and  that  knowledge  of  it  which  is  capable  of  being  put  into  words;  in  short, 
all  empirical  interpretations  of  external  impressions  are  reduced  to  naught. 
The  patient  has  thus  l)ecome  impoverished  for  ideas,  eventually  nothing  either 
true  or  false  enters  his  head — he  has  become  an  idiot. 


D.    FINAL   SURVEY 

It  is  likely  that  in  the  more  complicated  mental  processes  all  the  associa- 
tion and  sensory  centers  cooperate,  since  they  are  united  with  each  other  by 
numerous  nerve  fibers,  and  that  from  this  cooperation  results  the  harmony 
of  the  cerebral  functions. 

Flechsig  has  worked  out  some  views  with  regard  to  the  mechanics  of  the 
higher  brain  functions,  which  I  shall  abstract  briefly  here,  because  among 
modern  researches  on  the  brain  which  have  a  physiological  bearing  those  of 
Flechsig  undoubtedly  take  first  rank. 


THE   ASSOCIATION   CENTERS   OF   FLECHSIG  671 

Since  the  memory  always  suffers  to  a  great  extent  from  destruction  of  the 
association  centers,  the  nervous  elements  with  which  the  ability  to  recall  sense 
impressions  is  connected  must  unquestionably  be  sought  inainly  in  those  cen- 
ters. The  ganglion  cells  play  the  chief  role  in  this  because,  so  far  a.s  our 
experience  yet  goes,  they  alone  of  all  the  nervous  elements  are  able  to  store 
up  impulses  and  to  become  charged  with  energ}'.  Without  knowing  anything 
about  it,  wo  may  suppose  that  the  number  of  nerve  elements  which  are  active 
in  the  simplest  event  of  consciousness  must  be  very  great. 

What  we  do  knoAv  with  certainty  is,  that  tokens  of  memory  (memory  pic- 
tures) which  are  imprinted,  so  to  speak,  in  the  brain  elements  are  more  or 
less  firmly  related  to  each  other ;  and  the  basis  of  this  organic  unity  of  memory 
lies  in  the  systematic  arrangement  of  the  numberless  disparate  constituents 
of  its  physical  groundwork. 

The  question  as  to  what  are  the  physical  forces  which  bring  the  memory 
pictures  back  to  consciousness  is  one  of  particular  interest.  We  commonly 
attribute  the  greatest  importance  to  our  sense  impressions,  impressions  of  the 
outer  world,  and,  as  a  matter  of  fact,  throughout  our  waking  hours,  these 
are  all  the  time  rousing  memory  tokens. 

But  a  second  important  factor  comes  in  here.  External  impressions  act 
to  rouse  the  imagination  or  a  reflective  train  of  thought  most  potently  if 
they  at  the  same  time  rouse  certain  feelings  or  emotional  impulses.  Anything 
that  pleases  not  only  stimulates  but  also  quickens  the  imagination. .  But 
hunger,  thirst,  sexual  passion  and  many  other  bodily  sensations  have  a  direct 
summoning  influence  on  all  agreeable  ideas  connected  with  them.  We  have 
then  in  the  bodily  feelings  and  general  bodily  spirits,  which  are  the  real 
primary  forces  of  the  imagination,  a  second  regulating  factor  upon  which 
rests  a  very  substantial  and  by  no  means  the  most  sordid  part  of  art  and 
poetry. 

Primarily  the  senses  appear  to  be  only  subordinate  helps  to  the  impulses 
coming  from  within,  but  they  provide  us  a  store  of  material  for  the  expression 
of  our  feelings.  The  artistic  perfection  of  the  pictures  which  we  create  with 
our  minds  will  depend  in  large  part  upon  the  care  with  which  this  preparatory 
work  is  done,  upon  the  sharpness  of  our  grasp  of  the  actual ;  and  the  imagina- 
tion will  work  to  a  given  end  the  more  effectively,  the  more  this  sensory 
material  is  allowed  to  appeal  to  our  feelings,  and  so  to  take  on  tokens  by 
which  it  can  be  recalled  to  mind. 

But  even  in  the  most  magnificent  creations  of  the  imagination  we  have 
to  do  to  a  certain  extent  with  simple  mechanical  processes.  Here  again  con- 
ducting pathways,  nerve  fibers,  which  connect  the  mechanisms  concerned  in 
the  production  of  bodily  feelings  with  the  central  workshops  of  organized 
memory,  namely  the  association  centers,  have  a  part  to  play.  And  since  the 
nerves  which  serve  to  bring  the  sensory  impulses  to  consciousness  push  tlirough 
to  the  cortex  and  enter  the  sensory  centers,  we  have  converging  toward  the 
same  cortical  regions  nerve  paths  which  make  us  aware  of  the  treasures  and 
charms  of  the  outer  world,  and  those  which  bring  to  consciousness  the  every- 
day needs  of  the  l)ody  in  the  form  of  desires.  Both  without  distinction  act 
from  these  their  highest  ])oints  of  attack  upon  the  motor  mechanisms  on  the 
one  hand  and  upon  the  intellectual  centers  on  the  other. 


672  PHYSIOLOGY  OF  THE  CEREBRUM 

The  pathways  between  the  centers  which  rouse  our  desires  and  the  intel- 
lectual regions  of  the  cortex  are  not  called  upon  merely  to  clothe  the  content 
of  sense  experiences  in  ideas,  to  idealize  them  in  short,  nor  merely  to  facilitate 
their  satisfaction  by  recognition  of  means  to  that  end.  But  there  is  set  up 
along  some  associative  pathway  an  interplay,  a  working  of  ideas  which  leads 
to  the  maturation  of  self-consciousness  as  a  contest  between  sense  and  reason. 
Along  with  inciting  impulses  there  arise  some  with  which  feelings  of  restraint 
are  connected — and  thus  the  discharge  of  memory  pictures  through  the  bodily 
desires  comes  to  have  a  distinctly  moral  significance.  The  motives  are  neces- 
sarilv  robbed  of  all  their  ideal  character — the  struggle  between  the  sensuous 
and  the  moral  feelings  is  sure  to  lapse,  the  moment  the  force  of  the  intellectual 
centers  is  paralyzed  and  the  rational  content  of  the  emotions  disappears.  Con- 
trol of  the  emotions  requires  a  powerful  cerelirum,  which  probably  means  in 
the  first  instance  soundness  of  the  frontal  association  centers. 

A  purely  mechanical  factor  is  concerned  in  this  control  of  the  lower  im- 
pulses of  the  cerebrum.  In  so  far  as  the  bodily  impulses  do  not  arise  by  the 
automatic  excitations  of  the  central  nerve  cells,  they  belong  Ity  nature  to 
the  category  of  reflex  processes,  and  like  all  reflexes  are  continually  held  in 
check  by  the  cerebrum.  When  the  cerebrum  becomes  weak  this  mechanical 
restraint  is  relaxed  and  the  bodily  incentive  gains  greater  control  over  the 
rational  centers. 

Through  the  investigation  of  the  material  conditions  of  the  mind's  activity, 
medicine  is  thus  brought  into  immediate  relations  with  the  moral  sciences, 
and  it  is  indeed  conceivable  that  once  she  has  properly  grasped  the  problem, 
she  will  unhesitatingly  press  forward  to  the  front  rank  of  those  forces  which 
have  made  the  moral  elevation  of  mankind  their  chief  concern.  Investigation 
to-day  is  not  led,  as  was  the  philosophy  of  the  Enlightenment  in  the  Eighteenth 
Century,  by  an  instinctive  hatred  for  the  dogma  of  the  immateriality  of  the 
soul,  for  that  dogma  in  no  way  prevents  our  undertaking  the  moral  elevation 
of  the  race  from  the  bodily  side.  What  we  must  insist  upon  is  merely  this — 
that  the  moral  powers  of  the  mind  like  its  other  powers  depend  to  a  great 
extent  upon  the  body. 

A  general  clearing  up  of  problems  pertaining  to  the  hygiene  of  the  brain 
is  therefore  eminently  necessary.  Much  remains  to  l^e  done  along  this  line, 
if  we  are  to  succeed  in  strengthening  and  establishing  the  natural  grounds 
of  the  moral  feelings  even  for  future  generations.  Certain  it  is  that  our 
efforts  will  be  successful  in  a  measure  directly  proportional  to  the  opportunities 
afforded  the  mentally  and  morally  unfortunate  of  profiting  by  the  deeper 
insight  and  better  desires  of  those  whose  lives  are  ruled  by  high  ideals. 

But  it  is  not  alone  the  practical  goals  of  life  of  which  we  get  a  glimpse 
in  these  considerations  of  the  mechanics  of  the  mind.  As  that  which  we 
already  realize  to  ])e  one  of  the  noblest  sides  of  our  being,  and  which  is 
bestowed  on  mankind  in  virtue  of  the  intellectual  centers  of  the  brain,  becomes 
embodied  in  the  desire  to  comprehend  the  natural  order  of  things  in  the 
realm  of  spirit  also,  the  real  advances  of  our  knowledge  in  this  realm  of 
natural  science  lead  us  with  the  compelling  force  of  a  natural  law  at  last  to 
an  ideal  view  of  the  world.  The  more  the  true  magnitude  of  the  real  power 
resident  in  the  realm  of  mind  itself  is  revealed  to  us,  the  more  clearlv  do  we 


THE  TIME  CONSUMED   BY    PSYCHOPHYSICAL   PROCESSES         673 

feel  tliat  l)ack  of  the  world  of  phenomena  powers  are  at  work  for  which  human 
knowledge  can  scarcely  find  an  adequate  metaphor. 


§  4.    THE   TIME   CONSUMED    BY   PSYCHOPHYSICAL   PROCESSES 

There  remains  for  us  to  summarize  briefly  what  has  been  discovered  with 
reference  to  the  time  occupied  by  psychophysical  processes. 

The  point  of  departure  in  all  investigations  of  this  subject  is  the  time 
required  for  a  person  to  react  with  a  definite  voluntary  movement  to  some 
external  stimulus  {simple  reaction  time).  It  will  be  apparent  at  once  that 
some  measurable  time  is  required  for  such  reactions,  if  we  but  reflect  that 
the  propagation  alone  of  a  stimulus  along  the  afferent  and  efferent  nerves  con- 
cerned consumes  a  certain  amount  of  time  (cf.  page  417).  But  in  the  process 
which  we  are  considering  now,  something  takes  place  in  the  sensorium  and 
something  in  the  motor  region,  and  between  these  something,  probably,  else- 
where in  the  cortex,  all  of  which  constitute  the  psychophysical  factors.  The 
special  interest  attaching  to  these  determinations  is  that  they  will  give  us 
some  information  as  to  how  much  time  is  required  for  these  purely  central 
processes. 

Experiments  in  this  field  are  usually  carried  out  by  having  the  subject  of 
the  experiment  open  the  current  of  an  electric  signal  the  moment  he  receives 
a  given  stimulus.  If,  for  example,  the  reaction  time  is  being  taken  for  an 
auditorj^  stimulus,  it  is  necessary  to  have  in  the  same  electrical  connection : 
(1)  the  signal,  (2)  a  key  for  the  subject,  (3)  a  key  by  which  the  current  is 
closed  by  the  director  of  the  experiment  and  which  at  the  same  instant  causes 
a  sound  to  be  made  by  (4)  an  electric  bell  or  other  device.  The  sound  which  is 
made  when  the  current  is  closed  constitutes  the  stimulus  to  which  the  subject 
reacts  by  opening  the  current.  If  the  electric  signal  be  arranged  so  as  to  record 
on  a  moving  surface  the  instants  of  opening  and  closing,  the  time  which  inter- 
venes will  be  the  reaction  time.  This  time  can  be  determined  directly  if  a 
clockwork  whose  hands  mark  thousandths  of  a  second  be  set  in  motion  by  the 
closing  and  stopped  by  the  opening  of  the  current.  Such  an  instrument  is 
knowm  as  a  chronoscope. 

The  simple  reaction  time  varies  all  the  way  from  0.11  to  0.55  second 
according  to  the  nervous  organization  of  the  subject,  and  the  kind  of  sensory 
stimulus  em])loyed.  Likewise  if  a  series  of  experiments  be  carried  out  on 
the  same  person  and  with  the  same  kind  of  stimulus,  only  varying  in  strength, 
a  considerable  variation  in  the  reaction  time  is  noted,  which  cannot  be  due 
to  any  variation  in  the  rate  of  propagation  in  the  nerves  exercised,  conse- 
quently must  be  accounted  for  by  dift'erences  in  the  time  consumed  in  the 
psychophysical  processes.  Such  variations  moreover  can  be  perceived  sub- 
jectively, so  that  one  can  tell  within  0.05-0.0()  of  a  second  whether  a  given 
reaction  time  was  longer  or  shorter  than  a  previous  one.  Remembering  that 
the  propagation  of  the  sensory  stimulus  before  it  rouses  the  conscious  sensa- 
tion, as  well  as  the  motor  impulse  after  it  has  once  been  discharged,  is  an 
entirely  unconscious  process,  we  see  that  the  time  subjectively  estimated  covers 
the  span  between  perception  of  the  sensory  impulse  and  release  of  the  volun- 
tary impulse. 


674 


PHYSIOLOGY   OF  THE  CEREBRUM 


The  following  tal>le  will  give  u^^  sonie  idea  of  the  reaction  time  for  the 
different  s^enses : 


Author. 

Sight. 

Hearing. 

Electric  stimulation 
of  the  skin. 

Hirsch 

0.200 
0.206 
0.188 
0.186 
0.222 
0.193 
0.191 
0.168 

0.149 
0.151 
0.180 
0.182 
0.167 
0.120 
0.122 
0.115 

0.182 

Hankel  

0.155 

Donders     

0.154 

V.  Wittich 

0.130 

Wundt        

0.201 

V.  Kries 

0.117 

Auerbach  

0.146 

Buccola 

0.141 

For  the  sense  of  taste  v.  Yintschgau  has  found  the  following  reaction 
times  for  common  salt,  sugar  and  quinin :  tip  of  the  tongue,  0.597,  0.753  and 
0.993  second  respectively;  for  the  hase  of  the  tongue,  0.543,  0.553  and  0.503 
second  respectively.  The  reaction  time  for  different  odors  (oil  of  peppermint, 
oil  of  rose  and  hergamot  oil)  varies  in  Moldenhauer's  findings  between  0.199 
and  0.374  second. 

It  is  not  surprising  that  the  reaction  times  found  by  the  different  authors 
for  a  given  sense  differ  considerably,  for  the  nervous  organization  of  the  sub- 
ject has  always  to  be  taken  into  account. 

In  most  cases  it  requires  some  time  for  odoriferous  and  sapient  substances 
to  come  in  contact  with  the  appropriate  nerve  endings ;  hence  the  longer  time 
consumed  ])y  a  reaction  to  these  stimuli  than  to  others. 

The  differences  ob.-^erved  between  the  reaction  times  for  sight,  hearing  and 
touch  are,  as  Wundt  remarks,  probably  dependent  upon  the  different  intensities 
of  these  stimuli.  For  one  and  the  same  sense  the  reaction  time  is  always 
shorter  the  stronger  the  stimulus.  We  cannot  ordinarily  compare  the  intensity 
of  a  certain  auditory  stimulus  with  that  of  a  certain  visual  stimulus,  for  there 
is  no  standard  of  measurement  common  to  the  two.  The  threshold  stimuli 
for  the  different  senses,  however,  being  in  all  cases  just  sufficient  to  produce 
an  effect,  must  be  relatively  of  the  same  strength.  Wundt  found  in  fact  that 
the  reaction  times  for  the  visual,  auditory  and  tactile  stimuli  in  the  neighbor- 
hood of  their  threshold  values  were  almost  exactly  equal,  namely  0.331,  0.337, 
and  0.327  .second  respectively.  We  infer  from  this  and  the  facts  .summarized 
in  the  table  that  auditory  stimuli  in  general  are  more  powerful  than  optical 
or  cutaneous  stimuli. 

The  reaction  time  is  increased  as  the  body  or  mind  becomes  fatigued,  also 
as  the  result  of  all  sorts  of  exciting  influences,  but  is  reduced  by  practice,  in 
some  cases  very  considerably.  All  this  goes  to  prove  that  the  length  of  the 
reaction  time  depends  essentially  on  the  duration  of  the  psychophysical  process, 
or  in  other  words,  that  we  dare  not  look  upon  the  psychophysical  process  as  a 
perfectly  constant  factor. 

If  warning  be  given  of  the  signal  just  before  it  is  made,  the  reaction  time 
is  considerably  shorter  than  otherwise.  The  subject  has  his  whole  attention 
fixed  on  the  coming  event,  and,  by  sufficient  practice,  he  can  make  the  central 
connection  so  tense  as  to  give  the  response  almost  as  promptly  as  if  it  were  a 


THE  TIME   CONSUMED   BY   PSYCHOPHYSICAL  PROCESSES  675 

pure  reflex.  The  muscular  process  particularly  is  facilitated  in  this  way  and 
the  reaction  is  then  described  as  muscular  reaction.  A  reaction  in  which  the 
attention  is  strained  more  especially  to  receive  the  impression  is  called  a  sen- 
sory reaction.  If  the  attention  be  not  first  aroused,  it  requires  more  time  also 
to  perceive  a  stimulus.  Thus  Wundt  found  in  one  experiment  with  the  auditory 
stimulus  that  when  warninfr  was  given  the  sound  was  heard  in  0.076  second, 
when  not  given,  in  0.253  second. 

The  study  of  the  changes  produc(>(l  in  the  reaction  time  by  nerve  poisons, 
such  as  alcohol,  coH'oe  and  tea,  is  an  important  means  of  learning  the  physio- 
logical effects  of  these  substances. 

If  instead  of  a  single  stimulus,  a  series  of  stimuli  following  each  other 
at  a  definite  interval  be  given,  the  reacting  person  repeats  the  rhythm  to  a 
certain  extent  independently,  and  the  reaction  time  sinks  to  nil.  An  absolute 
determination  of  the  time  cannot  be  made  under  these  circumstances:  the 
reaction  may  take  place  either  at  the  instant  of  stimulation,  or  a  little  after 
or  even  a  little  before.  According  to  Martius  the  errors  amount  to  ±  0.01 
of  a  second. 

We  very  often  meet  with  phenomena  of  this  kind  in  our  everyday  life. 
The  j)laying  of  an  orchestra  under  the  direction  of  a  leader,  dancing  and 
marching  to  music,  are  all  cases  in  point;  likewise  the  enumeration  of  heart 
beats.  But  if  the  rhythm  of  stimuli  be  not  perfectly  uniform  and  the  inter- 
vals not  exactly  equal,  it  is  impossible  to  react  to  them  synchronously,  and 
the  ordinary  reaction  time  comes  into  play  again.  By  varying  the  method  of 
experimentation,  we  can  penetrate  still  farther  into  this  question  of  the  time 
consumed  by  the  psychophysical  process.  The  methods  employed  for  this 
purpose  can  best  be  explained  by  a  few  concrete  examples. 

Suppose  the  stimulus  be  applied  either  to  the  right  or  left  foot:  in  the 
first  case  the  subject  is  to  respond  with  the  right  hand,  in  the  second  with 
the  left.  He  has  then  not  only  to  perceive  a  stimulus,  but  to  distinguish  a 
definite  property  and  to  choose  between  two  movements.  On  the  average  the 
time  required  for  this  reaction  is,  according  to  de  Jeager,  0.066  second  longer 
than  the  simple  reaction  time. 

In  the  case  just  given  the  choice  was  a  relatively  easy  one,  because  a  stimulus 
on  one  foot  naturally  suggests  a  reaction  with  the  hand  of  the  same  side.  But 
if  the  experiment  be  so  arranged  that  when  a  red  disk  appears  the  subject  is  to 
react  with  the  right  hand,  and  when  a  blue,  with  the  left,  the  time  is  on  the 
average  0.154  second  longer  than  the  simple  reaction  time.  The  psychophysical 
processes  in  this  case  are  of  exactly  the  same  kind  as  the  former:  the  greater 
interval  of  time  is  due  to  the  fact  that  there  is  no  natural  connection  between 
the  sense  imj)ression  and  the  movement,  consequently  the  choice  is  more  diffi- 
cult. The  time  is  shorter  if  a  reaction  be  required  for  only  one  of  two  stimuli. 
For  example,  a  red  or  a  blue  disk  may  appear:  the  subject  is  to  react  to  the 
latter,  but  not  to  the  former.  The  time  is  then  on  the  average  0.034  second 
longer  than  the  simple  reaction  time  and  thus  0.12  second  shorter  than  in  the 
case  last  mentioned.  The  principle  of  this  method  of  simple  choice  is  exactly 
the  same  as  the  other:  the  individual  must  recognize  a  definite  quality  in  the 
stimulus  and  choose  between  acting  and  not  acting".  But  the  reason  why  the 
choice  can  be  made  more  quickly  is  that  the  attention  is  concentrated  on  the  par- 


676  PHYSIOLOGY  OF  THE  CEREBRUM 

ticular  impression  Avhich  calls  for  the  reaction.  The  time  found  is  practically 
the  time  required  to  perceive  a  given  quality  in  an  impression,  and  is  called  the 
discrimination  time. 

APPENDIX 


NOURISHMENT   OF  THE   BRAIN 

1.  Blood  Supply. — As  already  remarked  at  page  572,  the  normal  activity 
of  the  brain  is  very  much  dependent  on  the  blood  supply.  If  the  blood  supply 
is  greatly  diminished,  unconsciousness  is  the  result;  this  usually  happens,  for 
example,  when  the  carotids  are  compressed.  Convulsions  may  also  be  produced 
in  the  same  way.  Thus  if  the  right  innominate  artery  and  the  left  subclavian 
central  to  the  A'ertebral  be  ligated  in  a  rabbit,  the  animal  almost  immediately 
falls  into  convulsions. 

Variations  in  the  blood  supply  to  the  brain  have  been  discussed  at  page  240. 

In  cases  of  accidental  defect  in  the  skull,  the  brain  pulsates  in  grown  per- 
sons just  as  do  the  fontanels  in  young  children.  Mosso  has  found  on  such 
persons  that  the  blood  supply  to  the  brain  increases  with  mental  work,  and  to 
a  marked  degree  also  when  the  person  is  under  strong  emotional  excitement,  and 
that  the  vessels  to  the  extremities  become  at  the  same  time  constricted. 

If  now  it  is  true,  as  supposed  by  the  majority  of  authors,  that  vasomotor 
nerves  are  wanting  in  the  vessels  of  the  brain,  such  changes  in  the  blood  supply 
can  only  be  explained  by  supposing  that  in  mental  work  or  under  the  stress  of 
emotions  the  vasomotor  center  is  stimulated  and  constriction  produced  in  vari- 
ous extracranial  vascular  regions. 

•  Likewise  in  undisturbed  sleep,  when  no  conscious  processes  are  going  on  in 
the  brain,  the  blood  supply  to  the  brain  may  be  increased  by  all  sorts  of  sensory 
stimuli,  without  waking  the  individual. 

2.  Fatigue  and  Sleep. — Not  only  mental  work  but  the  waking  condition  of 
itself  fatigues  the  brain,  or  more  correctly  the  cerebrum,  and  it  must  from  time 
to  time  be  given  an  opportunity  to  recuperate.  This  recuperation  of  the  brain 
takes  place  in  sleep.  If  a  person  is  denied  sleep  for  a  long  time,  very  profound 
physical  and  mental  disorders  result. 

Experiments  have  been  made  to  determine  the  soundness  of  sleep  by  finding 
the  threshold  value  of  an  auditory  stimulus  necessary  to  wake  the  person  at 
different  intervals  after  he  fell  asleep.  According  to  Monninghoff  and  Pies- 
bergen,  the  depth  of  sleep  increases  very  gradually  up  to  the  second  quarter  of 
the  second  hour.  Within  the  second  and  third  quarters  of  the  same  hour  it 
increases  very  rapidly  and  very  greatly  and  then  decreases  just  as  rapidly  up 
to  the  first  quarter  of  the  third  hour.  From  this  point  onward  there  is  a  gradual 
decrease  of  depth  which  continues  to  the  second  half  of  the  fifth  hour.  Here 
a  second  slight  rise  begins,  but  the  level  is  comparatively  uniform  from  about 
the  fifth  hour  onward  (cf.  Fig.  299). 

Metabolism  is  less  active  in  sleep  than  in  the  waking  condition  and  the  fall- 
ing off  is  greater  the  sounder  the  sleep.  If  the  carbon  dioxide  output  be  taken  as 
a  measure  of  the  metabolism,  that  of  sleep  is  related  to  that  of  the  waking 
condition  (not  working  nor  yet  completely  resting)  as  100:145.  This  reduction 
of  metabolism  in  sleep  is  dependent  in  the  main  upon  the  cessation  of  volun- 
tary movements,  for  it  may  reach  just  as  low  a  level  in  the  waking  condition  if 
the  muscles  be  completely  relaxed  and  every  voluntary  motion  be  suppressed 
(Johansson). 


NOURISHMENT  OF  THE  BRAIN 


677 


According  to  some  experimental  determinations  the  carbon  dioxide  elimi- 
nation reaches  its  minimum  in  the  second  hour  of  sleep,  and  this  probably 
constitutes  to  a  certain  extent  the  expression  of  the  deepest  sleep  in  a  sleeping 
period  of  perhaps  six  to  eight  hours. 

The  following  peculiarities  have  also  been  observed  in  sleep.  The  eyes  with 
pupils  contracted  are  turned  inward  and  somewhat  upward.  The  respiratory 
movements  are  less  frequent  than  in  the  w^aking  condition,  and  even  in  the  man 
are  mainly  of  the  costal  type.  The  respirations  are  also  sometimes  periodically 
suspended.  The  heart  action  is  retarded;  the  vascular  tone  decreases  in  the 
cutaneous  vessels  and  probably  also  in  the  visceral  vessels,  and  as  a  consequence 
the  blood  pressure  falls.  This  in  its  turn  is  said  by  many  authors  to  cut  down 
the  supply  of  blood  to  the  brain,  to  produce  in  short  a  condition  of  cerebral 
anaemia. 

Howell  has  observed  the  volumetric  variations  of  the  hand  and  the  lower 
part  of  the  forearm  in  sleep  by  means  of  the  plethysmograph,  and  has  found 


Fig.  299. — C'ur\e   roiiri-.stntiiig   tlic  depth  of  sleep,   after  Piesbergen.      Tlic  abscissa;   represent 

hours. 


that  the  amount  of  blood  in  the  part  increases  gradually  from  the  beginning  of 
sleep  and  reaches  its  maximum  within  one  to  one  and  three-quarter  hours.  It 
remains  at  this  level  until  about  three-quarters  of  an  hour  before  awakening 
and  then  falls  rather  rapidly  to  the  end  of  sleep. 

The  inception  of  sleep  is  favored  by  cutting  off  the  sensory  stimuli,  espe- 
cially if  t'lie  attention  be  not  kept  aroused  by  any  active  mental  processes. 
Striimpell  has  rept)rted  a  case  in  which  the  patient  became  blind  in  one  eye 
and  deaf  in  one  ear  merely  by  stnp})ing  all  cutaneous  sensations.  As  soon  as 
the  good  eye  was  closed  and  the  functional  ear  was  stopped  he  fell  asleep. 

Sleep  does  not  depend  entirely  upon  processes  going  on  in  the  cerebral  cor- 
tex, for  as  mentioned  at  page  623  a  change  from  the  sleeping  to  the  waking 
condition  and  vice  versa  can  be  observed  on  decerebrated  animals. 

[Perhaps  the  most  satisfactory-  theory  which  has  yet  been  given  to  exi)lain 
the  cause  of  sleep,  is  that  of  Howell.  The  dilatation  of  the  cutaneous  vessels 
during  sleep  observed  by  this  author,  taken  in  conjunction  with  many  other 
observations  that  there  is  during  sleej)  a  reduction  of  the  general  blood  i)ressure, 
and  that  there  is  at  the  same  timP  a  diminished  blood  flow  to  the  brain,  sug- 
gested the  idea  that  the  depression  of  the  psychical  activities  below  the  threshold 
of  consciousness  is  due  primarily  to  anaemia  of  the  brain   (cf.  page  240).     To 


678  PHYSIOLOCJY   OF   THE  CEREBRUM 

account  for  this  ana>niia  Howell  supposes  that  that  portion  of  the  vasomotor 
center  which  maintains  the  tonus  of  the  cutaneous  vessels  periodically  becomes 
fatigued,  just  as  the  cells  of  the  cortex  w^hich  mediate  the  psychical  processes 
may  be  supposed  also  to  become  fatigued.  If  under  these  circumstances  the 
usual  external  stimuli  which  serve  to  keep  the  vasomotor  center  active  be 
withdrawn ;  as  for  example,  the  eyes  be  closed,  noises  be  excluded  and  the 
voluntary  muscles  be  relaxed,  the  vasomotor  center  relaxes  its  control  of  the 
cutaneous  vessels,  the  resulting  dilatation  withdraws  blood  from  the  cortical 
cells  and  the  consequence  of  this  is  a  further  and  a  comparatively  sudden  de- 
cline of  cerebral  activity  below  the  threshold  of  consciousness.  When  the 
vasomotor  center  has  been  recuperated  it  reasserts  its  activity,  blood  is  again 
supplied  to  the  cortical  cells  and  consciousness  returns. — Ed.] 

3.  The  Temperature  of  the  Brain. — By  means  of  a  very  delicate  thermometer 
Mosso  made  a  careful  study  of  the  temperature  of  the  brain  in  animals  and  in 
men  with  defects  in  the  cranium,  and  found  among  other  things  that  on  account 
of  its  slight  covering  it  has  a  lower  temperature  than  the  rectum.  But  a  rise 
in  temperature  is  caused  by  the  local  effects  of  atropine,  cocaine  and  alcohol,  by 
electrical  stimulation,  by  anaemia  and  asphyxia — in  all  these  cases  due  to  altera- 
tions in  the  circulation.  Chloroform,  painful  sensations,  etc.,  produce  no  change 
in  the  temperature  of  the  brain  worth  mentioning.  In  like  manner  the  con- 
scious activities  of  the  brain  produce  so  slight  an  effect  on  the  temperature 
that  they  cannot  be  recognized,  or  else  they  occur  along  with  other  processes, 
as  the  result  of  which  the  brain  is  cooled,  even  though  the  psychical  functions 
continue.  ' 

On  the  other  hand  some  unconscious  processes  brought  on  hy  external 
agencies  increase  the  temperature  of  the  brain. 

4.  The  Intracranial  Pressure. — The  cerebro-spinal  fluid  filling  the  subarach- 
noid space  exerts  a  pressure  on  the  walls  of  the  cerebro-spinal  canal,  which  when 
measured  by  a  manometer  of  suitable  construction  inserted  into  an  opening  in 
the  skull,  is  found  to  be  about  equal  to  the  venous  pressure  (5-10  mm.  of  Hg.), 
if  the  animal  is  in  a  horizontal  position.  When  the  hind  parts  of  the  body  are 
raised  above  the  head  the  pressure  becomes  greater,  when  they  are  lowered  it 
falls  and  may  even  become  negative  (Siven). 

According  to  Bayliss  and  Hill,  there  is  no  mechanism  for  maintaining  a 
constant  intracranial  pressure;  the  functions  of  the  brain  appear,  within  wide 
limits,  to  be  independent  of  intracranial  pressure,  so  long  as  the  circulation  is 
not  impaired.  If  the  foramen  magnum  be  constricted  so  as  to  obstruct  the 
circulation,  the  centers  of  the  medulla  may  be  affected  and,  among  other  things, 
the  respiration  be  retarded  and  finally  stopped,  the  heart  action  retarded,  and 
the  blood  pressure  increased. 

The  outlet  for  the  cerebro-spinal  fluid  is  by  way  of  the  veins.  Within 
fifteen  to  thirty  minutes  after  injection  of  methylene  blue,  in  a  salt  solution 
into  the  cranial  cavity,  the  color  appears  in  the  urine  (Hill), 

References. — Beevor,  Horsley,  Schdfer  and  others,  several  articles  in  the 
Philosophical  Transactions  for  1887,  1888,  ISdO.— Charcot  and  Pitrrs,  "' Les 
centres  moteurs  corticaux  chez  I'homme,"  Paris,  1895. — S.  Exner,  "  Entwurf 
zu«  einer  physiologischen  Erklarung  der  psychischen  Erscheimungen,"  Wien, 
1894. — Flechsig,  "  Gehirn  und  Seele,"  second  edition,  Leipzic,  1896. — Flechsig, 
"Die  Lokalization  der  geistigen  Vorgange,"  Leipzic,  1896. — Franck,  "  Les 
fonctions  motrices  du  cerveau,"  Paris,  1887.— Goltz,  "  Uber  die  Yerrichtungen 
des  Grosshirns,"  Bonn,  1884. — Goltz,  several  articles  in  Archiv  f.  d.  ges.  Physi- 
ologie,  Bds.  34,  42,  51,  76. — Hitzig,  "  Untersuchungen  iiber  das   Gehirn,"  Ber- 


NOURISHMENT   OF  THE   BRAIX  679 

lin,  1874. — Tlitzig,  "  Physiologische  und  klinisehe  Untersuchungen  iiber  das 
Gehirii,"  Berlin,  1904.— Howell,  "  A  Contribution  to  the  Physiology  of  Sleep," 
in  the  Journal  of  Experimental  Medicine,  vol,  ii,  1897. — v.  Monakow,  "  Gehirn- 
pathologie,"  Wien,  1897. — //.  Munh,  "  Uber  die  Functionen  der  Grosshim- 
rinde,"  second  edition,  Berlin,  1890. — Noihnagel,  "  Topische  Diagnostik  der 
Gehirnkrankheiten,"  Berlin,  1879. — Wilhrand  and  Saenger,  "  Anatomie  und 
Physiologie  der  optischen  Bolmen  und  Zentren,"  Wiesbaden,  1904. —  Wund, 
"  Grundziige  der  physiologisehen  Psychologie,"  iii,  Leipzic,  1903. 


40 


CHAPTEE    XX Y 

PHYSIOLOGY    OF    SPECIAL    XERVES 

The  innervation  of  the  different  organs  and  organ  systems  has  been  dis- 
cussed in  connection  with  their  functions,  hence  in  this  chapter  we  need  only 
present  the  pliysiology  of  special  nerves  in  the  broadest  outlines.  For  details 
and  controverted  points,  reference  must  be  made  to  the  previous  chapters 
of  this  book,  and  for  tlie  purely  anatomical  data  to  the  text-books  of  anatomy. 

§  1.    THE   CRANIAL   NERVES 

I.  The  olfnciorij,  or  the  nerve  of  smell  (of.  page  48G). 

II.  The  optic,  or  the  nerve  of  vision  (cf.  page  508).  contains  not  only 
afferent  ])ut  efferent  fibers. 

III.  The  ocuJomotor.  or  the  common  nerve  of  the  eye  muscles,  innervates 
the  levator  palpel)r»  superioris.  the  superior,  inferior  and  internal  recti,  the 
inferior  oblique,  the  ciliary  muscle  or  the  muscle  of  accommodation  (cf.  page 
532)  and  the  sphincter  of  the  pupil  (cf.  page  528). 

IV.  The  trochlearu,  or  pathetictis,  innervates  only  the  superior  oblique 
muscle  of  the  eye. 

V.  The  trigeminal,  or  trifacial,  contains  both  afferent  and  efferent  fibers. 

The  efferent  fibers  innervate  the  jaw  muscles  (masseter,  temporal,  ptery- 
goids), also  the  niA-lohyoid,  the  tensor  palati  and  the  tensor  tympani  (cf. 
page  497)  and  the  anterior  belly  of  the  inferior  digastric.  Besides  it  is  stated 
that  the  trigeminal  contains  secretory  fibers  for  the  lachrymal  glands  and  the 
sweat  glands  of  the  face,  vasodilator  fibers  for  the  skin  of  the  face  and  the 
eye,  etc. 

The  afferent  fibers  of  the  trigeminal  constitute  first,  the  sensory  nerves  of 
almost  all  the  skin  of  the  face,  of  the  eye,  the  nose,  the  mucous  momljrane  of 
the  mouth,  the  tongue  and  the  teeth.  Secondl}',  the  trigeminal  carries  a 
number  of  nerves  of  taste   (cf.  page  484). 

VI.  The  ahducens  innervates  the  external  rectus  and  is  said  also  to  con- 
tain fibers  for  the  sphincter  of  the  pupil. 

VII.  The  facial,  or  nerve  of  expression,  contains  secretory  fibers  for  the 
submaxillary,  sublingual  (cf.  page  257)  and  lachrymal  glands,  vasodilato^r 
fibers  for  the  submaxillarA^  glands  and  anterior  part  of  the  tongue,  and  motor 
nerves  for  the  stapedius  muscle.  Its  chief  significance,  however,  is  that  it 
innervates  the  muscles  of  the  face  by  contraction  of  which  the  skin  of  the  face 
is  folded  in  various  ways,  producing  the  different  expressions. 

680 


THE  CRANIAL   NERVES  681 

VIII.  The  auditory,  or  nerve  of  hearing,  by  its  cochlear  root  mediates 
auditory  sensations  (cf.  Fig.  199)  and  by  the  vestibular  root  (cf.  page  473) 
the  various  functions  of  the  semicircular  canals  and  otolith  sacs. 

Various  experimental  observations  indicate  that  the  vestibular  root  prob- 
ably has  no  signiiicance  whatever  for  the  auditory  sensations.  Since  the  eighth 
cranial  nerve  therefore  is  at  least  not  exclusively  auditory  in  function,  J.  K. 
Ewald  has  proposed  that  it  be  simply  called  the  eighth  nerve  (N.  octavus). 

IX.  The  glossopharyngeal  conveys,  besides  some  motor  fil)ers  to  the  tongue 
and  pharynx,  secretory  fibers  to  the  parotid  glands  (cf.  ])age  25?)  and  vaso- 
dilator fibers  to  the  anterior  pillars  of  the  fauces  and  tonsils.  Among  its 
afferent  fibers  are  the  taste  fibers,  also  sensory  fibers  for  the  mucous  mem- 
brane of  the  tympanic  cavity  and  Eustachian  tube. 

X.  The  vagus,  or  pncu7nogastric,  and 

XI.  The  spinal  accessory. 

In  view  of  the  fact  that  these  two  nerves  are  intimately  related  anatomi- 
cally and  that  diverse  views  are  held  as  to  the  share  each  takes  in  controlling 
the  organs  innervated  Ijy  them,  it  is  most  profitalde  to  consider  them,  as  Gross- 
man has  proposed,  as  one  nerve  composed  of  three  bundles  named,  in  order 
of  their  exit  from  the  medulla,  the  upper,  middle  and  lower.  The  upper 
bundle  can  readily  l)e  separated  in  the  monkey  and  in  man  from  the  glosso- 
pharyngeal. The  lower  bundle  is  the  outer  branch  of  the  spinal  accessory 
which  innervates  the  trapezius  and  the  sterno-cleido-mastoid  muscles.  There 
remains  then  the  trunk  composed  of  the  vagus  and  the  inner  or  true  accessory 
branch  in  which  are  to  be  distinguished  an  anterior  and  a  middle  portion. 

According  to  the  experimental  results  of  Ivreidl  on  the  monkey,  motor 
nerves  pass  in  this  anterior  portion  (the  vagus  of  anatomists)  to  the 
palatoglossal  and  palatopharyngeal  muscles  as  well  as  to  the  constrictors  of 
the  pharynx  and  oesophagus.  Moreover,  it  is  here  that  the  motor  fillers 
of  the  superior  laryngeal  are  found,  also  the  afferent  pulmonary  fibers  which 
assist  in  the  automatic  regulation  of  respiration,  and  in  the  rabbit,  dog  and 
cat  at  least,  the  depressor  fibers   (Fuchs,  Codman ;  cf.  page  193). 

In  the  middle  bundle  (accessory  of  the  anatomists)  are  the  inhibitory 
fibers  of  the  heart  (cf.  page  188),  the  motor  fibers  for  the  levator  palati  and 
the  motor  fibers  contained  in  the  inferior  laryngeal  nerve. 

Ill  the  trunk  of  the  vagus  are  the  following  fibers,  the  origin  of  which  is  not 
fully  known:  (1)  efferent  fibers,  a.  To  the  circulatory  organs:  accelerator  fibers 
to  the  heart  (page  191);  vasoconstrictor  fibers  for  the  heart,  the  stomach,  intes- 
tine, kidneys,  spleen,  and  possibly  the  lungs  (page  210)  ;  vasodilator  fibers  for  the 
coronary  vessels  and  the  lungs  (page  235).  h.  Digestive  organs:  motor  nerves 
for  the  stomach  ("page  284),  the  small  intestine  and  the  upper  part  of  the  large 
intestine  (page  289)  ;  inhibitory  fibers  for  the  cardiac  sphincter  of  the  stomach 
and  the  longitudinal  muscles  of  the  small  intestine  (pages  284,  289) ;  secretory 
nerves  for  the  gastric  mucosa  and  the  pancreas  (pages  263,  269).  c.  Respiratory 
organs  :  motor  and  jxissibly  inhibitory  fibers  for  the  bronchial  muscles  (page  324). 

(2)  Afferent  fibers.  Respiratory  organs:  afferent  fibers  from  the  larvnx 
(page  330). 

XII.  The  hypoglossal  innervates  the  musculature  of  the  tongue. 


682  PHYSIOLOGY  OF  SPECIAL   NERVES 


§  2.    SPINAL   NERVES 

The  anterior  and  posterior  roots  of  the  same  side  belonging  to  each  segment 
of  the  spinal  cord  unite  peripherally  to  the  spinal  ganglion  to  form  a  mixed 
nerve  trunk.  Each  of  these  nerve  trunks  then  divides  into  a  dorsal  and  a 
ventral  branch.  The  dorsal  branches  are  relatively  small  and  supply  only  the 
skin  and  muscles  of  the  back ;  the  ventral  branches,  which  are  much  larger, 
are  allotted  to  the  anterior  and  lateral  parts  of  the  neck,  thorax,  abdomen  and 
extremities. 

The  dorsal  branches  all  run  separately  to  their  destination ;  but  with  the 
exception  of  the  twelve  thoracic  nerves,  the  ventral  branches  anastomose  freely 
with  one  another,  forming  plexuses  corresponding  to  the  main  divisions  of 
the  body. 

A  number  of  experimental  and  clinical  researches  have  been  made  on  the 
distribution  of  the  fillers  arising  from  the  different  roots.  We  shall  here  pay 
regard  chiefly  to  the  exposition  given  by  Kocher  on  the  relations  obtaining 
in  man. 

A.    SENSORY   NERVES 

Each  spinal  nerve  root,  even  if  its  fillers  unite  with  others  to  form  a  plexus, 
supplies'  a  continuous  region  of  the  skin.  These  regions  overlap,  however, 
so  that  a  single  region  on  the  lateral  aspect  of  the  body  is  provided  with  a 
twofold  or  even  a  threefold  supply  (Sherrington). 

Fig.  300  represents  schematically,  according  to  Kocher,  areas  of  distribu- 
tion of  the  different  spinal  roots.  This  is  constructed  on  the  liasis  of  clinical 
observations  of  patients  with  total  lesions  of  the  spinal  cord.  The  boundary 
lines  in  the  figure  mark  the  upper  limits  of  sensibility  for  lesions  at  the 
different  levels.  In  reality  the  regions  supplied  by  the  different  nerves,  in 
man  as  in  animals,  overlap  considerably  both  above  and  below.  The  areas 
blocked  out  in  the  figure  represent  therefore  the  central  parts  of  the  fields 
actually  supplied  by  the  separate  roots. 

B.    MOTOR  NERVES 

In  the  following  table  are  summarized,  after  Kocher,  the  distributions 
of  the  different  motor  roots : 

ROOT.  MnSCLES. 

I  C  Small  neck  muscles ;   sternohyoid ;   sternothyroid ;   omohyoid. 

II  C.  Sterno-cleido-mastoid ;  trapezius. 

III  C.  Platisma  myoides.  * 

IV  C.  Scaleni ;  diaphragm. 

V  C.     Rhomboidci;  supra-  and   infraspinatus;  coracobrachialis;   biceps; 
brachialis  anticus;  deltoid;  sui)inator  longus  and  brevis. 
VI  C     Subscapularis;   pectoralis  major   and   minor;    pronator   teres   and 
quadratus;    latissimus    dorsi ;    teres   major;    triceps;    serratus 
magnus. 
VII  C.     Extensors  and  flexors  of  the  wrist. 
VTTT  C,     Extensors  and  flexor  longus  of  the  fingers. 


rig.:. 


Fig.l 


Fig.   300. — Distribution  of  the  superficial   areas  served   by  the  different   sensory   roots,    after 

Kocher. 

Red :    area  of  cervical  roots — C-i  to  Ct. 
Yellow :    area  of  dorsal  roots — D\  to  D12. 
Green :    area  of  lumbar  roots — L\  to  Lk. 
Blue :   area  of  sacral  roots — <Si  to  Sk. 


THE  SYMPATHETIC   NERVES  685 

I  T.  All  the  small  muscles  of  the  hand  and  fingers. 

I-XII  T.  Muscles  of  the  back. 

I-XI  T.  Intercostal  muscles. 

VII-XII  T.  Abdominal  muscles. 

I  L.  Lowermost  parts  of  the  abdominal  muscles;  quadratus  lumborum. 

II  L.  Cremaster, 

III  L.  Psoas ;  sartorius ;  iliacus  minor ;  pectineus ;  adductors  of  the  thigh. 

IV  L.  Quadriceps  femoris;  gracilis;  obturator  externus   (?). 

V  L,     Gluteus  medius  and  minimus ;  tensor  fasciae  femoris ;  semitendi- 

nosus ;  semimembranosus ;  biceps. 
I  S.     Pyriformis ;     obturator    internus ;     gemelli ;     quadratus     femoris ; 
gluteus  maximus ;  long  extensors  of  the  foot  and  toes ;  pero- 
neus  longus  and  brevis. 
II  S.     Long  flexors  of  the  foot  and  toes;  large  calf  muscles;  small  foot 
muscles. 

III  S.     Ejaculator  muscles;  muscles  of  the  perineum. 

IV  S.     Sphincter  and  detrusor  muscles  of  the  bladder;  sphincter  ani. 

V  S.     Levator  ani. 

The  same  must  be  said  of  this  summary  that  was  said  of  the  sensory  nerves, 
namely,  that  a  given  muscle  is  supplied  by  more  than  one  spinal  root.  Accord- 
ingly the  data  given  here  indicate  the  central  regions  of  distribution,  or.  the 
other  way  about,  the  chief  nerve  supply  for  the  separate  muscles.  Starr  finds, 
for  example,  that  the  scaleni  muscles  are  innervated  by  the  second  and  third 
cervical  roots,  the  diaphragm  by  the  third  and  fourth,  the  deltoid  by  the 
fourth  and  fifth,  the  biceps  by  the  fifth  and  sixth  cervical,  the  sartorius  by 
the  first  and  second  lumbar,  the  quadriceps  femoris  by  the  second  and  third, 
the  adductors  of  the  thigh  by  the  third  and  fourth,  etc. 

It  was  formerly  asserted  by  Preyer  and  Krause  that  the  skin  covering  any 
given  muscle  is  supplied  with  sensory  fibers  by  the  same  spinal  nerve  as  that 
which  supplies  the  underlying  muscle  with  motor  fibers.  Sherrington  finds, 
how^ever,  that  this  is  not  the  case;  for  certain  displacements  occur  causing  the 
skin  region  to  be  situated  farther  distally  than  the  corresponding  muscle.  The 
flexor  sides  of  the  thigh  and  fore  leg  and  the  extensor  side  of  the  arm  appear 
to  be  the  only  exceptions  to  this  rule.  The  different  sensorv  fibers  of  the 
muscles  themselves  appear  to  belong  to  the  same  segment  as  the  motor  fibers. 


§  3.    THE    SYMPATHETIC    NERVES 

A.    RELATIONS   OF   THE   SYMPATHETIC   NERVES   TO   THE   CENTRAL 

NERVOUS   SYSTEM 

The  nerve  fibers  traversing  the  sympathetic  nerves  are  both  afferent  and 
efferent  in  function;  and  they  mediate  a  great  variety  of  functions  not  under 
direct  influence  of  the  will.  To  tliese  belong  the  vasoconstrictor  and  vaso- 
dilator nerves,  accelerator  nerves  of  the  heart,  motor  and  inhibitory  nerves 
of  the  stomach,  intestine,  bladder,  etc.  They  constitute  therefore  the  greater 
part  of  the  visceral  nerves.  It  is  justifiable  to  enumerate  along  with  the  com- 
ponents just  named  the  visceral  fibers  contained  in  certain  cranial  nerves 
and  those  arising  from  the  sacral  roots.     Doing  this,  we  can  then  say,  that 


686 


PHYSIOLOGY   OF  SPECIAL   NERVES 


the  sympathetic  or  autonomic    (Langlev)    nervous  system  presides  over   all 
of  the  functions  not  under  the  direct  control  of  the  will. 

All  these  nerves  agree  in  having  their  origin  in  the  central  nervous  sys- 
tem.    In  the  strict  sense  the  sympathetic  nerves  constitute  processes  of  the 

lateral  horn  cells  on  the 
same  side  of  the  cord. 

The  efferent  fibers 
belonging  to  the  auto- 
nomic nerves  are  slen- 
der in  comparison  with 
other  efferent  nerve 
fibers,  and,  unlike  the 
motor  nerves  to  the 
skeletal  muscles,  connect 
somewhere  along  their 
course  with  ganglion 
cells  from  which  new 
fibers  issue  to  complete 
the  pathway. 

The  afferent  fibers 
found  in  the  sympa- 
thetic nerves  are  for  the 
most  part  offshoot*  from 
the  ganglion  cells  in  the 
spinal  ganglia ;  there  are 
among  them  some  which 
spring  from  peripheral 
ganglion  cells,  and  thus 
constitute  true  sympa- 
thetic fibers. 

The  most  important 
visceral  fibers  of  the 
cranial  nerves  have  al- 
ready been  studied.  We 
have  then  to  consider 
only  the  visceral  fibers 
coming  from  the  spinal 
cord. 

The  preganglionic 
fibers,  to  use  Langley's 
term,  make  their  exit 
exclusively  in  the  white  rami  communicantes  of  the  spinal  cord  (Gas- 
kell),  and  all  of  them  end  with  their  terminal  arborizations  about  ganglion 
cells  situated  at  a  greater  or  less  distance  from  the  cord.  There  are  no 
connections  between  the  separate  ganglion  cells  either  within  the  same  or 
different  ganglia. 

The  length  of  these  fibers  varies  greatly  (cf.  Fig.  301,  m^ — z,?-).     Some 


S^' 


-Ph 


Fig.  301. — Schematic  representation  of  the  connections  of 
the  sympathetic  fibers,  after  Kolliker.  PG,  peripheral 
ganglion:  C}s,  chain  ganglion;  Pk,  Pacinian  corpuscle; 
Rca,  white  ramus  conimunicans;  Rcgr,  gray  ramus  com- 
municans;  St,  sympathetic  trunk.  The  preganglionic  fibers 
are  black,  the  postgangUonic  red,  the  afferent  fibers  blue. 


THE   SYMPATHETIC   NERVES  687 

of  them  (7??i)  end  a])out  the  cells  of  the  nearest  ganglion,  others  (m^,  wj 
pass  through  several  ganglia  hefore  reaching  their  endings,  and  by  means  of 
collaterals  may  therefore  act  iipon  a  nnnd^er  of  cells.  Still  others  find  their 
destination  only  when  they  reach  ganglion  cells  situated  far  away  in  the 
periphery. 

Postganglionic  fihers  (g,  g.^,  g^,  g.-  Qi)  arise  in  the  sympathetic  ganglia 
and.  without  any  connection  with  other  ganglion  cells,  terminate,  sometimes 
near,  sometimes  far  awa}',  in  the  free  endings  on  smooth  muscle  cells,  gland 
cells,  etc.  Langley  believes  that  the  course  of  each  fiber  or  collateral  is  inter- 
rupted by  one  ganglion  cell  only.  ( See  page  582  for  Langley's  use  of  nicotine 
in  this  connection.) 

Part  of  the  postganglionic  fibers  traverse  the  gray  rami  communicantes 
to  the  spinal  nerves  and  reach  their  destination  by  these  paths;  part  of  them 
belong  to  branches  which  run  an  independent  course  to  the  periphery. 

The  plexuses  of  Auerbach  and  Meissner.  found  in  the  wall  of  the  alimentary 
canal  from  the  lowermost  part  of  the  oesophagus  onward,  which  are  commonly 
included  in  the  sympathetic  system,  present  some  variations  from  the  general 
behavior  of  the  symjiathetie  nerves.  For  this  reason  they  are  set  apart  by  Lang- 
ley  in  a  class  by  themselves.  Nothing  definite  can  be  said  at  present  as  to  their 
physiological  status. 

B.    COURSE   OF   THE   SYMPATHETIC   FIBERS 

According  to  Gaskell.  the  sympathetic  trunk  itself  receive-  preganglionic 
fibers  only  from  the  first  thoracic  to  the  second  to  fourth  or  fifth  lumbar  roots. 
The  cervical  roots  convey  no  visceral  nerves;  but  visceral  nerves  are  found 
in  the  first  or  second  and  third  sacral.  These  latter  do  not  unite  with  the 
sympathetic  but  contain  fibers  which  are  autonomic  in  function. 

The  preganglionic  fibers  belonging  to  the  sympathetic  unite  either  with 
cells  in  the  ganglia  of  the  sympathetic  chain  (lateral  ganglia),  or  with  cells 
in  ganglia  situated  farther  toward  the  periphery   (collateral  ganglia). 

The  following  account  of  the  course  of  pre-  and  postganglionic  fibers  and 
their  connections,  relating  to  the  cat.  is  taken  from  Langley. 

The  cervical  sympathetic  receives  fibers  from  the  first  to  the  seventh  tho- 
racic roots;  in  their  exit  from  the  spinal  cord  they  are  to  a  certain  extent 
arranged  according  to  their  function.  The  most  powerful  effect  on  the  dilator 
of  the  pupil  is  obtained  from  the  first  and  second,  on  the  nictitating  membrane, 
on  the  eyelids,  etc.,  from  the  first  to  the  third,  on  the  submaxillary  glands  from 
the  second  and  third,  on  the  vessels  of  the  ear  and  the  conjunctiva  from  the 
second  to  the  fourth,  on  the  pilomotor  nerves  of  the  head  and  neck  from  the 
fourth  to  the  sixth.  These  details  are  mentioned  because  they  are  important 
for  a  proper  conception  of  the  regeneration  j^henomena  to  be  described  presently. 

All  these  fibers  terminate  in  the  superior  cervical  ganglion,  the  cells  of 
which  send  out  postganglionic  fibers  to  the  plexuses  about  the  blood  vessels,  to 
certain  cranial  nerves,  and  to  the  three  upper  cervical  nerves.  These  joining 
the  last  named  accompany  their  sensory  branches  to  the  skin  and  innervate  the 
erector  muscles  of  the  hair,  constituting  therefore  the  pilomotor  nerves. 

The  stellate  ganglion  receives  fibers  from  the  (third)  fourth  to  the  eighth 
(ninth)   thoracic  roots.     Among  its  postganglionic  fibers  pilomotor  fibers  pass 


688 


PHYSIOLOGY   OF  SPECIAL   XERVES 


to  the  third  to  the  eighth  cervical  nerves  and  the  first  to  the  third  (fourth) 
thoracic  nerves :  they  make  their  exit  through  the  fifth  to  the  eighth  thoracic 
roots.  Vasomotor  and  sweat  nerves  for  the  fore  paw  are  contained  in  the  fourth 
to  the  ninth  thoracic  roots.  They  unite  with  cells  in  the  stellate  ganglion,  from 
which  postg-anglionic  fibers  are  given  off  to  the  brachial  nerves,  the  latter  like 
the  pilomotor  fibers  running  in  the  posterior  branches  of  those  nerves.  This 
ganglion  also  sends  accelerator  nerves  to  the  heart  and  possibly  vasomotor  nerves 
to  the  lungs;  but  it  is  not  yet  conclusively  proved  that  these  nerves  actually 
proceed  from  cells  in  the  stellate  ganglion. 

Those  spinal  nerve  roots  which  send  out  fibers  to  the  chain  ganglia  l.ying 
distally  to  the  stellate  ganglion,  each  supply  three,  four  or  more  ganglia.  The 
postganglionic  fibers  (pilomotor  and  vasomotor)  unite  with  the  corresponding 
spinal  nerves  and  accompany  their  dorso-cutaneous  branches  to  the  skin. 

The  vasomotor  and  sweat  nerves  to  the  hind  paw  pass  out  probably  in  the 
twelfth  thoracic  to  the  second  lumbar  nerve  roots;  they  unite  with  the  sixth 
lumbar  to  the  second  sacral  ganglia  to  be  continued  in  the  cutaneous  branches 
of  the  spinal  nei-ves. 

The  inhibitory  and  vasomotor  nerves  contained  in  the  splanchnic  are  con- 
nected for  the  most  part  with  cells  in  the  solar  plexus  and  have  no  relay  station 
in  the  chain  ganglia.  They  proceed  from  all  roots  between  the  fifth  thoracic 
and   second   lumbar  nerves. 

The  organs  of  the  pelvis  receive  nerves  both  from  the  lumbar  sympathetic 
and  the  sacral  (cf.  page  393).  The  former  arise  from  all  roots  between  the 
twelfth  thoracic  and  fifth  lumbar,  and  traverse  the  sympathetic  cord  either 
to  the  inferior  mesenteric  ganglion  or  to  the  sacral  ganglia.  Those  entering 
the  inferior  mesenteric  ganglion  unite  for  the  most  part  with  its  cells,  but  to 
a  less  extent  also  with  ganglion  cells  situated  in  the  peripheral  organs.  Most 
of  the  sympathetic  nerv^es  to  the  external  genital  organs  are  connected  with 
cells  in  the  sacral  ganglia. 

The  autonomic  fibers  passing  out  through  the  first  to  the  third  sacral  roots 
and  uniting  to  form  the  nervd  erigentes  connect  with  the  cells  of  ganglia  strewn 
along  their  course  and  l.ving  for  the  most  part  in  the  immediate  vicinity  of 
the  organs  for  which  they  are  destined. 


Ganglia  of  the  Sympathetic  System 


Spinal  Root. 

Cervical. 

Thoracic. 

Lumbar. 

Sacral. 

I 

II  .... 

III  . . . 

IV  ... 

V  ... 

VI  ... 

vn  .. 
vin.. 
IX  ... 

Sup.  cerv. 

Sup.  cerv. 

Sup.  cerv. 

Sup.  and  inf.  cerv. 

Sup.  and  inf.  cerv. 

Sup.  (f)  and  inf.  cerv. 

Inf.  cerv. 



l'.  2 

1,2,3 
1,2,3,4 
1.  2,  3,  4,  5 
i  2,3,4,5 
i  3,4,5 

Thoracic 

1,2 

1,  2,  3,  4,  5 

1,2,3,4,5,6,7.8,9 

^  5,6,7,8,9,10,11,12 

i  8,9,10,11,12 

11,12 

12 

X 

XI  ... 

XII     . 



1 

Lumbar 

I.  ... 

1   2  3 

II ... 

12  3  4  5 

On    the   basis    of   his   experiments    upon   animals    and    on   the   basis    of 
comparative  anatomy,  Langley  has  constructed  the  above  table  illustratinoj 


THE  SYMPATHETIC   NERVES  689 

the  relations  of  the  spinal  roots  to  the  ganglia  of  the  sympathetic  system  in 
man.  It  will  he  observed  that  the  main  outflow  of  sympathetic  fibers  takes 
place  between  the  first  thoracic  and  second  lumbar  roots. 


C.    REGENERATION   IN   THE   SYMPATHETIC   NERVOUS   SYSTEM 

Regeneration  in  the  sympathetic  system  is  of  particular  interest  because  it 
is  the  only  place  in  the  entire  nervous  system  where  ganglion  cells  are  found 
interpolated  in  the  direct  course  of  definite  nerve  fibers.  As  we  have  already 
seen  (page  G8T)  the  fibers  running  in  the  cervical  sympathetic  which  are  inter- 
rupted by  the  superior  cervical  ganglion  are  distributed  to  the  different  spinal 
roots  according  to  their  destination.  If  now  the  cervical  sympathetic  is  cut, 
after  a  time  regeneration  takes  place  just  as  in  all  the  nerves.  But  what  is 
specially  remarkable  in  this  case  is  this:  that  stimulation  of  the  separate  spinal 
roots  after  regeneration  produces  in  the  main  the  same  effects  as  before  they 
had  been  sectioned.  Again,  if  the  superior  cervical  ganglion  be  painted  with 
nicotine  after  regeneration,  we  get  the  same  negative  results  as  if  the  paint- 
ing were  done  previous  to  sectioning.  It  follows  that  the  regenerated  nerve 
fibers  have  re'estahlished  their  old  connections,  or  have  made  new  connections  in 
the  same  ganglion  ivith  cells  of  exactly  the  same  kind.  It  would  seem  that  the 
growing  nerve  fibers  must  be  guided  by  some  chemotropic  influence  to  the  very 
cells  with  which  they  were  formerly  connected   (Langley). 

By  the  same  method  Langley  has  found  that  postganglionic  fibers  likewise 
regenerate  and  reestablish  their  old  connections  and  that  they  also  form  new 
ones. 

When  the  superior  cervical  ganglion  is  cut  out,  the  cervical  sympathetic 
does  not  recover  its  functions  possibly  because  the  preganglionic  fibers  are  not 
capable  of  establishing  functional  connection  with  the  peripheral  tissues  directly. 
We  may  suppose  that  the  nutritive  influence  of  the  ganglion  cell  does  not  extend 
far  enough  to  permit  the  fibers  to  grow  farther  than  the  interpolated  ganglion. 
It  is  likewise  impossible  to  bring  about  a  union  of  the  true  efferent  cranial  or 
spinal  nerve  fibers  with  the  postganglionic  fibers,  although  union  of  these  nerves 
with  preganglionic  fibers  has  often  been  demonstrated. 


D.    AFFERENT  NERVES   IN    THE   SYMPATHETIC 

The  sympathetic  contains  afferent  fibers,  whose  tro])hic  centers  are  for  the 
most  part  in  the  spinal  ganglia.  The  number  of  such  fibers  is  much  smaller 
than  that  of  the  efferent  fibers.  Thus  Langley  has  found  by  the  method  of 
regeneration  that  only  one-tenth  of  all  the  fil)ers  in  the  hypogastric  are  afferent 
in  function;  in  the  nervus  erigens  the  number  is  one-third. 

Stimulation  of  any  one  of  the  white  rami  communicantes  produces  reflex 
movements  and  variations  in  the  blood  pressure.  Hence  they  must  contain 
afferent  fibers.  It  appears  that  such  fibers  run  almost  exclusively  to  the  thoracic 
and  abdominal  viscera,  and  that  they  probably  have  the  same  distribution  as 
the  corresponding  efferent  nerves.  It  is  probable  that  they  account  for  such 
conscious  sensations  as  "  referred  pains,"  so  called  because  they  are  referred  to 
regions  of  the  skin  innervated  from  the  same  root  as  the  diseased  organ.  Im- 
pidses  from  the  latter  are  therefore  conveyed  in  some  way,  either  by  mediation 


690  PHYSIOLOGY  OF  SPECIAL   NERVES 

of  the  spinal  ganglia  or  by  mediation  of  the  nerve  cells  of  the  spinal  cord,  to 
the  sensorj'  neurons  of  the  skin. 

For  reflexes  from  the  sympathetic  ganglia,  cf.  page  583. 

Refkrexcks. — Gaskell,  Journal  of  Phi/sinlogij,  vol.  vii,  1886. — Kocher, 
"  ^Mittheilungen  ans  den  Grenzgebieten  der  Medizin  und  Chirurgie,"  vol.  i,  1886. 
—LangJey,  several  articles  in  the  Journnl  of  Physiology,  vols,  xii,  xv,  xvii, 
xviii,  xix,  xx,  xxiii,  xxv,  xxvii-xxxi;  1891-1904. — Langley,  "  Ergebnisse  der 
Physiologic,"  ii,  2,  Wiesbaden,  1903. 


CHAPTER    XXVI 

REPRODUCTION    AND    GROWTH 

FIRST    SECTION 

REPRODUCTION 

The  physiology  of  reproduction  in  general  covers  so  wide  a  field  and  is 
related  to  so  many  l)ranches  of  biology  that  even  a  superficial  presentation 
of  its  most  salient  features  would  require  more  space  than  we  have  at  our 
disposal.  We  shall  therefore  limit  the  discussion  to  those  features  of  repro- 
duction in  man  and  the  higher  animals  which  are  very  important  from  the 
standpoint  of  human  physiology,  but  which  are  not  usually  treated  as  belong- 
ing to  the  special  province  of  embryology.  The  following  brief  survey  of 
this  field  will  indicate  the  scope  we  have  in  mind. 

Reproduction  in  most  of  the  higher  animals  is  inaugurated  by  the  conjuga- 
tion of  two  different  sexual  elements,  the  male  and  the  female.  The  female 
element,  the  ovum,  is  formed  in  the  ovary:  it  was  first  demonstrated  for  the 
mammals  by  v.  Baer  in  1837.  The  male  element,  the  spermatozoon,  is  formed 
in  the  testes  and  represents  the  "  seminal  bodies  "  discovered  by  Leuwenhoeck 
in  1677. 

In  manunals  the  spermatozoa  are  introduced  into  the  female  body  by  the 
act  of  cojtulation.  If  fertilization  of  the  ovum  then  takes  |)lace,  there  develops 
within  the  female  body  a  new  individual,  which,  when  it  has  reached  a  certain 
stage  in  its  development,  is  expelled  from  the  body  of  the  mother.  This 
latter  process  is  called  hirth  or  parturition. 

At  l)irth  the  new  individual  is  not  developed  far  enough  to  seek  inde- 
pendently and  to  utilize  the  ordinary  food  of  the  species,  but  must  for  a  time 
derive  its  nourishment  from  the  mother.  The  milk  glands  of  the  mother 
at  this  time  are  roused  to  a  high  degree  of  activity,  and  furnish  a  secretion, 
the  milk,  which  contains  in  proper  proportions  the  foodstuffs  necessary  for 
the  maintenance  of  the  newborn  child. 

The  physiology  of  reproduction,  as  we  shall  limit  the  subject  here,  will 
accordingly  include:  the  functions  of  the  male  and  female  sexxial  organs,  the 
processes  of  copulation  and  conception,  hirth.  and  the  secretion  of  milk. 

§  1.    THE   MALE    SEXUAL    ORGANS 

These  are:  the  testes,  which  produce  the  spermatozoa;  the  accessory  glands 
(vesicular  glands,  prostate  body,  and  the  glands  of  Cowper),  which  produce 

691 


692  REPRODUCTION   AND   GROWTH 

secretions  to  be  mixed  with  the  spermatozoa  in  the  seminal  fluid:  and  the 
male  organ,  the  penis,  by  which  the  seminal  fluid  is  introduced  into  the  female 
organs. 

A.    THE  TESTES 

Sexual  mnturitij.  or  puberfi/,  appears  in  the  man  at  about  the  age  of  fifteen. 
The  testes  begin  to  increase  in  volume  and  to  secrete  seminal  fluid.  At  the 
same  time  the  foreskin  becomes  loosened  from  the  glans  penis,  and  the  rest 
of  the  body  exhibits  many  changes :  the  bones  and  the  muscles  become  stronger 
(cf.  below,  page  709) ;  the  larynx  increases  in  size,  in  consequence  of  which 
the  voice  becomes  fuller  and  deeper,  etc. 

"\Mieu  the  testes  are  removed  by  castration  before  sexual  maturity,  these 
changes  do  not  take  place — which  proves  clearly  that  they  are  occasioned  by 
the  testes. 

The  general  character  of  the  individual  also  is  changed  by  castration,  as 
mav  be  seen  best  perhaps  by  comparison  of  the  disposition  of  an  ox  with  that 
of  a  bull.  It  follows  that  all  the  characteristics  by  which  a  man  is  distin- 
guished from  a  woman  depend  essentially  upon  the  testes  and  their  activity 
(cf.  also  page  357). 

The  spermatozoa  are  minute  bodies  consisting  of  a  thick  head  and  a  slender 
tail,  which,  in  virtue  of  the  whiplike  movements  of  the  tail,  are  capal)le  of 
independent  motion.  The  speed  of  their  locomotion,  considered  with  refer- 
ence to  their  size,  is  rather  high,  namely,  0.05  to  0.15  mm.  per  second. 

The  spermatozoa  are  formed  by  a  peculiar  transformation  of  certain  cells 
in  the  testes,  known  as  spermatids.  According  to  Lode,  in  1  cu.  mm.  of 
human  seminal  fluid  there  are  about  60,000  spermatozoa.  The  quantity  of 
seminal  fluid  discharged  at  a  single  ejaculation  may  be  estimated  at  about 
3  cc. ;  whence  the  total  number  of  spermatozoa  in  a  single  ejaculation  would 
be  in  the  neighborhood  of  180,000,000 — a  perfectly  enormous  number  in  view 
of  the  fact  that  but  a  single  spermatozoon  is  necessary  for  fertilization  of 
the  ovum. 

Foges  reports  the  interesting  observation  that  the  testis  of  a  cock  trans- 
planted into  the  abdominal  cavity  will  continue  to  produce  spermatozoa,  from 
which  we  may  conclude  that  spermatogenesis  is  in  part  at  least  independent  of 
the  nervous  system. 

B.    THE  ACCESSORY  SEXUAL   GLANDS 

In  a  castrated  animal  the  accessory  glands  atropliy.  showing  that  they 
must  play  some  essential  part  in  the  sexual  functions.  If  castration  be 
performed  before  sexual  maturity,  they  do  not  develop  at  all. 

Xothing  is  known  at  present  as  to  the  special  functions  of  the  separate 
glands;  but  from  the  fact,  established  by  comparative  anatomical  studies,  that 
there  is  considerable  variation  in  their  relative  sizes  in  different  species,  we 
may  surmise  that  they  all  have  an  essentially  common  purpose. 

The  so-called  seminal  vesicles  are  not  properly  a  receptacle  for  the  seminal 
fluid,  although  they  do  always  contain  a  greater  or  less  number  of  spermato- 


THE   MALE   SEXUAL   ORGANS  693 

zoa :  they  produce  a  secretion  of  their  o\\ti,  which  has  led  Owen  to  describe 
them  as  the  vesicular  glands.  When  they  are  extirpated  either  alone  or  in 
conjunction  with  the  prostate  body,  sexual  desire  remains  unimpaired,  and 
copulation  takes  place  in  the  same  way  as  in  the  normal  animal  and  with  the 
usual  frequency. 

The  fecundity  of  the  animal,  however,  is  very  much  reduced  by  the  extir- 
pation of  the  vesicular  glands  (in  white  rats)  and  if  the  prostate  body  be 
removed  along  with  them,  the  procreative  power  is  entirely  lost.  The  acces- 
sory sexual  glands  therefore  are  absolutely  necessary  for  the  full  fruition  of 
the  male  sexual  functions   (Steinach). 

Probably  their  most  important  purpose  is  to  provide  for  the  dilution  of  the 
testicular  secretion — a  condition  which  is  indispensable  for  the  motility  of 
the  spermatozoa.  In  the  testis  itself  and  in  the  epididymis  where  the  fluid  is 
thick  the  spermatozoa  are  not  motile;  but  when  semen  from  the  testes  is  mixed 
with  physiological  salt  solution,  active  movements  appear  wherever  an  actual 
mixing  takes  place  (Iwanoff).  The  ova  of  rabbits,  guinea  pigs  and  dogs  can 
be  successfully  fertilized  by  injecting  into  the  vagina  a  mixture  of  sperm  from 
the  epididymis  and  physiological  salt  solution  (Walker). 

On  the  other  hand  it  was  found  in  Steinach's  experiments  that  the  sperma- 
tozoa remain  motile  in  the  prostate  secretion  from  seven  to  ten  times  longer 
than  they  do  in  the  physiological  salt  solution.  This  shows  that  the  secretion 
contains  other  substances  which  have  a  favorable  action  upon  the  spermatozoa. 
Since  acids  are  very  harmful  to  the  spermatozoa,  it  is  possible  that  the  secre- 
tion has  the  additional  function  of  neutralizing  any  acid  that  may  chance  to 
be  present  in  the  vaginal  mucus. 

In  the  guinea  pig  and  other  rodents,  the  secretion  of  the  vesicular  gland 
coagidates  in  the  vagina  so  as  to  form  a  plug  which  prevents  the  escape  of  the 
seminal  fluid.  This  coagulation  is  caused  by  the  action  of  an  enzyme  occurring 
in  the  secretion  of  the  prostate  (Camus  and  Glej-). 

The  vasa  deferentia  in  the  cat  receive  their  motor  nerves  from  the  (second) 
third  to  fourth  (fifth)  lumbar  roots;  these  nerves  have  about  the  same  peripheral 
course  as  the  lumbar  nor\-es  to  the  bladder  (Langley  and  Anderson;  cf.  page  393). 

The  vesicular  glands  of  the  guinea  pig  receive  motor  as  well  as  secretory 
fibers  by  the  hypogastric  nerves;  they  leave  the  spinal  cord  in  the  second  to  the 
fourth  lumbar  nerves  (Akutsu). 

Mislawsky  and  Bormann  state  that  the  secretoi-y  fibers  of  the  prostate  run 
in  the  hypogastric  nerves  and  that  its  muscles  are  supplied  also  with  fibers  from 
the  nervi  erigentes. 

C.    ERECTION   AND   EJACULATION 

Just  previous  to  the  act  of  copulation  the  penis  becomes  rigid  and  erect, 
thus  fitted  to  be  introduced  into  the  vagina.  Friction  of  the  glans  against 
the  walls  of  the  vagina  sets  up  a  reflex  by  which  the  seminal  fluid  containing 
all  the  secretions  of  the  accessory  glands  is  discharged  into  the  female  organ 
(ejaculation).  Tlie  rigidity  of  the  male  organ  then  passes  off  and  the  act 
of  copulation  is  ended. 

Erection  is  due  to  an  in-rush  of  1)lood  into  the  three  cavemou.s  bodies 
of  the  penis,  caused  ])y  dilatation  of  its  arteries  under  the  influence  of  vaso- 
dilator neives.     These  nerves    (nervi  erigentes)   discovered  by   Eckhard  and 


694  REPRODUCTION   AND  GROWTH 

studied  later  b}'  Loven  and  others,  leave  the  spinal  cord  in  the  anterior  roots 
of  the  first  to  tliird  sacral  nerves,  unite  with  the  hypogastric  plexus  and  run 
thence  to  the  penis.  They  have  their  center  in  the  lowermost  part  of  tJie 
cord,  so  that  erection  can  still  be  reflexly  induced  after  section  of  the  spinal 
cord  between  the  dorsal  and  the  luml)ar  regions  (cf.  page  588).  In  fact,  at 
the  moment  of  making  such  a  section  (in  the  guinea  pig)  erection  and  ejacu- 
lation occur  (Spina). 

According-  to  L.  E.  Miiller  erection  and  ejaculation  can  be  induced  (in  the 
dog)  by  rubbing  the  penis  after  extirpation  of  the  lumbar  and  upper  part  of 
the  sacral  cord.  It  is  likely  therefore  that  the  reflex  can  be  mediated  by  periph- 
eral ganglion  cells. 

Erection  may  be  brought  about  also  through  the  influence  of  higher  nerve 
centers.  Eckhard  was  al)le  to  induce  the  phenomenon  in  animals  l)y  the  elec- 
trical stimulation  of  the  cervical  cord,  of  the  pons,  and  of  the  crura  cerebri. 
The  fact  that  in  man  erection  often  occurs  merely  as  the  result  of  erotic 
ideas,  is  evidence  that  the  nervi  erigentes  may  be  excited  in  the  same  way 
also  by  the  cerebrum. 

Stimulation  of  the  nervi  erigentes  increases  the  volume  of  blood  flowing 
through  the  pudenda  interna  vein  beyond  the  mouth  of  the  penis  vein  to  about 
eightfold  the  volume  flowing  during'  the  relaxed  condition  of  the  penis.  Since, 
however,  erection  occurs  as  the  result  of  the  same  stimulation  the  inflow  of 
blood  must  be  still  greater.  In  erection  as  it  occurs  naturally  the  veins  of  the 
penis  are  compressed  by  contraction  of  the  musculature  about  the  urethra, 
thereby  rendering  the  outflow  of  blood  from  the  penis  more  difficult,  which  in 
turn  serves  to  heighten  the  degree  of  erection.  Compression  of  these  veins 
alone  however  does  not  cause  erection. 

Erection  obviously  must  be  closely  related  to  the  functions  of  the  testes; 
and  yet  observations  on  both  men  and  animals  go  to  show  that  erection  is  pos- 
sible after  castration  and  that  sexual  passion  may  not  be  entirely  destroyed. 

Wheu  ejaculation  occurs,  the  seminal  fluid  is  thrown  by  forcible  contrac- 
tions of  the  vasa  deferentia  into  the  urethra  in  the  direction  of  the  pars  mem- 
branacea  urethra^.  Entrance  to  the  urinary  bladder  is  prevented  chiefly  by  the 
sphincter  of  the  bladder  and  by  contraction  of  the  musculature  of  the  prostate. 

The  ejaculatory  ducts  open  at  the  summit  of  the  seminal  eminence,  while 
the  mouths  of  the  numerous  ducts  from  the  prostate  are  so  arranged  that  they 
empty  their  secretion  in  exactly  the  opposite  direction.  When  the  semen  pours 
out  of  the  ejaculatory  ducts,  numerous  streams  of  the  secretion  from  the  pros- 
tate are  at  the  same  time  poured  into  the  urethra  and  there  results  a  very 
uniform  mixture  of  the  two  fluids  (Walker). 

The  seminal  fluid  is  expelled  from  the  urethra  by  contraction  of  the  bulbo- 
cavernosus  and  the  ischio-cavernosus  muscles ;  according  to  Walker  the  sphincter 
uretbrte  membranacese  should  play  an  essential  part  in  this  also. 

Ejaculation  may  take  place  without  erection — in  the  guinea  pig,  for  example, 
when  the  spinal  cord  is  crushed  by  means  of  an  exploring  instrument.  In  the 
same  animal  Remy  found  on  the  inferior  vena  cava  at  the  level  of  the  renal 
veins  a  small  ganglion  electrical  stimulation  of  which  produced  a  sudden  ejacu- 
lation. Sexual  desire  was  not  destroyed  by  section  of  the  nerves  issuing  from 
this  ganglion,  but  erection  and  ejaculation  were  no  longer  possible. 


THE   FEMALE  SEXUAL  ORGAxNS  695 


§  2.    THE    FEMALE    SEXUAL    ORGANS 

A.    THE   OVARIES   AND   OVIDUCTS 

The  primordial  ova,  which  are  destined  ultimately  to  become  the  mature 
ova  capable  of  fertilization,  are  formed  at  a  very  early  stage  of  intrauterine 
life.  In  the  further  course  of  development  they  become  surrounded  by  a 
layer  of  germinal  epithelial  cells,  the  whole  group  ])eing  then  known  as  the 
primary  follicle. 

From  this  primary  follicle  what  is  known  as  a  Graafian  foUicIe  is  devel- 
oped in  the  following  manner:  The  epithelium  which  surrounds  the  ovum 
begins  to  proliferate  and  becomes  many-layered.  Then  in  the  space  between 
these  layers  a  fluid  gradually  collects,  partly  by  transudation  from  the  sur- 
rounding blood  vessels  and  partly  by  disintegration  of  epithelial  cells.  In  the 
human  ovary  this  liquor  foUicuhiris  is  found  only  in  that  part  of  the  follicle 
presenting  toward  the  surface  of  the  ovary.  On  the  medial  side  of  the  follicle 
the  epithelium  forms  a  mass  of  cells  surrounding  the  ovum  and  projecting 
into  the  follicular  cavity  as  the  discus  proligeriis.  The  follicle  is  also  sur- 
rounded by  a  connective  tissue  envelope  known  as  the  theca  foUiculi. 

At  the  same  time  the  ovum,  its  nucleus  (germinal  vesicle)  and  nucleolus 
(germinal  spot)  grow  in  size  and  the  ovum  becomes  surrounded  by  a  mem- 
brane, the  zona  peUucida,  secreted  by  the  follicular  epithelium.  The  mem- 
brane, however,  is  separated  from  the  ovum  l)y  a  small  space. 

In  the  further  development  of  the  ovum,  the  protoplasm  from  the  center 
outward  becomes  transformed  into  yoJk  spherules,  until  Anally  there  remains 
of  the  true  protoplasm  only  a  thin  layer  situated  peripherally,  and  containing 
the  nucleus. 

Development  of  the  primary  follicle  into  the  Graafian  follicle  takes  place 
before  sexual  maturity,  in  fact  before  the  birth  of  the  young  female.  But 
the  ova  are  not  yet  capable  of  being  fertilized  and  will  not  be  before  the 
beginning  of  sexual  maturity — i.  o.,  about  the  fourteenth  year.  By  this  time 
the  ova  are  about  twice  as  large  as  when  the  Graafian  follicle  was  formed, 
measuring  now  about  0.2  mm.  in  diameter,  and  have  extruded  from  them- 
selves half  the  chromntin  (staining  substance)   of  their  nuclei. 

When  the  follicle  has  reached  a  certain  size,  an  internal  proliferation  in 
the  inner  layer  of  the  theca  folliculi  takes  place  which  finally  leads  to  its 
rupture  and  to  the  consequent  liberation  of  the  ovum.  The  processes  con- 
cerned in  this,  according  to  Xagel's  description,  shape  themselves  on  this 
wise : 

The  vessels  of  the  theca  become  strongly  developed,  and  the  cells  about 
them  juultiply  enormously.  At  the  same  time  the  protoplasm  of  the  cells 
becomes  filled  with  a  material  (lutein)  which  gives  the  whole  inner  wall  of  the 
follicle  a  yellow  cast.  The  hilnn  cells  become  bulged  out  in  the  form  of  a 
papilla  on  the  inner  layer  of  the  theca  and  this  bulging  continues,  crowding 
the  follicular  contents  more  and  more  toward  the  thinnest  part  of  the  follicular 
wall  turned  toward  the  surface  of  the  ovary,  imtil  finally  the  follicle  bursts. 
Hand  in  baud  with  this  proliferation  of  the  lutein  cells  tbere  goes  a  fatty 
degeneration  of  tliC  follicular  epithelium,  by  which  the  ovum  with  its  epi- 


696  REPRODUCTION   AND  GROWTH 

thelium  is  released  from  the  discus  proligerus.  The  contents  of  the  follicle 
are  replaced  in  part  at  least  hv  a  blood  clot :  we  then  have  instead  of  the 
Graafian  follicle  a  corpus  lutcum. 

Thus  the  ovum  comes  into  the  abdominal  cavity  and  is  ready  to  enter  the 
Fallopian  tube  to  be  passed  on  into  the  uterus.  The  abdominal  opening  of 
the  tube  spreads  out  in  the  form  of  a  funnel  surrounded  by  fringelike  proc- 
esses known  as  fimhri(F,  one  of  which,  the  fimhria  ovarica,  comes  quite  close 
up  to  the  ovary.  Along  this  fimbria,  extending  from  the  ovary  to  the  tube, 
runs  a  groove,  which,  like  the  fimbria  themselves  and  the  mucous  membrane 
lining  the  tubes,  is  clothed  by  a  ciliated  epithelium.  These  cilia  beat  in  the 
direction  of  the  tube,  creating  a  current  in  the  surrounding  capillary  spaces 
between  the  viscera,  which  probably  plays  a  predominant  part  in  guiding  the 
ovum.  The  production  of  this  current  is  materially  aided  by  the  peculiar 
position  of  the  tube,  its  relation  to  the  ovary  being  such  as  to  form  about 
the  latter  a  sort  of  pocket,  closed  off  from  the  alxlominal  cavity. 

Once  in  the  Fallopian  tube  the  ovum  is  carried  along  to  the  uterus  by  the 
movements  of  the  cilia.  In  this  journey,  which  requires  about  three  days,  the 
remains  of  the  follicular  epithelium  adherent  to  the  ovum  when  it  is  set 
free,  become  stripped  off,  leaving  the  ovum  naked. 

It  is  probable  that  many  of  the  ova  set  free  from  the  ovary  never  reach  the 
Fallopian  tubes,  but  are  lost  in  the  abdominal  cavity. 

Opinions  differ  very  much  as  to  the  time  of  ovulation  (liberation  of  the 
ovum  from  the  ovary),  and  a  definite  decision  between  them  cannot  be  given 
at  this  time.  Some  authors  suppose  that  it  takes  place  only  in  connection  with 
menstruation  (before  or  after),  others  that  it  can  occur  at  any  time  in  connec- 
tion with  copulation. 

B.    THE  UTERUS 

The  uterus  is  a  hollow  organ  which  serves  the  purpose  of  harboring  the 
ovum  during  its  development  into  the  mature  foetus  and  of  supplying  the 
necessary  nourishment  for  this  development.  The  wall  of  the  uterus  con- 
sists externally  of  numerous  smooth  muscle  fibers  interlaced  together,  and 
internally  of  a  mucous  membrane  lined  with  a  ciliated  epithelium,  invagina- 
tions of  which  toward  the  muscle  layer  constitute  the  mucous  glands.  The 
cilia  of  the  epithelium  beat  from  above  downward — i.  e.,  from  the  fundus 
toward  the  mouth  of  the  uterus. 

The  uterus  differs  radically  from  all  other  organs  of  the  body  in  that  its 
tissues  undergo  profound  alterations  under  perfectly  normal  circumstances. 
Some  of  these  alterations  are  related  to  menstruation,  some  of  them  to 
pregnancy. 

By  menstruation  is  meant  a  periodic  discharge  of  blood  from  the  uterus 
of  the  sexually  mature  female,  which  occurs  about  every  twenty-eight  days 
and  continues  on  the  average  about  four  days.  It  begins  at  about  the  four- 
teenth year  of  age  and  constitutes  the  external  sign  of  sexual  maturity.  The 
quantit}'  of  blood  discharged  at  each  period  has  been  estimated  at  from 
100-200  cc,  but  the  amount  is  subject  to  great  variations.  At  the  age  of 
forty-five  to  fifty  years  menstruation  gradually  ceases,  and  with  it  the  ability 
to  bear  young  is  permanently  lost.     This  age  is  designated  as  the  climacteric. 


THE   FEMALE   SEXUAL  ORGANS  697 

It  had  long-  been  supposed  that  menstruation  was  due  to  some  nervous  influ- 
ence of  the  ovary  over  the  uterus.  But  it  has  been  observed  that  in  monkeys 
menstruation  can  take  place  even  when  the  ovaries  have  been  removed  from 
their  normal  position  in  the  body  and  transplanted  elsewhere,  all  nervous  con- 
nections with  the  ovary  being  severed.  Hence  it  is  not  improbable  that  the 
internal  secretion  of  the  ovary  is  the  essential  medium  of  influence  (cf.  page  358). 

Just  as  in  man,  the  appearance  of  puberty  in  woman  is  marked  by  other 
changes  in  the  body:  the  mammary  glands  increase  in  size,  the  figure  loses 
its  childish  delicacy  and,  by  the  deposition  of  subcutaneous  fat,  becomes  more 
robust.  Castration  of  the  female  (extirpation  of  the  ovaries)  likewise  pro- 
duces more  or  less  sharply  pronounced  changes   (cf.  page  358). 

The  monthly  changes  in  the  uterus  proceed  as  follows :  five  to  ten  days 
before  the  period  of  discharge  the  blood  vessels  of  the  mucous  membrane 
become  dilated,  the  membrane  itself  as  a  result  swells  up  and  a  proliferation 
of  its  more  superficial  layers  takes  place.  Then  follows  a  hemorrhage  in  the 
subepithelial  tissue  which  is  probably  not  due  to  rupture  of  blood  vessels,  but 
to  the  escape  from  them  of  red  blood  corpuscles.  The  nutritive  condition 
of  the  mucous  membrane  thus  becomes  impaired,  and  as  a  consequence  its 
outermost  layers  (the  decidua  menstrualis)  slough  off  (according  to  some 
authors  the  loss  of  the  mucous  membrane  is  not  due  to  lack  of  nutrition,  but 
to  pressure  of  the  escaping  blood  in  the  subjacent  tissues)  ;  the  period  of 
discharge  continues  for  about  four  days,  when  a  process  of  restitution  sets 
in.  These  changes  proceed  by  a  regeneration  of  tissue  from  the  remaining 
epithelium  and  its  invaginations,  and  last  from  five  to  ten  days.  Hence  the 
tissue  changes  accompanying  menstruation  cover  all  told  from  fourteen  to 
twenty-four  days  out  of  each  month. 

The  physiological  significance  of  menstruation  probably  consists  in  a 
preparation  of  the  uterine  wall  for  the  reception  of  the  fertilized  ovum. 

Like  the  rest  of  the  mucous  membrane  of  the  uterus,  that  of  the  cervix  bears 
on  its  surface  a  ciliated  epithelium,  invaginations  of  which  form  the  cervical 
glands.  These  glands  secrete  a  clear,  viscid  mucus  which  collects  in  the  cervi- 
cal canal  soon  after  conception  and  remains  there  as  a  plug  serving  to  keep  the 
passage  closed  throughout  pregnancy. 

After  the  climacteric  has  been  passed,  and  ova  are  no  longer  being  formed, 
the  mucous  membrane  of  the  uterus  shrivels  up,  the  connective  tissue  under- 
lying it  increases  in  quantity,  the  cervical  glands  atrophy,  and  the  epithelium 
loses  its  cilia. 

C.    PREGNANCY   AND   BIRTH 

Spermatozoa  are  independently  motile,  and  in  virtue  of  this  property  of 
motility  can  traverse  great  distances,  relatively  speaking.  Their  entrance  into 
the  uterus  and  Fallopian  tubes  is  due  no  doubt  to  some  chemotactic  influence 
over  them  exercised  by  the  secretions  of  those  organs,  and  their  ascent  toward 
the  ovaries  within  the  tubes  is  traceable  to  their  rheotadic  properties  (cf. 
page  50).  Coming  into  contact  with  the  ovum,  the  spermatozoon  enters  it, 
possibly  under  the  spell  of  a  fliif/nintdiiir  influence  (cf.  page  ")(;).  Inside  the 
ovum  the  spermatozoon  produces  changes  comprehended  under  the  term  fer- 
tilization, which  make  it  possible  for  the  ovum  to  develop  into  a  new  individual. 


698  REPRODUCTION   AND   GROWTH 

\Yi\en  the  ovum  has  been  fertilized,  it  becomes  attached  to  the  mucous 
membrane  of  the  uterus  already  prepared  for  it,  and  later  becomes  surrounded 
by  the  proliferating  epithelium  of  the  mucous  membrane. 

The  material  necessary  for  the  nourishment  of  the  ovum  is  received  from 
the  mother  through  the  placenta.  As  the  ovum  grows  the  uterus  increases 
in  size,  so  that  while  before  impregnation  its  capacity  is  3-5  cc,  at  the  close 
of  pregnancy  it  is  5,000-7,000  cc.  This  colossal  development  produces  re- 
markably little  change  in  the  organism  as  a  whole,  and  the  only  permanent 
alterations  remaining  after  pregnancy  are  certain  folds  in  the  subcutaneous 
connective  tissue  of  the  abdomen  caused  by  the  extreme  tension  to  which  it 
has  been  subjected,  and  certain  anatomical  differences  in  the  wall  of  the  uterus. 

The  period  of  gestation  covers  ten  menstrual  periods — i.  e.,  about  two 
hundred  and  eighty  days — at  the  end  of  which  time  birth  takes  place. 

The  foetus  is  discharged  from  the  uterus  by  powerful  contractions  of  its 
muscular  walls,  aided  by  simultaneous  contractions  of  the  diaphragm  and 
abdominal  muscles.  The  first  effect  of  the  uterine  contractions  is  to  draw 
the  cervix  on  all  sides  tightly  against  the  foetus  and  to  dilate  the  passage  way 
until  the  child  can  be  forced  through.  This  stage  of  labor  is  called  the 
opening  period;  that  following,  which  terminates  in  the  complete  discharge 
of  the  offspring,  is  called  the  expulsion  period.  In  cases  of  first  births  the 
former  period  lasts  about  twelve  hours,  in  subsequent  births  six  hours;  the 
length  of  the  expulsion  period  is  estimated  at  two  hours.  These  however  are 
only  average  figures,  and  the  duration  of  birth  may  vary  considerably 
either  way. 

Owing  to  their  painful  character  the  contractions  of  the  uterus  in  child- 
l)irth  are  commonly  called  labor  jHiins.     They  are  not  continuous,  but  like 


Fig.  302. — Normal  curve  of  a  contraction  of  the  uterus,  after  "Westermark.     To  be  read  from  left 

to  right. 

the  contractions  themselves  are  intermittent  and  become  progressively  longer 
and  more  severe  until  near  the  culmination  of  labor. 

The  frequency  of  labor  pains  is  variable.  At  the  beginning  of  the  first 
stage  of  labor,  the  interval  between  them  is  greatest,  but  it  becomes  steadily 
less  until  it  reaches  its  minimum  (less  than  one  hundred  seconds)  at  the  end 
of  this  stage  or  some  time  during  the  second.  When  the  pains  are  unusually 
long  and  severe,  the  pauses  are  also  longer. 

So  long  as  there  is  no  change  in  the  volume  of  the  contents  of  the  uterus, 
the  intrauterine  pressure  during  the  pauses,  as  estimated  l)y  Schatz,  Polallion, 
Westermark,  and  others,  remains  remarkably  even  in  any  particular  case  of 
labor :  liut  in  different  cases  of  labor  it  varies  from  20  to  70  mm.  Hg.  When 
the  amnion  is  ruptured  a  decrease  in  the  volume  of  the  uterine  contents  takes 


THE   FEMALE   SEXUAL   ORGAXS  699 

place,  and  this  occasions  a  fall  of  the  intrauterine  pressure  at  the  next  pause. 
After  this  fall,  however,  the  pressure  during  the  following  pauses  tends  to 
return  to  its  original  level,  although  that  level  is  seldom  reached,  partly 
because  the  amniotic  fluid  escapes  during  each  contraction  of  the  wall,  and 
partly  because  the  child  is  pressed  deeper  and  deeper  into  the  pelvis,  thus 
decreasing  the  volume  of  the  uterine  contents. 

During  a  single  pain  the  intrauterine  pressure  increases  slowly  at  first, 
then  rather  rapidly,  and  finally  slowly  again  until  it  reaches  its  highest  point. 


Fig.  303. — Pressure  curve  of  the  last  contraction  of  the  uterus  in  parturition,  after  Westermark. 
The  high  curve,  reaching  a  pressure  of  400  mm.  Hg.,  represents  the  effect  of  the  abdominal 
muscles.     To  be  read  from  left  to  right. 

For  about  eight  seconds  it  remains  at  this  maximum,  after  which  it  falls  at 
first  slowly,  then  for  five  to  twenty-five  seconds  more  rapidly  and  at  the  last 
very  slowly  (  Fig.  302 ) . 

The  highest  pressure  due  to  the  contractions  of  the  uterus  alone,  attained 
during  the  individual  pains,  increases  during  the  progress  of  birth  and  reaches 
its  maximum  at  the  end.  Out  of  587  determinations  made  by  Westermark 
the  lowest  was  20  mm.  Hg.,  the  highest  220,  and  the  average  109  mm.  The 
value  naturally  is  considerably  increased  when  the  abdominal  pressure  also  is 
brought  to  bear  on  the  wall  of  the  uterus.  Especially  is  this  the  case  during 
the  last  pains  of  the  expulsive  period,  where  values  of  400  mm.  Hg.  have 
been  observed  (Fig.  303). 

A  short  time  after  the  birth  of  the  child  the  placenta  becomes  loosened  and 
with  the  amnion  is  expelled  from  the  uterus  as  the  afterbirth.  The  severe 
hemorrhafrc  which  occurs  at  first  is  stopped  by  the  powerful  contractions  of  the 
uterus.  Then  the  organ  gradually'  returns  to  its  original  size,  the  mucous  mem- 
brane becomes  regenerated,  the  muscle  fibers  decrease  in  length  and  breadth. 
Connected  with  these  regeneration  changes,  which  are  complete  after  about  two 
months,  there  is  for  a  couple  of  weeks  a  discharge  of  a  slimy,  and  at  first  bloody, 
material.  The  first  menstruation  however  does  not  as  a  rule  appear  until  about 
the  tenth  month,  when  lactation  has  ceased  (cf.  §3). 

41 


700  REPRODUCTION   AND   GROWTH 

D.    INNERVATION    OF  THE  SEXUAL   ORGANS 

Experimental  data  on  the  innervation  of  the  uterus  differ  widely.  While 
some  authors  state  that  the  circular  muscle  fibers  are  innervated  by  the  nervi 
erigentes  and  the  longitudinal  fibers  by  the  hypogastric,  Langley  and  Ander- 
son have  reached  the  conclusion  that  (in  the  rabbit  and  cat)  only  the  lumbar 
nerves  convey  motor  fibers  and  that  these  supply  both  the  longitudinal  and 
circular  musculatures.  The  effect  of  unilateral  stimulation  is  felt  chiefly  on 
the  same  side. 

Nagel  describes  the  innervation  of  the  uterus  in  the  woman  as  follows:  one 
trunk  arises  from  the  hypogastric  plexus,  while  others  arise  from  the  sacral 
nerves.  The  former  receives  fibers  from  the  third  sacral  and  sends  a  branch  to 
the  ureter.  It  then  betakes  itself  to  the  cervical  ganglion  (plexus  utero-vagi- 
nalis)  which  lies  in  the  neig'hborhood  of  the  lateral  vaginal  fold. 

Besides  this  ganglion,  \\hich  receives  branches  from  the  fourth  sacral  and 
is  also  connected  with  the  hemorrhoidalis  nerve,  there  are  found  in  the  vicinity 
of  the  ureter  two  other  ganglia  (the  vesical  plexus)  :  the  three  ganglia  are 
connected  with  one  another  and  send  branches  to  the  uterus,  the  vagina,  etc. 
Mo£t  of  the  uterine  nerves  come  from  these  ganglia;  a  smaller  part  of  them 
pass  directly  from  the  hypogastric  plexus. 

The  nerves  of  the  ovaries  arise  from  the  plexus  renalis  and  from  the  lower 
portion  of  the  plexus  aorticus  abdominalis. 

The  plexus  surrounding  the  vagina  arises  from  the  cervical  and  vesicular 
ganglia,  but  also  receives  twigs  from  the  third  and  fourth  sacral  nerves. 

Movements  of  the  uterus  can  be  produced  by  stimulation  of  the  different 
parts  of  the  central  nervous  system  (lumbar  cord,  medulla  oblongata,  anterior 
part  of  the  optic  thalami,  cerebral  cortex,  probably  the  motor  zone).  But  the 
uterus  contracts  spontaneously  at  a  certain  rhythm  even  when  it  is  cut  out 
of  the  body,  and  birth  has  been  known  to  take  place  in  a  perfectly  normal 
manner  with  all  the  uterine  nerves  cut  (Rein)  and  after  entire  extirpation 
of  the  lower  end  of  the  spinal  cord  (Goltz  and  Ewald,  cf.  page  583).  The 
central  nervous  system  therefore  plays  a  relatively  unimportant  part  in  con- 
trolling the  movements  of  the  uterus. 

According  to  Keilmann  and  Knupffer,  parturition  takes  place  at  once  if 
the  cervix  be  everted  as  far  as  the  ganglion  of  the  cervix.  But  Rein  states 
that  (in  the  dog)  parturition  takes  place  also  after  extirpation  of  the  ganglion. 

§  3.    SECRETION   OF   MILK 

The  newborn  child  is  not  far  enough  developed  to  seek  and  to  take  food 
without  help.  Its  digestive  organs  are  not  yet  capable  of  modifying  the 
ordinary  mixed  diet  of  man,  consequently  nourishment  for  the  child  must 
be  prepared  for  some  months  in  the  body  of  the  mother.  This  is  accomplished 
through  the  activity  of  the  mammary  glands  which  form  and  secrete  the  milk. 

A.    MILK 

l\rilk  constitutes  the  natural  food  of  the  child  and  hence  contain;^  in  proper 
relative  proportions  all  the  foodstuffs  necessary  for  the  maintenance  and  devel- 


SECRETION  OF  MILK  701 

opment  of  the  young  bod}'.     We  therefore  find  in  milk  proteid,  fat,  carbo- 
hydrate and  mineral  substances. 

Among  the  proteids  of  milk  we  find :  in  small  quantities  lact-glol)ulin, 
which  is  probably  identical  with  serum  globulin;  lact-albumin,  which  is  dis- 
tinguished by  certain  properties  from  serum  albumin;  and,  most  important 
of  all,  casein.  Cow's  milk  contains  on  the  average  about  3  per  cent  of  casein 
and  0.5  per  cent  of  other  proteids. 

Casein  of  cow's  milk  is  a  nucleo-albumin  (cf.  page  75)  which  is  charac- 
terized chiefly  by  the  fact  that  it  coagulates  under  the  influence  of  rennin  (cf. 
page  250).  In  the  dried  state  casein  is  a  fine  white  powder.  It  is  insoluble  in 
water  and  very  difficultly  soluble  in  solutions  of  the  common  neutral  salts,  but 
in  water  to  which  a  very  slight  trace  of  alkali  has  been  added  it  is  very  readily 
soluble.  It  is  soluble  also  in  the  presence  of  calcium  carbonate  from  which  the 
casein,  acting  as  an  acid,  displaces  the  carbon  dioxide.  Its  solutions  do  not 
coagulate  on  boiling  and  are  not  precipitated  by  magnesium  sulphate,  metallic 
salts,  or  mineral  acids  in  excess. 

The  casein  of  woman's  milk  is  distinguished  from  that  of  cow's  milk  chiefly 
in  the  form  of  the  clot.  While  the  clot  of  cow's  milk  is  composed  of  dense, 
compact  masses,  in  the  coagulation  of  woman's  milk  a  very  loose  and  finely 
flocculent  precipitate  is  formed.  This  difference,  as  will  be  readily  understood, 
is  a  matter  of  great  importance  for  digestion  in  the  stomach  of  the  infant. 
Besides,  the  casein  of  woman's  milk  does  not  always  coagulate  under  the  influ- 
ence of  rennin,  and  in  its  digestion,  according  to  Kobrak,  pseudonuclein  is 
formed  in  very  much  smaller  quantities  than  in  digestion  of  cow's  milk  casein. 

Various  other  circumstances  point  to  the  conclusion  that  the  casein  of 
woman's  milk  is  a  compound  of  a  nucleo-albumin  similar  to  the  casein  of  cow's 
milk  with  a  basic  proteid  body,  probably  a  histon  or  a  protamin.  In  fact  it  is 
possible  to  prepare  from  the  casein  of  woman's  milk  a  body  which  in  its  coagu- 
lation forms  a  compact  cake  not  unlike  that  of  cow's  milk  casein  (Kobrak). 

Finally,  there  has  been  found  in  woman's  milk  a  proteid  substance,  very 
rich  in  sulphur  and  relatively  poor  in  carbon,  called  opalisin  (Wroblewsky), 
which  occurs  in  cow's  milk  only  in  very  slight  quantities. 

The  fat  of  milk  is  present  in  the  form  of  small  droplets.  For. a  long  time 
it  was  jjelieved  with  Ascherson  that  these  droplets  were  surrounded  by  a 
proteid  membrane  (haptogen  membrane).  Later  researches  seemed  to  have 
shown  that  this  is  not  true,  but  that  the  fusion  of  milk  droplets  is  prevented 
only  by  the  surface  tension  of  the  constituents  of  different  specific  gravity 
present  in  milk,  or  l)y  a  layer  of  casein  or  proteid  solution  held  about  the 
droplets  by  molecular  attraction.  But  more  recently  the  former  view  has  lieen 
taken  up  again,  and  it  is  now  stated  very  definitely  by  Voltz  that  the  milk 
droplets  possess  envelopes  of  solid  substance,  which  are  probably  true  mem- 
branes. These  envelopes  contain  both  nitrogenous  and  nonnitrogenous  com- 
pounds, as  well  as  inorganic  substances  of  which  calcium  is  the  chief.  Their 
chemical  composition  varies  greatly. 

In  woman's  milk  the  fat  droplets  are  larger  and  their  number  smaller  than 
in  cow's  milk. 

Butter,  which  is  the  fat  of  milk,  consists  mainly  of  palmitin  and  olein. 
Besides  we  find :  stearic  acid,  myristinic  acid,  small  quantities  of  butyric  acid, 
caproic  acid,  etc.,  in  the  form  of  triglycerides.     The  melting  point  of  the  fat 


702 


REPRODUCTION  AND  GROWTH 


of    woman's    milk    is    34°    C,    the   congealing    point.    20°    C,    and    its    specific 
gravity  0.966. 

The  most  important  carholiydraie  of  mill-  is  viill-  sugar  (cf.  page  81). 

Bunge  has  made  the  very  remarkable  observation  that  in  dogs  and  rabbits 
the  mineral  constituents  are  present  in  the  same  relative  proportion  as  in  the 
ash  of  newborn  animals,  while  the  percentage  composition  of  the  ash  of 
the  blood  and  blood  serum  are  quite  different  (cf.  the  following  table). 


One  Hundred  Parts 
Ash  Contain 

Suckling 
dog. 

Dog's 
milk.  ■ 

Dog's 
blood. 

Dog's 
serum. 

Young 
rabbit. 

Rabbit's 
milk. 

K^O 

NaoO 

8.5 
8.3 

35.8 
1.6 
0.34 

39.8 
7.3 

10.7 
6.1 

34.4 
1.5 
0.14 

37.5 

13.4 

3.1 

45.6 

0.9 

0.4 

9.4 

13.3 

35.6 

2.4 
53.1 
2.1 
0.5 
0.12 
5.9 
47.6 

10.8 
6.0 

35.0 
3.3 
0.23 

41.9 
4.9 

10.1 

7.9 

CaO      .           

35.7 

MgO 

PeaOs                  

3.2 

0.08 

P205  

39.9 

CI 

5.4 

This  agreement  is  wanting,  however,  when  we  compare  the  composition 
of  human  milk  with  that  of  the  ash  of  the  human  infant,  as  the  following 
summaries  of  observations  by  de  Lange,  Hugonenq  and  Soldner  will  show. 


One  Hundred  Parts 
Ash  Contain 

Infant. 

Mother's  milk, 

soldner, 
I. 

Soldner, 

n. 

Hugonenq. 

De  Lange. 

average 
composition. 

KjO 

8.9 
10.0 
33.5 

1.3 

1.0 
37.7 

8.8 

6.8 
8.3 

38.7 
0.6 
0.7 

40.2 
6.6 

6.2 
8.1 

40.5 
1.5 
0.4 

35.3 
4.3 

6.5 
8.8 

38.9 
1.4 
1.7 

37.6 
6.3 

30.1 

NaaO 

14.8 

CaO 

MgO 

15.6 

2.8 

FcaOa 

0.5 

P^Oo 

16.3 

CI 

30.1 

Bunge  refers  this  striking  difference  to  the  circumstance  that  the  com- 
position of  milk  ash  agrees  more  closely  with  that  of  the  ash  of  the  young, 
the  more  rapidly  the  animal  grows  in  weight  after  birth,  pointing  out  that 
it  is  only  Iw  means  of  such  an  agreement  that  it  would  be  possible  for  the 
rapidly  growing  animal  to  get  every  necessary  mineral  constituent  in  tlie 
proper  proportion  for  its  growth.  In  the  slowly  growing  human  infant  this 
agreement  is  not  necessary.  But  it  is  important  that  those  constituents  of 
the  ash  that  serve  to  keep  the  composition  of  the  urine  normal  should  ho 
supplied ;  hence  the  woman's  milk  is  found  to  contain  relatively  more  alkaline 
chlorides  than  the  dog  or  rabbit  milk. 

In  support  of  this  view,  Bunge  compares  the  percentage  composition  of 
milk  in  tissue-forming  substances,  proteid  and  ash  (calcium  and  phosphoric 
acid)  in  rapidly  and  slowly  growing  animals.  It  will  be  obsened  from  the 
following  table  that  these  percentages  are  much  higher  in  the  foi-mer  than  in 
the  latter. 


SECRETION  OF  MILK 


703 


Time  in  which  the  Ne 

WBORN  Off- 
Weight. 

One  Hundred  Parts  Mti^  Contain— 

SPRI.NG  Doubles  its 

Proteid. 

Ash. 

Milk. 

Phosphoric 
acid. 

IMaii 

Horse 

Cow 

180  days. 
60     " 
47     " 
22     " 
15     " 
14     " 

9     " 

6     " 

1.6 
2.0 
3.5 
3.7 
4.9 
5.2 
7.4 
10.4 

0.2 
0.4 
0.7 
0.8 
0.8 
0.8 
1.3 
2.5 

0.033 
0.124 
0.160 
0.197 
0.245 
0.249 
0.455 
0.891 

0.047 
0.131 
0.197 

Goat 

0.284 

Sheep 

Swine 

0.293 
0.308 

Dog 

Rabbit 

0.508 
0.997 

The  average  composition  of  cow's  milk,  taken  from  a  very  larsre  number 
of  analyses,  is:  87.3  per  cent  water,  12.8  per  cent  solids,  3.0  per  cent  casein, 
0.5  per  cent  albumin,  3.7  per  cent  fat,  4.9  per  cent  sugar  and  0.7  per  cent 
mineral  constituents. 

Woman's  milk  contains:  87-89  per  cent  water.  10.8-12.4  per  cent  solids, 
1-2  per  cent  proteid,  3-4  per  cent  fat,  5-8  per  cent  sugar  and  0.2-0.4  per 
cent  mineral  matter. 

In  general  woman's  milk  is  poorer  in  proteid  and  mineral  constituents  and 
richer  in  sugar  and  lecithin  than  cow's  milk.  The  absolute  quantity  of  milk 
secreted  during  the  lactation  period  increases  up  to  the  twenty-eighth  week, 
and  then  falls  off.  The  proteid  content,  however,  shows  an  almost  constant 
decrease,  as  the  following  figures  from  Soldner  will  show.  Part  of  the  data 
are  from  different  individuals. 


Time  after  Delivery 
OF  Child. 

Percentage  of  N. 

""'"^  ^7cHi?r"=""             Percentage  of  N. 

5-6  days  

8-9     "     

0.327 
0.247 
0.235 
0.278 
0.270 
0.279 

'  20-21  days 

0.218 

29-30     "■    

0.180 

9      "     

74     "     

0.153 

9  and  11     "     

113     ••    

0.152 

4,  5,  and  11      "     

229     "     

0.141 

11      "     

The  fat  content  likewise  decreases  somewhat  in  the  course  of  the  lactation 
period;  but  the  percentage  of  sugar  increases,  at  first  pretty  rapidly,  then 
more  and  more  slowly. 

According  to  Bunge  the  mineral  constituents  of  woman's  milk  have  the 
following  distribution  per  1,000  parts:  K,,0  0.703.  Xa.O  0.257,  C'aO  0.343, 
MgO  0.0G5,  Fe.Og  0.006,  P.-O,  0.469,  CI  0.445. 

The  quantity  of  milk  secreted  daily  by  both  ])reasts  of  a  nursing  mother 
mav  be  estimated  at  about  1.300  g.,  but  this  quantity  is  subject  to  great 
variations. 

B.    SECRETION   OF   MILK 

The  milk  is  secreted  Ity  tln'  mammary  glands.  Each  gland  consists  of 
15-20  lobes  grouped  about  as  many  ducts  which  open  in  the  nipple.     They 


704  REPRODUCTION   AND  GROWTH 

are  fully  formed  in  the  boy  as  well  as  in  the  girl  at  birth,  and  up  to  the  end 
of  the  second  to  eighth  week  after  birth  they  secrete  a  milky  fluid  called 
"  witch's  milk."  In  males  the  mammary  glands  as  a  rule  become  only  slightly 
developed  and  never  produce  any  secretion.  In  the  female  they  begin  at 
puberty  to  grow  and  increase  considerably  in  size  at  that  time.  But  a  really 
important  increase  takes  place  only  in  connection  with  pregnancy.  During 
the  last  few  weeks  of  gestation,  a  fluid  which  differs  considerably  in  com- 
position from  the  milk  and  is  known  as  the  colostnini,  is  given  off,  and  after 
birth  has  occurred  the  glands  enter  upon  a  period  of  vigorous  activity  which, 
with  the  child  at  the  breast,  continues  for  months.  When  the  child  is  not 
nursed  b}'  the  mother,  the  mammary  glands  atrophy  and  shrivel  up  to  a 
small  mass  of  connective  tissue. 

The  nerves  of  the  mammary  glands  end  about  the  gland  cells  as  a  net  of 
cirrous  arborizations.  In  the  human  species  they  arise  from  the  fourth  to 
sixth  intercostal  nerves. 

In  animals  the  mammary  glands  are  situated  more  distally  and  accordingly 
are  supplied  by  more  distal  nerves.  In  the  guinea  pig*,  which  has  only  a  single 
pair  of  mammary  glands,  the  nerves  come  from  the  spermatics.  The  five  pairs 
of  glands  in  the  dog  receive  their  nerves  from  this  and  several  other  nerve 
trunks. 

The  influence  of  the  nervous  system  on  the  secretion  of  milk  is  a  subject 
which  has  not  yet  been  sufficiently  investigated.  From  the  observations  of 
Goltz  and  Ewald  on  animals  with  the  lower  end  of  the  spinal  cord  exsected 
(page  583),  we  learn  that  the  mammary  glands  can  secrete  milk  independ- 
ently of  the  central  nervous  system.  But  the  milk  secreted  by  glands  whose 
nerves  have  been  sectioned  exhibits  morphological  changes  which  go  to  show 
that  the  secretion  is  influenced  in  certain  ways  by  the  nervous  system  (K. 
Basch).  Besides  in  the  a])ove  experiments  of  Goltz  and  Ewald  the  influence 
of  the  peripheral  sympathetic  ganglia  was  not  excluded. 

Concerning  the  mechanism  of  milh  secretion,  the  most  divergent  views 
have  Ijeen  expressed,  and  for  the  present  we  cannot  decide  whether  the  gland 
cells  become  disintegrated  and  contribute  their  own  substance  to  the  secretion, 
or  whether  they  prepare  the  constituents  of  the  milk  from  other  materials. 
It  seems,  however,  that  there  can  be  no  very  extensive  destruction  of  cells, 
and  the  real  question  therefore  narrows  down  to  whether  or  not  nuclei  and 
protoplasm  become  to  some  extent  transformed  into  secretion.  Most  recent 
writers  on  the  subject  think  that  this  is  the  case;  l)ut  that  only  the  free  end 
of  the  gland  cell  is  lost,  and  that  after  the  secretory  products  have  in  this 
way  been  discharged,  a  regeneration  of  the  protoplasm  from  the  basal,  nucle- 
ated end  of  the  cell  takes  place,  and  the  same  process  of  transformation, 
disintegration,  etc.,  is  repeated.  For  more  detailed  information  we  must  refer 
to  the  literature  bearing  on  the  subject.  Here  we  may  only  add  that  during 
lactation  a  varying  number  of  leucocytes  wander  out  of  the  interstitial  con- 
nective tissue  into  the  alveoli  of  the  glands.  It  is  possible  that  in  the  event 
of  arrested  lactation,  they  convey  the  fat  away  from  the  mammary  gland. 

Xoither  casein  nor  milk  sugar  is  found  in  the  blood;  hence  it  is  evident 
that  they  must  he  formed  in  the  mammary  gland  itself. 


GROWTH  OF  THE  HUMAN   BODY  705 

K.  Baseh  conceives  that  casein  is  formed  by  combination  of  a  pseudonuclein, 
which  is  set  free  from  the  nuclei  of  the  gland  cell,  with  proteid.  He  bases 
this  view  on  the  fact,  among  other  things,  that  by  the  action  of  a  xanthin-free 
and  sugar-free  nucleic  acid,  prepared  from  the  mammarj-  gland,  on  the  serum 
of  ox  blood,  he  was  able  to  get  a  substance  which  had  all  the  physical  and 
chemical  properties  of  cow's  milk  casein. 

The  percentage  of  fat  in  the  milk  can  be  raised  by  feeding  fat.  This  increase 
is  explained  in  different  ways  by  different  authors;  but  it  is  fairly  probable  that 
some  of  the  fat  of  the  food  at  least  is  carried  over  into  the  secretion.  The  fact 
that  when  iodized  swine  fat  has  been  fed,  it  can  be  demonstrated  in  the  milk 
in  fairly  large  quantities  (Winternitz)  would  favor  this  view.  When  iodine 
alone  or  potassium  iodide  is  fed  only  the  merest  traces  of  iodine  are  found  in 
the  milk  (Caspari). 

On  the  other  hand  we  have  observations  by  Henriques  and  Hansen  which 
indicate  that  the  fat  of  the  food  in  its  passage  through  the  cells  of  the  milk 
glands  suffers  changes  in  its  composition. 

Even  when  an  animal  in  lactation  receives  a  diet  which  is  poor  in  fat,  the 
milk  contains  a  considerable  quantity  of  fat.  In  this  case  the  milk  fat  must 
have  been  formed  either  from  the  carbohydrates  fed  or  from  the  large  deposits 
of  fat  in  the  body.  This  is  demonstrated  especially  by  the  appearance  of  iodized 
fat  in  the  milk  at  a  time  when  there  was  no  iodized  fat  in  the  food,  but  when 
iodized  fat  had  previously  been  stored  in  the  body  (Caspari). 

A  cow  on  a  restricted  diet  naturally  secretes  less  milk  than  on  a  full  diet; 
but  the  fat  in  her  milk  still  has  a  lower  melting  point  than  the  body's  fat.  This 
means  that  when  the  fat  deposited  in  the  body  is  called  into  requisition,  rela- 
tively more  olein  is  mobilized  than  palmatin  and  stearin  (Henriques  and 
Hansen). 

It  has  ofttimes  been  confirmed  that  both  the  quantity  of  milk  and  the  per- 
centage of  fat  secreted  increases  on  a  diet  which  is  rich  in  proteid,  and  this 
can  only  mean  that  proteid  either  directly  or  indirectly  is  a  source  of  fat. 

According  to  Thierfelder  the  sugar  of  milk  arises  from  some  mother  sub- 
stance not  yet  definitely  identified,  by  the  action  of  an  enzyme  associated  with 
the  gland  cells. 

The  following  may  be  mentioned  here  among  the  many  different  external 
agencies  which  influence  the  quantity  and  quality  of  the  milk:  (1)  Frequent 
milking  favors  the  activity  of  the  glands.  When  the  milking  is  done  at  stated 
intervals,  the  last  milk  stripped  from  the  glands  is  richest  in  fat.  This  is 
probably  due  to  the  adherence  of  many  fat  particles  to  the  walls  between  the 
folds  of  the  mucous  membrane  as  the  earlier  milk  flowed  through,  the  stripping 
process  being  necessarj-  to  dislodge  them.  (2)  Too  vigorous  exercise  diminishes 
the  quantity  of  the  milk,  probably  because  the  blood  stream  is  diverted  from 
the  glands  to  the  muscles.  On  the  other  hand,  moderate  exercise  increases  the 
secretion  of  milk  in  women,  probably  owing  to  its  favorable  effects  on  respira- 
tion, circulation,  digestion,  etc.  (H.  Munk). 


SECOXD    SECTIOX 

GROWTH   OF   THE    HUMAN    BODY 

Several  different  periods  may  be  reooenizod  in  the  life  of  an  individual 
human  being.  They  are  not  marked  off  by  sharply  defined  Ijoundaries,  so 
that  one  can  say  for  e.xample  that  on  a  certain  day  the  individual  is  a  youth 


706 


REPRODUCTIOX   AND  GROWTH 


and  the  next  day  a  man  or  woman;  but  are  recognized  by  the  characteristics 
which  phiinly  prevail,  once  they  are  fully  establi.-hed.     These  periods  are: 

(1)  Period  of  the  Newborn,  from  birth  to  the  loss  of  the  umbilical  cord, 
which  usually  takes  place  in  four  or  five  days. 

(2)  Period  of  Infancij.  up  to  the  appearance  of  the  first  teeth,  from  the 
seventh  to  the  ninth  month. 

(3)  Later  Childhood,  up  to  the  appearance  of  the  permanent  teeth  a1)out 
the  seventh  year. 

(4)  Age  of  Boyhood  and  Girlhood,  up  to  the  beginning  of  puberty,  thir- 
teenth to  fourteenth  years. 

(5)  Age  of  Youth  or  Adolescence,  up  to  the  time  of  bodily  maturity, 
nineteenth  to  twenty-first  year. 

(6)  Age  of  Maturity,  up  to  the  prime  of  life  (climacteric  in  the  woman), 
fortv-fifth  to  fiftieth  vear. 

(;)    Old  Age. 

The  first  five  periods  are  the  ones  of  particular  interest  here  because  they 
cover  almost  the  entire  period  of  growth.  The  sixth  period  is  the  age  within 
which  man  reaches  his  full  ph^'sical  and  mental  development.  During  the 
seventh  period  various  disorders,  caused  more  or  less  by  chronic  ailments  of 
one  kind  or  another,  gradually  encroach  upon  the  normal  functions,  and  the 
physical  and  mental  powers  are  on  the  wane. 

In  turning  now  to  the  subject  of  the  size  relations  of  the  body,  let  it  be 
understood  that  the  data  presented  are  average  results  and  that  many  indi- 
vidual variations  from  them  are  to  be  observed.  In  any  exhaustive  discussion 
of  the  subject  it  would  be  necessary  to  consider  these  variations  and  their 
meaning,  but  it  will  be  impossible  to  do  so  here.  The  following  is  a  concrete 
example  of  the  method  employed  in  arriving  at  average  results. 

Quetelet  and  Altherr  carried  out  a  series  of  observations  on  the  weight  of 
the  newborn  child,  and  found  the  mean  value,  irrespective  of  sex,  to  be  3,100  g. 
The  extremes  however  were  very  considerable,  for  among  the  children  weighed 
there  were  some  under  1.5  kg.,  and  some  over  4.5  kg.  In  order  to  get  a  general 
view  of  the  variations  and  thus  to  be  able  to  grasp  the  significance  of  the  mean 
value  more  correctly,  the  entire  series  of  observations  may  be  divided  into 
groups  according  to  weight :  1.0-1.5,  1.5-2.0,  etc.,  and  the  proportion  of  indi- 
vidual cases  belonging  to  each  calculated  in  percentages  of  the  entire  number. 
We  get  in  this  way  the  following  table,  the  results  of  which  might  be  made  still 
more  clear  by  a  graphic  representation  like  that  in  Fig.  302. 


Body  Weight  of  the  Kewborn 
Child,  in  Kilograms. 

Number  of  cases. 

Percentage  of  cases. 

1  0-1  5    

2 

8 
54 

180 

251 

88 

15 

1 

0.33 

1.5-2  0                      

1.34 

2.0-2.5  

9.01 

2.5-3.0 

3.0-3.5                                

30.05 
41.90 

3.5-4.0..                   

14.69 

4.0-4.5 

2.51 

4.5-5.0 

0.17 

GROWTH   OF  THE   HUMAN    BODY 


'07 


The  weight  of  the  child  at  terra  is.  on  the  average.  3,000-3,500  g.  (ex- 
tremes, 2.400-5,500).     Boys  are  usually  from  80  to  150  g.  heavier  than  girls. 

The  length  of  the  newborn  child  is.  on  the  average,  50-51  cm.  Boys  appear 
as  a  rule  to  be  1  cm.  longer  than  girls. 

The  weight  of  the  newborn  child  increases  with  the  number  of  pregnancies 
and  with  the  age  of  the  mother  up  to  her  fortieth  year,  as  the  following  com- 
pilations by  Ingerslew  will  show: 


Number  of  thk 
Pregnancy. 

Weight  of  the  child 
at  birth,  in  grams. 

Agb  op  thk  Mother. 

Weight  of  the  child 
at  birth,  in  grams. 

1 

3.254 
3.391 
3.400 
3.424 
3.500 

15-19  

3.241 

2 

20-24  

3.299 

8 

25-29  

3.342 

4  . 

30-34      

3,375 
3,428 

5 

35-39     

40-44  

3,326 

The  general  physical  condition  and  development  of  the  mother  also  have 
much  to  do  with  the  weight  of  the  child.  The  greater  the  length  of  the  mother's 
body,  and  the  better  its  nutritive  condition,  the  heavier  and  longer,  generally 
speaking,  will  be  the  weight  and  length  of  the  child  at  birth. 

During  the  first  two  days  after  birth  the  child's  body  loses  100-200  g.  in 
weight,  but  about  the  third  day  it  begins  to  grow,  and  on  the  fifth  to  seventh 
day  reaches  its  first  weight  again. 

From  this  time  on  the  growth  in  weight  is  very  rapid,  and  by  the  twenty- 
fourth  week  it  has  doubled.  At  the  end  of  the  first  year  it  is  two  and  three- 
quarter  times  what  it  was  at  birth.  The  average  monthly  increase  as  given  by 
Albrecht  for  the  first  twelve  months  is  as  follows:  900  g.,  870,  8T0,  720,  600, 
540,  420,  330,  330,  270,  240,  and  210  g. ;  within  the  entire  twelve  months, 
therefore,  a  total  of  6,300  g.  is  gained.  Hence  at  the  end  of  the  year  the 
weight  is  about  9,500  g. 

The  length  of  the  infant's  body  at  the  end  of  five  months  is  about  68  cm. 
and  at  the  end  of  the  first  year  about  77  cm.  Growth  therefore  is  more  rapid 
at  first  than  at  any  subsequent  time. 

The  food  of  the  child  may  be  set  down  as  the  most  important  factor  in 
determining  the  rate  of  growth  during  the  first  year.  So  far  as  we  are  able  to 
judge  from  published  observations  on  the  subject,  the  child  thrives  better  and 
its  weight  increases  more  rapidly  when  it  is  fed  exclusively  at  the  breast  through- 
out the  infancy  period.  This  doubtless  signifies  that  no  artificial  means  of 
nourishment  has  ever  been  found  which  makes  so  little  exactions  on  the  delicate 
digestive  apparatus  as  the  mother's  milk. 


In  three  years  the  child's  body  has  already  reached  half  the  length  it  will 
be  when  fully  grown.  During  this  period  a  boy  will  on  the  average  have 
attained  to  a  weight  of  18-21  kg.,  and  a  girl,  17-21  kg. 


708 


REPRODUCTION   AND  GROWTH 


Tlie  growth  of  the  boch^  in  length  during  the  later  years  of  childhood  will 
be  evident  from  the  following  table: 


Year  op  Age. 

Boys:  length  in  cm. 

Gir'iS :  length  in  cm. 

2 

74.2 
85.3 
91.9 
96.6 
103.2 
106.5 

77.2 

3 

83.5 

4    

.  90.0 

5 

96.1 

6 

100.6 

7 

104.9 

Obviously  it  is  much  more  difficult  to  get  an  extensive  series  of  observations 
on  the  growth  of  the  child  during  the  first  five  or  six  years  of  life  than  it  is 
later.  Within  the  years  of  seven  and  nineteen  the  material  is  much  more 
accessible  and  the  total  number  of  observations  on  the  rate  of  growth  in  length 
and  body  weight,  made  on  children  of  school  age  by  Bowditch  in  Boston,  Key 
in  Sweden,  Kotelmann  in  Hamburg,  Pagliani  in  Turin,  Roberts  in  England 
and  Porter  in  St.  Louis,  foots  up  a  total  of  more  than  125,000  individuals. 

But  we  should  not  be  warranted  in  drawing  an  average  from  all  of  this 
material  taken  together.  There  are  certain  racial  characteristics  which  would 
need  to  be  taken  into  account  in  so  doing,  and  our  purpose  here  will  be  better 
served  if  the  material  chosen  be  as  homogeneous  as  possible.  The  observations 
of  Key  in  Sweden  probably  fulfill  this  requirement  as  well  as  any.^  It  may 
be  remarked  however  that  the  conclusions  drawn  from  this  material  have 
been  fully  confirmed  in  the  gross  by  observations  in  other  countries.  Certain 
age  differences  only  are  to  be  noted. 

Fig.  304  represents,  according  to  Key,  the  mean  height  and  mean  weight 
of  male  and  female  pupils  in  the  higher  schools  of  Sweden  between  the  years 
of  seven  and  twenty-one. 

Up  to  and  including  the  eleventh  year  boys  are  both  taller  and  heavier 
than  girls.  From  the  twelfth  year  to  the  sixteenth  this  relationship  changes : 
girls  are  then  both  taller  and  heavier  on  the  average  than  boys.  With  the 
seventeenth  year  the  relationship  once  more  changes  and  the  curve  of  devel- 
opment for  boys  rises  above  that  for  girls  and  the  difference  becomes  greater 
and  greater  thereafter  until  complete  maturity. 

The  yearly  increase  in  height  and  weight  in  hoys  for  the  seventh  year  is 
5  cm.  and  2.3  kg.,  and  for  the  eighth  year,  5  cm.  and  3.4  kg.  For  the  ninth 
to  the  thirteenth  year  the  growth  in  height  by  years  is  4,  2,  3,  4,  4  cm.,  and 
the  growth  in  weight  by  years  is  1.7,  1.0,  1.9,  2.3,  3.1  kg.  The  growth  in 
boys  is  at  its  feeblest  during  the  twelfth  and  thirteenth  years.  With  the 
fourteenth  year  the  period  of  puberty  is  reached  and  the  growth  both  in 
height  and  weight  becomes  much  more  rapid,  the  increase  in  the  former 
for  the  fourteenth,  fifteenth,  sixteenth  and  seventeenth  years  being  5,  7,  6, 
5  cm.,  and  the  increase  in  the  latter  being  4.7,  4.5,  5.5,  5.3  kg.  respectively. 
The  most  rapid  growth  in  height  takes  place  earlier  (fifteenth  and  sixteenth 

'  Certainly  much  better  than  would  observations  made  in  any  of  the  larger  cities  of 
the  United  States. — Ed. 


GROWTH  OF  THE   HUMAN   BODY 


709 


years)  than  the  greatest  growth  in  weight  (sixteenth  and  seventeenth  years). 
Since  increase  in  weight  is  of  greater  significance  than  increase  in  height, 
the  sixteenth  and  seventeenth  years  may  be  regarded  as  the  years  of  most 
rapid  physical  development  (cf.  page  14-i). 

After  the  seventeenth  year  the  yearly  rate  of  growth  in  height  and  weight 
is  less,  but  the  increase  continues  until  about  the  twenty-first  year,  when  the 


Age 

yrs. 

7 

8 

F 

to 

n 

12 

13 

th 

15 

16 

17 

18 

19 

ZO 

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Kn 

Crrv 

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IlnVS 

_- 

90 

m 

Le 

A 

Ciii,- 

^ 

^ 

f-i 

mo 

Boya 

/ 

^ 

^, 

M 

i.i'i 

W 

isht. 

Girls 

// 

?"> 

iw 

// 

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7(7 

7V'; 

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fW 

/; 

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pn 

711 

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20 

31 

8? 

109 

77 
121 

693 

1236 

173? 

2096 

Z076 

Ig'rS 

1608 

1127 

893 

623 

626 

i.  S 

6 

21 

60 

151 

277 

357 

395 

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293 

18t 

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26 

18 

Fig.  304. — Curves  representing  the  height  and  weight  of  boys  and  girls  of  different  age,  after  Key. 

youth  reaches  his  full  physical  stature.  The  height  at  this  time  is  on  the  aver- 
age 172  cm.  and  the  body  weight  (55.2  kg.  The  man  continues  to  grow, 
though  very  slowly,  for  several  years  more. 

The  physical  development  of  girls  runs  quite  a  different  course.  The 
period  of  feeble  growth,  which  is  so  sharph-  marked  for  boys  just  previous 
to  puberty,  comes  earliei'  for  girls,  namely,  so  far  as  concerns  height,  in  the 
ninth  year.  The  yearly  increase  in  height  of  girls  from  the  ninth  to  the  seven- 
teenth year  is  7,  4,  5,  5,  6,  5,  4,  2,  1  cm.  The  increase  in  weight  for  the 
same  years  is  3.4,  1.9,  2.5,  2.5,  4.0.  3.7,  5.2,  4.1,  2.7,  3.0  kg.  respectively. 
We  see  that  there  is  a  period  in  the  development  of  girls  also,  from  the  ninth 
to  tlio  eleventh  3'ears  inclusive,  when  the  rate  of  growth  in  weight  is  relatively 
slow.  The  true  puberty  period,  which  is  characterized  by  a  rapid  growth  in 
weight,  begins  in  the  twelfth  year  and  lasts  until  the  fifteenth  year  (inclusive;. 

Witli  girls  the  growth  in  height  continues  until  only  about  the  sevt^nteenth 
year,  while  the  increase  in  weight  can  be  demonstrated  up  to  the  twentieth 
year. 


710 


REPRODUCTION  AND  GROWTH 


From  these  and  many  other  observations  it  follows  that  the  physical  devel- 
opment of  girls  is  run  through  in  less  time  than  that  of  boys  and  that  it 
terminates  more  abruptly. 

Hand  in  hand  with  the  more  rapid  development  in  height  and  weight  dur- 
ing the  puberty  period,  there  goes  also  a  correspondingly  stronger  development 
of  the  chest,  as  contrasted  with  the  development  during  the  years  just  preceding- 
puberty.  The  mean  increase  in  the  chest  measurement  at  the  position  of  deepest 
inspiration,  in  boys  from  ten  to  seventeen  years  of  age,  is  given  by  Kotelmann 
(for  Hamburg)  as  follows:  1.G8  cm.,  1.97,  1.82,  0.99,  3.78,  3.47,  4.02,  2.44  cm. 
respectively. 

According  to  Key's  observations,  the  resistance  of  the  body  to  harmful  influ- 
ences during  the  years  just  previous  to  puberty  is  relatively  weak.  But  in  the 
course  of  the  puberty  period,  when  the  youthful  life  asserts  itself  in  all  its  vigor. 


% 

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6 

7 
G 

^ 

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5 

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H 

f 

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^^ 

/ 

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3 

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3 

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s. 

Z 

1 

y 

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1,50     i 

<♦        6        8      1,60      it       <<        6        8      1,70     Z       h       f,        d      1,80     2.       "t        6       8      190      1 

1 

Fig.  30.5. — Variations  in  the  height  of  military  recruits  in  Sweden,  after  Hultkranz.  The  ordi- 
nates  represent  the  percentage  of  the  whole  number  (232,367)  of  individuals  who  were  of  the 
height  (in  meters)  represented  by  the  abscissae. 


the  resistance  of  the  body  increases,  the  percentage  of  sickness  in  the  schools 
declines  and  reaches  its  minimum  in  the  last  year  of  this  period  (seventeen). 

The  economic  circumstances  in  which  the  children  live  exercises  a  very  con- 
siderable influence  on  their  physical  development.  The  children  of  the  poorer 
classes  fall  behind  their  companions  of  the  same  age  from  the  homes  of  the 
well-to-do,  both  in  height  and  weight.  The  period  of  feeble  development  just 
before  puberty  is  longer  for  the  poorer  children.  But  once  puberty  begins,  the 
period  of  rapid  growth  seems  to  proceed  all  the  more  rapidly  in  spite  of  its 
delay,  and  to  terminate  in  the  same  year  as  for  children  of  the  well-to-do.  The 
whole  period  is  therefore  shorter  for  poor  children,  but  is  characterized  by  an 
even  more  active  development  during  its  last  years  (Key). 

Malling-Hansen  has  shown  by  a  very  extensive  series  of  observations  in  Den- 
mark that  there  is  a  seasonal  variation  in  the  rate  of  growth  in  children.  From 
the  end  of  November  or  the  beginning  of  December  to  the  end  of  March  or  the 
middle  of  April  children  grow  very  feebly — so  much  so  that  the  increase  in 
height  is  less  than  usual,  however  slow  that  may  be.  After  this  period  of  feeble 
growth  follows  a  period  during  which  growth  in  height  is  very  active,  but  the 
increase  in  weight  is  reduced  to  a  minimum.  Indeed,  children  even  lose  in 
weight  during  this  period  of  most  active  growth  in  height,  almost  as  much  as 
they  have  gained  in  the  preceding  period.    This  period  lasts  from  March  or  April 


GROWTH  OF  THE  HUMAN   BODY  711 

to  July  or  August.  Then  follows  a  third  period  which  continues  until  Novem- 
ber or  December.  The  increase  in  height  is  now  very  feeble,  but  the  increase 
in  weight  rises  rapidly  and  becomes  considerable. 

The  weight  of  the  adult  body  varies  greatly,  but  may  be  estimated  at 
65-70  kg.  for  men  and  56-60  kg.  for  women.  At  a  mature  age  the  weight 
in  Ijoth  sexes  as  a  rule  becomes  greater  by  the  deposit  of  fat. 

The  height  of  men  of  different  nationalities  is  somewhat  variable,  as  the 
following  table  compiled  from  average  measurements  of  military  recruits  at 
the  age  of  twenty  to  twenty-one  years  in  the  different  countries  will  show : 

Laplander 150.0             cm. 

Hungarian 16o.3  " 

Bavarian 163.8  " 

Russian 164.2  " 

French 164.9 

Italian  (from  different  provinces) 156.0-166.5    " 

Finlander  (from  different  provinces) 165.!)-169.9    " 

English  and  Irish 169.0 

Silesian 169.2  " 

Dane 169.2 

Norwegian 109.6  169.8  " 

Scot 170.8 

United  States 173.3  " 

A'ariations  within  the  same  nationality  are  considerable,  as  may  be  seen 
from  Fig.  305.  This  represents,  according  to  Ilultkranz.  the  height  of 
Swedes  as  determined  by  measurements  of  232,367  military  recruits  made 
between  1887  and  1894.^ 

We  have  no  measui'ements  similar  to  these  for  women  but  from  observa- 
tions which  have  been  made,  we  may  say  that,  on  the  average,  a  grown  woman 
is  about  12  cm.  shorter  than  a  grown  man. 

Eefeukncks. — Beyer,  Proceedings  of  the  United  States  Naval  Institute,  xxi, 
lS95.—Daffner,  "Das  Wachstum  des  Menschen,"  Leipzic,  lS97.—Ex-ner,  "Physi- 
ologic der  Miinnlichen  Geschlechtsfunktionen,"  in  the  "  Ilandbuch  der  Urologie," 
Wien,  1003. — Keii,  Yerliandlungen  des  X.  internationalen  medizinischen  Kon- 
gresses,  vol.  i,  Berlin.  ISOO.^IV.  Nagel,  "  Die  Weiblichen  Geschlechtsorgane." 
in  V.  Bardetehen^s  Handhuch  der  Anatomie  des  Menschen,  vii,  2,  1.  Jena.  1896. 
— W.  T.  Porter,  Transactions,  Academy  of  Science,  St.  Louis.  1893-1894. — 
Yierordt,  "  Die  Physiologic  des  Kindesalters,"  in  "  Gerhardt's  Ilandbuch  der 
Kinderkrankheiten,"  i.  Tubingen,  1881.—^.  B.  Wilson,  "  The  Cell  in  Develop- 
ment and  Inheritance,"  second  edition,  Xew  York,  1900. 


INDEX 


Abdominal  pressure,  299,  699. 

Abdominal  t\-pe  of  respiration,  317,  318,  Fig. 

126,  A. 
Abdominal  viscera,  vasomotor  nerves  of,  233, 

235. 
Abducens  nerve,  680. 
Aberration,  chromatic,  526,  Fig.  221. 

spherical,  223,  522,  Fig.  218. 
Absorption,  31,  35,  301. 
from  serous  cavities,  353. 
influence  of  stimulants  on,  302. 
of  carbohydrates,  303. 
of  fats,  304. 
of  gases,  by  liquids,  334. 

by  naked  cells,  31. 
of  iron,  307,  Fig.  119;  308. 
of  mineral  substances,  308. 
of  proteid,  305. 
of  water,  302. 

relative  power  of,  in  different  divisions  of  the 
alimentary  canal,  302. 
Accelerator  nerves  of  heart,  191,  688. 
Acces.sory  sexual  gland.s,  691,  692. 
Accommodation  in  vision,  529. 
center  for,  535,  Fig.  230. 
mechanism  of,  530  seq. 

protrusion  of  iris,  531,  Fig.  226. 
reflected  images,  531,  Fig.  225. 
structure  of  ciliary  muscle,  532,  Fig.  227. 
theory  of  Helmholtz,  533. 
theorj'  of  Schon,  534,  Fig.  229. 
zonule  of  Zinn,  533,  Fig.  228. 
range  of,  529,  530. 
Acerebral  rigidity,  616. 
Acetic  acid,  384. 
Aceto-acetic  acid,  376. 
Acetone  bodies,  376,  384. 
Achroodextrin,  246. 
Acids  as  excitants  of  pancreatic  secretion,  269, 

270. 
Acid  albumin,  292. 
.\cid  albuminate,  74,  249. 
Acid  equivalent  of  fats,  79. 
Acid  of  gastric  juice,  247. 
Acid  sulphur,  373. 
Acid  taste,  484. 
Actinia,  56. 


Action  currents,  defined,  48. 

in  glands,  48. 

in  heart,  13,  Fig.  13;  179,    Fig.  63;  180,  Fig. 
64. 

in  muscle  and  nerve,  48,  410,  431. 

in  plants,  49,  50. 
Activation  of  oxygen,  19,  note. 

of  zymogen,  38. 
Active  movements,  perception  of,  471. 
Adamkiewicz's  reaction  for  proteid,  73. 
Adaptation  of  eye  to  different  lights,  540. 
Adelomorphous  secreting  cells,  266. 
Adenin,  76,  372. 
Adolescence,  period  of,  706. 
Adrenal  bodies,  internal  secretion  of,  364  seq. 
Adrenalin,  366. 

.■\.fferent  and  efferent  nerves,  564,  565. 
Afferent  and  efferent  pathways  in  cord,  591, 

592,  593,  595,  596. 
Afterbirth,  699. 

Afterbrain  or  myelencephalon,  600,  602. 
.A.fter  extension  of  muscle,  412. 
After-image,  negative,  539. 

positive,  538. 
After-loading  of  muscle,  435. 
After  shortening  of  muscle,  412. 
Age,  changes  due  to,  66. 

influence  of,  on  metabolism,  120. 

influence  of,  on  rate  of  heart  beat,  197. 
Agglutination,  149,  156. 
Agraphia,  musical,  665. 
.\ir,  alveolar,  exchange  of,  with  blood,  340. 

atmospheric,  composition  of,  334,  342. 

changes  produced  in,  by  respiration,  342. 

complemental,  residual,  etc.,  320. 

exchange  of,  in  lungs,  319. 

expired,  342. 

explanation  of  evil  effects  of,  345. 
poisonous  ga-ses  in,  344. 
Air    pressure,     influence    of,    on    number    of 

corpuscles,  149. 
Air  pump,  334. 

Air  space,  noxious,  in  lungs,  320. 
.\ir-transmission,  method  of  recording  by,  11. 
.AJanin,  70,  373. 
.■Vlbuminates,  74. 

.\lbumins,  properties  of,  73.  ' 

713 


•14 


INDEX 


Albuminous  glands,  261. 
Albumoid,  78. 
Albumoses,  74,  249. 

food  value  of,  108. 

influence  of,  on  coagulation,  159. 

poisonous  effects  of,  250. 

primary'  and  secondary,  formed  in  digestion, 
249. 
Alcohol,  food  value  of,  110. 

formed  in  body,  376. 
Alcoholic  fermentation,  28,  40,  SO. 
Alcoholism,  30. 
Aldehyde,  glycerin,  373. 
Alexia,  or  word  blindness,  663,  669. 
Algae  at  high  temperature,  29. 
Alimentary  canal,  digestion  in  different  divi- 
sions of,  290. 

movements  of,  278. 
Alimentary-  glycosuria,  127,  363,  374. 
Alkali  albuminates,  74. 
-ykaline  taste,  484. 
"All  or  none"  law,  183. 
Allantoln,  373,  382. 

AUoxuric  bases,  76;  see  also  Pyrin  bases. 
Alveoli,  exchange  of  gases  in,  340. 

partial  pressure  of  gases  in,  341. 
Amacrine  cells,  515,  Fig.  211. 
Amhlystoma,  59,  60. 

.Amino  acids,  part  played  by,  in  synthesis  of 
proteid,  23. 

as  products  of  digestion,  249,  255. 

as  a  source  of  urea,  370. 
Amino-acetic  acid,  70. 
Amino-butyric  acid,  70,  72. 
Amino-caproic  acid,  70. 
Amino-ethyl-sulphonic  acid,  253. 
Amino-propionic  acid,  70. 
Amino-pyro-tartaric  acid,  70. 
Amino-succinic  acid,  70,  110. 
Amino-valerianic  acid,  70,  72,  249. 
Ammonia,  formation  of,  in  body,  370. 

in  expired  air,  345. 

in  urine,  372,  382. 
Ammonium  carbamate,  370. 
Ammonium  carbonate,  370. 
Ammonium  isocyanate,  381. 
Ammonium  lactate,  371. 
Amnestic  aphasia,  662. 
Amaba,  ingestion  of  food  bj-,  36. 

movements  of,  42. 

under  low  temperature,  29. 

protoplasmic  currents  in,  43,  Fig.  26. 

successive  phases  in  life  of,  36,  Fig.  21. 
Amceba  polypodia,  35,  Fig.  20. 
Amphibolous  biliarj'^  fistula,  243. 
AmphioxuK,  functions  of  "brain  of,"  618. 
Ampulla  of  semicircular  canal,  474. 
Amusia,  665. 
Amylolytic  enzyme,  243. 


Amylolytic  enzyme,  in  the  bile,  254. 

in  the  pancreatic  juice,  251. 

in  the  saliva,  246. 
Anaemia,  effect  of,  on  fatigue,  445. 

of  brain  in  sleep,  677. 

on  power  of  localization,  464. 
Anaerobic  bacteria,  28. 
Anaesthesia,  360,  597. 

Anag\'rin,  producing  vasoconstriction,  583. 
Analysis  of  sound,  493. 
Anatomy,  comparative,  2. 
Anelectrotonus,  425,  Fig.  162. 
Angle  a,  525. 
Angle  of  incidence,  509,  Fig.  206. 

of  refraction,  509,  Fig.  206. 

visual,  518. 
Angular  convolution,  639,  Fig.  289. 
Animal  diet,  145. 
Animal  gum,  82. 
Animal  heat,  relation  of  muscular  activity  to, 

116;  see  also  Heat  production. 
Anisotonic  solutions,  32. 
Anode,  reduction  of  excitability  by,  425. 

stimulating  effect  of,  59,  424. 
Answering  organ,  defined,  411. 
Aaitagonistic  muscles,  inhibition  of,  by  stimu- 
lation of  cortex,  636,  640. 
Anteyinularia  antenina,  64,  Fig.  37. 
.\nterior  coliunns  of  spinal  cord,  562,  Fig.  254. 
Anterior  horn  of  spinal  cord,  563. 
Anterior  roots  of  spinal  cord,  563,  566,  593. 
Antero-lateral  columns    of    spinal    cord,    595. 
Anthrax  bacillus,  ingestion  of,  37,  Fig.  22. 
Anthrax  spores,  survival  of,  at  low  tempera- 
ture, 29. 
Antibodies,  156. 
Antienzymes  in  blood,  155. 

in  organs,  269. 
Antih-tic  effect  in  blood,    157. 
Antiperistalsis,  289,  Fig.  117. 
Antiprecipitating  effect  in  blood,  157. 
Antiseptic  methods,  5. 
Antitoxin  in  blood,  156. 
Antrum  pylori,  283. 

Anus,  innervation  of  sphincters  of,  299. 
An\-il  of  oar,  495,  Fig.  197;  496,  Fig.  198. 
Aorta,  162. 

blood  pressure  curve  in,   170,  Fig.   57;  171, 
Fig.  58. 

cubic  enlargement  of,  201. 
Apex  beat,  172  serj. 

curve  of,  in  horse,  173,  Fig.  60. 

schema  illustrating  Lud wig's  theory  of,  172, 
Fig.  59. 

time  relations  of,  in  man,  175,  Fig.  62. 
Aphasia,  663. 

alexia  (word  blindness),  633,  669. 

amnestic,  662. 
motor,  663. 


LXDEX 


"15 


Apliasia,  senson,-,  664. 

vocal  motor,  665. 
Apbjfda,  35. 
Apnoea,  332 

true  and  fal.-*e,  333. 
Apparatus  figured 
Circulation: 

capillary  pressure,  221,  Fig.  91. 
cardiograph,  174,  Fig.  61. 
li;emodroniograph,  209,  Fig.  81. 
heart  .sound,  168,  Fig.  5.5. 
manometer,  ela,sticor  membrane,  9,  Fig.  5. 
manometer,  mercur\',  8,  Fig.  3. 
plethysmograph,  211,  Fig.  83. 
sphygmograph,  21.5,  Fig.  87. 
sphygmomanometer  of  Erlanger,  203,  Fig. 

76. 
.stromuhr,  209,  Fig.  80. 
General  methods: 

electric  signal,  10,  Fig.  7. 
kymograpli,  6,  Fig.  1 ;  9,  Fig.  6. 
recording  tambour  of  Marey,  11,  Fig.  9. 
Mu.scle  anil  nerve  physiology: 

capillary  electrometer,  13,  Fig.  12. 
elasticity  apparatus,  412,  Fig.  151. 
ergograph,  444,  Fig.  179. 
induction  coil,  420,  Fig.  158. 
muscle  lever,  6,  Fig.  1. 
nonpolarizable  electrodes,  419,  Fig.  157. 
rlieocord,  418,  Fig.  1.56. 
rheotomc,  4.32,  Fig.  169. 
tension  recorder,  414,  Fig.  153. 
Wagner  hammer,  421,  Fig.  159. 
Metabolism: 

face  mask,  85,  Fig.  .39. 
respiration    calorimeter    of    At  water    and 
Benedict,  schenaa,  86,  Fig.  40. 
of  Sond.'-n  and  Tigerstedt,  88,   Fig.  42. 
of  Voit  and  Pettenkoffer,  87,  Fig.  41. 
Respiration: 

air-pump  of  Ludwig,  .334,  Fig.  130. 
illustrating  experiment  with  rabbit's  lungs, 

311,  Fig.  120. 
hmg     catheter,     Ludwig's     construction, 

.341,  V\g.  133. 
registering    volume    of    expired    air,    313, 

Fig.  122. 
spirometer,  320,  Fig.  128. 
Special  senses: 

black  and  white  discs,  .539,  Fig.  233. 
entoptic  phenomena,  .521,  Fig.  216. 
olfactometer  of  Zwaardemaker,  487,  Fig. 

192. 
resonator  of  Helmholtz,  493,   Fig.   195. 
siren  of  Secbeck,  490,  Fig.  193. 
stereoscope  of  Brew.ster,  5.58,  Fig.  2.51. 
Appetite,   importance  of,   in  indigestion,   263, 

264,  290. 
Aqueduct  of  Sylvius,  614. 
42 


Aqueous  humor,  508,  509. 

refractive  index  of,  512. 
Arabino.se,  81. 
Arcellse,  motility,  45. 
Arcnicola  cristata,  effects  of  salt.s  on  larvae  of, 

25. 
Arginin,  70,  255. 
Argon  in  blood,  335. 
Aromatic  oxyacids,  378. 
Arterial  blood,  ga.ses  in,  339. 

tension  of  carbon  dioxide  and   oxygen   in, 
341. 
Arterial  pulse,  212;  see  also  Pulse. 
Arteries,  161. 

blood  pressure  in,  204. 

coronary,  180. 

cubic  enlargement  of,  201,  Fig.  75. 

elasticity  of,  200,  201. 

flow  of  blood  in,  200. 

innervation  of,  231,  234. 

movements  of  blood  in,  218. 

resistance  in,  205. 

resistance  of,  to  rupture,  201,  202. 

velocity  of  blood  flow  in,  209. 
Arterin,  1.50. 

Ascaris,  anaerobic  mode  of  life  of,  27. 
Ash  constituents,  see  Mineral  substances  and 
Inorganic  substances. 

ab.sorption  of,  307. 

in  blood,  1 54. 

in  food,  83. 

in  milk,  702. 

in  urine,  384. 
Asparagin,  food  value  of,  110. 
Aspartic  acid,  70,  72,  249,  370. 
Asphyxiation,  333,  396,  .580. 

resistance  of  different   nerve  cells   to,   573, 
Fig.  257. 
Aspiration  of  thorax,  310,  311;  see  also  Suc- 
tion in  thoracic  cavity. 

effect  of,  on  veins,  223. 
Assimilation,  22,  26. 
Assimilative  proce.s.ses  induced  by  stimulation, 

62. 
As.sociation  centers  of  Flechsig,  66-5  seq. 

anterior,  668. 

cooperation  of,  with  sen.sory  areas,  670. 

mechanics  of,  670-673. 

middle,  668. 

po.sterior,  669. 

seat  of  organized  memory  in,  671. 
A.ssociation  fibers,  663,  664,  668. 
As.sociation  pathways,  664,  670. 
Astasia,  607. 
Asterinn,  56. 
.Vsthenia,  607. 
Astigmatism,  .522,  .524,  Fig.  219. 

correction  of,  525. 
Ata.xia,  472. 


716 


INDEX 


Ataxia,  cerebellar,  611. 

Atmospheric  air,  334;  see  also  Air. 

Atonia,  607. 

Atrio-ventricular  valves,  165,  166,  Fig.  .54. 

Atrophy,  448. 

Atropine,  formation  of  urine  and,  389. 

secretion  of  saliva  and,  258. 
Auditorj'  area  of  cortex,  654,  Fig.  20.3. 
Auditory  meatus,  external,  494,  Pig.  196. 
Auditorj'  nerve,  681. 

excitation  of,  498  seq. 
Auditory  ossicles,  495. 
Auditory  sensations,  489. 
Auerbach's  plexus,  284,  Fig.  114;  288,  687. 
Augmentation  of  reflexes,  579. 
Atirelia,  osnaotic  relations  in,  34. 
.Auricle,  161;  see  also  Heart. 

in  cardiogram,  173,  Fig.  60. 

maximum  pressure  in,  169. 

negative  pressure  in,  177. 

time  relations  in,  173,  Fig.  60. 
Autochthonous  fibers,  575. 
Autointoxication,  295. 
Autolytic  processes,  38. 
Automatic  excitation,  52,  356,  570,  580. 
Automatism  of  the  heart,  185,  186. 
Autonomic  nervous  system,  686. 
Auxotonic  contraction,  435,  436. 
Aviditj'  of  two  acids  for  a  base,  338. 
Axis  cylinder  processes,  5.59. 
Axis   of   rotation  of   the    eye,   549;    550,  Fig. 

240. 
Axis,  visual  or  optical,  513,  Fig.  210;  525. 
Axon  reflex,  584,  Fig.  258. 
Axons,  559. 
Azobacteria,  24. 

Bacillum  volutans,  55. 
Bacillus  typho.sus,  156. 
Bacteria,  anaerobic,  28. 

decomposition  of  proteids  by,  250. 

in  the  blood,  1.55,  156. 

in  the  intestine,  295,  297. 

in  the  respiratory  passages,  323. 

in  the  stomach,  247,  note;  291. 

production  of  light  bj',  45. 
Bacterium  'photomctricum,  57,  Fig.  33. 
Bacterium  phosphorescens,  29. 
Basal  ganglia  of  the  brain,  632. 
Basilar    membrane,  organ  of  Corti,  499;  500, 

Fig.  199. 
Bathmotropic  effect  of  vagus,  189. 
Beats  in  musical  sound,  501. 
Becquerel  rays,  58. 
Bell's  doctrine,  .566. 
Benzoic  acid,  378. 
Benzoyl-glycocoll,  378,  383. 
Bilateral     movements     from     stimulation     of 
cortex.  r>4n. 


Bile,  253. 

absorption  of,  from  intestine,  273. 

antiseptic  properties  of,  298. 

circulation  of,  273. 

composition  of,  254. 

digestion  after  exclusion  of,  296. 

discharge  of,  into  intestine,  275,  Fig.  110. 

enzymes  in,  254. 

excretory  products  in,  254. 

influence  of,  on  amylolj'tic  digestion,  251. 

influence  of,  on  tryptic  digestion,  294. 

reabsorption  of,  from  lymphatics,  275. 

secretion  of,  272. 

dependence  of,  on  blood  sujDply,  273. 
specific  excitants  of,  275. 

solubility  of  fatty  acids  in,  254,  296. 
Bile  acids,  253,  384. 
Bile  pigments,  253. 

in  urine,  384. 
Bile  salts,  253,  254. 
Biliary  ducts,  275. 
Biliarv^  fistula,  243,  298. 
Biliprasin,  253. 
Bilirubin,  253. 
Biliverdin,  253. 
Biliverdinic  acid,  254. 

Binocular  field  of  vision,  551 ;  652,  Fig.  242. 
Birds,  extirpation  of  cerebrum  in,  622. 

extirpation  of  liver  in,  371. 
Birth,  697. 
Bitter  taste,  484. 
Biuret  reaction,  73. 
Bladder,  gall,  275. 

urinary,  391. 
Blind  .spot,  516. 
Blood,  147. 

amount  of,  in  body,  148. 

amount  of,  supplied  to  different  organs,  240. 

antitoxins  in,  156. 

bacteriocidal  action  of,  15(3. 

coagulation  of,  147,  154,  157. 

constituents  of,  147. 

constitution  of,  variable  according  to  organ, 
157. 

corpuscles  of,  red,  148,  150. 
white,  1.53. 

cytolytic  action,  156. 

distribution  of,  in  body,  239. 

effect  of  condition  of,  on  respiratory  center, 
331. 

enzymes  in,  1.5.5. 

gases  in,  335. 

general  survey  of  movements  of,  161. 

menstrual,  696. 

precipitins  in,  1.56. 

quantitative  composition  of,  1.54. 

quantity  of,  supplied  to  different  organs,  240. 

reaction  of,  147. 

in  urine,  384. 


INDEX 


717 


Blood,  viscosity  of,  222. 
Blood  corpuscles,  red,  148,  150. 
clieinical  composition  of,  150,  1.52. 
destruction  of,  150,  368. 
dry  substance  in,  149. 
formation  of,  1.50. 
ga.ses  in,  336,  338. 
haenaoglobin  content  in,  152. 
movements  of,  in  capillaries,  221, 
nuclei  of,  17. 
number  of,  149. 

percentage  of,  in  whole  blood,  149. 
permeability  of,  33. 
specific  gravity  of,  149. 
stroma  of,  150. 
Blood  corpuscles,  white,   153;  see  also  Lciico- 

ct/tcs. 
Blood  crystals,  150,  Fig.  46;  153,  Fig.  49. 
Blood  flow  in  arteries,  200,  218. 
in  capillaries,  219. 
in  veins,  223. 
muscular  work  and,  449. 
through  coronarj'  vessels,  180. 
through  heart,  165. 
velocitj'  of,  in  arteries,  209. 

in  diastole  and  .systole,  210. 
variations  of,  in  man,  212. 
in  capillaries,  221. 
in  veins,  224. 
Blood  gases,  333. 

distribution     of,     between     corpuscles    and 

pla.sma,  340. 
methods  of  determining,  335,  341. 
quantity  of,  339. 
tension  of,  341. 
Bloodletting,  208. 

Blood    pigment.s,    150,    1.52;    see    al.so    Htemo- 
glnbin . 
in  urine,  384. 
Blood  plasma,  154. 
Blood  platelets,  153. 
Blood  pressure,  202. 

comparative,    in   arteries  of  different   sizes, 

208. 
curves  of,  8,  Fig.  4;  205,  Fig.  77;  206,  Fig.  78; 
207,  Fig.  79. 
in  left  ventricle  and  aorta,   171,   Fig.  5S. 
intracardial,  169,  Fig.  .56. 

compared  with  apex  beat,  173,  Fig.  60. 
effect  of  adrenalin  on,  366. 
effect  of,  on  heart,  171. 
effect  of  vagus  stimulation  on,  205,  Fig.  77; 

206,  Fig.  78;  207,  Fig.  79. 
factors  determining,  204,  205,  206. 
fall  in,  206,  Fig.  78. 
heart  freipiency  and,  205. 
height  of,  204. 
in  arteries,  204,  208. 
m  capillaries.  219,  221,  Fig.  91. 


Blood  pressure  in  muscular  work,  449. 
in  pulmonary  vessels,  228,  229. 
in  veins,  223. 
ma.ximum  systolic,  204. 
minimum  diastolic,  204. 
refle.x  fall  in,  237,  Fig.  98. 
reflex  rise  in,  236,  Fig.  97. 
regulation  of,  194,  219. 
regulation     of     respiratory     variations     in, 

230. 
respiratory  variations  in,  22<). 
Blood  serum,  1.54,  155. 

agglutination  of  Bacillus  typhosus  by,  156. 
Blood  supply  to  brain,  676. 
to  different  organs,  240. 
to  heart,  180. 
Blood  volume,  influence  of,  on  blood  pressure, 

206. 
Bodily  movements,  see  Muscular  work. 
influence  of,  on  blood  pressure,  449. 
on  metabolism,  108,  110,  123. 
on  pulse  rate,  197. 
on  respiration,  318. 
on  storage  of  proteid,  63. 
Body,  human,  chemical  constituents  of,  68. 
di.stribution  of  blood  in,  239. 
growth  of,  705. 
influence  of  attitude  of,    on  blood  flow,  226, 

227. 
height  of  adult,  711. 
weight  of,  96,  711. 

temperature  of,  398;  see  also  Temperature  of 
body. 
Bones,  destruction  of,  in  starvation,  98. 

conduction  of  sound  through,  494. 
Bony  fish,  extirpation  of  cerebrum  in,  619. 
Boyhood,  age  of,  706. 
Boys,  growth  of,  708,  709,  Fig.  304. 

nutritive  requirements  for,  144. 
Bowman's  capsule,  385,  Fig.  144;  386. 
Brain,  as  organ  of  the  mind,  629,  670. 
blood  supply  to,  676. 
divisions  of,  600,  Fig.  267. 
fatigue  and  recoverj'  in,  676,  677. 
influence  of  anterior  parts  of,  on  respiration, 
329. 
Brain  of  Amphioxus,  618. 

of  bony  fish   (Squalius  ccphaluf),   618,   Fig. 

274. 
of  dog,  624,    Fig.   280;   625,   Fig.   281 :   632, 

Fig.  282. 
of  dog  shark  (Scyllium  caniculci),  619,   Fig. 

275. 
of  lizard  (Hatteria  punctata),   621,  Fig.  277. 
of  pigeon,  622,  Fig.  278. 
of  rabbit,  623,  Fig.  279. 
principles  of  interpreting  results  in  study  of, 

601. 
temperature  of,  678. 


718 


INDEX 


Brain-stem,  functions  of,  as  a  wliole,  618  seq. 

methods  of  study  of,  599. 

physiology  of,  599. 
Breath  volume,  319. 
Brightness,  highest  in  spectrum,  541. 
Broca's  area,  631,  662,  Fig.  296. 
Broca's  convolution,  664. 
Bronchial  muscles,  324. 
Bronchial  sound,  322. 
Brunner,  glands  of,  255. 
Burdach's  column,  591,  Fig.  264;  592. 
Butter,  701. 
Butyric  acid,  701. 

C:X  ratio  in  fsece-s,  90. 

in  proteid,  92. 

in  urine,  90. 
Cadaverin,  249. 
Cacum,  289,  298. 

Calcarine  fissure,  639,  Fig.  290;  657. 
Calcium,  absorption  and  excretion  of,  133. 

effect  of,  on  heart,  25. 

in  coagulation,  158. 

on  muscular  movements  of  larvae,  25. 
on  skeletal  muscles,  25. 
on  smooth  muscles,  25. 

hunger,  98. 

importance  of,  in  plant,  24. 

in  milk  of  cow,  351;  see  also  Milk,  composi- 
tion of. 

rennin  and,  250. 

salts   of,  certain   ones   favorable   for   higher 
animals,  poisonous  for  unicellular,  26. 
Calcium  chloride,  25. 
Calcium  oxalate  formed  in  cells,  41. 
Calorie,  definition  of,  26,  note. 
Calorimetry,  direct  and  indirect,  94. 
Cane  sugar,  81,  126,  127,  251,  255. 
Capillaries,  blood  flow  in,  219. 

blood  pressure  in,  221. 

contractility  of,  220,  Fig.  89. 

lymph  formation  from,  .350  seq. 

nerves  for,  221. 

stimulated  and  not  stimulated,  220,  Fig.  90. 

structure  of,  220. 

velocity  of  blood  flow  in,  221. 
Capillary  electrometer,  13,  Fig.  12. 
Caproic  acid,  701. 
Capsule,  internal,  647,  Fig.  292. 
Carbamic  acid,  155,  370. 
Carbamide,  381 ;  see  als*^   Urea. 
Carbohydrate  grovip  in  nucleic  acid,  77. 
Carbohydrate  groups  in  proteid  molecule,  71. 
Carbohydrates,  absorption  of,  303. 

chemical  nature  of,  80. 

decomposition  of,  374. 

determination  of,  in  food,  84. 

digestion  of,  in  stomach,  291. 

formation  of  dycogen  from,  374,  375. 


Carbohydrates  formed  from  jiroteid,  127,  373. 
in  blood,  155,  374. 
in  intestines,  297. 
influence  of,  on  metabolism,  10.^. 
influence    of    pancreas    on    metabolism     of, 

364. 
metabolism,   total,    according   to   supply  of, 

106. 
metabolized  before  fats,  105. 
metabolized  in  muscular  work,  113. 
quantity  of,  in  diet,  142. 
relation  of,  to  proteid  retention,  121. 
specific  need  of  body  for,  128. 
storage  of,  in  body,  124,  364. 
utilization  of,  139. 
Carbolic  acid,  effect  of,  on  nervous  system,  .574. 
Carbon,  channels  of  excretion  of,  89,  90,  342, 
397. 
in  expired  air,  89. 
in  fieces,  90. 
in  urine,  89. 
Carbon    dioxide,     absorption    of,     bj-    liEemo- 
globin,  339,  Fig.  132. 
coefficient  of  absorption  of,  338. 
determination  of,  in  metabolism,  8.5  seq. 
diurnal    variations   of,    344,    Fig.    1.35;   345, 

Fig.  136. 
effect  of,  on  respiratory  center,  332. 
elimination  of,  by  young,  1  IS,  143. 
daily,  per  hour,  346. 
through  skin,  397. 
formation  of,  in  nerve,  434. 
in  atmospheric  air,  342. 
in  blood,  337. 

combination  of,  337. 

distribution   of,    between    .orpuscles    and 

plasma,  340. 
influence  of,  on  absorption  of  oxygen,  337. 
percentages    of,     in    arterial    and    venous, 

339. 
tension  of,  in  blood  and  lungs,  341. 
increased  output  of,  in  fatigue,  446. 
in  expired  air,  89,  342,  343. 
in  lymph,  348. 

production  of,  by  animals  and  plants,  27. 
reduction  of,  by  chlorophyll,  23. 
tension  of,  in  tissues.  342. 
Carcinu."    (green    crab),    osmotic    pressure    in, 
34. 
neurofibrils  in,  560. 
reflex  movements  of,  58.5. 
Cardia  of  stomach,  282. 

innervation  of,  284,  Fig.  114. 
opening  of,  in  deglutition,  282. 
Cardiac    inhibitory    center,    resistance    of,    to 

asphyxiation,  573,  Fig.  257. 
Cardiac  nerve  centers,  195. 
Cardiac  nerves,  188. 
of  dog,  191,  Fig.  67. 


I 


INDEX 


719 


Cardinal  points  of  eye,  512;  513,  Fig.  210. 
Cardiogram,  173,  Fig.  60;  175,  Fig.  62. 
Cardiograph,  17-4. 
Cardiographic  sound,  168,  Fig.  55. 
Carniferrin,  307,  Fig.  119. 
Carnin,  413. 
Carno-^in,  413. 

Casein,  coagulation  of,  in  stomach,  250. 
digestion  of,  255,  291. 
formation  of,  705. 
of  woman's  and  of  cow's  milk,  701. 
percentage  composition  of,  82. 
trypsin  and,  252. 
Castration,  357,  358,  367,  note,  692. 
Catelectrotonus,  424,  Fig.  161. 
Catheter,  lung,  of  Ludwig,  341,  Fig.  133. 
Cathode,  increase  of  excitability  by,  425 
resistance  to  impulse  caused  by,  426. 
stimulating  effect  of,  59,  424. 
Cell,  animal,  like  young  plant  cell,  21. 
as  elementary  organism,  1,  15. 
assimilation  of,  induced,  62. 
automatic  excitation  of,  52. 
chemical  stimulation  of,  52. 
conductivity  in,  62. 
consumption  of  oxygen  by,  27. 
contents,  kinds  of,  21,  Fig.  16;  22. 

morphology  of,  20,  21. 
dependence  of,  upon  temperature,  28. 
digestion  in,  38. 

effect  of  external  influences  on,  50. 
effects  of  ultra  violet  rays  on,  57. 
of  X-rays  on,  58. 
of  Becquerel  raj's  on,  58. 
electrical  stimulation  of,  59. 
elimination  of  decomposition  products  by, 

40. 
form  and  size  of,  16. 
formation  of  heat  in,  46. 
generation  of  electricity  by,  46. 
ingestion  of  food  by,  30. 
mechanical  stimulation  of,  56. 
membrane,  16. 
motility  of,  42. 
osmosis  in,  31. 
osmotic  pressure  in,  31. 
oxidative  processes  of,  39. 
processes,     protoplasmic    of,    42;    see    also 

Psendopodia. 
production  of  light  by,  45. 
sap  of,  21,  Fig.  16. 
secretion  in,  41. 
stimulation  of,  by  means  of  heat,  58. 

by  means  of  light,  56. 
vital  phenomena  of,  22. 
Cellulose,  digestion  of,  297. 
food  value  of    110. 
properties  of,  82. 
Cellulose  membrane  of  foods,  139. 


Centers,   see  the  various  organs  and  nerves. 
Central  convolutions,  634,  637,  639,  Fig.  289. 
importance  of,  for  vegetative  functions,  649, 

650. 
motor  cortical  areas  in,  636,  638. 
sensory  cortical  areas  in,  652. 
Central  nervous  system,   see    variou:   parts  of 

nervous  system. 
Cereals  as  food,  139. 
Cerebellar  peduncles,  593,  612. 
Cerebellar  tracts  in  the  cord,  593,  595. 

section  of,  611. 
Cerebellum,  600,  605. 

afferent  tracts  to,  in  cord,  593,  611. 
artificial  stimulation  of,  60.5. 
bilateral  movements  from,  640. 
compensation  for  effects  of  removal  of,  612. 
connectiorLs  of,  605,  610,  Fig.  271. 
distributor  of  cerebral  impulses,  641. 
effects  of  complete  extirpation  of,  in  various 
lower  animals,  605  seq. 
in  dog,  606,  Fig.  270;  607. 
(unilateral),  612. 
example  of  regulating  influence  of,  611. 
field  of  chief  influence  of,  609. 
forced  movements  from,  612. 
lesions  of,  in  man,  607. 
relation  of,  to  labyrinth  of  ear,  611. 
relaxation    of    antagonistic    muscles    from, 
636,  640. 
Cerebral  cortex,  electrical  stimulation  of,  601, 
631,  632,  633. 
histological  structure  of,  634,  Fig.  284. 
influence  of,  on  vegetative  functions,  599,  649. 
mechanical  stimulation  of,  633. 
motor  areas  in,  632. 

proofs  that  stimulation  of,  is  possible,  633. 
sensory  areas  in,  650. 
Cerebral  functions,  moral  significance  of,  672. 
Cerebral  hemispheres,  cooperation  of,  641. 
Cerebral   localization,    in   brain   of   apes,    637, 
638,  Fig.  288. 
in  brain  of  man,  639. 
in  brain  of  monkey,   635,    Figs.    285,    286; 

636,  637,  Fig.  287. 
phrenology  compared  witli,  631. 
Cerebrosides,  79. 
Cerebro-spinal  fluid,  678. 
Cerebrum,  commissures  of,  641. 

compensating  of  loss  of  semicircular  canals 

by,  478. 
definition  of,  601. 

effects  of  removal  of,  from  birds,  622,  623. 
from  bony  fish,  619. 
from  dog  (Goltz's),  625. 
from  dog  shark,  619,  620. 
from  frog,  620. 
from  lizard,  621. 
from  rabbit,  624. 


720 


INDEX 


Cerebrum,  effects  of  removal  of,  from  turtle, 
621. 

myelogenetic  areas  of  Flechsig  of,  667. 

physiology  of,  629. 

psycho-physical  functions  of,  658. 

summarj'  of  effects  of  removal  of,  627. 

vegetative  functions  of,  649. 

wanting  in  human  monster,  627. 
Cervical  sympathetic,  see  Sympathetic  nerves. 
as  pupilo-dilator  nerve,  528. 
as  secretory  nerve,  258. 
as  vasodilator  nerve,  235. 
Chemotaxis,  53,  54,  Fig.  31 ;  697. 
Chemotropic  influence,  689. 
Chest  tones,  505. 
Cheyne-Stokes  respiration,  333. 
Chief  cells  of  gastric  glands,  266. 
Child,  growth  of,  707. 

heat  regulation  in,  409. 

weight  of,  at  birth,  706,  707. 
Childhood,  period  of,  706. 
Children,  metabolism  in,  118,  119. 

nutrition  of,  143,  144. 
Chlorophyll,  21,  22. 

function  of,  23. 

movements  of,  in  Lemna,  42,  Fig.  25. 
Cholagogic  substances,  273. 
Cholera  spirilla,  survival  of,  at  low  tempera- 
tures, 29. 
Cholesterin,  80,  254. 

percentage  composition  of,  82. 
Choleic  acid,  253. 
Cholic  acid,  253. 
Cholin,  2.54. 

Chondroitin-sulphuric  acid,  77. 
Chondro-mucoid,  82. 
Chondro-proteids,  77. 
Chorda  tympani  as  secretorj'  nerve,  257. 

as  vasodilator  nerve,  235. 
Chordse  tendinse,  166. 
Choroid  coat,  527. 

Chromatic  aberration,  526,  Fig.  221. 
Chromatin,  695. 
Chromophyll,  24. 
Chronoscope,  673. 

Chronotropic  effect  of  vagus  excitation,   189. 
Cilia,  43,  44. 

mechanism  of  action  of,  44. 
Ciliarj'  movements,  effects  of  salts  on,  25. 
Cihary  muscle,  532,  Fig.  227. 
Ciliated  epithelium  of  air  passages,  323. 

of  oviduct,  69.6. 
Circulating  proteid,  134. 
Circulation,  see  Blond. 

course  of,  161,  162,  Fig.  50. 

effect  of  suction  of  thorax  on,  176. 

greater  or  systemic,  162. 

influence  of  adrenal  bodies  on,  365. 

influence  of  pituitary  body  on,  367. 


Circulation,  lesser  or  pubnonarj',  227. 

mechanics  of,  200,  Fig.  74. 

significance  of,  for  heat  regulation,  407. 
Circulation  of  organic  elements  in  nature,  67. 
Circulation  of  protoplasm  in  plant  cells,  42. 
Circulatory  system,  function  of,  30. 
Chyle,  304,  305. 

Chjde  vessels,  innervation  of,  349. 
Chyme,  285,  291. 
Chymosin,  250. 

Clarke's  column,  562,  Fig.  254;  563. 
Cleavage,  hydrolytic,  70,  297. 
Climacteric,  358,  696,  697. 
Closing  contraction,  420,  423. 
Clostridium  Pasteurianutn,  23. 
Clothing,  natural  and  artificial,  use  of,  405,  406. 
Clotting,  see  Coagulation  of  blood. 
Coagulation  of  blood,  154,  157. 

importance  of,  159. 

why  not  in  blood  ve.ssels?  159. 
Coagulation  of  milk,  250. 

of  proteid,  75. 

of  protoplasm,  29. 
Cocaine,  effect  of,  on  sen.se  of  taste,  485. 

on  membranous  labyrinth,  476. 
Cochlea,  473. 

Cochlear  nerve,  course  of,  653,  655. 
Cock,  castration  of,  357,  367,  note. 
Cold-blooded  animals,  46,  442. 

reaction  of,  to  external  temperature,  114. 
Cold,    influence   of,    on  metabolism   of   warm- 
blooded animals,  114,  115,  401. 

of  simple  organisms,  29. 

sensations  of,  4.58. 
Cold  nerves,  408. 

end-organs  of,  468. 
Cold  sense,  459;  460,  Fig.  183. 
Cold  spots  or  points  on  skin,  458,  459,  Fig.  182; 

461. 
Collagen,  78. 

percentage  composition  of,  82. 
Collateral  fibers  in  spinal  cord,  563;  Fig.  255; 

592. 
Collateral  ganglia,  687. 
Color,  theories  of,  544,  546. 

induction,  successive,  542,  Fig.  236. 

mixture,  542. 

reactions  of  proteid,  72. 

sensations,  541. 

system,  dichromatic,  546. 
trichromatic,  545. 

tone,  .541,  543. 
Color  blindness,  546,  547. 
Colors,  complementarj-,  .543. 
Colostrum,  704. 

Column  cells  in  spinal  corfl,  .563,  Fig.  2.55. 
Columns  of  the  spinal  cord,  .562,  Fig.  254;  .589, 
Fig.  261;  591,  Fig.  264;  592,  Fig.  265; 


INDEX 


721 


Combination  tones,  501. 
Combustion,  26,  27. 

as  source  of  animal  heat,  402. 
heat  of,  92. 

of  foodstuffs,  92. 
of  faeces,  9.3. 
of  urine,  93. 
Commissures    between    cerebral    hemispheres, 

641;  see  also  Corpus  callosum. 
Compensation  in  ataxia,  473. 

after  extirpation  of  labyrinths,  478. 
after  lesions  in  cerebellum,  612. 
Compensatory  pause,  183,  Fig.  65. 
Complemental  air,  320. 
Complementarj^  colors,  543. 
Concomitant  respiratorj^  movements,  321. 
Conducting    pathways,    from    motor     cortical 
areas,  647. 
in  spinal  cord,  afferent,  592,  Fig.  265;  593, 
595,  596. 
efferent,  .594,  Fig.  266;  595. 
methods  of  determining,  589. 
to  auditory  area,  614. 
to  visual  area,  656,  Fig.  295;  657. 
Conduction,  isolation  of,  in  nerves,  41 
of  excitation,  411. 
radiation  of  heat  and,  40.3. 
Conductivity,  a  general  property  of  protoplasm, 
62. 
in  both  directions  in  ners^es,  410. 
not  same  as  sxcitability,  411. 
resistance  to,  in  nerves,  425,  426. 
Conjugated  proteids,  75. 

Conjugation  of  male  and  female  elements,  691. 
Consciousness,  simplest  state  of,  451,  note. 
Conservation  of  energy,  2,  93. 
Consonant  intervals,  490. 
Con.sonants,  507. 
Constant  current,  60. 

alterations  of  excitability  produced  by,  424. 
stimulating  effects  of,  423. 
Constituents,  chemical,  of  the  body,  68. 
inorganic,  of  animals,  25. 
of  plants,  24. 
Contractile    cells    embracing    capillaries,    220, 

Fig.  89. 
Contractile  vacuoles,  22. 
Contraction,  auxotonic,  435. 
clonic,  633,  642. 
isometric,  414;  438,  Fig.  176. 
isotonic,  415,   435;  4.36,   Fig.   173;  438,  Fig. 

176;  442,  Fig.  178. 
musical  tone  of,  434. 
opening  and  closing,  420,  423. 
of  pseudopodia,  43. 
Pfliiger's  law  of,  423. 
secondary,  433. 

simple,    of   cross-striated  muscle,   415,    Fig. 
154. 


Contraction,  simple,  of  smooth  mascle,  448. 

simple  projectile,  436,  Fig.  173. 

summated,    of    cross-striated    muscle,    415, 
429. 
of  .smooth  mascle,  448. 

tetanic,  429,  Fig.  166;  430,  Fig.  167. 

veratrin,  437,  Fig.  175. 

voluntary',  430. 

tonic,  of  vascular  wall,  238. 
of  smooth  muscle,  448. 
Contractions,  fibrillarj-,  of  heart,  181. 
Contracture  after  destruction  of  motor  cortex, 
646. 

after  destruction  of  cerebellum,  606. 
Contrast,  .simultaneous,  in  \-ision,  547. 

explanation  of,  548,  549. 
Convergence  of  the  eyes,  534,  .556. 

accommodation  and,  534,  557. 

a.ssjTnmctrical,  .552. 

center  of,  535,  Fig.  230;  616. 
Convolutions  of  cerebrum,  see  under  individual 

names. 
Cooking,  importance  of,  110,  242. 
Coordination  of  movements,  473. 

determination  of,    refiexly,  .587. 

in  acerebral  rigidit\-,  617. 

loss  of,  by  destruction  of  internal  car,  478. 
b}'  lesions  of  cerebellum,  607,  608. 
by  loss  of  motor  sensations,  472. 
Copper  ferrocyanide  as  semipermeable  mem- 
brane, 31. 
Copulation,  691,  693. 
Cornea,  form  of,  .522. 

radius  of  curvature  of,  510,  512. 

refractive  index  of,  509. 

refractive  power  of,  513. 
Corona  radiata,  647. 
Coronary  arteries,  180. 
Coronary  veins,  181. 

Corpora  geniculata,  600,  614,  617,  655,  657 
Corpora  quadrigemina,  600,  613. 

frontal  section  of,  615,  Fig.  272. 

relation  of,  to  auditory  impressions,  614. 
to  ej'e  movements,  613. 
Corpora  striata,  600. 

as  heat  center,  408. 
Corpus  callosum,  641. 

section  of,  641,  660. 

stimulation  of,  641. 
CorpiLs  geniculatum  external,  617,  6.57. 
Corpus  geniculatum  internal,  614,  6.55. 
Corpus  luteum,  696. 
Corpuscles,  red,  148;  see  also  Blood  corpuscles. 

white,  153;  see  also  Lrucoojtes. 
Correspondence  of  the  retina»,  555. 
Corti,  organ  of,  499,  .500,  Fig.  199. 

pillars  of,  499,  500,  Fig.  199. 
Cortical  a^eas,  see  Motor  and  Sensory  cortical 
areas. 


722 


INDEX 


Cortical   areas  for   vegetative   functions,   649, 

650. 
Cortical  epilepsy,  632,  641,  642,  Fig.  291;  652. 

progress  of,  642. 

spread  of,  through  subcortical  centers,  643. 
Cortical  lesions,  see  Lesions. 
Cortico-spinal  tract  in  the  cord,  593. 
Cosmic  influences  on  the  body,  61. 
Coughing,  321. 
Cowper's  glands,  691. 
Crab,  green,  osmotic  relations  of  blood  of,  34. 

neurofibrils  in,  560. 

reflex  movements  of,  585. 
Cramp  fish,  49. 
Cramplike    contractions    in   cortical   epilepsy, 

641,  642. 
Cranial  nerves,  680. 

crossing  of  motor  fibers  of,  647. 
Cra-n-fish,  osmotic  relations  of  blood  of,  34. 

ners-e  fibrils  in,  560. 
Creatin,  155,  264,  413,  434. 
Creatinin,  264,  382,  383,  434. 
Cretinous  child,  360,  Fig.  1.38. 
Crico-arj^tenoid  muscle,  lateral,  action  of,  503, 
Fig.  201. 

posterior,  action  of,  503,  Fig.  200. 
Cricoid  cartilage,  502. 
Crista  acustica,  474. 

Crossing    of    nerve    fibers    in    the   brain,    647, 
592. 

in  the  optic  chiasm,  657. 

in  the  spinal  cord,  592,  593,  596,  597. 
Crystalline  lens,  distance  of,  from  cornea,  510. 

radius  of  curvature  of,  510,  512. 

refractive  index  of,  509. 

relation    of,    to    accommodation,    531,    Fig. 
225;  .532  seq. 
Crura  cerebri,  600,  613,  614. 
Ctenolabrus,  egg  of,  in  absence  of  o.xygen,  26. 
Cubic  enlargement  of  aorta  of  rabbit,  201,  Fig. 
75. 

of  vena  cava  of  cat,  223,  Fig.  92. 
Cucumaria,  56. 

Curare  as  lymph  producer,  351. 
Curare  in  artificial  respiration,  5. 
Current  clock,  209,  Fig.  81. 
Currents,  electrical;  see  also  under  individual 
names. 

action,  48. 

constant,  59. 

demarcation,  47,  48. 

frog,  47. 

in  plants,  49. 

induction,  fatal  strength  of,  61. 

skin,  49. 
Curves,  central  nerv-ous  system: 

asphyxiation,  resistance  of  various  centers 

to,  573,  Fig.  257. 
cortical  epilepsy,  course  of,  642,  Fig.  291. 


Curves,  central  nervous  system: 

latent  period  of  muscular  contractions  in- 
duced from  cortex  underlying  wliitc  mat- 
ter, 633,  Fig.  283. 
preliminary  reflex  movements  of  frog's  leg, 

571,  Fig.  256. 
Circulation: 

action  current  of  heart,  13,  Fig.  13;  179, 

Fig.  63;  180,  Fig.  64. 
apex  beat.  173,  Fig.  60;  175,  Fig.  62. 
blood  pressure: 

depressor,  194,  Fig.  70. 

in  aorta,  170,  Fig.  57;  171,  Fig.  58. 

in  auricle,  169,  Fig.  56;  173,  Fig.  60. 

in  ventricles,  169,  Fig.  .56;  170,  Fig.  57; 
171,  Fig.  58;  173,  Fig.  60. 

reflex  fall,  237,  Fig.  98. 

reflex  ri.se,  236,  Fig.  97. 

respirator^'    variations,    229,    Fig.    95; 
230,  Fig.  96. 

vagus   stimulation,   205,    Fig.    77;   206, 
Fig.  78;  207,  Fig.  79. 
cubic  enlargement  of  aorta,  201,  Fig.  75. 

of  veins,  223,  Fig.  92. 
influence  of  temperature  on,  184,  Fig.  66. 
isolated    cat's    heart,    direct    stimulation, 

183,  Fig.  65. 
plethysinographic  curve,  212,  Fig.  84. 
pulse  curve,  12,  Fig.  11;  216,  Fig.  88. 
pulse  rate,  192,  Fig.  68;  197,  Fig.  71. 
vagus  and  accelerator  compared,  192,  Fig. 

68. 
velocity-  curve,  210,  Fig.  82. 
Digestion: 

digestive  action  of  gastric  juice,  265,  Fig. 

104. 
discharge  of  bile  into  intestine,  27.5,  Fig. 

110. 
enzymes  of  pancreatic  juice,  271,  Fig.  108. 
secretion  of  gastric  juice,  265,  Fig.  10,3. 
secretion   of   pancreatic   juice,    270,    Figs. 

106,  107. 
Growth: 

in  length  and  weight,  in  boys  and  girls, 

709,  Fig.  304. 
variations  in  length  of  adult  body,   710, 

Fig   305. 
Metabolism: 

excretion  of  nitrogen  in  2-lir.  periods,  102, 

Fig.  44. 
excretion   of  urea  in  a   fasting  dog,    101, 

Fig.  43. 
Muscle  and  nerve: 

alterations  of  excitability,  424,  Fig.   161 ; 

425,  Fig.  162. 
elasticity,  412,  Fig.  150;  413,  Fig.  152. 
entrance  of  current  through  skin  to  nerve, 

428,  Fig.  165. 
ergogram,  444,  Fig.  180;  445,  Fig.  181. 


INDEX 


'23 


Curves,  Muscle  and  nerve: 

fatigue,  441,  Fig.  177;  442,  Fig.  178. 
isometric  contraction.s,  438,  Fig.  176. 
isotonic  contractions,  436,  Fig.   173;  438, 

Fig.  176;  442,  Fig.  178. 
projectile  motion,  436,  Fig.  173;  436,  Fig. 

174. 
rate  of  conductivity,  417,  Fig.  155. 
simple  muscle  cur\'e,  7,  Fig.  2;  415,  Fig. 

154. 
stimulation  by  make  and  break  induction 

shocks,  426,  Fig.  163. 
strength  of  stimuli  and  height  of  contrac- 
tion, 435,  Fig.  172. 
tetanu.s,  429,  Fig.  166;  430,  Fig.  167. 
veratrinized  muscle,  437,  Fig.  175. 
Reproduction: 

curves  of  intra-uterine  pressure  in  labor, 
698,  Fig.  302;  699,  Fig.  303. 
Respiration: 

absorption  of  CO2   by  haemoglobin,   339, 

Fig.  132. 
absorption  of  O2  by  blood,  337,  Fig.  131. 
elimination   of   CO2,    343,    Fig.    134;   344, 

Fig.  135;  345,  Fig.  136. 
number   of   respiratory   movements,    319, 

Fig.  127. 
pneumorgraphic  curve  of  man,  313,  Fig. 

121. 
respirations    influenced    by    vagus,     328, 

Fig.  129. 
respiraton,'  cur\-e  of  rabbit,  314,  Fig.  123; 
328,  Fig.  129. 
Special  sen.ses: 

excitation  of  different  components  of 
visual  organ  by  light  rays  of  different 
wave  lengths,  544,  Fig.  237;  545,  Fig. 
238. 
excitation  of  retina  as  function  of  time 
exposed,  540,  Fig.  235. 
Temperature  of  body: 

daily  variations  in,  399,  Fig.  147. 
po.st  mortal  fall  of,  401,  Fig.  149. 
Cutaneous  nerves,  reflex  action  of,  on  respira- 
tion, 331. 
Cutaneous    sen.sations,    458;    see    al.so    under 
Sensations. 
tracts  for,  in  the  cord,  597. 
Cystein,  373. 
Cystin,  70,  249. 
Cytolytic  action  of  blood,  156. 
Cytosin,  77. 

Dalton's  law,  for  absorption  of  gases,  334. 
Death,  66.v__ 

Decidua  menstrualis,  697. 
Decomposition  of  carbohydrates,  374. 

of  fat,  376. 

of  proteids,  369. 


Decomposition    products,    elimination    of,    by 
elementary  organism,  40. 
in  blood,  155. 

influence  of,  on  organs,  356. 
.stimulating  action  of,  52. 
Defecation,  298,  299. 

Degeneration,  of  peripheral  tissues,  568. 
secondan.',  in  nerve  cells,  567,  568. 

in  spinal  cord,  590,  Fig.  262. 
Wallerian,  567. 
Deglutition,  279. 
muscles  of,  281. 
reflex  nature  of,  280. 
sounds  of,  282. 
Delomorphous  secreting  cells,  267. 
Demarcation  current,  47,  Fig.  29;  48. 

in  spinal  cord,  588. 
Dendrites  of  nerve  cell,  5.59. 
Density  of  current,  420. 
Depressor  nerve  of  heart,  193. 
Depth,  perception  of,  in  vision,  556. 
Deuteroalbumoses,  249. 
Development,  .see  Growth. 

of  myelin  .substance  in  brain,  667. 
Dextrins,  formation  of,  in  cUgestion,  246. 

properties  of,  82. 
Dextro.se,  as  product  of  digestion,  246,  251. 
as  source  of  glycogen,  127. 
from  alanin,  373. 
from  lactic  acid,  374,  note, 
from  leucin,  374. 
in  urine,  383;  see  also  Diabetes. 
properties  of,  80. 
Diabetes  mellitus,  127,  375. 
Diabetes,  pancreatic,  127,  128,  362,  375. 
pl.loridzin,  127,  374,  375. 
puncture,  375. 
Diamino  acids,  70. 
Diamino-caproic  acid,  70. 
Diamino-valcrianic  acid,  70,  72,  370. 
Diaphragm,     movements    of,    in    respiration, 
316. 
paralysis  of,  324. 
Diaphragmatic  type  of  respiration,  318. 
Diastatic  enzyme,  definition  of,  243. 
in  bile,  254. 
in  intestinal  juice,  25.5. 
in  pancreatic  juice,  251. 
in  saliva,  246. 
in  sweat,  .395. 
preserved  in  stomach,  291. 
Diastole,  definition  of,  162. 
suction  r)f  heart  in,  177,  225. 
time  relations  of,  175,  Fig.  62;  176. 
Dibasic  monamino  acids,  70. 
Dichromatic  color  sy.stem,  546. 
Dichrotic  elevation,  175. 

on  cardiogram,  173,  Fig.  60;  175,  Fig.  62. 
on  sphygmogram,  216,  Fig.  88. 


724 


INDEX 


Diencephalon,  600,  601,  617;  see  also  'Tween- 

brain. 
Diet,  see  Nutrition  and  Nutritive  requirements. 

animal  and  vegetable,  145. 

construction  of,  145. 

digestibility  of,  in  stomach,  293. 

importance  of  variation  in,  134. 

mixed,  utilization  of,  139. 

natural,  of  man,  146. 
Difference  tones,  501. 
Difflugiae,  motility  of,  45. 
Diffusion,  absorption  and,  353 ;  see  also  Osmosis. 

of  odors,  486,  487. 

relation  of,  to  excretion,  41. 
Digestibility-  of  food  in  stomach,  293. 
Digestion,  artificial,  244,  248. 

definition  of.  38. 

Bacterial,  in  intestine,  297. 

in  different  divisions  of  alimentary  canal, 
290  seq. 

in  intestine,  294  seq. 

in  large  intestine,  298. 

in  mouth.  290. 

in  stomach,  291. 

in  unicellular  organisms,  38. 

intracellular  and  extracellular,  38. 

metabolism  and  work  of,  108. 
Digestive  enzymes,  243;  see  also  Enzymes. 
Digestive    fluids,    242    seq.;    see    also    under 
individual  names. 

methods  of  study  of,  243. 

secretion  of,  256  seq. 
Digestive  glands,  256  seq. ;  see  also  indi^^dual 
glands. 

conditions  for  secretion  in,  256. 

electric  phenomena  of,  48,  49,  257. 

extracts  of,  243. 

fistula;  of,  243. 

heat  production  in,  257. 

morphological  changes  in,  260,  Fig.  100;  261, 
Fig.  101;  262,  Fig.  102;  272,  Fig.  109; 
277,  Fig.  111. 

specific  excitants  of,  264,  271,  275. 
Digestive  products,  effects  of  injection  of,  into 

blood,  250. 
Digestive  system,  function  of,  30. 
Dihexosamin,  249. 
Dilator  center  of  pupil,  .529. 
Dilator  nerves  of  pupil,  .528. 
Diopter,  definition  of,  .513,  note. 
Dioxj'-phenyl-acetic  acid,  384. 
Dioxy-pyrimidin,  76. 
Direct  vision,  514. 
Direction,  lines  of,  in  vision,  518. 
Directive  influences  on  movements  of  organ- 
isms, 59,  note. 
Disaccharides,  properties  of,  81. 
jiercentage  composition  of,  82. 
Discrimination  time,  676. 


Discus  proligerus,  695. 
Dispersion  circle,  517. 

Dissimilation  equivalent  to  oxidation,  27. 
Dissimilation,  necessity  of,  to  growth,  26. 
Dissimilation  source  of  kinetic  energy,  26. 
Dissociation,  electrolytic,  32. 
Distances,  estimation  of,  with  eye,  554. 
Distribution  of  blood  in  bodj-,  239. 
Diuresis,  390. 

Diuretic  substances,  273,  389,  390. 
Dizziness  in  the  deaf  and  dumb,  481. 
Dog,  extirpation  of  cerebrum  in,  625. 

extirpation  of  spinal  cord  in,  581,  582,  587. 
Dorsolateral  cerebellar  tract,  -593. 
Double  refraction  of  contractile  protoplasm,  20. 
Double  vision,  5.5.5. 
Dromotropic  effect  of  vagus,  189. 
Drj-  rigor,  20. 
Dn,-  substance,  determination  of,  in  food,  84. 

utilization  of,  in  body,  139. 
Dulcite,  80. 

Duodenum,    influence    of,    on    evacuation    of 
stomach,  28.5. 

secretion  of  pancreatic  juice  and,  270. 
Dyspncea,  332. 

Ear,  analysis  of  sound  in,  493,  498. 

auditorj'  ossicles  of,  495. 

beats,  how  explained,  501. 

cochlea  of,  498. 

combination  tones  in,  .501. 

Eustachian  tube  of,  497,  498. 

excitation  of  auditory  nerve  in,  498. 

external,  494. 

movements   of,    on   stimulation   of  brain, 

658. 
vasodilator  nerves  of,  235. 

intrinsic  muscles  of,  497. 

middle,  494,  495,  Figs.  196,  197. 

organ  of  Corti  in,  499,  .500,  Fig.  199. 

otolith  sacs  of,  473,  481. 

resonance  theory  of  hearing  in,  498. 
objections  to,  501. 

resonators  in,  498. 

semicircular  canals  of,  473. 

transmission  of  sound  in,  493. 

t\"mpanic  cavitj-  of,  495,  497. 

t^Tiipanic  membrane,  494,  49.5,  496. 
Earthworm,  phototaxis  of,  57. 
Echinoderms,  galvanotaxis  of,  60. 
Echinoderms  (Asterino),  geotaxis  of,  56. 
Eck  fistula,  227,  274,  371. 
Ede.stin,  70,  71. 
Egg,  white  of,  245. 
Egg  albumin,  74,  264. 
Eggs,  dependence  of,  on  oxygen,  26. 

osmotic  phenomena  in,  34. 

thigmotactic  influence  of,  697. 
Ejaculation,  693. 


INDEX 


725 


Elastic  manometer,  9,  Fig.  5. 
Elastic  tubes,  flow  of  liquid  in,  199. 

waves  in,  212. 
Elasticity,  coefficient  of,  in  arteries,  201. 

of  arterial  wall,  200,  201. 

of  lungs,  310;  311,  Fig.  120;  317. 

of  resting  muscle,  412,   Fig.   1.50;  413,   Fig. 
152. 
Elasticity  apparatus,  412,  Fig.  151. 
Elastin,  78. 

percentage  composition  of,  82. 
Electric  fislies,  48,  50. 

Electric  phenomena  in  central  nervous  system, 
570,  588. 

in  cutaneous  glands,  48. 

in  digestive  glands,  257. 

in  muscles  and  nerves,  47,  431. 

in  plants,  49,  50. 

in  resting  miLscle,  47. 

in  retina,  537. 

in  .skin,  49. 

in  starch  formation,  49,  50. 
Electric  signal,  10,  Fig.  7. 
Electrical  stinuilation  in  general,  59,  418. 
Electrical  stimulation  of  the  cord,  588. 
Electrical  stimulation  of  the  cerebral  cortex, 

601,  631,  632,  633. 
Electrical  stimulation  of  human  nerves,  427. 
Electricity,  see  Electric  currents. 

action  of  strong  currents  of,  61. 

animal,  46. 

generation  of,  46. 
Electrodes,  noniujlarizable,  418,  419,  Fig.  157. 
Electrolysis  in  nerves,  434. 
Electrolytes,  relation  of,  to  osmotic  pressure, 

32. 
Electrometer,  capillary,  13,  Fig.  12. 
Electrotonic  currents,  433,  Fig.  171. 
Electrotonus,     see    Anclectrotonus     anil     Cat- 

electrotomi.1. 
Elements,    chemical,  behavior  of,  in  metabo- 
lism, 131  seq. 

necessary  for  animal  body,  2.5,  26. 
Elements  of  speech,  506. 
Emmetropic  eye,  519. 
Emotions,  rationalized,  moral  power  of,  672. 

summoning  influence  of,  on  memorj-,  671. 
EmuLsion  in  intestine,  295,  296. 
Encephalon,  600;  see  also  Brain. 
End  products,  of  proteid  iligestion,  249. 
End  products,  nitrogen  equilibrium  on,  124. 
Endbrain,  600,  601 ;  see  also  Cerebrum. 
Endolymph,  in  cochlea,  497,  498. 

movements  of,   in  semicircular  canals,   479, 
480. 
Energy,  conservation  of,  2. 

in  animal  body,  93,  94. 

kinetic,  26. 

liberated,  greater  than  energy  of  stimulus,  51. 


Energy,  potential,  measure  of,  in  substance,  26. 
of  foodstuffs,  92. 

stored  in  processes  of  assimilation,  26. 
transformation  of,  into  external  work,  113. 
utilization  of,  in  diet,  139. 

production  of,  in  cells,  26. 

requirements  of,  of  an  adult  man,  140. 
of  an  adult  woman,  143. 
of  children,  144. 

source  of,  in  muscular  work,  112,  113. 

total  output  of,  in  muscle,  439. 
Entoptic  phenomena,  521. 
Enterokinase,  252,  255. 
Enucleated  cells,  18. 
Enzymes,  38,  356. 

amylolytic,  243,  251. 

in  bile,  254. 

in  blood,  155. 

in  liver  cells,  375. 

in  pancreatic  juice,  251. 

lipolytic,  243,  253. 

measure  of  activity  of,  245. 

precursors  of,  244. 

preotolytic,  243,  252. 

properties  of,  38. 

reversible  processes  of,  39. 
Epididymus,  693. 

Epiglottis  in  swallowing,  281,  Fig.  112;  282. 
Epiglottis  laryngoscopic   picture  of,   504,    Fig. 

202. 
Epilepsy,  cortical,  632,  641,  642,  Fig.  291;  652. 
Epilepsy  in  myxcedema,  360. 
Epithalamus,  600. 

Equilibrium,    loss   of,    after   removal   of   cere- 
bellum, 606. 

nitrogenous,  91,  100,  103,  120,  121,  122. 

of  substance  in  body,  137. 
Equimolecular  .solutions,  32,  33. 
Erection,  588,  693. 

center  of,  694. 
Erepsin,  255,  305. 
Ergograpli,  443.  444,  Fig.  179. 
Ergographic   record,   444,   Fig.   180;  445,   Fig. 

181. 
Erlanger's    apparatus,    for    determination    of 

blood  jiressure  in  man,  203,  Fig.  76. 
Erucic  acid,  130. 
Erythrodextrin,  240. 
Ethereal  sulphates,  373,  379. 
Eudendrium,  64. 
Euglobulin,  154. 
Eustachian  tube,  498. 
Evacuation  of  large  intestine,  299. 

of  stomach,  285. 
Excitability,  alterations  of,  52,  425. 

by  extraction  of  water,  53. 

influence  of  heat  on,  58. 
Excitants,    specific,    in    secretion,    264,    271, 
275. 


726 


INDEX 


Excitation,  see  Stinuilation. 

accompanied  by  heat  and  electricity,  51. 

automatic,  52,  356,  570,  580. 

of  muscle  and  nerve,  414. 

polar  law  of,  424,  426. 

propagation  of,  through  the  heart,  187. 

rate  of  transmission  of,  see  Transmission  of 
stimulus. 
Excrements,  see  Fcrces. 

Excreta,  apportionment  of  chemical  elements 
to,  89. 

determination    of,     in    metabolism    experi- 
ments,  84;   see  also  various  excretory 
organs. 
Excretion,  definition  of,  40. 

by  kidney,  384. 

by  lungs,  346. 

by  skin,  394. 

in  unicellular  organisms,  40. 

of  carbon  dioxide,  89. 

of  iron,  308,  309. 

of  nitrogen,  89,  90. 

through  intestine,  133,  298,  309. 
Excretory  organs,  function  of,  31. 
Expansion  of  thorax,  310,  312. 
Expansion  movements  of  pseudopodia,  43. 
Expiration,    .see   Respiration   and   Respiratory 
movonents. 

definition  of,  310. 

description  of,  317. 

effects  of,  on  arterial  blood  pressure,  230. 

muscles  of,  317. 

pre.ssure  changes  in  air  passages  in,  .321,  322. 
in  thorax  in,  310,  312. 
Expired  air,  composition  of,  342. 

poisonous  constituents  in,  344. 
Expulsion  period  in  parturition,  698. 
Extension,  curve    of,    in    resting   muscle,    412, 

Fig.  150;  413,  Fig.  1.52. 
External  auditory  meatus,  494,  Fig.  196. 
Extractives,  effect  of,  on  gastric  glands,  264. 

food  value  of,  109. 
Extremities,  vasoconstrictor  nerves  of,  232. 

vasodilator  nerves  of,  235. 
Eye,  accommodation  in,  529  seq. 

after-images  of,  negative,  539. 
positive,  538. 

binocular  field  of  vision  of,  551,  552,  Fig.  242. 

blind  .spot  of,  516,  Fig.  212. 

cardinal  points  of,  512,  513,  Fig.  210. 

changes  produced  in  retina  of,  by  action  of 
light,  537,  Fig.  231 ;  538,  Fig.  232. 

choroid  coat  of,  527. 

convergence  of  visual  axes  of,  534,  556,  557, 
Fig.  230. 
center  for,  535. 

dichromatic,  546. 

dispersion  circles  in,  517. 

emmetropic,  519,  Fig.  215. 


Eye,  excitation  of  retina  of,  5.36. 
far-point  of,  520. 
fatigue  and  recovery  of,  539. 
focal  distances  of,  512. 
fovea  centralis  of,  514,  517,  541. 
hypermetropia  of,  519,  Fig.  215;  520. 
images,  formation  of,  on  the  retina  of,  .513, 

.556,  Fig.  248. 
iris  of,  527. 

light-perceiving  layer  of  retina  of,  514. 
muscular  .strabism  of,  555. 
myopia  of,  .519,  Fig.  215. 
near-point  of,  529. 
optical  constants  of,  508. 
optical  defects  of,  520. 

angle  between  line   of   vision   and   visual 

axis,  525. 
astigmatism,  522,  524,  Fig.  219. 
chromatic  aberration,  526,  Fig.  221. 
entoptic  phenomena,  521,  Fig.  216;  522, 

Fig.  217. 
form  of  refracting  surfaces  in,  522. 
spherical  aberration,  522,  523, 
ora  serrata  of,  514. 
perception  of  depth  by,  556. 
primary  position  of,  549. 
pupil  of,  constriction  of,  528. 
center  for,  529. 
dilatation  of,  528. 
center  for,  529. 
reduced,  512. 
refracting  media  of,  508. 
refraction  in,  510,  Fig.  207. 
rotation  center  of,  549. 
schematic,  511,  513,  Fig.  210. 
sensations  of  color  in,  541. 
complementary  colors,  543. 

successive  color  induction,  542. 
theories  of  color  vision,  544,  546. 
simultaneous  contrast  in  vision  in,  547. 

explanation  of,  548,  549. 
static  refraction  of,  519,  Fig.  215. 
stereoscopic  vision  of,  558. 
trichromatic,  545. 
ultra-red  rays,  effect  of,  on,  536. 
ultra-violet  rays,  effect  of,  on,  53'"-. 
vi.sible  rays  of  spectrum  in,  536. 
visual  angle  and  limits  of  vision  in,  517. 
Eye  as  an  optical  instrument,  508. 
Eye  movements,  549. 

induction  of,  by  stimulation  of  cerebral  cor- 
tex, 640,  658. 
hmits  of,  .551,  Fig.  241. 
relation  of  corpora  quadrigemina  to,  613. 
significance  of,  for  projection  of  visual  im- 
pressions, 552. 
synergic,  616. 
Eye  muscles,  .549. 

action  of,  549,  550,  Fig.  240. 


INDEX 


727 


Eye  muscles,  axes  of  rotation  in,  550,  Fig.  240. 

centers  for,  614,  615,  Fig.  273. 

innervation  of,  680. 
Eyes,  single  vision  with  two,  55.5. 

Face    mask    for    respiration    experiments,    85, 

Fig.  39;  105. 
Face  muscles,  contraction  of,  by  stimulation  of 

cortex,  640. 
Facial  nerve,  680. 

as  nerve  of  expression,  680. 

as  nerve  of  taste,  484,  Fig.  191. 

as  secretory  nerve  of  salivary  gland,  257. 
Fa'ces,  demarcation  of,  85. 

formation  of,  298. 

heat  of  combustion  of,  93. 

in  fasting,  96. 

metabolic  significance  of,  90. 

N:C  in,  90. 
Fallopian  tubes,  696. 
Falsetto  voice,  505. 
Far-point,  520. 
Fasting,  95. 

cause  of  death  by,  98. 

fieces  formed  in,  96. 

in  animals  of  different  size,  117. 

influence  of,  on  different  organs,  97,  98. 
on  fatigue,  445. 

metabolism  in,  95,  96. 

of  elementary  t)rganisms,  28. 

physiological  condition  in,  95. 
Fat,  ab.sorption  of,  304. 

cells,  21. 

cliemical  nature  of,  79. 

cleavage  theory  of  digestion  of,  296. 

determination  of,  in  food,  84. 

digestion  of,  by  pancreatic  juice,  253. 
in  intestine,  29.5. 
in  stomach,  2.50. 

droplets  in  various  cells,  22. 

tlynamic  value  of,  93. 

enuilsion  theory  of  tligestion  of,  295. 

final  decomposition  of,  376. 

form  of,  in  milk,  701. 

formation  of,  in  mammary  glands,  705. 

from  fattj'  acids,  130. 

in  blood,  155. 

in  mucin^;,  74. 

in  muscle,  413. 

influence  of,  on  gastric  digestion,  28.5,  293. 
on  metaboli.sm,  104. 

metabolism  of,  in  fasting,  97,  KM. 
in  muscular  work,  113. 

percentage  composition  of,  82. 

physiological  lieat  value  of,  93. 

proteid  sparer,  as  a,  121. 

relation  of,  to  glycogen,  128. 
to  pancreatic  secretion,  270. 
to  proteid  retention,  121. 


Fat,  resynthesis  of,  304. 

.sources  of,  in  body,  129,  130. 

storage  of,  in  body,  129. 

subcutaneous,    as    protection    against    heat 
loss,  40.5. 

transportation  of,  in  body,  376. 

utilization  of,  138. 
Fatigue,  6.5. 

effect  of,  on  power  of  localization,  464. 

influence  of  mental  work  on,  446. 

local,  442. 

of  brain,  676. 

of  car,  499. 

of  muscles,  441. 
human,  443. 

of  nerves,  442. 
lumian,  443. 

of  olfactory  organ,  488. 

of  visual  organ,  .539. 

rate  of  stimulation  and,  446. 

record   of,    with   ergograph,    444,    Fig.    180; 
445,  Fig.  181. 
Fatty  acids,  food  value  of,  109. 

production  of,  by  digestion,  29.5. 

solubility  of,  in  bile,  254,  296. 
Fatty  degeneration,  129. 
Fatty  infiltration,  129. 
Fat-splitting    enzymes,     2.50,     253;    see    also 

St  ea  pain. 
Feathers  as  protection  against  heat  lo.ss,  405. 
Fechner's  psyclio-physical  law,  4.57,  note. 
Feeding,  fictitious,  263. 
Feeling,  general  state  of,  4.52. 
Feeling  of  effort  in  motor  .sensation,  470. 
Feelings,   summoning   power  of,   on  memory, 

671. 
Fellic  acid,  2.53. 
Female   sexual    organs,    69.5;   see   also   Sexual 

orijaiix. 
Fenestra  ovalis,  496. 
Fenestra  rotunda,  497. 
Ferment  action,  40. 
Fermentation,  alcoholic,  28,  40,  80. 
Ferments,  organized,  40;  see  al.so  Enzymes. 
Fertilization,  691,  697. 
Fibrillary  contractions  of  heart,  181 
Fibrin,  147. 

formation  of,  157,  158. 
Fibrin  ferment,  158. 
Fibrinogen,  1.54,  1.57. 

cleavage  of,  1.58. 
Fibrino-globidin,  159. 
Fillet,  .592. 

lateral,  614,  6.55. 
Filtration,  theory  of,  in  urine  formation,  387. 

in  lymph  formation,  349. 
Fimbria  ovarica,  696. 
Fish,  effect  of  low  temperature  on,  29. 

electric,  48,  50. 


728 


INDEX 


Fish,  extirpation  of  cerebrum  in,  619. 

gcotaxis  of,  56. 
Fissure,  calcarinq,  639,  Fig.  290;  659. 

cruciate,  624,  Fig.  280. 

of  Rolando,  6.39,  Fig.  289. 

of  Sylvius,  624,  Fig.  280;  639,  Fig.  289. 
Fistula,  biliary,  243,  298. 

Eck's,  227,  274,  371. 

fundus,  264. 

gastric,  243,  246. 

intestinal,  243,  295. 

oesophageal,  263. 

pancreatic,  243,  251. 

pyloric,  267. 
Flagella,  definition  of,  43,  44. 

vibrations  of,  independent  of  NaCl,  25. 
Flagellata,  44. 
Flavors,  133. 
Flechsig's  tract  or  bundle  in  the  cord,  591,  Fig. 

264; 593. 
Flow  of  blood  in  arteries,  200  se<i.,  218. 

in  capillaries,  219. 

in  veins,  223. 
Flow  of  liquid  in  elastic  tubes,  199. 

in  rigid  tubes,  198,  Fig.  72;  199,  Fig.  93. 
Fluids,  absorption  of,  gases  by,  334. 
Fluttering  of  heart,  187. 
Focal  distances  of  the  eye,  512. 
Focal  lines,  523,  524,  Fig.  219. 
Focal  points  in  eye,  512,  513,  Fig.  210. 

in  optical  system,  510,  Fig.  207;  511,   Fig. 
208. 
Folin's  theory  of  proteid  metabolism,  137. 
Follicle,  graafian,  695. 

primary,  695. 
Food,  construction  of  diet  from  different  articles 
of,  145. 

definition  of,  137. 

influence  of,  on  metabolism,  98. 
Food  requirements,  see  Nutrition. 

of  grown  man,  140. 

of  grown  woman,  143. 

of  infants,  144. 

of  youths,  143. 
Foodstuffs,  see  Metabolism,  Nutrition  diet,  and 
individual  foodstuffs. 

decomposition  of,  369. 

definition  of,  83. 

inorganic,  S3,  131. 

effect  of  deprivation  of,  131. 
organic,  83. 
plastic.  111. 
potential  energy  of,  92. 
replace  one  another,  93. 
respirator  J',  111. 
Foraminifera,  41. 

Forced  movements  and  positions,  612. 
Forebrain,  600. 
Fovea  cfntralis,  514,  517,  541. 


Freezing  point,  lowering  of,  32. 
Frittillaria  imperialis,  21,  Fig.  16. 
Frog,  extirpation  of  cerebrum  in,  620. 

behavior  of,  in  absence  of  O2,  27. 

galvanotaxis  of,  60. 

geotaxis  of,  56. 

osmotic  relations  in,  34. 
Frog  current,  47. 

Frontal  association  centers,  668,  669. 
Frontal  convolutions,  631,  637,  638,  639,  Figs. 

289,  290;  664. 
Frontal  lobes,  extirpation  of,  668. 
Frontana  leucas,  41,  Fig.  24. 
Fructose,  80;  see  also  Levidose. 
Fruit  sugar,  80;  see  also  Levulose. 
Fruits  as  exclusive  food  of  man,  146. 
Fundamental  colors,  544,  547. 
Fundamental  tone,  491,  492,  Fig.  194. 
Fundic  glands,  266. 
Fundulus,  egg  of,  25,  34. 
Fundus  fistula,  264. 

Galactose,  80,  81,  251. 
Gall  bladder,  275. 
Galvani's  discovery,  46. 
Galvanotaxis,  60. 
Galvanotropism,  64,  65. 
Ganglia,  basal,  of  brain,  632. 

collateral,  687. 

lateral,  687. 

peripheral,  583;  584,  Figs.  258,  259. 

spinal,  chief  purpose  of,  584. 

sympathetic,  reflexes  through,  .583. 
table  of  connections  of,  688. 
Ganglion,   inferior    mesenteric,  392,  Fig.   145; 
393,  688. 

stellate,  687,  688. 

superior  cervical,  689. 

superior  mesenteric,  392,  Fig.  145;  393. 
Ganglion  cells,  degeneration  of,  585. 

in  heart,  186,  190. 

in  intestinal  wall,  288;  see  also  Auerbach's 
plexus  and  Meissner's  plexus. 

in  stomach  wall,  284,  Fig.  114. 

in  ureter  wall,  391. 

peripheral,  functions  of,  583. 
reflexes  through,  584,  Fig.  2.59. 
Gas  pump,  334,  Fig.  130. 
Gases,  absorption  of,  in  liquids,  334. 

exchange  of,  between  alveolar  air  and  blood, 
340. 
between  blood  and  lymph,  342. 

in  blood,  333,  339. 

in  intestine,  295. 

pressure  of,  in  alveoli,  341. 

tension  of,  in  tissues,  342. 
Gastric  glands,  266. 

morphological  changes  in,  268. 

nerves  of,  263. 


INDEX 


729 


Gastric  juice,  246. 

acid  of,  247. 

antiseptic  properties  of,  292. 

hourh^   course   of   digestive  action  of,   265, 
Figs.  103,  104. 

pepsin  in,  248,  268. 

rennin  in,  250,  267. 
Gastric  mucus,  266. 
Gastric  steapsin,  250. 
Gelatin,  78. 

composition  of,  75,  82. 

digestion  of,  247,  252. 

food  value  of,  109. 

products  of  digestion  of,  75,  78. 
Gelatin  peptones,  78. 
Gelatin-forming  substances,  247. 

digestion  of,  247,  252,  291,  294. 

food  value  of,  109. 
Generation,  organs  of,  see  Srxiial  organs. 
vasomotor  nerves  of,  233,  23-5. 

spontaneous,  16. 
Geotaxis,  56. 
Geotropism,  64. 
Germinal  spot,  695. 
Germinal  vesicle,  695. 
Gestation,  period  of,  698. 
Giant  cells  of  alg:p,  16. 

of  bone-marrow,  16. 
Girlhood,  age  of,  706. 
Girls,  food  requirements  of,  144. 

growth  of,  70S,  709. 
Glands,  albuminous,  245,  261. 

gastric,  266. 

lachrymal,  245. 

mixed,  245. 

mucous,  245,  261. 

of  large  intestine,  277,  Fig.  111. 

of  small  intestine,  276. 

parotid,  245,  257. 
of  cat,  261,  Fig.  101. 
of  rabbit,  260,  Fig.  100. 

preputial,  of  mouse,  394,  Fig.  146. 

salivary,  257  .seq. 

sebaceous,  394. 

sublingual,  245,  257,  258. 

submaxillary,  245,  257,  258. 
Globin,  7.5,  152. 
Globulins,  74. 

alkaline  combination  of,  in  blood,  338. 

of  blood,  154. 
Glomerulus  of  kidney,  385. 
Glos-sopharyngeal  nerve,  484.  TSl. 

as  nerve  of  ta.ste,  484,  Fig.  191. 

a.s  secretory  nerve  of  salivary  glands,  2.57. 

respiration  and,  331. 
Glottis,  502. 
Glucosamin,  71,  72. 
Glucose,  80;  see  also  Dextrose. 
Glutamic  acid.  70.  72.  249. 


I    Glutin-f orming  substances,  250 ;  see  also  Gelatin- 
forming  substances. 
Glyceric  acid,  377. 
Glycerides,  79. 
Gh'cerin,  food  value  of,  110. 

from  cleavage  of  fat,  295. 

in  blood,  155. 
Glycerin  aldehyde,  373. 
Glycerin-phosphoric  acid,  78. 
Glycocholic  acid,  253. 
GlycocoU,  70,  72,  253,  370,  378. 
Gh'cogen,  81,  124,  374  seq. 

afifected  by  extirpation  of  pancreas,  364. 

amount  of,  stored  in  body,  125. 

consumption  of,  in  muscular  work,  126. 

formation  of,  from  carbohydrates,  126. 
from  fats,  128. 
from  proteids,  127. 

in  liver,  125,  126,  Fig.  45. 

in  muscle,  413. 

in  nature,  occurrence  of,  81. 

percentage  of,  in  various  organs  of  body,  125. 

transformation  of,  into  sugar,  375. 
Glycogenic  function  of  the  liver,  375. 
Glycol,  377. 
Glycolic  acid,  377. 

Glycosuria  alimentary,  127,  363,  374. 
Glycuronic  acid,  376,  379,  383. 
Glyoxylic,  377. 
Golgi's  method,  559. 

GoU's  column  in  the  cord,  591,  Fig.  264;  592. 
Gower's  tract  or  bundle  in  the  cord,  591,  Fig. 

264;  .593. 
Graafian  follicle,  695. 
Grape  sugar,  80;  .see  also  Dextrose. 
Graphic  method,  6. 
Gray,  extracellular,  of  Xi.ssl,  561. 
Gray  matter  of  spinal  cord,  562,  589. 
Gray  rami   communicantes,  687. 
Green  blindne.ss,  .546. 
Gromia  oviformis,  35,  Fig.  19. 
Growth  energy-,  inherent  in  cells,  63. 
Growth  of  human  body,  70.5  seq. 

by  years,  70S,  709. 

of  males  and  females,  709,  Fig.  304. 

factors  determining  rate  of,  707. 

influence  of  economic  circumstances  on,  710. 
of  puberty  on,  708,  709,  710. 
of  season  on,  710. 

periods  of,  706. 
Guanidin  rest,  70,  72. 
Guanin,  76,  2.52,  413. 
Guanylic  acid,  77. 
Gudden's  method  of  tracing  nerve  paths,  568, 

591. 
Gums,  properties  of,  82. 
Gymnemic  acid.  485. 
Gyrus  angulans,  662.  Fig.  296;  663. 
GjTus  fornicatus,  639,  Fig.  290;  653. 


rso 


IXDEX 


Gyrus  marginalis,  634. 

Gyrus  sigmoides,  266,  632,  Fig.  282. 

Gyrus  supramarginalis,  662,  !•  ig.  296 

Hallucinations,  visual,  4-54. 
Haploscope,  555. 

Haptogen  membrane  of  milk,  701. 
Ha?matin,  152. 
Hsematinic  acid,  2.54. 
Ha?matogpn.s,  308. 
Hsematoidin,  254. 
Htematoporphyrin,  152,  383. 
Ha'min  crystals,  153,  Fig.  49. 
Ha?mochromogen,  7.5,  152. 
Hsemodromograph,  209,  Fig.  81. 
Ha>nioglobin,  1.50,  151. 

absorption  of  CO2  by,  339,  Fig.  132. 

absorption  of  O2  by,  336. 

absorption  spectra  of,  1.51,  Figs.  47,  48. 

carbon-dioxide,  152. 

carbon-monoxide,  152. 

nitric-oxide,  152. 

percentage  of,  in  red  blood  corpuscles    150. 
_  relation  of,  to  bile  pigments,  254. 

union  of,  witli  COj,  339. 
Haemoglobins,  75. 
Ha?mopyrrol,  152. 

Hair  as  protection  against  lo.ss  of  beat,  405. 
Hair  cells  of  organ  of  Corti,  499,  500,  Fig.  199. 
Hammer  of  middle  ear,  495,  Fig.  197;  496   Fig. 

198. 
Head,  vasomotor  nerves  of,  232,  235. 
Head  tones,  505. 
Hearing,  see  Ear. 

cortical  field  for,  653,  654,  Fig.  293. 

range  of,  490. 

reaction  time  to,  673,  674. 

sense  of,  451,  489. 
Heart,  action  current  of,  13,  Fig.  13;  179,  Fig. 
63;  180,  Fig.  64. 

anaemia  of,  181. 

artificial  nourishment  of,  2.5,  182. 

automatism  of,  18.5. 

chambers  of,  161 ;  see  also  under  individual 
names. 

changes  in  form  of,  163,  164. 

changes  of  pressure  in,  168  seq. 

compensatory  pause  of,  183,  Fig.  65. 

contraction  of,  nature  of,  179. 

coronary  circulation  in,  180. 

cross  section  through,  163,  Fig.  51. 

diastole  of,  162,  176. 

electrical  stimulation  of,  182  seq. 

fibrillarj'  contractions  of,  181. 

filling  of,  in  diastole,  176. 

fluttering  of,  187. 

influence  of  thoracic  suction  on,  176. 

intruisic  ganglia  of,  186. 

Krehl's  cone  of,  163,  Fig.  52. 


Heart,  movements  of,  162. 

nutrient  medium  for,  2.5,  note,  182. 

nutrition  of,  ISO. 

period  of  ejection  of,  171. 

period  of  rising  tension  of,  170,  17.5. 

power  of,  177,  178. 

pressure  in  different  chambers  of,  169. 

propagation  of  excitation  wave  in,  187. 

muscular  theory,  186. 

nervous  theory,  187. 
pulse  volume  of,  204. 
reflexes,  193. 

refractory  period  of,  183,  Fig.  6.5. 
separation    of    auricles    from    ventricles    in, 

18.5,  189. 
.sounds,  167,  168,  175. 
structure  of  wall  of,  162,  163. 
suction  of,  in  diastole,  177. 
systole  of,  162. 
tactile  sensations  in,  194. 
tenacity  of  life  in,  182. 
tetanus  of,  184. 
time  relations  of  events  in,   170,   171 ;  173, 

Fi^.  60:  175,  Fig.  62;  176. 
valves  of,  165. 
variations    of    electrical    potential    in,    179, 

Fig.  63. 
vasomotor  nerves  of,  233,  235. 
work  of,  178. 
Heart   beat,    acceleration   of,    by   inflation   of 
lungs,  195. 
cause  of,  18.5. 
force  of,  188. 

influence  of  blood  on,  184,  204. 
of  vagus  on,  189. 
frequency  of,  as  affected  by  age,  197. 

by  food,  197,  Fig.  71. 

by  individual  peculiarities,  198. 

by  mu.scular  exercise,  197. 

by  .sex,  197. 

by  size  of  body,  197. 

by  temperature,  184,  Fig.  66;  19 

by  vagus  nerve,  188. 
Heart  muscle,  contraction  of,  nature  of,  179. 
propagation  of  excitation  wave  in,  187. 
properties  of,  179. 
Heart  nerves,  188. 

accelerator,  191,  Fig.  67;  688. 
afferent,  193. 
centers  for,  195. 
depressor,  193,  Fig.  69;  681. 
efferent,  188. 

inhibitory,  188;  191,  Fig.  67. 
reflexes  through,  19.3. 
Heat,  conduction  and  radiation  of,  403. 
formation  of,  universal  in  nature,  46. 
influenced  of,  on  elementary  organisms,  29. 
production  of,  in  cold-blooded  animals,  46. 

in  man,  402. 


INDEX 


731 


Heat,  production  of,  in  plants,  46. 
Heat  as  stimulus,  58. 
Heat  cen  ters,  408. 

Heat  loss,  from  the  body  by  different  means, 
403. 

protection  against,  404. 

regulation  of,  407. 
Heat  nerves,  408. 

end  organs  of,  468. 
Heat  production,  46,  402. 

amount  of,  in  human  body,  94. 

in  glands,  402. 

in  muscles,  402,  439. 

in  nervous  system,  402. 

influenced  by  amount  of  food,  407. 
by  muscular  work,  116. 
by  surrounding  temperature,  114. 

ratio  of,  to  external  work  of  muscle,  440. 
Heat  regulation,  407. 

centers  for,  408. 

disturbances  to,  by  extirpation  of  thyroid, 
361. 

in  the  newborn,  409. 
Heat  sense,   459;  see  also   Temperature  sensa- 
tions. 

topographical  distribution  of,  460,  Fig.  18.3. 

tracts  for,  in  the  cord,  597. 
Heat  .spots  on  the  skin,  458;  459,  Fig.  182;  461. 
Heat  units,  26,  note. 
Heliotropism,  64. 
Heller's  test  for  proteid,  69,  384. 
Hemiamblyopia,  655,  660. 
Hemianopia,  657. 
Hemilesion  of  the  cord,  597. 
Hemiplegia,  646. 

Hemisection  of  the  cord,  .59.5,  596,  640. 
Hemispheres  of  the  brain,  600. 
Henle's  loop,  385,  Fig.  144;  386. 
Henry's  law  of  absorption  of  gases,  334. 
Hepato-pancrcas  of  isopod,  244,  Fig.  99. 
Hering's  theory  of  color  vision,  544,  546. 
Hennann's  theory  of  animal  current,  48. 
Heteroalbumose,  249. 

food  value  of,  lOS. 
Hexoses,  occurrence  of,  SO. 
Hindbrain,  or  rhonienccphalon,  600,  601. 

secondary,  or  metcncephalon,  600,  601. 
Hippuric  acid,  155,  378,  383. 
Histidin,  72,  255. 
Histological  methods,  4. 
Histons,  77. 

Homocentric  bvmdle  of  light  rays,  523,  note. 
Homoiothcrmous  animals,  46,  398,  404,  442. 
Hvaloplasm,  19. 
Hydrobilirubin,  254. 
Hydrochloric  acid,  action  of,  on  ptyalin,  246. 

antiseptic  properties  of,  292. 

influence  of,  on  tryptic  digestion,  294. 

of  gastric  juice,  247. 
43 


Hydrochloric  acid,  where  formed,  268. 
Hyoglossal  muscles,  action  of,  in  deglutition, 

280,  281. 
Hydrolytic  cleavage,  70,  243. 
Hydrometric  pendulum,  210. 
Hypera'mia,  influence  of,  on  transudation,  349. 
Hyperaesthesia,  597. 
Hypermetropia,  519;  Fig.  215;  520. 
Hypertonic  solutions,  32. 
Hypogastric  nerves,  392,  Fig.  145;  693,  700. 
Hypogastric  plexus,  392,   Fig.    145,   393,  694, 

700. 
Hj-poglossal  nerve,  681. 
Hjpophysis    cerebri,    367;   see    also   Pituitary 

body. 
Hypotonic  solutions,  32. 
Hypoxanthin,  76,  252,  372,  373,  413. 

Ideas,  definition  of,  451,  note. 

formation  of,  662. 
Idiocy,  670. 
Images  in  eye,  513  seq.,  5.56,  Fig.  248. 

in  optical  system,  511,  Figs.  208,  209. 
Imbecility,  669. 

Imbibition,  capillary  and  molecular,  .3.53. 
Immunity,  156. 

Inanition,  state  of,   15.5;  .see  also  Fasting. 
Incidence,  angle  of,  509,  F'ig.  206. 
Incoordination   of   movements,    608;   .see   also 

Coordination  of  movements,  loss  of. 
Incubation,  liberation  of  oxygen  in,  27. 
Incus  of  middle  ear,  49.5,  Fig.  197. 

articulation  of,  with  malleus,  496,  Fig.  198. 
Indican,  370. 
Indigosulphate  of  .sodium,  elimination  of,   by 

kitlneys,  388. 
Indol,  378,  379. 
Indol  nucleus  in  proteid,  71. 
Indoxyl,  379. 

Indoxyl-sulphuric  acid,  379. 
Induction  coil,  419,  420,  Fig.  158. 

currents,  426. 

shocks,  422,  423. 

stimulation  of  muscles  and  nerves  by,  418, 
422,  Fig.   160. 

unipolar  effects  of,  426,  Fig.  16.3. 
Infundibuluni,  600. 
Infusoria,  chemota.xis  of,  55. 

geotaxis  of,  56. 

ingestion  of  food  in,  by  ciliary  action,  37. 

osmotic  relations  in,  34. 
Ingesta,  determination  of,  in  metabolism,  83. 
Ingestion  of  food  by  elementary  organism,  30, 

36,  Fig.  21 ;  37. 
Ingestion  of  foreign  bodies  by  leucocytes,  37. 
Inhibition,  definition  of,  50. 

of  auricle,  ISO. 

of  central  veins,  189. 

of  muscles,  antagonistic,  640. 


732 


INDEX 


Inhibition  of  reflexes,  577. 

of  ventricle,  189. 
Inhibitory  centers,  579. 
Inhibitory  nerves,  564. 
of  ga.stric  glands,  263. 
of  intestinal  glands,  276. 
of  intestinal  movements,  288,  289,  290. 
of  heart,  188  seq. 
centers  for,  195. 
course  of,  191,  Fig.  67;  681. 
of  pancreas,  269. 
of  stomach  musculature,  284. 
Inoculation,  protective,  29. 
Inorganic  foodstuffs,  83. 

Inorganic  substances,  see  Mineral  substances. 
absorption  of,  139,  307. 
of  blood,  154. 
of  diet,  139. 
of  food,  S3, 
of  milk,  702. 
of  urine,  384. 
Inotropic  effect  of  vagus  on  heart,  189. 
Inosinic  acid,  413. 
Inosit,  413. 
lodin,  amount  of,  in  blood  of  dog,  351. 

a-s  constituent  of  thyroid  gland,  26,  362. 
lodothyrin,  362. 
Ions,  dissociation  of,  32. 

permeability  of  cells  to,  34,  35. 
relation  of,  to  sense  of  taste,  485. 
stimulating  effects  of,  53. 
Insensible  perspiration,  397. 
Inspiration,    influence    of,    on    arterial    blood 
pressure,  229. 
pressure  changes  in  air  passages  in,  321. 
in  thoracic  cavity  in,  312. 
Inspiratory  muscles,  315,  316. 
Insula,  see  Island  of  Reil. 
Intercellular  bridges,  62,  Fig.  36. 
Intercostal  muscles,  315,  324. 
Interference  of  sound  waves,  501. 
Intermediary  myelogenetic  regions  of  the  cor- 
tex, 667. 
Internal  capsule,  motor  fibers  in,  637,  Fig.  287; 

647,  Fig.  292. 
Internal  secretion,  definition  of,  356. 
of  adrenal  bodies,  364. 
of  kidneys,  367. 
of  ovaries,  358. 
of  pancreas,  362. 
of  pituitary  body,  367. 
of  spleen,  368. 
of  testes,  357. 
of  thyroid,  358. 
Interrupter,  automatic,  of  induction  coil,  421, 

Fig.  159;  422,  Fig.  160. 
Intersystole,  170,  Fig.  57;  174. 
Intoxication,  30. 
Intracanlial  ganglion  cells,  186. 


Intracardial  pressure,  169,  Fig.  56. 
Intracranial  pressure,  678. 
Intrathoracic  pressure,  310. 
data  for,  in  man,  312. 
demonstration  of,  311,  Fig.  120. 
methods  for  determining,  311 
Intrauterine  pressure,  698,  699. 
Intravascular  clotting,   1.59;  see  also  Coagula- 
tion. 
Inversion  of  disaccharides,  81. 
Intestinal  epithelium    and    absorption    of    fat, 

304,  Fig.  118. 
Intestinal  fistulse,  243,  295. 
Intestinal  gases,  295. 
Intestinal  glands,  276. 
Intestinal  juice,  255. 
Intestinal  movements,  286,  288. 
Intestinal  putrefaction,  297,  298. 
Intestine,  large,  absorption  in,  302 
digestion  in,  277,  298. 
extirpation  of,  298. 
innervation  of,  289,  290. 
movements  of,  289. 
small,  absorption  in,  302  seq. 
digestion  in,  294. 
extirpation  of,  298. 
innervation  of,  288. 
movements  of,  286. 
Iris,  527. 

innervation  of,  .528. 

movements  of,  induced  from  cortex,  658. 
protrusion  of,  in  accommodation,  531,  Fig. 
226. 
Iron,  absorption  of,  307. 
elimination  of,  308. 
in  chlorophyll,  24. 
in  hjpmoglobin,  152. 
in  red  blood  corpuscles,  26. 
Irritability,  definition  of,  50. 

of  nerves,  410. 
Fsland  of  Reil,  655,  662,  Fig.  296;  668. 
Isobutyl-amino-acetic  acid,  70. 
Isodynamic  quantities  of  foodstuffs,  93. 
Lsolacto.se,  39. 

Isolated  conduction  in  nerves,  411. 
Isomaltose,  246,  383. 
Isometric  contractions,  414. 
Isotonic  contractions,  41.5. 
Isotonic  solutions,  32. 
Isthmus,  rhombencephali,  600. 

Jaw,    lower    movements    of,    in    mastication, 
278. 
in  sucking,  279. 
Jecorin,  79. 
Jennings'  theor3'  of  animal  behavior,  55. 

Keratin,  77. 

percentage  composition  of,  82. 


INDEX 


■33 


Kidney  extract,    effect   of   injecting,  intrave- 
nously, 368. 
Kidneys,  blood  supph-  to,  38n,  Fig.  143. 

effect  of  removal  of,  367,  390. 

internal  secretion  (?)  of,  367. 

tubules  of,  385,  Fig.  144. 

va.somotor  nerves  of,  233,  23.5. 

volume  of  blood  flow  through,  240. 
"Klopfversuch,"  578. 
Knee-jerk,  587. 
Kymograph,  6,  Fig.  1 :  7. 

endle.s.s  paper,  9,  Fig.  6. 

long  paper,  10. 

Labor,  698. 

Labor  pains,  698,  Fig.  302;  699,  Fig.  303. 
Laborers'  rations,  141. 

Labyrinth,    membranous,    e.xtirpation    of,    in 
pigeon,  476,  Figs.  187,  188,  189;  see  also 
Semicircular  canals,  Cochlea,  Otolith  sacs. 
Lact-albumin,  701. 
Lacta.se,  251. 
Lactation  period,  703. 
Lact-globulin,  701. 

Lactic  acid,  155,  297,  373,  374,  376,  434,  447. 
Lactose,  81. 
Lagena,  473,  475. 
Lakcd  blood,  1.50. 
Lampyris,  45. 
Language  faculties,  661. 

affected  by  lesions  in  cortex,  663,  664. 
how  acquired,  661,  662. 
recovery  of,  after  lesions  in  corte.x,  665. 
Lanolin,  80,  296. 
Laryngeal  muscles,  .502. 

Laryngeal   nerves,   inferior,   motor  for  larynx, 
324,  681. 
superior,  681. 

influence  of,   on   respiratory  movements, 

330. 
motor  for  larynx,  324,  504. 
Laryngoscope,  504. 
Laryngoscopic  picture,  504,  Fig.  202;  .505,  Fig. 

203. 
Larynx,  .502. 

control  of,  by  cerebral  cortex,  649,  6.50. 
Latent    period   of   contractions   induced   from 
cortex,  633,  Fig.  283. 
of  motor  nerve  endings,  418. 
of  nnuscle,  415,  416,  424. 
Lateral  columns  of  the  cord,  .562,  Fig.  2.54. 
Lateral  horn  of  the  cord,  562,  Fig.  2.54. 
Lateral    pressure,    202,    223;    see    also    Blood 

pressure. 
Laughing,  321. 

Lecethin,  chemical  nature  of,  78. 
elective  solvent  power  of,  34. 
percentage  coinposition  of,  82. 
Lecethin-albumins,  79. 


Leech  extract,  1.59,  351. 

LeguminosiE,  root  tubercles  of,  23,  Fig.  18;  24. 

Lemna  tri-^cula,  42,  Y\g.  25. 

Leptriplana,  64,  note. 

Lesions  of  cerebellum,  608. 

of  corona  raiUata,  647,  66.3. 

of  frontal  a.ssociation  center,  668. 

of  midbrain,  613. 

of  motor  cortex,  645,  646,  660,  661. 

of  posterior  as.sociation  center,  669. 

of  sensory  corte.x,  650,  652,  653. 

of  speech  tract,  66.3,  664,  665. 

of  spinal  cord,  59.5. 

of  temporal  convolutions,  665. 

of  'tweenbrain,  617. 
Leucin,  70,  72,  249,  255,  370,  374,  384. 
Leucocytes,  chemotaxis  of,  .54. . 

formation  of,  3.53. 

ingestion  of  foreign  bodies  by,  37,  Fig.  22. 

movements  of,  described,  42,  4.3,  Fig.  27. 

participation  of,  in  absorption  of  proteid  (?), 
306. 

permeability  of,  to  various  solutions,  33. 

phagocytic  function  of,  37. 
Leucomaines,  29-5. 
Levator  ani,  299. 
Levatores  costarum,  315. 
Lever,  recording,  6,  Fig.  1 :  7. 
Levulo.se,  behavior  of,  in  diabetes,  363. 

properties  of,  80. 

source  of  glycogen,  127. 
Lieberkiihn,  glands  of,  276,  277. 
Liebig's  classification  of  foodstuffs.  111. 
Light,  action  of,  on  iris,  527,  528. 
on  retina,  537. 

modifications  of,  541. 

physical  cause  of,  536. 

physiological  cause  of,  453. 

production  of,  by  li%nng  cells,  45. 

stimulation  by  means  of,  56. 
Light  rays  of  .solar  spectrum,  .5.36. 
Light  rays,  relation  of,  to  organ  of  vision,  541. 
Lingual  nerve  as  .secretory  nerve,  257. 

as  va.somotor  nerve,  234. 
Lipolytic  enzymes,  243. 

in  pancreatic  juice,  253. 

in  stomach,  2.50. 
Liquor  follicularis,  695. 
Listing's   schematic   eye,   511,    513,    Fig.    210; 

518. 
Liver,  blood  supply  to,  273,  274. 

exclusion  of,  from  circulation,  227,  274,  371. 

extirpation  of,  in  birds,  371. 

glycogen  formation  in,  37.5. 

regeneration  of,  6.5. 

regulation  of  circulation  by,  207,  227. 

secretion  in,  272. 

sugar  formation  in,  375. 

urea  formation  in,  371. 


734 


INDEX 


Li\-ing  substance,  15;  see  also  Protoplasm. 

beha\-ior  of,  in  metabolism,  135,  137. 

constitution  of,  20. 

form  of,  1.5. 

impetus  to  formation  of,  63,  64,  note. 
Load,  effect  of,  on  performance  of  muscle,  435, 

446,  449. 
Lobule,  paracentral,  638,  639,   Fig.  290;  652. 
Localization,  in  retina,  518. 

in  skin,  463. 

of  temperature  sense,  464. 

power   of,  affected  by  different   conditions, 
464. 
Local  sign,  463. 

Locomotor  movements,  control  of,  by  spinal 
cord,  586. 

in  decapitated  animals,  587. 
Lophiits  pif:catoriit&,  572. 
Loudness  of  sound,  489. 
Ludwig's  air  pump,  3.34,  Fig.  130. 
Lumbar  nerves,  innervation  of  urinary  bladder 

by,  392,  Fig.  145. 
Lung  catheter,  341,  Fig.  133. 
Lungs,  see  Respiration  and  Respiratory  move- 
ments. 

circulation  in,  227. 

ela.sticity  of,  310. 

exchange  of  air  in,  319. 

means  of  protection  for,  32.3,  330. 

noxious  air  space  in,  320. 

vasomotor  nerves  of,  233,  235. 

vital  capacity  of,  320. 
Lutein,  695. 
Lutein  cells,  69.5. 
Lymph,  chemical  properties  of,  347. 

composition  of,  348. 

definition  of,  347. 

formation  of,  349. 

filtration  theory,  349,  350. 
secretion  theorj',  350. 

gases  in,  348. 

medium  for  tissue  cells,  30, 

movements  of,  348. 

quantitj'  of,  formed  in  24  hrs.,  348. 
Lymph  glands,  352. 
LjTnph  hearts  of  amphibia,  349. 
Lymph  vessels,  contractions  of,  349. 

valves  of,  349. 
Lymphocytes,  153. 
LjTTiphogogic  substances,  352. 
Lymph-producing  substances,  350,  351. 
Lysin,  70,  72,  249. 

Maculae  acusticse,  475. 

Magendie's  doctrine,  565. 

Magnesium,  absorption  and  excretion  of,  133. 

in  bones,  26. 
Magnesivim  salts,   effect   of,    on   ciliary   move- 
ments, 25. 


Magnesium  salts,  importance  of,  in  plants,  24. 

Malapterunis,  50. 

Male  sexual  organs,  691. 

Malic  acid,  54. 

Malleus  of  middle  ear,  494,  Fig.  196 ;  495. 

articulation  of,  with  incus,  496,  Fig.  198. 
Malonic  acid,  377. 
]\Ialpighian  corpuscle,  386. 
Malt  sugar,  81 ;  .see  also  Malto.se. 
Maltase,  246,  251. 
Maltose,  81. 

action  of  reversible  enzyme  on,  39. 
Mammary  glands,  703. 

fat  in,  705. 

innervation  of,  704. 

morphological  changes  in,  704. 
Mannite,  80. 
Mannose,  80. 
Manometer,  elastic,  9,  Fig.  5. 

in  determination  of  blood  pressure,  202. 

mercury,  8,  Fig.  3. 
Marginal  gyrus,  634. 

Mariotte's  experiment,  515,  516,  Fig.  212. 
Marrow,  red,  of  bones,  150. 
Marsh  gas,  295. 
Mastication,  278. 
Maturity,  period  of,  706. 

sexual,  692,  696. 
Maxwell's  disks,  542. 
Meals,  83. 

Meat  as  article  of  food,  145;  see  also  Pmteid. 
Mechanical  stimulation,  56. 

of  cortex,  633. 

of  nerves,  418. 
Medulla  oblongata,  or  bulb,  600,  602. 

cardiac  centers  in,  19.5. 

functions  controlled  by,  604. 

importance  of,  604. 

nuclei  of  cranial  ner^'es  in,  603,  Fig.  269. 

respiratory  center  in,  325. 

transverse  section  of,  602,  Fig.  268. 

various  centers  in,  602,  603,  Fig.  269. 

va.somotor  centers  in,  238. 

vomiting  center  in,  286. 
Meissner's  plexus,  288,  687. 
Membrane,  animal,  osmotic  properties  of,  32, 
352. 

basilar,  of  organ  of  Corti,  499,  500,  Fig.  199. 

of  cells  in  general,  16. 

of  plant  cells,  21,  Fig.  16. 

semipermeable,  31. 
Memory,  seat  of,  671. 

Memory  pictures,  660,  663,  665,  669,  671. 
Menstruation,  cause  of,  697. 

cosmic  phenomena  and,  62. 

description  of,  696. 

physiological  significance  of,  697. 
Mental  work,  influence  of,  on  fatigue,  446,  6"6. 
Mesencephalon,  600,  613. 


INDEX 


735 


Mesocarpzis  scalaris,  54,  Fig.  31. 
Mesopoqjhyrin,  152. 
Mesoxalic  acid,  377. 
Metabolic  products,  84. 

influence  of,  on  organs,  356. 

removal  of,  by  massage,  44.5. 
Metabolism  after  extirpation  of  pancreas,  363. 
of  thyroid,  360. 

after  feeding  thyroid  extract,  361. 
Jletabolism,  definition  of,  83. 

effect  of  ca.=tration  on,  357,  358. 

experiment  in,  example  of,  91,  92. 

in  different  organs,  402. 

in  fasting,  95. 

influence  of  age  on,  119,  120. 
of  food  on,  98. 
of  muscular  work  on,  110. 
of  size  of  body  on,  117. 
of  temperature  on,  114. 

intermediary,  373,  376,  377. 

in  the  young,  118,  119. 

methods  of,  83  seq. 

of  albumoses,  108. 

of  alcohol,  110. 

of  asparagin,  110. 

of  carbohydrates,  105. 

of  cellulose,  110. 

of  fat,  104. 

of  fatty  acids,  109. 

of  gelatin,  109. 

of  gelatin-forming  substances,  109. 

of  peptones,  108. 

of  proteid,  102. 

theories  of,  134  seq. 
Metacasein,  252. 
Metallic  taste,  484. 
Metathalamus,  600. 
Metencej'jhalon,  600. 
Mctiiiemoglobin,  151. 
Methyl-glyco-cyanamid,  .382. 
Mcth_^^-indol-amino-acot)c  acid,  71. 
Methyl  mercaptan,  295. 
Micturation,  .390. 

center  for,  393,  588. 
Midbrain,  600,  613. 

importance  of,  in  fishes,  619. 
in  turtles,  621. 
Middle  ear,  494. 
Milk,  TOO. 

coagulation  C)f,  2.50. 

composition  of,  701,  703. 

effect    of,    on    properties    of    gastric    juice, 
265. 

secretion  of,  70.3. 

influence  of  nerves  on,  704. 
meciianism  of,  704. 
cjuantity  of,  705. 
Milk  sugar,  81 ;  see  also  Lactose. 

origin  of,  70.5. 


Millon's  reaction,  72. 

Mind  blindness,  669,  670. 

Mind,  mechanics  of,  670,  67.3. 

Mineral  substances,  see  Inorganic  substances. 

absorption  of,  139,  307. 

in  young  animals  and  milk,  702. 

required  by  animals,  25,  26. 
by  plants,  24. 
Minimal  air,  320. 
Minimal  requirements  of  food,  95. 

of  proteid,  124. 
Minimal  stimulus,  51. 
Mitral  valve,  16.5. 
Modalities  of  sensation,  453. 
Moderate   worker,    nutritive   requirements   of, 

142. 
Molisch's  reaction,  73. 
Monamino  acids,  70. 

Monokow's  bundle  in  the  cord,  593,  596. 
Monosaccharides,  80. 

percentage  composition  of,  82. 
Moral  significance  of  cerebral  processes,  672. 
Morphinism,  30. 

Morphological     changes     during     activity     of 
gastric  glands,  268. 

of  hepato-pancreas  of  isopod,  244,  Fig.  99. 

of  intestinal  glands,  277,  Fig.  111. 

of  mammary  glands,  704. 

of  nerve  cells,  574. 

of  pancreas,  272,  Fig.  109. 

of  retina,  537,  .538,  Fig.  232. 

of  salivary  glands,  260,  Fig.  100;  261,  Fig. 
101. 
Motility,  forms  of,  42. 
Motor  aphasia,  663. 

Motor  cortical    areas,    633;    see    also    Cerebral 
localization. 

action  on,  by  other  areas,  660,  661. 

connection  of,  with  motor  nerves,  594,  Fig. 
266 ;  647. 

development  of,  648. 

extirpation  of,  in  monkey,  644. 

finer  movements  dependent  on,  644.  I 

in  human  brain,  645. 

psycho-physical  significance  of,  659. 

stimulation  of,  601,  631,  632,  633. 
direct  and  crossed  effects  of,  640. 

suppression  of,  in  dogs,  643. 

recovery  of  functions  after,  646. 
Motor  nerves,  564. 

Motor  response  in  Paramwcium,  54,  Fig.  32. 
Motor  .sensations,  469.  • 

areas  of,  in  cortex,  652. 

conducting  tracts  of,  from  cortex  to  cord,  647. 

in  the  cord,  596. 

physiological  significance  of,  472. 
Motor  .sense,  462. 

Motor  .>?pinal  nerves,  distribution  of,  682,  G8.5. 
Motor  zone  of  corte.x,  634. 


736 


INDEX 


Mouth,  digestion  in,  290. 

sections  of  floor  of,  281,  Fig.  112. 
Mouth  cavit}',  closure  of,  in  sucking,  279. 
Movements,  active,  perception  of,  471. 
associated,  473. 
coordination  of,  473. 
passive,  perception  of,  469. 
voUintary,  449. 

how  acquired,  450. 

regulation  of,  472. 
Mo\-enients  of  abdominal  organs  in  respiration, 
316,  Fig.  125. 
of  alimentary  canal,  278. 
of  diaphragm,  316,  Fig.  125. 
of  elementary  organisms,  42. 
of  eyes,  549 ;  see  Eije  movements. 
of  intestine,  286. 
of  larynx,  in  deglutition,  281. 

in  respiration,  312. 

in  vocalization,  503. 
of  a?sophagus,  279. 
of  ribs,  314. 
of  stomach,  283. 

of  vocal  cords,  in  respiration,  312,  504,  Fig. 
202. 

in  vocalization,  503,  Figs.  200,  201;  505. 
Muscle,  cross-striated,  functions  of,  410. 

absolute  power  of,  438. 

action  currents  in,  48,  431. 

afferent  nerves  of,  reflexes  through,  470. 

blood  supply  to,  240,  449. 

central  innervation  of,  440. 

chemical  changes  in,  due  to  activity,  434. 

chemistry  of,  413. 

curves  of,  7,  414,  415,  417;  see  also  under 
Curves. 

degeneration  of,  448. 

effect  of  veratrin  on,  437,  Fig.  175. 

elasticity  of,  412,  Fig.  150;  413,  Fig.  152. 

electrical  phenomena  of,  47,  431. 

fatigue  of,  441  seq. 

general  properties  of,  410. 

glycogen  in,  81,  125,  374,  413. 

heat  formation  in,  402,  404,  439. 

latent  period  of,  415,  Fig.  154;  416. 

mechanical  work  of,  435,  Fig.  172. 

musical  tone  produced  by  contraction  of, 
434. 

permeability  of,  to  solutions,  34. 

polar  law  of  excitation  of,  428. 

Pfliiger's  law  of  contraction  of,  423. 

relation  of,  to  other  organs,  448. 

red  and  white,  comparison  of,  416. 

rigor  of,  447. 

signs  of  activity  in,  431. 

simple  contraction  of,  415;  see  also  Con- 
traction . 

stimulation  of,  414. 

summation  in,  415,  429. 


Muscle,  cross-striated,  tetanus  of,  429,  Fig.  166; 
430,  Fig.  167;  433;  see  also  Tetanus. 
tonus  of,  demonstration  of,  581. 
variations  in  tension  of,  414,  Fig.  15.3. 
voluntary  contractions  of,  430. 
work  done  by  single  contraction  of,  435. 
work  done  in  tetanus  of,  439. 
smooth,  general  physiology  of,  447. 
Muscles,  see  under  individual  names, 
skeletal,  afferent  nerves  of,  470. 
motor  nerves  of,  682. 

tonus  of  affected  by  removal   of   semicir- 
cular canals,  477. 
Muscular  sense,  469 ;  see  also  Motor  sensations. 

cortical  area  of,  652. 
Muscular  work,  CO2  production  in,  112. 
central  nervous  sj^stem  and,  448. 
destruction  of  nonnitrogenous  substances  in, 
112. 
of  proteid  in.  111. 
effect  of,  on  circulation,  449. 
on  digestion  in  stomach,  293. 
on  formation  of  living  substance,  63. 
on  heart  beat,  197. 
on  respiration,  318. 
in  tetanus,  439. 

maximum  capacity  for,  in  man,  447. 
metabolism  in,  110. 
ratio    of,    to    heat    production    in    muscle.s, 

440. 
regulation  of,  by  muscles  themselves,  437, 
439. 
Musical  agraphia,  665. 
Musical  aphasia,  665. 
Musical  faculties,  665. 
Musical  tone,  489. 
Mucin,  245. 

composition  of,  82. 
in  bile,  253. 
in  saliva,  245. 
Mucins,  74. 
Mucoids,  74. 
Mucous  glands,  245. 

morphological  changes  in,  262,  Fig.  102. 
Myelencephalon,  600,  602. 
Myelogenetic    areas,     of    cerebrum,   666,    Fig. 

297;  667,  Fig.  298. 
Mylohyoid  muscles,  importance  of,  in  degluti- 
tion, 280. 
Myochrome,  414. 
Myogen,  413. 
Myogram,  8. 

Myopia,  519,  Fig.  215,  520. 
Myosin,  413. 
Myosinogen,  413. 
Mj^ristinic  acid,  701. 
Myxoedema,  358. 

Myxoedematous  woman,  359,  Fig.  137. 
I    Myxomycetes,  27. 


INDEX 


737 


N :  C  ratio  in  faeces^  90. 

in  proteid,  92. 

in  urine,  90. 
Narcotics,  pliy.siological  effect  of,  65. 
Na.sal  breathing  compared  with  mouth  breath- 
ing, 323. 
Na.sal  cavity,  closed  in  swallowing,  281. 

closed  in  vomiting,  286. 
Native  proteids,  73. 
Nature,  limits  of  knowledge  of,  452. 
Negative  pressure  in  thorax,  310. 
Negative  variation,  433. 
Nerve    abducen.s,    etc.,    see    under    individual 

names. 
Nerve  cells,  central  functions  of,  566,  582. 

dependence  of,  on  blood  supply,  572. 

mode  of  reaction  of,  570. 

morphological  changes  in,  574. 

nutritive  functions  of,  567. 

physiological  stimuli  of,  569. 

physiology  of,  5.59  seq. 

regeneration  and  reproduction  of,  574. 

rhythm  of  discharge  of,  572. 
Nerve  centers,  fatigue  of,  676,  678. 

in  spinal  cord,  585;  see  also  Spinal  cord. 

in    medulla    oblongata,   603;    Fig.   269;  see 
also  under  individual  names. 
Nerve  endings,  of  pain  nerves,  467,  468. 

of  pressure  nerves,  461,  468. 

of  temperature  sense,  461,  468. 
Nerve  fibers,  autochthonous,  575. 

autonomic,  686. 

degeneration  in,  567. 

origin  of,  from  nerve  cells,  .559. 

physiological    differences    between    afferent 
and  efferent,  565. 

pre-ganglionic  and  post-ganglionic,  686,  687. 

regeneration  of,  564. 
Nerve  fibrils  a.s  conducting  elements,  560,  585. 
Nerve    impulse,    rate    of    transmission    of,    in 
motor  nerves  of  lower  animals,  417,  Fig. 
155. 
in  motor  nerves  of  man,  418. 
in  spinal  cord,  589. 
Nerve  processes,  559. 
Nerves,  accelerator,  191,  688. 

action  currents  in,  48,  431. 

afferent,  564,  56.5. 

alterations  of  excitability  in,  425. 

anclectrotonus  in,  425;  Fig.  162. 

carbon  dioxide  formeil  in,  434. 

cardiac,  188  .seii. 

catelectrotonus  in,  424,  Fig.  161. 

classification  of,  according  to  function,  .564. 

depressor,  of  heart,  193,  681. 

efferent,  564,  .565. 

electrical  excitation  of,  418. 
general  law  of,  420. 

electrolysis  in,  434. 


Nerves,  fatigue  of,  442,  443. 
general  properties  of,  410,  411. 
heat  production  in,  402. 
inhibitory,  188. 
intercostal,  324. 
isolated  conduction  in,  411. 
mechanical  stimulation  of,  418. 
motor,  of  bladder,  393. 

of  stomach,  284,  Fig.  1 14 :  see  also  Stomach. 
of  throat,  282,  Fig.  113. 
polar  law  of  excitation  of,  424. 
Pfliiger's  law  of  contraction  of,  59,  423. 
promoting,  192. 
pulmonary,  681. 

rate  of  transmission  in,  417,  418. 
signs  of  activity  in,  431. 
special,  physiology  of,  680. 
specific  response  of,  411. 
spinal,  682. 

stimulation  of,  by  induction  currents,  426, 
Fig.  163. 
in  arm  of  man,  427,  Fig.  164. 
sjTnpathetic,  685. 
trophic,  569. 

va.soconstrictor,  231,  .582,  681,  685. 
vasodilator,  233,  234.  449,  681,  685. 
Nervi  erigentes,  393,  6SS,  693,  694,  700. 
Nervous  system,  31. 
central,  559. 

effect  of  different  poisons  on,  574. 
elemental  structure  of,  summary,  561. 
influence  of  thyroid  on,  360. 

of  testes,  357. 
segmentation  of,  575. 
sjTnpathctic  or  autonomic,  686. 
Network,    intracellular,    of    nerve    cells,    560, 
Fig.  252. 
pericellular,  of  Golgi,  561,  Fig.  253. 
Neuro-fibrils,  .560,  585. 
Neuron  theorj^  559. 
Neurons,  559. 
Neuropile,  560,  561. 
Newborn,  period  of,  706. 

weight  of,  706,  707. 
Nicotin,  use  of,  in  tracing  ganglionic  connec- 
tions, .582. 
in  tracing  vagus  fibers,  190,  191. 
Nitric-oxide  hiomoglobin,  152. 
Nitrogen,  absorption  of,  by  the  blootl,  335. 
by  plants,  23.  24. 
channels  of  excretion  of,  89,  90. 
determination  of,  in  food  and  excreta,  S3,  84. 
fixed  by  Bacteria,  24. 
in  blood,  335. 

in  digestive  products  of  proteid,  295. 
in  expired  air,  89. 
in  fipces,  90. 
in  parotid  gland,  259. 
in  sweat,  89. 


738 


INDEX 


Nitrogen  in  urine,  89. 
Nitrogen  excretion,  89,  90. 

diurnal  variations  of,  102,  Fig.  44. 

in  .starvation,  100,  101. 

proportional  to  N  ab.sorbed,  101. 
Nitrogenous  equilibrium,  91,  120,  121,  122. 

minimum  proteid  for,  103. 

on  various  quantities  of  proteid,  100. 
Nitrogenous  substances  in  the  body,  68. 
Nodal  points  of  optical  system,  511,  Fig.  209. 

of  schematic  eye,  513,  Fig.  210. 
Nonnitrogenous   foodstuffs,    .see   Carbohydrates 
and  Fats. 

destruction  of,  in  muscular  work,  112. 
Nonnitrogenous  substances  in  the  body,  79. 
Nonnucleated  cells,  17. 
Nubecula  in  urine,  380. 
Nuclei  of  cranial  nerves,  603,  Fig.  269. 
Nucleic  acid,  digestion  of,  255. 

percentage  composition  of,  82. 
Nuclein  ba.ses,  76 ;  see  also  Purin  bases. 
Nucleins,  76,  351,  372. 

digestion  of,  252,  255. 

percentage  composition  of,  82. 
Nucleo-albumin-s,  75. 

Xucleo-histon,  percentage  composition  of,  82. 
Nucleo-proteids,  77. 

Nucleus,  agency  of,  in  activation  of  o.xygen,  19, 
note. 

form  and  size  of,  16. 

importance  of,  17,  18. 

number  in  cells,  16. 

of  cell,  16. 

of  ovum,  695. 

reciprocal  relations  of,  with  protoplasm,  17. 

red,  of  tegmentum,  593. 
Nvicleus  reticularis  tegmenti,  603. 
Nutrition,  see  Food  and  Nutritive  requirements. 

definition  of,  83,  note,  137. 

of  the  brain,  676. 

of  the  heart,  180. 

of  the  young,  143. 

physiology  of,  137. 
N\itritive  influence  of  cerebral  corte.x,  650. 

of  nerve  cells,  567,  568,  582,  584. 

of  spinal  ganglia,  .584. 
Nutritive  requirements  of  adult  males,  140. 

of  persons  of  different  ages,  144. 

Occipital  convolutions,  639,  Fig.  289;  657. 
Octave,  490. 
Oculo-motor  nerve,  680. 

accommodation  and,  534. 

nuclei  of,  535,  Fig.  230;  615,  Fig.  272;  616, 
Fig.  273. 

pupil  and,  528. 
Odors,  classification  of,  488. 

theories  of  transmission  of,  486,  487. 
(Esophageal  fistula,  263. 


(Esophagus,  inner\'ation  of,  281. 

movements  of,  in  swallowing,  280. 
Ohm's  law  for  analysis  of  sound,  493. 
Oil  and  coagulation  of  blood,  159. 
Old  age,  metabolism  in,  120. 

period  of,  706. 
Oleic  acid,  296. 
Olein,  79,  701. 
Olfactometer,  487,  Fig.  192. 
Olfactory  area.s  in  the  cortex,  653. 
Olfactory  cells,  487. 
Olfactory  epithelium,  486. 
Olfactory  lobe,  600,  619. 
Olfactory  nerves,  action  of,  on  respiration,  330. 

specific,  of  smell,  488. 
Opalina  ranarurn,  61,  Fig.  35. 
Opening  contraction,  420,  423. 
Opening  period  of  parturition,  698. 
Operative  interference,  5. 
Optic  cortex,  activity  of,  660. 

connections  of,  660,  662,  Fig.  296;  663. 

efferent  fibers  from,  657. 
Optic  lobes.  Figs.  274,  275,  276,  277,  278. 

equivalent   to    corpora   quadrigemina,    613; 
irhich  also  see. 
Optic  nerve,  330;  535,  Fig.  230:  656,  Fig.  295; 
657,  680. 

efferent  fibers  in,  515,  Fig.  211. 

reflex  effect  of,  on  respiration,  330. 
Optic  thalamus,  000. 

effect  of  lesions  in,  617. 

substitution  of  functions  in,  617. 
Optic  tracts,  schematic  representation  of,  535. 

Fig.  230;  656,  Fig.  295. 
Optical  axis,  513,  Fig.  210;  525. 
Optical  constants  of  the  eye,  508. 
Optical  defects  of  the  eye,  520. 
Optical  system,  nodal  points  of,  defined,  .511,. 
Fig.  209., 

of  the  eye,  509,  510. 
Optical  zone  of  the  cornea,  522. 
Optogram,  537. 

Organ  of  Corti,  499,  500,  Fig.  199. 
Organ  system,  definition  of,  30. 
Organic  foodstuffs,  S3. 
Organic  sensations,  469. 
Organs,  cooperation  of,  30. 

influence  of,  on  one  another,  1,  355. 

surviving,  6. 
Orientation,    importance    of    otolith    sacs  for, 

473,  481. 
Oscillaria,  29. 
Osmosis,  31. 

Osmotic   phenomena,    significance   of,    for   ab- 
sorption, 35,  301,  3.53. 
for  different  organs  and  tissues,  34,  355. 
for  elementary  organisms,  33,  34. 
for  excretion,  41. 
for  l^^nph  formation,  349. 


INDEX 


739 


Osmotic  phenomena,  ?ig;nificance  of,   for  pro- 
duction of  urine,  387. 
Osmotic  pressure,  definition  of,  31. 
0.smotic  ten.sion  in  animal  cells,  .35. 

in  plant  cells,  33. 
Ossein,  78. 

Ossicles  of  middle  ear,  495. 
Otolith,  481. 

Otolith  sacs,  function.s  of,  481. 
Ovaries,  69.5. 

internal  secretion  of,  358. 
Overtones,  definition  of,  491,  492,  Fig.  194. 

in  human  voice,  505. 
Oviduct,  095. 
Ovovitellin,  79. 
Ovulation,  696. 
Oxalic  acid,  41,  376,  377,  383. 
O.xidation,  27;  see  al.so  Combustion. 
Oxidative  processes  in  cells,  39. 
Oxyacids,  aromatic,  378. 
Oxybenzuric  acid,  378. 
Oxybutyric  acid,  37G,  384. 

Oxyethyl-trimethyl-ammonium  hydroxide,  78. 
Oxygen,  absence  of,  effect  on  eggs  of,  26. 
behavior  of  frogs  in,  27. 
suitability  of,  for  certain  Bacteria,  28. 
absorption  of,  by  blood,  336,  337,  Fig.  131. 

total  in  man,  346. 
activation  of,  19,  note. 

amount  of,  absorbed  under  different  circum- 
.stances,  346. 
consumed  by  elementary  organisms,  27. 
coefficient  of  absorption  of,  3.36. 
combination  of,  in  blood,  336. 
determination  of,   in  blood,   334,   Fig.    130; 
335. 
in  metabolism  experiments,  86,  88. 
distribution  of,  in  blood,  340. 
importance  of,  for  development,  26,  27. 
increa.sed  consumption  of,  in  fatigue,  446. 
partial  pressure  of,  in  alveolar  air,  336. 
percentage  of,  in  arterial  and  venous  blood, 
339. 
in  expired  air,  343. 
in  inspired  air,  342. 
stored  in  loo.se  compounds,  27. 
tension  of,  in  blood,  341. 
in  lymph,  348. 
Oxyha-moglobin,  1.50,  1.51. 

absorption  spectrum  of,  151,  Fig.  47. 
Oxymonamino  acids,  70. 
Oxyphenyl-amino-propionic  acid,  71. 
Oxyproteic  acid,  373,  382. 
O.xypyrimidin,  76. 
OxypyiTolidin-carboxylic  acid,  72. 

Pain,  465. 

after  hemilesion  of  the  cord,  597. 
area  for,  in  cortex,  652. 


Pain,  end  organs  of,  468. 

nerves,  (?)  467. 

physiological  cause  of,  466. 

tract  for,  in  the  cord,  597. 
Pain  points  in  the  skin,  467. 
Pains,  labor,  698,  Fig.  302. 
Pahxtnonete-s,  60,  Fig.  34. 
Pallium  of  the  brain,  600. 
Palmitic  acid,  79. 
Palmitin,  79,  701. 

Pancreatic  diabetes,  127,  128,  362,  37.5. 
Pancreatic  fistula,  243,  251. 
Pancreatic  juice,  2.51. 

action  of,  on  carbohydrates,  2.51,  297. 
on  fats,  253,  295. 
on  proteids,  252,  294. 

enzymes  in,  251,  271,  Fig.  108. 

influence  of  bile  on,  251,  294. 

of  food  on,  270,  Fig.  107;  271,  Fig.  108. 

properties  of,  251. 

secretion  of,  269. 

daily  course  of,  270,  Figs.  106,  107. 
ner\-ous  control  of,  269. 
Pancreas,  effects  of  extirpation  of,  127,  362,  375. 

internal  secretion  of,  362. 

morphological  changes  in,  272,  Fig.  109. 

specific  excitants  of,  270,  271. 
Papillary  muscles,  action  of,  166. 
Paraca.sein,  250. 

Paracentral  lobule,  638,  639,  Fig.  290;  652. 
Paracresol,  379. 
Paracresol-sulphuric  acid,  379. 
Paralactic  acid,  155. 
Paralysis,  definition  of,  50,  65. 

following  partial  destruction  of  the  cord,  596. 

following  removal  of  motor  corte.x,  644. 
Paramacium,  chemotaxis  of,  5.5. 

directive  influences  on,  55,  59,  note. 

electrical  stimulation  of,  59. 

geotaxis  of,  56. 

motor  respon.se  of,  55,  Fig.  32. 

starvation  of,  28. 

thermotaxis  of,  .59. 

thigmotaxis  of,  56. 
Paramyosinogen,  413. 
Paranuclein,  75. 

Para-plu'uyl-amino-propionic  acid,  71. 
Parenchyma  cells  of  root  cortex,  21,  Fig.  16. 
Parietal  cells,  267. 

secretion  capillaries  of,  267,  Fig.  10.5. 
Parietal  convolutions,  see  Central  convolutions. 
Parietal  lobes,  624,  Fig.  280;  645. 
Parotid  glands,  innervation  of,  257,  2.58. 

morphological  changes  in,  260,  Fig.  100;  261, 
Fig.  101. 
Paroxy-bcnzuric  acid,  .378. 
Paroxy-phenyl-acetic  acid,  378. 
Paroxy-phenyl-propionic  acid,  378. 
Pars  mamillaris  hypothalami,  600. 


740 


INDEX 


Pars  optica  hypothalami,  600. 

Partial  pressure  of  gases,  334. 

Parturition,  691,  697. 

Passive  movements,  perception  of,  469. 

Pathogenic  bacteria,  ingestion  of,  by  leucocytes, 

37. 
Pathology,  relation  of,  to  physiology,  4. 
Pectorales  as  muscles  of  respiration,  316. 
Peduncles  of  the  cerebellum,  593,  612. 
Pclomyxa,  57. 

Pendulum  hydrometric,  210. 
Pendulum  movements  of  the  intestine,  287. 
Penis,  692,  693. 
Penta-methyl-endiamin,  249. 
Pentoses,  81. 
Pepsin,  formation  of,  267. 

properties  of,  248. 
Pepsin-hydrochloric  acid,  action  of,  291. 
Pepsinogen,  248. 
Peptoids,  249. 
Peptones,  75,  249,  255,  351. 

food  value  of,  108. 

intestinal  juice  and,  255. 
Peptozymes,  250. 

Pericardium,  role  of,  in  action  of  heart,  177. 
Perilymph,  495. 
Period  of  ejection  of  the  heart,  171. 

of  relaxation  of  muscular  contraction,  416. 

of  rising  tension  of  the  heart,  171. 

of  shortening  of  muscular  contraction,  416. 

refractorj^,  of  heart,  183. 
of  nerves,  429. 
of  nerve  cells,  572. 
Peripheral  ganglia,  583,  584,  Figs.  258,  259. 
Periphery  of  retina,  adaptation  of,  to  light  and 
dark,  540. 

color  vision  with,  546. 

vision  with,  514. 
Peripleneta,  56. 
Peristalsis,  288. 
Permeability  of  blood  corpuscles,  33,  34. 

of  cross-striated  muscles,  34. 

of  living  and  dead  membranes,  34. 
Perspiration,  see  Sivcat. 

insensible,  394,  397. 
PfHiger's  law,  423. 
Phagocytosis,  37,  54. 
PharjTix,  action  of,  in  swallowing,  280. 
Phenol,  295,  378,  379. 
Phenolphthalein,  147,  379. 
Phenol-sulphuric  acid,  379. 
Phenyl-acetic  acid,  378. 
Phenylalanin,  71,  72,  249. 
Phenj'l-propionic  acid,  378. 
Phlebin,  150. 

Phloridzin,  127,  374,  note,  375. 
Pholas,  4.5. 

Phospho-carnic  acid,  413. 
Phosphorescence,  45. 


Phosphorus,  absorption  of,  132. 

excretion  of,  132. 

in  iodothyrin,  362. 

in  proteids,  75,  76,  82. 
Phosphorus  poisoning,  129. 
Photograplw,  registration  by,  13. 
Phototaxis,  57. 
Phrenic  nerve,  324,  331. 
Phrenology,  630. 
Phylloporphyrin,  152. 
Physical  methods  of  investigation,  4. 
Physiological  salt  solution,  53. 
Physiology,  general  and  special,  15. 

province  of,  2. 
Pigment  granules,  22. 
Pigments  in  the  bile,  253. 

in  the  blood,  150. 

in  the  eye,  527,  537. 

in  niuscle,  414. 

in  urine,  383. 
Pilocarpine  and  formation  of  urine,  389. 
Pilomotor  fibers,  687,  688. 

connection  of,  with  ganglion  cells,  582. 
Pineal  body,  600,  613. 
Pitch  of  .sound,  489. 

of  human  voice,  how  caused,  505. 
Pituitary  body,  internal  secretion  of,  367. 
Placenta,  698. 

Plasma,  chemical  constitution  of,  154. 
Plasmolysis,  33. 
Plastic  foodstuff. s.  111. 
Platelets  of  the  blood,  153. 
Plethysmograph,  211,  Fig.  83. 
Plethysmographic  curve,  212,  Fig.  84. 

in  sleep,  677,  Fig.  299. 
Plexus,  cardiac,  191,  Fig.  67. 

hypogastric,  392,  Fig.  145;  393,  694. 

myentericus,  288. 

of  .\uerbach,  284,  Fig.  114;  288,  687. 

of  Meissner,  288,  687. 

vesical,  392,  Fig.  145. 
Pneumographic  curve,  313,  Fig.  121. 
Poikilothermous  animals,  46,  442. 
Poisons,   physiological   significance  of  certain, 

574. 
Poisonous  constituents  in  expired  air,  344. 
Poisseuille's  formula,  222. 
Polar  law  of  excitation,  424. 
"Polar  failure"  of  excitation,  428. 
Polarizing  current,  425,  434. 
Polysaccharides,  chemical  constitution  of,  82. 

properties  of,  81. 
Polystomclla,  17,  Fig.  14. 
Pons,  600,  612. 
Portal  circulation,  137,  162. 
Portal  vein,  162;  see  also  Eck  fistula. 
Position  of  the  body,  influence  of,  on  flow  of 
blood,  226,  Figs.  93,  94;  227. 

perception  of,  469,  481. 


INDEX 


741 


Posterior  columns  of  the  cord,  562,  Fig.  254. 

Posterior  horn  of  the  cord.  563. 

Dosterior  roots  of  the  spinal    nerves,  563,  564, 

566. 
Postganglionic  fibers,  687,  688,  689. 
Potassium  salt.s,  effect  of,  on  heart,  25. 
on  smooth  muscle,  25. 

importance  of,  in  plants,  24. 

to.xicity  of  urine  due  to,  381. 
Potential,  electrical  differences  of,  47,  418. 
Potential    energy   of    foodstuffs,    92;   see   also 

Energy. 
Precipitins  in  the  blood,  156. 
Preganglionic  fibers,  686,  689. 
Pregnancy,  697. 
Presbyopia,  530. 
Pressure,  abdominal,  299,  699. 

in  the  mouth  cavity,  279,  280. 

in  the  respiratory  passages,  321. 

intracardial,  169,  Fig.  56;  170,  Fig.  57;  171, 
Fig.  58;  173,  Y\g.  60. 

intracranial,  678. 

intrathoracic,  228,  310. 

intrauterine,  698,  Fig.  302;  699,  Fig.  303. 

of  the  blood,  see  Blood  pressure. 

osmotic,  31 ;  see  also  Osmotic  phenomena. 
Pressure  points  or  spots  in  the  skin,  459,  Fig. 

182;  462. 
Pressure  sensatiorLs,  458,  461. 

application  of  Weber's  law  to,  456. 

local  sign  of,  463. 
Pre.s.sure  .sense,  461. 

area  for,  in  cortex,  652. 

end  organs  of,  468. 

nerves  of,  461. 

tract  for,  in  the  cord,  597. 
Primary  follicle,  695. 
Primordial    myelogenetic  regions  of  the  cortex, 

667. 
Primordial  ova,  695. 
Primordial  sheath,  33. 
Products    of    metabolism,    see    Decomposition 

products. 
Projection    of    scnsation.s    in    general    to    the 
external  world,  454. 

of  visual  sensations  to  the  external  workl, 
552. 
Projection  fibers  of  the  brain,  667. 
Promoting  nerves  of  the  heart,  192. 
Prosencephalon,  600. 
Prostate.  691. 

Prosthetic  group  in  compound  proteids,  75. 
Protagon,  79. 
Protamins,  70,  77. 
Protection,  against  less  of  heat,  404. 

insured  by  blood,  157. 

means  of.  for  lungs,  323,  324. 
Proteid,  absorption  of,  305. 

amount  of,  in  daily  ration,  142. 


Proteid,  chemistry  of,  see  Proteids. 
circulating,  134. 
decomposition  of,  in  body,  369. 
determination  of,  in  food,  83,  84. 
importance  of,  in  metabolism,  98. 
in  urine,  384. 
metabolism  of,  99. 

in  fa.sting,  97. 

in  muscular  activity,  112. 

influence  of  body  mass  on,  117. 

influence  of,  on  total  metabolism,  102. 

proportional  to  proteid  ingested,  99. 

with  carbohydrates,  105. 

with  fats,  104. 
physiological  heat  value  of,  93. 
putrefaction  of,  in  intestine,  378. 
relation  of,  to  living  substance,  20. 
requirements,  different  views  on,  142. 
retention,  120. 

in  growing  body,  123. 
source  of  fat  in  the  body,  129,  130. 
source  of  glycogen,  127. 
sjTithesis  of,  in  animals,  25. 

in  plants,  23. 
tissue,  134. 
utilization  of,  138. 
Proteids,  action  of  digestive  fluid-s  on,  248,  252, 
255. 
as  constituents  of  dead  protoplasm,  20. 
atomic  groups  in,  70. 
carbohydrate  groups  in,  71. 
chemical  constitution  of,  69,  70,  82. 
color  reactions  for,  72. 
compound,  75. 
conjugated,  75. 
crystallized,  68,  69,  Fig.  38. 
formation  of,  in  plants,  23. 
modified,  68. 
native,  69. 
of  blood,  154. 
of  milk,  701,  703. 
origin  of,  23. 

percentage  composition  of,  82. 
physiology  of,  see  under  Proteid. 
phosphorus-containing,  75,  76. 
precipitants  of,  69. 
properties  of,  68. 
salted  out,  69. 
simple,  75. 
solubility  of,  68,  69. 
Proteolytic  enzyme,  243. 
in  intestine,  255. 
in  pancrea.s,  252. 
in  stomach,  248. 
Proteoses,  250. 

Protoalbumose,  food  value  of,  108. 
Protoplasm,  appearance  of,  29. 
chemical  constitution  of,  20. 
chemical  nature  of,  68. 


742 


INDEX 


Protoplasm,  chemical  and  physical  properties 
of,  19. 

decomposition  products  of,  6S,  70,  ^49. 

differentiations  of,  16. 

formation  of,  in  animals,  25. 
in  plants,  23. 

inclosures  in,  21,  22. 

morphology  of,  20. 

motility  of,  42. 

osmotic  properties  of,  31  seq. 

power  of,  to  store  oxygen,  27. 

relation  of,  to  nucleus,  17. 

state  of  aggregation  of,  19. 
Protoplasmic  processes,  42. 

of  nerve  cells,  559. 
Pseudoglobulin,  154. 
Pseudohtemoglobin,  1.52. 
Pseudonuclein,  75. 
P.seudopodia,  36,  42. 

of  Amoeba,   35,    Fig.  20;  36,  Fig.  21;  42,  43. 

of  Gromia  oviformis,  35,  Fig.  19. 

of  Polystomella  venusta,  17,  Fig.  14. 

of  Thalassicola  nucleota,  18,  Fig.  15. 
Psycliical  activities,  organs  of,  666. 

substratum  of,  629. 
Psychical    disturbances    after    extirpation    of 

thyroid,  361. 
Psychical  influence  over  reflexes,  577,  579. 
Psychology  of  Gall,  629,  630. 
Psycho-physical  events,  time  required  by,  673. 
Psycho-physical    functions    of    the   cerebrum, 

658. 
Pterygoid  muscles  in  mastication,  278. 
Ptyalin,  245,  246. 
Puberty,  in  the  male,  692. 

in  the  female,  697. 

influence  of,  on  growth,  708,  709,  710 
Pulmonary  arteries,  161. 

pressure  in,  228. 
Pulmonary  circulation,  227  seq. 
Pulse,  arterial,  212. 

venous,  234. 
Pulse  curve,  12,  Fig.  11;  216,  Fig.  88. 
Pulse  rate,  see  Heart  beat. 

as  affected  by  food,  etc.,  197. 

at  dififerent  ages,  197,  Fig.  71. 
Pulse  volume,  204. 

dependence  of,  on  flow  from  great  veins,  184. 
Pupil,  constriction  of,  528. 

by  cortical  stimulation,  658. 
center  for,  529. 

dilatation  of,  528. 

by  cortical  stimulation,  6.58. 
center  for,  529. 
Purin  bases,  76,  255,  372,  382. 
Purkinje's  figure,  516. 

Putrefaction  m  the  intestine,  297,  298,  378. 
Putrefactive  products,  295,  378. 
Putrescin,  249. 


Pyloric  fistula,  267. 
Pyloric  glands,  266. 
Pylorus,  innervation  of,  284,  Fig.  114.  < 

movements  of,  283. 
Pyramidal  cells  of  the  cortex,  634,  Fig.  284. 
Pj'ramidal  tracts  in  the  cord,   593,   595,   596, 

647,  648. 
Pyrimidin,  76. 
Pyrrolidin  nucleus,  71. 
Pyrrolidin-carboxylic  acid,  71,  72.  249. 

Qualitative    relations    between    stimulus    and 

sensation,  451. 
Quantitative   relations  between    stimulus    and 

sensation,  455. 
Quotient,  respiratory,  105,  343. 

Radiation  of  heat,  403. 

Radium,  58. 

Rami  communicantes,  687,  689 

Ration,  Voit's,  142. 

Ration  for  woman,  143. 

Reaction  time,  673. 

as  effected  by  fatigue,  etc.,  674. 

discrimination,  676. 

muscular,  675. 

simple,  673. 

to  different  .sensory  stimuli,  674. 
Receptaculum  chyli,  349. 
Recovery  after  fatigue,  66. 

of  muscle,  445,  446. 

of  nerve,  443. 

of  visual  organ,  539. 
Recover}'  of  njuscular  functions  after  destruc- 

•  tion  of  cortex,  646. 
Rectum,  innervation  of,  289. 

reflex  induced  from,  299. 
Recurrent  fibers,  584. 
Recurrent  sensibilitj',  566. 
Red  blindness,.  546. 
Red  blood  corpuscles,  see  under  Blood. 
Red-green  blindness,  547. 
Reduced  eye,  512. 
Reducing  substance  in  urine,  383. 
Referred  pains,  689. 
Reflection  of  pulse  waves,  214,  218. 
Reflex,  causing  ejaculation,  693. 

contractions,  571,  Fig.  256. 

definition  of,  411,  570. 

fall  of  blood  pressure,  237,  Fig.  98. 

origin  of  tonus,  581. 

proces.ses,  575. 

responses  to  different  stimuli,  580. 

rise  of  blood  pressure,  236,  Fig.  97. 

stimulation  of  nerve  cells,  570,  571. 

touch,  660. 
Reflexes,  axon,  584,  Fig.  258. 

augmentation  of,  579. 

facilitation  of,  579. 


INDEX 


r43 


Reflexes,  flexor  and  extensor,  587. 

from  heart,  194. 

general  features  of,  576. 

inhibition  of,  577. 

locomotor,  617. 

purposive,  577,  586. 

p.sychical  influence  over,  577. 

reenforcement  of,  579. 

regulative,  576. 

respiratory,  327. 

segmental,  576. 

suppression  of,  .578,  579. 

tendon,  587. 

through  sympathetic  ganglia,  583. 

to  different  stimuli,  580. 

to  heart,  193. 

to  pancrea-s,  270. 

to  .salivary  glands,  260. 

to  stomach,  263. 

vasomotor,  23.5. 
Refraction,  angle  of,  509. 

in  eye,  510. 

of  light,  .508. 

static,  in  eye,  519. 
Refractory  period  of  heart,  183. 

of  nerve  cells,  572. 

of  nerves,  429. 

of  skeletal  muscle,  429. 
Regeneration,  64. 

determining  factor  in,  64,  note. 

in  .sj-mpathetic  system,  689. 

of  kidney  ti.-<sue,  65. 

of  liver  tissue,  65. 

of  nerve  tissue,  574. 
Registers  of  voice,  504. 
Registration,  see  Graphic  method. 

by  air-transmission,  11. 

by  photography,  13. 
Regulation  of  blood  pressure,  194,  219. 

of  heart  activity,  186,  194. 

of  respiration  Ijy  vagi,  .327. 

of  temperature  in  bofly,  406. 
Regurgitation  of  blood,  166,  167. 
Rennin,  250. 
Reproduction,  physiology  of,  691. 

post-embryonic,  of  nerve  celLs,  574. 
Re-serve  air,  320. 
Residual  air,  320. 
Resistance  in  arteries,  20.5. 

to  conduction  in  nerves,  411,  425,  426. 

to  electric  current,  418,  Fig.  156. 

to  fatigue  of  nerves,  442. 
Resonance,  492. 
Resonance  theory  of  hearing  musical  sounds, 

498. 
Resonance  tone  of  external  auditory  meatus, 
494. 

objections  to,  501. 
Resonator  of  Helmholtz,  493,  Fig.  195. 


Resonators  of  cochlea,  498. 
Respiration,  action  of  various  efferent  nerves 
on,  330. 

artificial,  5,  231,  325. 

effect  of  suction  in  thorax  on  work  of,  312. 

exchange  of  air  in  lungs  in,  319. 

heat  loss  and,  403. 

influence  of  higher  brain  centers  on,  329. 

innervation  of,  .323. 

movements  of,  310. 

muscular  work  and,  318. 

periodic  variations  in,  333. 

regulation  of,  by  vagi,  327. 

residual  air,  reserve  air,  etc.,  of,  320. 

types  of,  318,  Fig.  126;  3.33. 
Respiration  apparatus,  of  .\twatcr  and  Bene- 
dict, 86. 

of  Pettenkoffer,  86. 

of  Pettenkoffer  and  Voit,  87,  Fig.  41 ;  88. 

of  Sonden  and  Tigerstedt,  88,  Fig.  42;  89. 
Respiration  calorimeter,  86,  Fig.  40. 
Respiratory  center,  325. 

normal  stimulation  of,  331. 

resistance  of,  to  asphyxiation,  573,  Fig.  257. 
Respiratory  centers,  spinal,  325,  326. 
Respiratory  curve  of  rabbit,  314,  Fig.  123;  328, 

Fig.  129. 
Respiratory  exchange  of  gases,  340. 

amount  of,  345. 
Respiratory  foods.  111. 
Respiratory-  movements,  310. 

concomitant,  .321. 

effect  of,  on  blood  pressure,  227. 
on  heart,  176. 

force  of,  322. 

innervation  of,  323. 

number  of,  318,  319,  Fig.  127. 
registration  of,  312. 

special  forms  of,  321. 
Respiratory  nerves,  324. 
Respiratory  passages,  310,  323. 

ciliated  epithelium  in,  .323. 

pressure  variations  in,  321. 
Respiratorj'  products,  89,  342. 
Respiratory  quotient,  105,  34.3. 

use  of,  in  metabolism  experiments,  105. 

values    of,    under    different    circumstances, 
343. 
Respiratorj'^  reflexes,  327. 
Respiratory  sounds,  322. 
Respiratory  system,  31. 
Respiratory  variations  of  blood  pressure,  229, 

Fig.  95;  230,  Fig.  96. 
Restitution  after  lesions  of  corte.x,  646. 
Retention  of  proteid,  120. 

in  growing  body,  123. 
Reticulin,  78. 

percentage  composition  of,  82. 
Reticulum  of  the  neuropile,  560,  561,  585. 


744 


INDEX 


Retina,  action  current  in,  537. 

adaptation  of,  540. 

centrifugal  fibers  to,  515,  Fig.  211. 

excitation  of,  536  seq. 

fatigue  and  recovery  of,  539. 

histological  structure  of,  515,  Fig.  211. 

images  upon,  513. 

light-perceiving  layer  of,  514. 

morphological  changes  produced  in,  by  light, 
537,  538,  Fig.  232. 

relation  of   properties  of  light  to   different 
constituents  of,  541. 
Retina^,  correspondence  of,  555. 

projection  of,  on  cortex,  655. 

rivalry  of,  555,  Fig.  247;  556. 
Retinal  images,  511,  513. 

relation  of,  to  tactile  impressions,  556. 

size  of,  554. 
Retinal  pigment,  541. 
Retinal  vessels,  shadows  of,  516. 
Rheocord,  418,  Fig.  156. 
Rheotactic  influence  on  spermatozoa,  697. 
Rheotaxis,  56. 

Rheotome  experiment,  431,  Fig.  168. 
Rheotome  of  Bernstein,  432,  Fig.  169. 
Rheotropism,  64. 
Rhinencephalon,  600. 
Rhizopoda,  37. 
Rhombencephalon,  600. 
Rhythmical      contractions     of      cross-striated 

muscle,  53. 
Rhythmical  segmentation,  287,  288,  Fig.  116. 
Rib-lifting  muscles,  315. 
Ribs,  movements  of,  314. 
Rigor  mortis,  447. 
Ringer's  solution,  25  note;  182. 
Rise  of  temperature,  effect  of,  on  lower  organ- 
isms, 29. 
in  human  body,  401. 
Ritter's  tetanus,  421. 
Rivalry  of  retina?,  555,  Fig.  247;  556. 
Rods  and  cones,  515,  Fig.  211. 

functions  of,  541. 
Rontgen  rays,  58. 
Root  tubercles,  23,  Fig.  18;  24. 
Rotation,    an   effect   of   removing   cerebellum, 
608. 
in  protoplasm,  42. 
Rotation  axes  of  eye,  549,  550,  Fig.  240. 
Rotation  center  of  the  eye,  549. 
Round  window,  497. 
Rubro-spinal  tract  in  the  cord,  593,  595. 

Saccharinic  acid,  374. 

Saccharose,  81. 

Sacculus  of  internal  ear,  473. 

Sacral  nerves,  392,  Fig.  145;  393. 

Salicylic  acid,  378. 

Salicyluric  acid,  378. 


Saliva,  245,  246. 
Salivary  glands,  257. 

electrical  phenomena  of,  48,  257. 
morphological  changes  in,  261. 

nerves  of,  257,  258. 
centers  for,  261. 

specific  excitants  of,  260. 
Salt,  common,  physiological  importance,  25. 

physiological  solution  of,  53. 
Salt  hunger,  131. 
Salt  plasma,  157. 
Salt  taste,  484. 
Salting  out,  69. 

Salts,  required  by  animals,  25,  26;  see  also 
Inorganic  substances  and  Constituents, 
inorganic. 

by  heart,  25,  182. 

bj'  plants,  24. 
Sap  of  plant  cells,  21,  Fig.  16;  33. 
Saponification  ec)uivalent  of  fats,  79. 
Sarcolactic  acid,  376. 
Sarcolemma,  16. 
Saturation  of  color,  541. 
Scaleni  muscles,  315. 
Scheiner's  experiment,  553,  Fig.  243. 
Schematic  eye,  511,  513,  Fig.  210. 
Schwann's  experiment,  439. 
Scyllium  canicida,  brain  of,  619,  Fig.  275. 
Season,  influence  of,  on  growth,  710. 
Sebaceous  glands,  394. 
Sebum,  394. 

Secondary  contractions,  433. 
Secondary  sexual  characters,  357. 
Secondary  tetanus,  433. 
Secretin,  271. 
Secretion,  as  a  process,  definition  of,  41, 

conditions  for,  in  stomach,  265. 

filtration  theory  of,  259. 

in  intestinal  glands,  276. 

in  pancreas,  269. 

in  salivary  glands,  257. 

in  sebaceous  glands,  394. 

internal,     356;      see      also    Internal     secre- 
tion. 

of  bile,  272. 

of  digestive  fluids,  256. 

of  sweat,  396. 

paralytic,  259. 

psychical,  263. 
Secretion  as  a  product,  see  under  individual 

names. 
Secretion  capillaries,  267,  Fig.  105. 
Secretion  droplets,  244,  Fig.  99. 
Secretion  vacuoles,  261,  Fig.  101. 
Secretory  nerves,  564,  681 ;  see  also  under  differ- 
ent glands. 
Segmental  reflexes,  576. 

Segmentation  of  central  nervous  system,  575. 
Selachians,  extirpation  of  cerebrum  in,  619. 


INDEX 


745 


Self-consciousness,  origin  of,  672. 
Self-digestion  of  the  stomach,  269. 
Self-regulation  of  respiratory  movements,  328. 
Semicircular  canals,  473. 

artificial  stimulation  of,  479. 

e.xperimental  suppression  of,  476,  Figs.  1S7, 
188;  477,  Fig.  189. 
Semilunar  valves,  167. 

closure  of,  171. 

muscular  supports  of,  167. 

opening  of,  171. 
Seminal  fluid,  692,  693,  694. 
Seminal  vesicles,  692. 
Semipermeable  membrane,  33. 
Semipermeable  walls,  31. 
Senescence,  66. 
Sensations,  auditory,  489. 

correspondence  of,  to  reality,  452. 

definition  of,  451. 

degrees  of  distinction  of,  453. 

gustatory,  483. 

modalities  of,  453. 

motor,  469. 

physiological  significance  of,  472. 

of  color,  541. 

of  pain,  4.58,  465. 

of  position,  472,  473. 

of  pressure  and  touch,  458,  461. 

of  resistance,  461,  471. 

of  temperature,  458. 

of  weight,  456,  471. 

olfactory,  486. 

organic,  454,  469. 

place  of  origin  of,  454,  659. 

(jualitative  relations  of,  to  stimuli,  451. 

quantitative  relations  of,  to  stimuli,  455. 

specific,  doctrine  of,  455. 

tactile.  461,  466,  6.52. 

theoretical  explanation  of,  453. 

threshold  stimuli  of,  4.5.5. 

tickling,  462. 

transcendental,  in  essence,  455. 

visual,  .536. 

Weber's  law  concerning,  456. 
Sense  of  cold,  459. 

of  force,  469. 

of  hearing,  498. 

of  heat,  4.59. 

of  motion,  452. 

of  pain,  465. 

of  position,  469. 

of  pressure,  461. 

of  sight,  508. 

of  smell,  54,  486. 

of  taste,  483. 
Senses,    cla.ssification    of,    451,    452;    see    also 

Sensations. 
Sensory  aphasia,  664. 
Sensory  areas  of  cortex,  650. 


Sensory  areas  of  cortex,  cormected  together, 
659. 

general  sensation  and   touch    in,    654,  Figs. 
293  and  294. 

hearing  in,  654,  Fig.  293. 

psycho-physical  significance  of,  659. 

recapitulation  concerning,  6.58. 

ta.ste  and  smell  in,  653,  654,  Fig.  294. 

\-ision  in,  654,  Fig.  29.3. 
Sensory  impressions,   conduction  of,   in   cord, 

597. 
Sensory  spinal  nerves,  682. 

distribution  of,  683,  Fig.  300. 
Serin,  70,  72. 

Serous  cavities,  absorption  from,  3.53. 
Serrati  muscles,  316. 
Serum,  154. 

agglutinating  action  of,  156,  1.57. 

bacteriocidal  action  of,  155,  156. 

CO.,  in,  340. 

cj-tolytic  action  of,  156. 

mineral  substances  in,  154. 

organic  substances  in,  154,  155. 

oxygen  in,  340. 
Serum  albumin,  154. 
Serum  globulin,  154. 
Sex,  influence  of,  on  heart  beat,  197. 

on  metabolism,  144. 
Sexual  glands,  accessorj',  691,  692. 
Sexual  maturity,  in  man,  692. 

in  woman,  696. 
Se.xual  organs,  female,  695. 

male,  691. 
Shock,  effect  of,  in  experiments  on  respiration 
326. 
in  lesions  of  motor  areas,  646. 
Shrimp,  galvanotaxis  of,  60,  Fig.  34. 
Sighing,  321. 

Sight,  sense  of,  451;  508;   see  akso  Vision  and 
Eye. 

cortical  area  for,  655. 

reaction  time  to,  674. 
Sigmoid  fle.xure  of  colon,  299. 
Sigmoid  gyru.s,  266,  632,  Fig.  282. 
Signal,  electric,  10,  Fig.  7. 
Simultaneous  contrast,  547. 
Sinuses  of  Valsalva,  167. 
Siren,  Seebeck's,  490,  Fig.  193. 
Size,  judgment  of,  by  vision,  554,   Figs.  244, 

245,  246. 
Skatol,  295,  378,  379. 
Skatoxj'l,  379. 

Skatoxyl-sulphuric  acid,  379. 
Skeletal  mu.scles,  see  .\fu.iclcs. 
Skin,  electrical  phenomena  of,  48. 

excretory  functions  of,  394. 

glands,  stimulation  of,  by  alkalies,  59. 

heat  loss  by,  395,  403. 

insensible  perspiration  of,  397. 


746 


INDEX 


Skin,  sensory  functions  of,  45S. 

temperature  of,  399. 
Sleep,  676. 

curve  of  depth  of,  677,  Fig.  299. 

effect  of  loss  of,  on  fatigue,  445. 

Howell's  theory  of,  677. 

metabolism  in,  676. 
Small  intestine,  see  Intestine,  small. 
Smell,  see  Olfactory  sensations,  Odors,  etc. 

as  a  chemical  sense,  54. 

cortical  area  for,  653,  654,  Fig.  294. 

definition  of,  451,  483. 

quantitative  capacity  of,  488. 
Sneezing,  321. 
Soaps  as  fat  producers,  130. 
Soaps  in  intestine,  295. 

injected  into  blood,  305. 
Sobbing,  321. 

Sodium   chloride,   excretion  of,   in  starvation, 
131. 

importance  of,  for  heart,  25,  182. 

osmotic  pressure  of,  32. 
Sodium  glycocholate,  254. 
Sodium  taurocholate,  254,  351. 
Solar  spectrum,  see  Spectrum. 
Sorbite,  80. 
Sound,  cardiographic,  168,  Fig.  55. 

ciualities     of,     489,    491 ;     see     also    under 
Ear. 

transniis.sion  of,  in  ear,  493. 
Sounds,  respirator^-,  322. 
Sounds  in  swallowing,  282. 
Sounds  of  heart,  167,  168. 
Special  nerves,  physiology  of,  680. 
Specific  action  of  enzj-mes,  38,  39. 
Specific  affinities  in  absorption,  35. 
Specific  dynamic  action  of  foodstuffs,  107. 
Specific  excitants  of  digestive  glands,  264,  271, 

275. 
Specific    gravit}',    changes    of,    in    elementary 
organisms,  45. 

of  blood,  147. 

of  sweat,  395. 

of  urine,  380. 
Specific  response,  law  of,  in  nerves,  411. 
Specific  stimuli  for  end  organs,  .580. 
Spectrum,  visible  rays  of,  536. 
Speech,  center  of,  631. 

elements  of,  506. 

powers  of,  661,  662. 

tract  in  cortex,  662,  Fig.  296. 
Spermatozoa,  691,  692. 

chemotactic  influence  on,  54,  697. 
t  liigmotactic  influence  on,  56,  607. 
>;u'rmatozoids  of  fern,  chemotaxis,  54. 
Spherical  aberration,  523,  Fig.  218;  522. 
Spliincter  ani,  299. 
innervation  of,  299. 
tonus  of,  583,  588. 


Sphincter  o.  urmary  bladder,  391. 

innervation  of,  .393. 
Sphincter  pupilla>,  innervation  of,  528. 
Sphygmogram,  see  PultiC  curve. 
Sphygmograph,  215,  Fig.  87. 

spring  of,  214,  Fig.  86. 
Spliygmomanometer,  202,  203,  Fig.  76. 
Spinal  accessory  nerve,  681. 
Spinal  cord,  centers  in,  58.5. 

columns  of,  562,  Fig.  254;  .589,  Fig.  261 ;  591, 

Fig.  264;  592,  Fig.  265;  593. 
conducting  pathways  in,  588. 

afferent,  592,  Fig.  265;  593,  .595,  596. 
efferent,  593,  594,  Fig.  266;  595. 
motor,  594,  Fig.  266. 
sensor^-,  592,  Fig.  265. 
control  of  skeletal  muscles  by,  586. 
electrical  stimulation  of,  .588,  590,  Fig.  263. 
extirpation  of,  .581,  582,  587. 
hemisection  of,  595,  .596,  640. 
influence  of,  on  vegetative  organs,  587. 
rate  of  propagation  in,  589. 
section  of,  588,  .595,  597. 
structure  of,  562,  Fig.  2.54;  563,  Fig.  2.55. 
Spinal  ganglia,  563,  Fig.  255. 
chief  purpose  of,  584. 
delay  of  impulse  in,  585. 
Spinal  nerves,  682. 
Spinal  nerve  roots,  562,  564. 

efferent  fibers  in  posterior,  566. 
various  functions  of,  565. 
Spirogyra,  18. 
Spirometer,  320,  Fig.  128. 

Splanchnic  nerve,    688;    see    also    Sympathetic 
nerves. 
as  secretory  nerve  of  pancreas,  269. 
as  vasomotor  nerve,  233,  235. 
connection  of,  with  ganglion  cells,  582. 
intestinal  movements  and,  288. 
movements  of  stomach  and,  284. 
respiration  and  331. 
Spleen,  function  of,  368. 

trypsin  and,  252. 
Spongiopla.sm,  19. 
Spontaneous  generation,  16. 
Sqiialiu-f  cephalus,  brain  of,  618,  Fig.  274. 
Squint,  5.5.5. 

Stapedius  muscle,  494,  Fig.  196;  497. 
Stapes,  494,  Fig.  196 ;  496. 
Staphylococcus  pyof/eries  albtis,  54. 
Starch,  see  Carbohydrates. 
absorbed,  139. 
action  of  saliva  on,  246. 
digestion  of,  in  intestine,  251,  297. 
in  mouth,  291. 
in  stomach,  291. 
formation  of,  23. 
kinds  of,  81. 
Starch  cellulose,  81. 


INDEX 


747 


Starch  granules  in  food,  242. 

Starch  granulose,  81. 

Starch  pa-ste,  81. 

Sta.si.s  of  blood  in  heart,  207. 

Static  activity  of  cerebellum,  611. 

Static  refraction  in  the  eye,  519. 

Steap.sin,  gastric,  2.50. 

in  pancreatic  juice,  253. 
Stearic  acid,  79,  701. 
Stearin,  79. 
S  ten  tor,  43. 

Stereoscope,  Brewster'.s,  558,  Fig.  251. 
Stereoscopic  vision,  558. 
Sterkobilin,  295,  383. 
Sterno-cleido-ma.stoid  muscle,  316. 
Sthenic  activity  of  cerebellum,  611. 
Stimulation,  assimilation  and,  62. 

by  heat,  58,  59. 

by  light,  56,  57. 

chemical,  52. 

electrical,  59,  60,  418. 

general  laws  of,  420. 

mechanical,  56. 

of  muscle  and  nerve,  414. 
Stimuli,  in  general,  50. 

of  muscles  and  nerves,  410. 

of  nerve  cells,  .569. 

rapitlly  repeated,  428. 

summation  of,  572. 
Stimulus,  effect  of,  on  performance  of  muscle, 
435. 

effective,  from  minimum  onward,  51. 

qualitative  relations  of,  to  sensatioiLs,  451. 

quantitative  relations  of,  to  sensations,  455. 

threshold  value  of,  455. 
Stomach,  absorption  in,  303. 

antiseptic  function  of,  292. 

digestion  in,  291. 

evacuation  of,  285. 

innervation  of  musculature  of,  284,  Fig.  114. 

movements  of,  283. 

principles  as  to  digestibility  in,  293. 

protective  function  of,  294. 

why  not  digest  itself?  269. 
Stomach  fistula,  see  Gastric  fistula. 
Stomach  glands,  see  Gastric  glands. 
Storage  of  carbohydrates,  124. 

of  fat,  129. 

of  phosphorus,  1.32. 

of  proteid,  120;  see  Retention  of  proteid. 
Strabism,  muscular  in  the  eye,  555. 
Streamings  of  protoplasm,  42. 
Stretching  movements,  influence  of,  on  blood- 
flow,  225. 
Stroma  of  red  corpuscles,  1.50. 
Stromuhr,  209,  Fig.  SO. 
Strychnia,   effect  of,  on  nervous  system,  570, 

574. 
Sublingual  glands,  257;  see  also  Salivary  glands. 
44 


Sublingual  saliva,  245. 

Submaxillar}'^  glands,    257;  see   also  Salivary 

(jlnnds. 
Submaxillary  saliva,  245. 

Substance,  li\nng,  constitution  of,  20;  see  also 
Protoplasm. 

definition  of,  15. 

relative  stabiUty  of,  13.5,  137. 
Substitution  of  foodstuffs,  93. 

of  functions  in  the  optic  thalamus,  617. 

of  tracts  in  the  cord,  597. 
Succinic  acid,  297. 
Sucking,  279. 
Suction  in  heart,  177,  225. 

in  mouth,  279;  see  also  Sucking. 

in  thoracic  cavity,  176,  225,  310. 
diastole  of  heart  and,  176. 
effect  of,  on  blood  pressure,  229,  230. 
effect  of,  on  flow  of  lymph,  349. 

in  veins,  225. 
Sugar  in  blood,  155,  374. 

in  muscles,  413. 

in  urine,  127,  128,  362,  363,  374,  375,  384; 
see  al.so  Diabetes. 

origin  of,  23. 

product  of  decomposition,  373,  374. 

production  of,  in  liver,  374. 

storing  of,  as  fat  or  glycogen,  374. 
Sulphates,  373. 

ethereal,  373,  383. 
Sulphocyanic  acid,  373. 
Sulphocyanide  of  potassium  in  saliva,  245. 
I    Sulphur,  acid,  373. 

elimination  of,  373. 

in  bile,  254. 

in  proteid,  69. 

in  urine,  383,  384. 

neutral,  373. 
Sulphureted  hydrogen,  295. 
Sumniation  as  prof)erty  of  protopla.sm,  51. 
Sunxmation  in  central  nervous  system,  572. 

in  muscles  and  nerves,  429. 
Sur\-iving  organs,  6. 
Swallowing,  279. 

innervation  of,  281. 

sounds  of,  282. 
Swallowing  reflex,  280. 

Sweat,  collection  of,  in  metabolism  experiments, 
85. 

comf)o.sition  and  properties  of,  395. 

excretory  process  of,  396. 

nitrogen  in,  89. 

part  played  by,  in  heat  regulation,  403. 

quantity  of,  excreted,  396,  408. 
Sweat  ceijtcrs,  396,  588. 
Sweat  fibers,  connections  of,  582,  688. 
Sweat  glands,  395. 

innervation  of,  396. 
Sweet  taste,  484. 


748 


INDEX 


Sj-mbiosis,  22. 
Sympathetic  fibers,  686. 

afferent,  689. 

connection     of,     with     peripheral    ganglion 
cells,  582,  686,  Fig.  301. 

course  of,  687. 

po.«tganglionic,  687. 

preganglionic,  686. 

regeneration  of,  689. 
Sympathetic  ganglia,  582. 

connections  of,  686,  Fig.  301. 

reflexe.*  through,  583. 
Sympathetic  nerves,  685. 

accelerator,  of  heart,  191,  688. 

as  vasomotor  nerves,  231,  234,  685,  688. 

of  intestine,  288. 

of  pancreas,  269. 

of  receptaculum  cliyli,  349. 

of  salivary  glands,  258. 

of  sebaceous  glands,  394. 

of  stomach,  284,  Fig.  114. 

of  thoracic  duct,  349. 

of  urinary  bladder,  393. 
Sympathetic    vibration,   492;    see    also    Reso- 
nance. 
Syntheses  in  animals,  24;  see  also  Assitnilation. 

in  plants,  23. 

of  nonliving  substances,  65. 

organic,  24. 
Syntonin,  74. 

System  of  organs  defined,  30. 
Systole,  auricular,  duration  of,  176. 

definition  of,  162. 

ventricular,  duration  of,  176. 

Tabes  dorsalis,  472. 

Tactile  corpuscles,  468. 

Tactile  sense,  area  of,  in  cortex,  6.51,  652. 

Tail,  vasomotor  nerves  for,  233. 

Talbot's  proposition,  539. 

Tambour,  receiving,  12,  Fig.  10. 

recording,  11,  Fig.  9. 
Tartaric  acid,  377. 
Tartronic  acid,  377. 
Taste,  cortical  area  for,  653. 

definition  of,  451. 

effect  of  cocaine,  eucaine,  etc.,  on,  485. 

qualities  of,  484,  485. 

sense  of,  483. 
Taste  buds,  483. 
Taste  nerves,  484. 

reaction  time  to,  674. 
Taste  zone  on  tongue,  483,  Fig.  190. 
Taurin,  253,  373. 
Taurocholic  acid,  253. 
Tears,  layer  of,  on  cornea,  508. 
Tecto-spinal  tract  in  the  cord,  .593. 
Telencephalon  or  endbrain,  600,  601 ;    see  also 
Cerebrum. 


Temperature,  action  of,  on  heart,  184,  Fig.  66. 
effect  of,  on  elimination  of   CO;;  and  water 

vapor,  397,  403. 
influence  of,  on  elementar}'  organisms,  28. 

on  metabolism,  114. 
of  birds,  398. 

of  cold-blooded  animals,  46. 
of  human  body,  398,  399. 
after  death,  401,  Fig.  149. 
cause  of  variations  in,  399. 
importance  of  clothes  in  preserving,  405. 
importance  of  tln-roid  for,  361. 
in  fasting,  95. 
mode  of  recording,  398. 
normal  compared  with  CO2  excretion,  400, 

Fig.  148. 
normal    diurnal    variations    of,    399,    Fig. 

147. 
normal  for  man,  398. 
regulation  of,  406. 
supranormal,  401. 
of  mammals,  398. 
constanc}^  of,  401. 
Temperature  nerves,  461. 
Temperature  sensations,  458. 
Temperature  sense,  area  for,  in  cortex,  652. 

tract  for,  in  cord,  597. 
Temperature  spots  or  points  on  the  skin,  459, 
Fig.  182. 
topographical  distribution  of,  460,  Fig.  183. 
Temporal  convolutions,  639,  Fig.  289;  653,  655. 
Tendon  refle.xes,  587. 

Tension  of  gas  in  liquid,  method  of,  3.35. 
Tension  of  gas  in  blood,  method  of,  341. 
Tension  of  muscle,  414,  437. 
Tension,  osmotic,  see  Osmotic  pressure. 
Tensor  tympani  muscle,  497. 
Terminal  myelogenetic  regions  of  cortex,  667. 
Testes,  692. 

extirpation  of,  357,  692. 
internal  secretion  of,  357. 
Testicular  extract,  .3.57. 
Tetanu.s,  429,  Fig.  166;  430,  Fig.  167;  433. 
explanation  of,  430. 
number  of  stimuli  necessary  for,  429. 
of  red  and  white  muscles,  430,  Fig.  167. 
Ritter's,  421. 
secondary,  433. 
work  of  muscles  in,  439. 
Wundt's,  421. 
Tetra-oxyamino-caproic  acid,  374. 
Thalamencephalon,  600. 
Thalassicola  nucleata,  18,  Fig.  15. 

mode  of  movement  of,  45. 
Theca  folliculi,  695. 
Thermotaxis,  59. 
Thigmotaxis,  .56. 

of  spermatozoa,  56,  697. 
Thigmotropism,  64. 


INDEX 


749 


Thioalbumose,  249. 
Thio-monamino  acid,  70. 
T)iio-monamino-propioiiic  acid,  70. 
Tlioracic  cavit\',  314. 

importance  of  suction  of,  for  filling  heart,  177. 

suction  of,  176. 
Thoracic  duct,  muscles  and  nerves  of,  349. 
Thoracic  tj-pe  of  respiration,  317,  318,  Fig.  126. 
"  Threshold  difference,"  4.56. 
Tiireshold  value  of  stimulus,  455. 
Thrombin,  158. 
Thrombogen,  158. 
Thymin,  76. 
Tliyroid  cartilage,  502. 
Thyroid  extract,  359. 

effects  of  treatment  with,  359,  Fig.  137;  360, 
Fig.  138. 
Thyroid  gland,  358. 

blood  supply  of,  240. 

chemistry  of,  362. 

extirpation  of,  in  dogs,  358. 
in  man,  3-59. 
in  monkey,  360. 

histology  of,  361. 

innervation  of,  361. 

internal  secretion  of,  .3-58  seq. 

mori)iiological  changes  in,  361. 

transplantation  of,  359. 
Timbre  of  .sound,  cause  of,  491. 
Time,    determination    of,    in    psycho-phy.sical 

proces.ses,  673. 
Time  recorders,  10. 
Time  stimuli,  423. 
Tissue  proteid,  134. 
Tone  deafness,  665. 
Tone,  fundamental,  491. 

musical,  489. 

produced  by  muscle,  434. 
Tones,  combination  of,  .501. 
Tongue,  action  of,  in  swallowing,  279. 

tas^te  nerves  of,  484.  Fig.  191. 

vaisomotor  nerves  of,  235. 
Tonic  activity  of  cerebellum,  611. 
Tonic  excitation,  state  of,  581. 
Tonus,  cause  of,  581. 

definition  of,  581. 

demonstration  of,  in  cros.s-striated  mascles, 
581. 

inhibition  of,  by  stimulation  of  corte.x,  636, 
640. 

of  blood  ve.s-sels,  232. 
Torpedo,  49,  Fig.  30. 

Total    metabolism,    after   ingestion    of   carbo- 
hydrates, 106. 

after  ingestion  of  fat,  104. 

after  ingestion  of  proteiil,  102. 

in  fasting,  96. 

in  growing  children,  118. 

influence  of  work  of  digestion  on,  107. 


Touch,  definition  of,  451. 
end  organs  of,  468. 
sen.sations  of,  461. 
Touch  reflex,  660. 
Toxins,  40. 

in  blood,  1.56. 
Trachea,  .502. 

Tracts  in  spinal  cord,  563  seq. 
Transfusion,  207. 

TraiLsmission  of  stimulus,  rate  of,  in  muscle, 
417. 
in  nerves,  417. 
in  spinal  cord,  589. 
Transudation,  207. 
Treppe,  441. 

Trichromatic  color  system,  54.5,  546. 
Tricuspid  valve,  165. 
Trigeminal  or  trifacial  nerve,  680. 
as  nerve  of  smell,  488. 
a.s  nerve  of  taste,  484. 
influence  of,  on  respiration,  330. 
Triglycerides,  79,  701. 
Trioxypurin,  382. 
Trochlear  nerve,  680. 

nucleus  of,  614. 
Trophic  centers  in  spinal  ganglia,  568. 
Trophic  effect,  definition  of,  50. 
Trophic  influence  of  nerve  cells,  569. 
Tropliic  influence  through  motor  nerves,  63. 
Trophic  nerves,  569. 
Trophoblasts,  22. 
Trj'psin,  252. 

spleen  and,  368. 
Tryptophan,  71,  72,  109,  249. 
Tuber  cinereum,  600. 
Tuning  fork  as  time  recorder,  10. 
Turgor,  33. 

Turtle,  extirpation  of  cerebrum  in,  621. 
"Tweenbrain,  or  diencephalon,  600,  601,  617. 
importance  of,  in  birds,  624. 
in  bony  fish,  619. 
in  dogfish,  620. 
in  frog,  620. 
in  lizard,  621. 
in  rabbit,  625. 
in  turtle,  621. 
Tj-mpanic  cavity,  495,  Fig.  197;  497. 
Tympanies  membrane,  494,  Fig.  196;  495,  496. 
Tyrosin,  71,  72,  249,  255,  378,  384. 

Ultra-red  rays,  536. 
Ultra-violet  rays,  536. 

stimulating  effect  of,  57. 
Unicellular  organisms,  2,  15. 
Uracil,  76. 
Uraemia,  368. 
Ursemic  poisoning,  367. 
Urates,  .382. 
Urea,  amount  of,  in  urine,  381. 


750 


INDEX 


Urea,  amount  of.  in  various  organs,  382. 

as  product  of  metabolism,  89. 

crystal-,  382,  Fis;.  139. 

elimination  of,  in  fasting,  101,  Fig.  43. 

in  blood,  155,  389. 

m  sweat,  39.5. 

sources  of,  370,  373. 

■where  formed,  370  seq. 
Ureters,  391. 

muscular  contractions  of,  391. 
Urethra,  392. 
Uric  acid,  amount  of,  in  urine,  382. 

composition  of,  382. 

crA-stals,  382,  Fig.  140;  383,  Fig.  141. 

fate  of,  in  mammals,  373. 

in  blood,  155. 

microscopic  detection  of,  in  kidney,  388. 

production  of,  in  birds,  371. 

properties  of,  382. 

seat  of  destruction  of,  373. 

sources  of,  372. 
Urinary  bladder,  391. 

centers  for  control  of,  393. 

innervation  of,  392,  Fig.  145;  393. 
Urinary  tubules,  385,  Fig.  144. 
Urine,  amount  of,  excreted,  380. 

combustion  heat  value  of,  93. 

composition  of,  381. 

excretion  of,  384. 

filtration  theory,  387. 
secretion  theory,  388. 

general  properties  of,  379. 

ratio  of  X:C  in,  90. 

retention  of,  393. 
Urine  indican,  379. 
Urine  mucoid,  .380. 
Urobilin,  295,  383. 
Urochrome,  383. 
Urotoxy,  381. 
Uterus,  696. 

contractions  of,  698,  Fig.  302;  699,  Fig.  303. 

growth  of,  in  pregnancy,  698. 

inner\-ation  of,  700. 

menstrual  changes  in,  696. 

movements  of,  induced  in  various  ways,  700. 

pressure  curve  in,  in  parturition, 699,  Fig.  303. 
Utilization  of  foodstuffs,  138. 

of  energy,  139. 

of  mixed  diet,  1.39. 
Utriculus  of  internal  ear,  473. 

Vacuoles,  contractile,  22. 

in  plant  cells,  21. 
Vagina,  innervation  of,  700. 
Vagus  nerve,  681. 
components  of,  681. 

influence  of,  on  blood  pressure,  204  seq. 
on  heart,  188,  190. 
on  intestinal  movements,  289. 


A'agus  nerve,  influence   of,  on  movements  of 
stomach,  284,  Fig.  114. 
on  respiration,  327. 

explanation  of,  329. 
on  secretion  of  pancreas,  269. 
of  stomach,  263. 
Vagus  pneumonia,  569. 
Valves,  atrio-ventricular,  165. 
closure  of,  166,  Fig.  54. 
semilunar,  166,  167,  171. 
venous,  225. 
Vampyrella  spirogyrer,  37,  Fig.  23. 
Vasa  deferentia,  693,  694. 
Vascular  tonus,  232. 

adrenal  bodies  and,  366. 
Vasoconstrictor  nerves,  231,  596,  681,  685. 

connection  of,  with  ganglion  cells,  582. 
Vasodilator  nerves,  234,  681,  685. 
Vasomotor  centers,  237. 

influence  of,  on  distribution  of  blood,  239. 
resistance  of,  to  asphyxiation,  573,  Fig.  257. 
Vasomotor  nerves,  231,  234,  688. 
Vasomotor  reflexes,  235. 
Vegetable  diet,  145. 
Vegetable  starches,  81. 
Vegetarianism,  145. 

Vegetative    functions,    conducting    pathways 
for,  596. 
influence  of  cortex  on,  649. 
spinal  cord  on,  587. 
Veins,  blood  flow  in,  223. 

influence  of  position  of  body  on,  225,  226, 
Figs.  93,  94;   227. 
blood  pressure  in,  223. 
cubic  distention  of,  223,  Fig.  92. 
innervation  of,  233. 
valves  of,  225. 
Veins  of  Thebesius,  180,  181. 
Velocity  of  blood  in  arteries,  210,  Fig.  82. 
in  capillaries,  221. 
in  veins,  224. 
Velocity  of  current  in  tubes,  198,  199. 
Velocity  of  nerve  impulse,  417,  Fig.  1.55. 
Velocity  of  pulse  wave,  215. 
Vense  cavse,  161,  162. 
Venomotor  nerves,  233. 
Venous  blood,  percentage  of  ga.ses  in,  339. 

tension  of  gases  in,  341. 
Venous  ostia,  185. 
Venous  sinus,  automaticitj'  of,  183. 
Venous  valves,  225. 
Ventilation  of  the  lungs,  319. 
Ventricles,  161. 

maximum  pressure  in,  170. 
negative  pressure  in,  177. 
structure  of,  163. 
work  of,  178. 
Ventricular   cavities,    casts   of,   in  rigor,    164, 
Fig.  53. 


INDEX 


751 


Ventrolateral  cerebellar  tract,  593. 

Veratrin,  effect   of,    on   muscular   contraction, 

437,  Fig.  175. 
Vermis  of  cerebellum,  607. 

function  of,  609. 
Vertigo,  an  effect  of  cerebellar  lesions,  608. 
Vesical  plexus,  392,  Fig.  145;  393. 
Vesicular  glands,  691. 
Vesicular  noise,  322. 
Vestibular  nerve,  480,  681. 
Vestibulo-spinal  tract  in  cord,  593,  595. 
Vibration  frequency  of  tone,  489. 
Vibration  limits  for  organ  of  hearing,  490. 
Vicia  Faba,  root  tubercles  of,  23,  Fig.  18. 
Vision,  508;  see  also  Eye. 

binocular,  551,  552,  Fig.  242;  555. 

direct  and  indirect,  514. 

limits  of,  517,  518. 

line  of,  518. 

stereoscopic,  558. 
Visual  angle,  .518,  Fig.  214;  556,  557. 

importance  of,  for  perception  of  depth,  556. 
Visual  area  for  exact  vision,  657. 
Visual  area  of  cortex,  655,  663. 
Visual  axis,  525;  see  also  Optical  axis. 
Visual  conducting  pathways,  657. 
Visual  purple,  537,  541. 

Visual   sensations,   as   effected  by  eye  move- 
ments, 552. 

elaboration  of,  660. 

projection  of,  to  external  world,  552. 
Visual  substances,  546. 
Vital  capacity  of  the  lungs,  320. 
Vitalism,  theorj'  of,  2. 
Vitellin,  75. 
Vitellinic  acid,  76. 
Vitreous  body,  508,  509. 

entoptic  phenomena  in,  521. 

refractive  inde.x  of,  509. 
Vocal  cords,  502. 

movements  of,  in  respiration,  312;  504,  Fig. 
202. 
in  vocalization,  503,  Figs.  200,  201;  505. 
Voice,  502. 

change  of,  692. 

pitch  of,  determination  of,  505. 

production  of,  504. 

registers  of,  504. 
Voit's  theorj'  of  proteid  metabolism,  134. 
Volta's  discovery,  47. 
Volume,  breath,  319. 

pulse,  204. 
Voluntary  mu.scular  contractions,  430. 
Vomiting,  286. 
Vorticella,  44,  Fig.  28. 

contraction  in,  independent  of  NaCl,  25. 

motility  of,  43. 
Vowels,  how  produced,  505,  Fig.  204 ;  506,  Fig. 
205. 


Wagner's  hammer,  421,  Fig.  159. 
Wallerian  degeneration,  567. 
Warm-blooded    animals,     46,    398,    405,    406, 
441. 

reaction  of,  to  external  temperature,   114. 
Water,  absorption  of,  302. 

a  constituent  of  living  substance,  20. 

determination    of,    in    metabolism    experi- 
ments, 85  seq. 

elimination  of,  through  expired  air,  89,  342, 
404. 
through  kidneys,  89,  379. 
through  skin,  89,  397,  404. 

requirement  in  fasting,  95. 
Wave  lengths  of  visible  light  rays,  .536. 
Weber's  theory  of  the  pulse,  213,  Fig.  85. 
Weber's  law,  456. 
Weight,  estimation  of,  469,  470. 

growth  in,  of  human  body,  707  .seq. 

sensation  of,  471. 
Wliite  matter  of  spinal  cord,  562. 
White  rami  communicantes,  686,  689. 
Will,  influence  of,  as  stimulus,  570. 

power  of,  over  pain,  466. 
Window,  oval,  of  ear,  496. 

round,  of  ear,  497. 
Witch's  milk,  704. 
Word  blindness,  663,  669. 
Word  deafness,  664. 

W^ork,  assimilation  and,  63;  see  also  Muscular 
work. 

external,  and  total  energy,  113. 

of  heart,  178. 
Worker,  moderate,  nutritive  requirements  for, 

142. 
Woman's  milk,  701. 

Women,  nutritive  requirements  for,  143. 
Wundt's  tetanus,  421. 

X  rays,  58. 

Xantliin,  76,  252,  413. 
Xanthin  bases,  76,  434. 
Xantho-proteic  reaction,  72. 

Yellow  as  brightest  light,  541. 
Yellow-blue  blindness,  547. 
Yellow  spot,  517. 
Yolk  spherules  of  ovum,  695. 
Young,  metabolism  in  the,  118. 

nutrition  of  the,  143. 
Young-Helmholtz'  theory  of  color  vision,  544. 
Youth,  age  of,  706. 

Zona  pellucida,  16,  695. 
Zonule  of  Zinn,  .533,  Fig.  228. 
Z\Tnase,  40. 
ZjTnogens,  38,  244. 
activation  of,  38,  252. 

(1) 


NORMAL 
HISTOLOGY 

BY 

JEREMIAH  S.  FERGUSON,  M.Sc,  M.D. 

Instructor  in  Histology,  Cornell  University  Medical   College,  New  York   City 

With   462   Illustrations,    many   in   colors 
Cloth,  $4.00  Half  Leather,  $4.50 

SOLD  ONLY  BY  SUBSCRIPTION 


"  This  is  an  eminently  practical  and  useful  book,  and  one  in  which  the  subject 
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things  plain  which  comes  from  full  knowledge  and  an  aptitude  for  teaching. 
Since  histology  is  at  the  basis  of  our  comprehension  of  physiology,  pathology, 
bactenology,  and  clinical  medicine  unusual  space  has  been  devoted  to  all  those 
organs  which  serve  as  a  held  for  the  specialist  in  medicine.  This  is  especially 
true  of  the  chapters  on  the  central  nervous  system,  which  are  comprehensive 
and  exhaustive.  What  is  true  of  this  department  is  more  or  less  true  of  all,  and 
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structions of  organs,  which  should  be  of  great  assistance  to  the  student  in 
understanding  such  structures  as  the  adrenals,  various  glands,  the  blood,  and 
lymphatic  systems  of  different  regions,  etc.  .  .  .  The  minute  anatomy  of  the  eye 
and  of  the  ear  is  discussed  at  much  greater  length  than  is  customar)-,  and  the 
section  devoted  to  the  nervous  system  is  also  worthy  of  note,  both  on  account 
of  its  completeness  and  of  the  character  of  its  illustrations.  The  bibliography  is 
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— Xew  York  Medical  Record. 

"  Both  as  to  text  and  illustrations  this  work  is  the  most  comprehensive  and 
best-arranged  text-book  on  the  subject  which  has  as  yet  appeared  in  this 
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to  the  superiority  of  foreign  works,  for  Dr.  Ferguson  has  written  a  work  of  which 
nothing  but  praise  can  be  spoken." — Medical  Monthly,  Memphis,  Tenn. 

D.    APPLETON    AND    COMPANY,    Publi.shers 
436  Fifth  Avenue,  New  York. 


CHEMICAL  AND  MICROSCOPICAL 
DIAGNOSIS 

By  FRANCIS  CARTER  WOOD,  M.D. 

Adjunct  Professor  of  Clinical  Pathology,  College  of  Physicians  and  Surgeons,  Columbia 
University,  New  York;  Pathologist  to  St.  Luke's  Hospital,  New  York 

With  One  Hundred  and  Eighty-eight  Illustrations  in  the  Text  and 
Nine  Colored  Plates 

8vo.     Cloth,  $5.00  net 

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— New  York  Medical  Journal. 

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be  long  before  it  will  be  found  in  the  hands  of  every  laboratory 
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nounced one  of  the  best." — Medical  Review  of  Reviews. 

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appeared  in  the  English  language." 

— California  State  Journal  of  Medicine. 

D.     APPLETON     AND     COMPANY,     NEW     YORK 


Q-^SAr 


